SCHEDULE 2
Regulation 6
METHODS OF ANALYSIS
PART I
1. General
When two or more methods are prescribed in this part of this Schedule to
determine a component of a fertiliser the choice of the method shall, except
where otherwise indicated, be left to the agricultural analyst concerned; the
method used must however be indicated in the certificate of analysis.
2. Reagents
Except where otherwise specified in the method of analysis, all reagents
shall be of analytical quality. Where trace elements are to be determined,
the purity of the reagents used shall be checked by means of a blank test.
3. Water
(a) Except
where otherwise specified, a reference in this Part of this Schedule to water
shall be a reference to demineralized or distilled water.
(b) For
the determination of any form of nitrogen, water shall be free of all
nitrogenous compounds and carbon dioxide.
(c) Except
where the method of analysis specifies a particular solvent or diluent, all
dissolution, dilution, rinsing and washing operations mentioned in the methods
of analysis shall be carried out using water.
4. Apparatus
(a) Only special instruments
and apparatus and specifically required apparatus and equipment are mentioned
in the methods of analysis.
(b) Apparatus and equipment
shall be clean.
(c) The accuracy of
graduated glassware shall be assured by reference to the appropriate
standards.
5. Methods
of Analysis
1.
|
Preparation
of the sample for analysis
|
2.
|
Determination
of ammoniacal nitrogen
|
3.a
|
Determination
of nitrate and ammoniacal nitrogen — Ulsch method
|
b
|
Determination
of nitrate and ammoniacal nitrogen — Arnd method
|
c
|
Determination
of nitrate and ammoniacal nitrogen — Devarda method
|
4.a
|
Determination
of total nitrogen in calcium cyanamide — in the absence of nitrate
|
b
|
Determination
of total nitrogen in calcium cyanamide — in the presence of nitrate
|
5.
|
Determination
of total nitrogen in urea
|
6.
|
Determination
of cyanamide nitrogen
|
7.
|
Determination
of biuret in urea
|
8.a
|
Determination
of different forms of nitrogen in the same sample — in the presence of
cyanamide nitrogen
|
b
|
Determination
of different forms of nitrogen in the same sample — in the absence of
cyanamide nitrogen
|
9.a
|
Extraction
of total phosphorus — by mineral acids
|
b
|
Extraction
of phosphorus — by 2% formic acid
|
c
|
Extraction
of phosphorus — by 2% citric acid
|
d
|
Extraction
of phosphorus — by neutral ammonium citrate
|
e
|
Extraction
of phosphorus — by alkaline ammonium citrate (Petermann's method) at 65 C
|
f
|
Extraction
of phosphorus — by alkaline ammonium citrate (Petermann's method) at
ambient temperature
|
g
|
Extraction
of phosphorus — by alkaline ammonium citrate (Joulie's method)
|
h
|
Extraction
of phosphorus — by water
|
10.
|
Determination
of extracted phosphorus
|
11.
|
Determination
of water-soluble potassium
|
12.
|
Determination
of chlorides in the absence of organic material
|
13.a
|
Determination
of fineness of grinding — dry method
|
b
|
Determination
of fineness of grinding of soft natural phosphates
|
14.
|
Methods
of analysis and test procedures for ammonium nitrate fertilisers containing
more than 28% nitrogen by weight
|
a
|
Method
for the application of thermal cycles
|
b
|
Determination
of the oil retention value
|
c
|
Determination
of combustible ingredients
|
d
|
Determination
of the pH value
|
e
|
Determination
of the particle size
|
f
|
Determination
of the chlorine content (as chloride ion)
|
g
|
Determination
of copper
|
15.
|
Extraction
of total calcium, total magnesium, total sodium and total sulfur in the
form of sulfates
|
16.
|
Extraction
of total sulfur
|
17.
|
Extraction
of water-soluble calcium, magnesium, sodium and sulfur (in the form of
sulfates)
|
18.
|
Extraction
of water-soluble sulfur
|
19.
|
Extraction
and determination of elemental sulfur
|
20.
|
Manganimetric
determination of extracted calcium following precipitation in the form of
oxalate
|
21.
|
Determination
of magnesium by atomic absorption spectrometry
|
22.
|
Determination
of magnesium by complexometry
|
23.
|
Determination
of sulfates
|
24.
|
Determination
of the sodium extracted
|
25.
|
Trace
elements at a concentration less than 10%
|
a
|
Extraction
of total trace elements
|
b
|
Extraction
of water-soluble trace elements
|
c
|
Removal
of organic compounds from fertiliser extracts
|
d
|
Determination
of trace elements in fertiliser extracts by atomic absorption spectrometry
(general procedure)
|
e
|
Determination
of boron in fertiliser extracts by means of spectrometry with azomethine-h
|
f
|
Determination
of cobalt in fertiliser extracts by atomic absorption spectrometry
|
g
|
Determination
of copper in fertiliser extracts by atomic absorption spectrometry
|
h
|
Determination
of iron in fertiliser extracts by atomic absorption spectrometry
|
i
|
Determination
of manganese in fertiliser extracts by atomic absorption spectrometry
|
j
|
Determination
of molybdenum in fertiliser extracts by spectrometry of a complex with
ammonium thiocyanate
|
k
|
Determination
of zinc in fertiliser extracts by atomic absorption spectrometry
|
26.
|
Trace
elements at a concentration greater than 10%
|
a
|
Extraction
of total trace elements
|
b
|
Extraction
of water — soluble trace elements
|
c
|
Removal
of organic compounds from fertiliser extracts
|
d
|
Determination
of trace elements in fertiliser extracts by atomic absorption spectrometry
(general procedure)
|
e
|
Determination
of boron in fertiliser extracts by means of acidimetric titration
|
f
|
Determination
of cobalt in fertiliser extracts by the gravimetric method with
1-nitroso-2-naphthol
|
g
|
Determination
of copper in fertiliser extracts by the titrimetric method
|
h
|
Determination
of iron in fertiliser extracts by atomic absorption spectrometry
|
i
|
Determination
of manganese in fertiliser extracts by titration
|
j
|
Determination
of molybdenum in fertiliser extracts by the gravimetric method with
8-hydroxyquinoline
|
k
|
Determination
of zinc in fertiliser extracts by atomic absorption spectrometry
|
1.
PREPARATION
OF THE SAMPLE FOR ANALYSIS
1. SCOPE
The following procedure is to be used for the preparation of the sample for
analysis, taken from the final sample.
2. PRINCIPLE
2.1 Solid
fertilisers: the preparation of a final sample received at the laboratory is
a series of operations, usually sieving, grinding and mixing, carried out in
such a way that: —
(a) the
smallest amount weighed out laid down by the methods of analysis is
representative of the laboratory sample; and
(b) the
fineness of the fertiliser has not been changed by the preparation to the
extent that its solubility in the various extraction reagents is appreciably
affected.
2.2 Fluid
fertilisers: the final sample is mixed by shaking to ensure that any
insoluble matter, particularly crystalline material, is thoroughly dispersed
before each test portion is taken.
3. APPARATUS
3.1 Sample
divider (optional).
3.2 Sieves
with apertures of 0.2 mm and 0.5 mm.
3.3 250
ml flasks, stoppered.
3.4 Porcelain
pestle and mortar or grinder.
4. CHOICE
OF TREATMENT TO BE USED
Preliminary remark: if the product is suitable, only a representative
part of the final sample need be kept.
4. Final
samples which must not be ground
Calcium nitrate, calcium magnesium nitrate, sodium nitrate, Chile nitrate,
calcium cyanamide, nitrogenous calcium cyanamide, ammonium sulfate, ammonium
nitrates of over 30% N, urea, basic slag, natural phosphate rendered
partially soluble, precipitated dihydrated dicalcium phosphate, calcined
phosphate, aluminium calcium phosphate, soft ground rock phosphate.
4.2 Finals
samples which must be divided and part of which must be ground
These are products in respect of which certain determinations are carried out
without previous grinding (fineness of grinding for example) and other
determinations after grinding. They include all compound fertilisers
containing the following phosphate ingredients: basic slag, aluminium calcium
phosphate, calcined phosphate, soft ground rock phosphate and natural
phosphate rendered partially soluble. To that end, divide the final sample
into two parts, which are as identical as possible, using a sample divider or
by quartering.
4.3 Final
samples in respect of which all determinations are carried out on a grounded
product
These are all the other fertilisers on the list which are not to be found
under 4.1 and 4.2. The whole final sample shall be ground.
5. METHOD
The part of the final sample referred to under 4.2 and 4.3 is sieved rapidly
through a sieve with apertures of 0.5 mm. The residue is ground roughly as to
obtain a product in which there is a minimum of fine particles, and it is
then sieved. The grinding must be done in conditions such that the substance
is not appreciably heated. The operation is repeated as many times as is
necessary until there is no residue, and it must be effected as quickly as
possible in order to prevent any gain or loss of constituents (water,
ammonia). The whole ground and sieved product is placed in a non-corrodable
container provided with an air-tight closure.
Before
any weighing is carried out for the analysis, the whole sample must be
thoroughly mixed.
6. SPECIAL
CASES
(a) Fertilisers
comprising a blend of several categories of crystals
In this case, separation frequently
occurs. It is therefore absolutely essential to crush and pass the sample
through a sieve with apertures of 0.2 mm (for example, mixtures of ammonium
phosphate and potassium nitrate). The grinding of the whole of the final
sample is recommended in the case of these products.
(b) Residue which is
difficult to grind and does not contain fertilising substances
Weigh the residue and take account
of its mass when calculating the final result.
(c) Products which
decompose on heating
Grinding must be carried out in
such a way as to avoid any heating. It is preferable in this case to use a
mortar for grinding (for example, compound fertilisers containing calcium
cyanamide and urea).
(d) Products which
are abnormally moist or made into a paste by grinding
To ensure homogeneity, a sieve is
to be chosen which has the smallest apertures compatible with the destruction
of lumps by hand or with the pestle. This may be the case for mixtures,
certain ingredients of which contain water of crystallisation.
7. FLUID
FERTILISERS
Mix thoroughly by shaking, ensuring that any insoluble matter, particularly
crystalline material, is thoroughly dispersed, immediately before drawing a
portion of the sample of analysis.
2.
DETERMINATION
OF AMMONIACAL NITROGEN
1. SCOPE
This method is for the determination of ammoniacal nitrogen.
2. FIELD
OF APPLICATION
All nitrogenous fertilisers, including compound fertilisers, in which
nitrogen is found exclusively either in the form of ammonium salts, or
ammonium salts together with nitrates.
It
is not applicable to fertilisers containing urea, cyanamide or other organic
nitrogenous compounds.
3. PRINCIPLE
Displacement of ammonia by means of an excess of sodium hydroxide;
distillation; determination of the ammonia absorbed by a given volume of a
standard sulfuric acid and titration of the excess acid with a standard
solution of sodium or potassium hydroxide.
4. REAGENTS
4.1 Hydrochloric
acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid
(p=1.18 g/ml) with an equal volume of water.
4.2 Sulfuric
acid, 0.05 M solution
|
for
variant (a) (see page 16)
|
4.3 Sodium
or potassium hydroxide, 0.1 M solution, carbonate free
|
|
4.4 Sulfuric
acid, 0.1 M solution
|
for variant (b) (see page 16)
|
4.5 Sodium
or potassium hydroxide, 0.2 M solution, carbonate free
|
|
4.6 Sulfuric
acid, 0.25 M solution
|
for variant (c) (see page 16)
|
4.7
|
Sodium or potassium hydroxide, 0.5 M solution, carbonate free
|
|
4.8 Sodium
hydroxide solution, 30 g per 100 ml, ammonia free
4.9 Indicator
solutions:
4.9.1 Mixed indicator:
Solution A: dissolve 1 g methyl red in 37 ml sodium hydroxide solution 0.1 M
and make up to 1 litre with water.
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume
of solution A and 2 volumes of solution B.
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.
4.9.2 Methyl red indicator solution:
Dissolve 0.1 g methyl red in 50 ml ethanol (95%) make up to 100 ml with water
and filter if necessary. This indicator may be used (4 to 5 drops) instead of
the preceding one.
4.10 Anti-bump granules of pumice stone,
washed in hydrochloric acid and ignited.
4.11 Ammonium sulfate.
5. APPARATUS
5.1 Distillation
apparatus consisting of a round-bottomed flask of suitable capacity connected
to a condenser by means of a splash head.
Examples
of the different types of equipment recommended for this determination are
reproduced in Figures 1, 2, 3 and 4 in the Appendix.
5.2 Rotary
shaker, 35 to 40 turns per minute.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1.1 Solubility test
Carry out a solubility test on the sample in water at room temperature in the
proportion of 2 g per 100 ml.
7.1.2 Preparation of the solution
Weigh 5, 7 or 10 g of the sample to the nearest 0.001 g, as shown in the
Table, and place in a 500 ml graduated flask. From the result of the
solubility test, proceed as follows:
(a) Products
completely soluble in water
Add sufficient water to dissolve the sample; shake, and when completely
dissolved, make up to volume and mix thoroughly.
(b) Products
not completely soluble in water
Add 50 ml water and then 20 ml hydrochloric acid solution (4.1). Swirl and
leave undisturbed until the evolution of carbon dioxide has ceased. Add 400
ml water and shake for half an hour on the rotary shaker (5.2). Make up to
volume with water, mix and filter through a dry paper into a dry receiver.
Discard the first portion of the filtrate.
7.2 Determination
According to the variant chosen, place in the collecting flask a measured
quantity of standard sulfuric acid as indicated in the Table on page16. Add
the appropriate quantity of the chosen indicator solution (4.9.1 to 4.9.2)
and, if necessary, water to obtain a volume of at least 50 ml. The condenser
outlet must be below the surface of the standard acid in the collecting
flask.
Transfer by pipette, according to the details given in the Table, an aliquot
portion of the clear solution into the distillation flask of the apparatus.
Add water to obtain a volume of about 350 ml and several grains of pumice to
control the boiling.
Assemble the distillation apparatus and, taking care to avoid any loss of
ammonia, add to the contents of the distillation flask 10 ml of concentrated
sodium hydroxide solution (4.8) or 20 ml of the reagent in the cases where 20
ml hydrochloric acid (4.1) have been used in order to dissolve the sample.
Warm the flask gently and when boiling commences distil at such a rate that
about 200 ml are obtained in 30 minutes.
When no more ammonia is likely to be evolved, lower the receiving flask so
that the tip of the condenser is above the surface of the liquid.
Test the subsequent distillate by means of an appropriate reagent to ensure
that all the ammonia has been completely distilled. Wash the condenser with a
little water and titrate the excess acid with the standard solution of sodium
or potassium hydroxide prescribed for the variant adopted (see Note).
Note: Standard
solutions of different strengths may be used for the titration provided that
the volumes used do not, as far as possible, exceed 40 to 45 ml.
7.3 Blank
Carry out a blank test under the same conditions (omitting only the sample)
and allow for this in the calculation of the final result.
7.4 Control
test
Before carrying out analyses, check that the apparatus is working properly
and that the correct application of the method is used by taking an aliquot
portion of a freshly prepared solution of ammonium sulfate (4.11) containing
the maximum quantity of nitrogen prescribed for the chosen variant.
8. EXPRESSION
OF RESULT
Express the result of the analysis as the percentage of ammoniacal nitrogen
in the fertiliser as received for analysis using the formula
%N =
|
(50
- A) × F for variants (a) and (b) and
|
%N =
|
(35
- A) × F for variant (c)
|
where
|
50 (or 35 where variant (c) applies)
|
=
|
millilitres
of standard solution of sulfuric acid in the receiving flask.
|
A =
|
millilitres
of sodium or potassium hydroxide used for the titration.
|
F =
|
factor
taking into account the weight of sample, the dilution, the volume of the
aliquot portion distilled and the volumetric equivalent.
|
TABLE
FOR METHOD 2
Determination of the ammoniacal nitrogen and of the ammoniacal and nitrate
nitrogen in fertilisers. Table of the weighing, dilution and calculation to
be carried out for each of the variants (a), (b) and (c) of the method.
Variant (a), —
|
Approximate
maximum quantity of nitrogen to be distilled = 50 mg
|
|
Sulfuric
acid 0.05 M to be placed in the receiving flask = 50 ml
|
|
Titration
with sodium or potassium hydroxide, 0.1 M solution
|
Declaration N%
|
Amount
to be weighed (g)
|
(Volume) Dilution (ml)
|
Volume of sample solution to be
distilled (ml)
|
Factor F
|
0 - 5
|
10
|
500
|
50
|
0.14
|
5 - 10
|
10
|
500
|
25
|
0.28
|
10 - 15
|
7
|
500
|
25
|
0.40
|
15 - 20
|
5
|
500
|
25
|
0.56
|
20 - 40
|
7
|
500
|
10
|
1.00
|
Variant (b), —
|
Approximate
maximum quantity of nitrogen to be distilled = 100 mg
|
|
Sulfuric
acid 0.1 M to be placed in the receiving flask = 50 ml
|
|
Titration
with sodium or potassium hydroxide, 0.2 M solution
|
Declaration N%
|
Amount
to be weighed (g)
|
(Volume) Dilution (ml)
|
Volume of sample solution to be
distilled (ml)
|
Factor F
|
0 - 5
|
10
|
500
|
100
|
0.14
|
5 - 10
|
10
|
500
|
50
|
0.28
|
10 - 15
|
7
|
500
|
50
|
0.40
|
15 - 20
|
5
|
500
|
50
|
0.56
|
20 - 40
|
7
|
500
|
50
|
1.00
|
Variant (c), —
|
Approximate
maximum quantity of nitrogen to be distilled = 200 mg
|
|
Sulfuric
acid 0.25 M to be placed in the receiving flask = 35 ml
|
|
Titration
with sodium or potassium hydroxide, 0.5 M solution
|
Declaration N%
|
Amount
to be weighed (g)
|
(Volume) Dilution (ml)
|
Volume of sample solution to be
distilled (ml)
|
Factor F
|
0 - 5
|
10
|
500
|
200
|
0.175
|
5 - 10
|
10
|
500
|
100
|
0.350
|
10 - 15
|
7
|
500
|
100
|
0.500
|
15 - 20
|
5
|
500
|
100
|
0.700
|
20 - 40
|
5
|
500
|
50
|
1.400
|
3a.
DETERMINATION
OF NITRIC AND AMMONIACAL NITROGEN — ULSCH METHOD
1. SCOPE
This method is for the determination of nitric and ammoniacal nitrogen with
reduction according to Ulsch.
2. FIELD
OF APPLICATION
All nitrogenous fertilisers, including compound fertilisers, in which
nitrogen is found exclusively in nitrate form, or in ammoniacal and nitrate
form.
3. PRINCIPLE
Reduction of nitrates and nitrites to ammonia by means of metallic iron in an
acidic medium and displacement of the ammonia thus formed by the addition of
an excess of sodium hydroxide: distillation of the ammonia and determination
of the ammonia absorbed in a known volume of standard sulfuric acid solution.
Titration of the excess sulfuric acid with a standard solution of sodium or
potassium hydroxide.
4. REAGENTS
4.1
|
Hydrochloric
acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid
(p=1.18 g/ml) with an equal volume of water.
|
4.2
|
Sulfuric
acid, 0.05 M solution.
|
4.3
|
Sodium
or potassium hydroxide, 0.1 M solution, carbonate free.
|
4.4
|
Sulfuric
acid solution, approximately 30% H2SO4 (W/V), ammonia free.
|
4.5
|
Powdered
iron reduced in hydrogen. (The prescribed quantity of iron must be able to
reduce at least 0.05 g nitrate nitrogen.)
|
4.6
|
Sodium
hydroxide solution, 30 g per 100<+>ml, ammonia free.
|
4.7
|
Indicator
solutions:
|
|
4.7.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre.
|
|
Mix
1 volume of solution A and 2 volumes of solution B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution; use 0.5 ml (10 drops).
|
|
4.7.2
Methyl red indicator solution:
|
|
Dissolve
0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and
filter if necessary.
|
|
This
indicator may be used (4 - 5 drops) instead of the preceding one.
|
4.8
|
Anti-bump
granules of pumice stone, washed in hydrochloric acid and ignited.
|
4.9
|
Sodium
nitrate.
|
5. APPARATUS
See Method 2.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution
See Method 2.
7.2 Determination
Place in the receiving flask an exactly
measured quantity of standard sulfuric acid (4.2) as indicated in the Table
of Method 2 (variant (a)) and add the appropriate quantity of indicator
solution (4.7.1 or 4.7.2).
The end of the extension tube of the condenser must be below the surface of
the standard acid in the receiving flask.
Using a pipette, transfer an aliquot part of the clear solution as indicated
in the Table of Method 2 (variant (a)) to the distillation flask of the
apparatus. Add 350 ml water, 20 ml 30% sulfuric acid solution (4.4), stir,
and add 5 g of reduced iron (4.5). Wash the neck of the flask with several ml
of water, and place a small, long-stemmed funnel in the neck of the flask.
Heat in a boiling water bath for an hour and then wash the stem of the funnel
with a few ml of water. Allow to cool to room temperature.
Taking care to avoid any loss of ammonia, add 50 ml concentrated sodium
hydroxide solution (4.6) to the contents of the distillation flask, or in the
cases where 20 ml of hydrochloric acid (4.1) has been used to dissolve the
sample, add 60 ml of concentrated sodium hydroxide solution (4.6). Assemble
the distillation apparatus. Distil the ammonia according to the procedure
given in Method 2. Titrate the excess acid with the standard solution of
sodium or potassium hydroxide (4.3).
7.3 Blank
test
Carry out a blank test (omitting only the sample) under the same conditions
and allow for this in the calculation of the final result.
7.4 Control
test
Before analysis check that the apparatus is working properly and that the
correct application of the method is used by taking an aliquot portion of a
freshly prepared solution of sodium nitrate (4.9) containing 0.045 g to 0.05
g of nitrogen.
8. EXPRESSION
OF RESULTS
Express the results of analysis as a percentage of nitric nitrogen, or
combined ammoniacal and nitric nitrogen, contained in the fertiliser as
received for analysis.
3b.
DETERMINATION
OF NITRIC AND AMMONIACAL NITROGEN — ARND METHOD
1. SCOPE
This method is for the determination of nitric and ammoniacal nitrogen with
reduction according to Arnd (modified for each of the variants (a), (b) and
(c)).
2. FIELD
OF APPLICATION
See Method 3a.
3. PRINCIPLE
Reduction of nitrates and nitrites to ammonia in a neutral aqueous solution
by means of a metallic alloy composed of 60% Cu and 40% Mg (Arnd's alloy) in
the presence of magnesium chloride.
Distillation of the ammonia and absorption in a known volume of standard
sulfuric acid solution. Titration of the excess acid with a standard solution
of sodium or potassium hydroxide.
4. REAGENTS
4.1
|
Hydrochloric
acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid
(p=1.18 g/ml) with an equal volume of water.
|
4.2
|
Sulfuric
acid, 0.05 M solution
|
for variant (a) (see page16)
|
4.3
|
Sodium
or potassium hydroxide, 0.1 M solution, carbonate free
|
|
4.4
|
Sulfuric
acid, 0.1 M solution
|
for variant (b) (see page 16)
|
4.5
|
Sodium
or potassium hydroxide, 0.2 M solution, carbonate free
|
|
4.6
|
Sulfuric
acid, 0.25 M solution
|
for variant (c) (see page 16)
|
4.7
|
Sodium
or potassium hydroxide, 0.5 M solution, carbonate free
|
|
4.8
|
Sodium
hydroxide solution, approximately 2 M.
|
4.9
|
Arnd's
alloy — powdered to pass through a sieve with square apertures less than
1.00 mm.
|
4.10
|
Magnesium
chloride solution, 20% (W/V):
Dissolve 200 g magnesium chloride (MgCl2.6H2O) in approximately 600 - 700
ml water in a one litre flat bottomed flask. To prevent frothing, add 15 g
magnesium sulfate (MgSO4.7H2O). After dissolution add 2 g magnesium oxide
and a few anti-bump granules of pumice stone and concentrate the suspension
to 200 ml by boiling, thus expelling any trace of ammonia from the
reagents. Cool, make up the volume to 1 litre and filter.
|
4.11
|
Indicator
solutions:
|
|
4.11.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1
volume of A with 2 volumes of B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops).
|
|
4.11.2
Methyl red indicator solution:
|
|
Dissolve
0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and
filter if necessary. This indicator may be used (4 to 5 drops) instead of
the preceding one.
|
|
4.11.3
Congo red indicator solution:
|
|
Dissolve
3 g Congo red in 1 litre warm water and filter if necessary after cooling.
This indicator may be used, instead of the two described above, in the
neutralisation of acid extracts before distillation, using 0.5 ml per 100
ml of liquid to be neutralised.
|
4.12
|
Anti-bump
granules of pumice stone washed in hydrochloric acid and ignited.
|
4.13
|
Sodium
nitrate.
|
5. APPARATUS
See Method 2.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution for analysis
See Method 2.
7.2 Determination
According to the chosen variant, place in the receiving flask a measured
quantity of standard sulfuric acid as indicated in the Table of Method 2. Add
the appropriate quantity of chosen indicator solution (4.11.1 or 4.11.2) and
if necessary water to give a volume of a least 50 ml. The end of the
extension tube of the condenser must be below the surface of the solution.
Using a pipette, take, according to the Table, an aliquot part of the clear
solution and place in the distillation flask. Add sufficient water to obtain
a total volume of about 350 ml (see Note), 10 g Arnd's alloy (4.8), 50 ml
magnesium chloride solution (4.10) and a few fragments of pumice stone
(4.12). Rapidly connect the flask to the distillation apparatus. Heat gently
for about 30 minutes. Then increase the heating to distil the ammonia.
Continue the distillation for about an hour.
After this time, the residue in the flask ought to have a syrupy consistency.
When the distillation has finished, titrate the quantity of excess acid in
the receiving flask according to the procedure in Method 2.
Note: When
the sample solution is acidic (addition of 20 ml hydrochloric acid (4.1) to
dissolve the sample) the aliquot part taken for analysis is neutralised in
the following way: to the distillation flask containing the aliquot part add
about 250 ml water, the necessary quantity of one of the indicators (4.11.1,
4.11.2, 4.11.3) and swirl or mix carefully. Neutralise with 2 M sodium
hydroxide solution (4.8) and acidify again with a drop of hydrochloric acid
(4.1). Then proceed as indicated in 7.2.
7.3 Blank
test
Carry out a blank test under the same conditions (omitting only the samples)
and allow for this in the calculation of the final result.
7.4 Control
test
Before analysis, check that the apparatus is working properly and that the
correct technique is applied using a freshly prepared solution of sodium
nitrate (4.13) containing 0.050 g to 0.150 g nitrogen depending on the
variant chosen.
8. EXPRESSION
OF RESULTS
Express the results of the analysis as a percentage of nitric nitrogen, or
combined ammoniacal and nitric nitrogen, contained in the fertiliser as
received for analysis.
3c.
DETERMINATION
OF NITRIC AND AMMONIACAL NITROGEN — DEVARDA METHOD
1. SCOPE
This method is for the determination of nitric and ammoniacal nitrogen with
reduction according to Devarda (modified for each of the variants (a), (b)
and (c)).
2. FIELD
OF APPLICATION
See Method 3a.
3. PRINCIPLE
Reduction of nitrates and nitrites to ammonia in a strongly alkaline solution
by means of a metallic alloy composed of 45% A1, 5% Zn and 50% Cu (Devarda's
alloy). Distillation of the ammonia and absorption in a known volume of
standard sulfuric acid; titration of the excess sulfuric acid with a standard
solution of sodium or potassium hydroxide.
4. REAGENTS
4.1
|
Hydrochloric
acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid
(p=1.18 g/ml) with an equal volume of water.
|
4.2
|
Sulfuric
acid, 0.05 M solution
|
for variant (a) (see page 16)
|
4.3
|
Sodium
or potassium hydroxide, 0.1 M solution, carbonate free
|
|
4.4
|
Sulfuric
acid, 0.1 M solution
|
for variant (b) (see page 16)
|
4.5
|
Sodium
or potassium hydroxide, 0.2 M solution, carbonate free
|
|
4.6
|
Sulfuric
acid, 0.25 M solution
|
for variant (c) (see page 16)
|
4.7
|
Sodium
or potassium hydroxide, 0.5 M solution, carbonate free
|
|
4.8
|
Devarda's
alloy — powdered so that 90 to 100% will pass through a sieve with
apertures less than 0.25 mm square, 50 to 75% will pass through a sieve
with apertures of less than 0.075 mm square. (Pre-packed bottles containing
a maximum of 100 g are recommended.)
|
4.9
|
Sodium
hydroxide solution, 30 g per 100 ml, ammonia free.
|
4.10
|
Indicator
solutions:
|
|
4.10.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1
volume of A with 2 volumes of B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops).
|
|
4.10.2
Methyl red indicator:
|
|
Dissolve
0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and
filter if necessary. This indicator (4 to 5 drops) may be used instead of
the preceding one.
|
4.11
|
Ethanol,
95%.
|
4.12
|
Sodium
nitrate.
|
5. APPARATUS
5.1 Distillation
apparatus consisting of a round bottomed flask of suitable capacity,
connected to a condenser by means of a splash head, equipped, in addition,
with a bubble trap on the receiving flask to prevent any loss of ammonia.
An example of the type of apparatus recommended for this determination is
reproduced in Figure 5 in the Appendix.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution for analysis
See Method 2.
7.2 Determination
According to the variant chosen, place in the receiving flask an exactly
measured quantity of standard sulfuric acid as indicated in the Table. Add
the appropriate quantity of the chosen indicator solution (4.10.1 or 4.10.2)
and sufficient water to give a volume of 50 ml. The end of the extension tube
of the condenser must be below the surface of the solution. Fill the bubble
trap with distilled water.
Using a pipette, take an aliquot part of the clear solution as indicated in
the Table and place in the distillation flask. Add sufficient water to the
distillation flask to obtain a volume of 250 - 300 ml, then add 5 ml ethanol
(4.11) and 4 g Devarda's alloy (4.8).
Note: In
the presence of calcium salts such as calcium nitrate and calcium ammonium
nitrate, it is necessary to add 0.7 g disodium hydrogen phosphate
(Na2HPO4.2H2O) before distillation for each gram of sample present in the
aliquot part, to prevent the formation of calcium hydroxide.
Taking
the necessary precautions to avoid loss of ammonia, add to the flask about 30
ml of 30% sodium hydroxide solution (4.9) and finally, in the case of
acid-soluble samples, an additional quantity sufficient to neutralise the
quantity of hydrochloric acid (4.1) present in the aliquot part taken for the
analysis. Connect the distillation flask to the apparatus, ensuring the
tightness of connections. Carefully swirl the flask to mix the contents.
Warm gently, so that the release of hydrogen decreases appreciably over about
half an hour and the liquid begins to boil. Continue the distillation,
increasing the heat so that at least 200 ml of liquid distils in about 30
minutes. (Do not prolong the distillation beyond 45 minutes.)
When the distillation is complete, disconnect the receiving flask from the
apparatus, carefully wash the extension tube and bubble trap, collecting the
rinsings in the titration flask. Titrate the excess acid according to the
procedure in Method 2.
7.3 Blank
test
Carry out a blank test under the same conditions omitting only the sample and
allow for this in the calculation of the final results.
7.4 Control
test
Before carrying out the analysis, check that the apparatus is working
properly and that the correct application of the method is used, by taking an
aliquot portion of a freshly prepared solution of sodium nitrate (4.12)
containing, according to the variant chosen, 0.050 g to 0.150 g.
8. EXPRESSION
OF RESULTS
Express the results of analysis as a percentage of nitric nitrogen, or
combined ammoniacal and nitric nitrogen, contained in the fertiliser as
received for analysis.
4a.
DETERMINATION
OF TOTAL NITROGEN IN CALCIUM CYANAMIDE — IN THE ABSENCE OF NITRATE
1. SCOPE
This method is for the determination of total nitrogen in nitrate-free
calcium cyanamide.
2. FIELD
OF APPLICATION
Exclusively to calcium cyanamide (nitrate free).
3. PRINCIPLE
After digestion using the Kjeldahl method, the ammoniacal nitrogen formed is
displaced by sodium hydroxide and collected in a standard solution of
sulfuric acid. The excess sulfuric acid is titrated with a standard solution
of sodium or potassium hydroxide.
4. REAGENTS
4.1
|
Sulfuric
acid solution 50% (V/V): dilute an appropriate volume of sulfuric acid
(p=1.84 g/ml) with an equal volume of water.
|
4.2
|
Potassium
sulfate.
|
4.3
|
Copper
oxide (CuO), 0.3 - 0.4 g for each determination or an equivalent quantity
of copper sulfate pentahydrate (0.95 to 1.25g) for each determination.
|
4.4
|
Sodium
hydroxide solution 30g per 100 ml, ammonia free.
|
4.5
|
Sulfuric
acid, 0.05 M solution
|
for variant (a) (see page 16)
|
4.6
|
Sodium
or potassium hydroxide, 0.1 M solution, carbonate free
|
|
4.7
|
Sulfuric
acid, 0.1 M solution
|
for variant (b) (see page 16)
|
4.8
|
Sodium
or potassium hydroxide, 0.2 M solution, carbonate free
|
|
4.9
|
Sulfuric
acid, 0.25 M solution
|
for variant (c) (see page 16)
|
4.10
|
Sodium
or potassium hydroxide, 0.5 M solution, carbonate free
|
|
4.11
|
Indicator
solutions:
|
|
4.11.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume
of A with 2 volumes of B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops).
|
|
4.11.2
Methyl red indicator:
|
|
Dissolve
0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and
filter if necessary. This indicator (4 to 5 drops) may be used instead of
the preceding one.
|
4.12
|
Anti-bump
granules of pumice stone, washed in hydrochloric acid and ignited.
|
4.13
|
Potassium
thiocyanate.
|
5. APPARATUS
5.1 Distillation
apparatus. See Method 2.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution
Weigh to the nearest 0.001 g, 1 g of the prepared sample and place it in the
Kjeldahl flask. Add 50 ml 50% sulfuric acid (4.1), 10-15 g potassium sulfate
(4.2) and one of the prescribed catalysts (4.3). Heat slowly to drive off the
water, boil gently for two hours, allow to cool, and dilute with 100-150 ml
water.
Cool again, transfer the suspension quantitatively to a 250 ml graduated
flask, make up to volume with water, shake and filter through a dry filter
into a dry flask. Discard the first portion of the filtrate.
7.2 Determination
According to the variant chosen (see Method 2) transfer with a pipette 50,
100 or 200 ml of the solution to the distillation apparatus and add
sufficient sodium hydroxide solution (4.4) to ensure a considerable excess.
Distil the ammonia and titrate the excess acid as described in Method 2.
7.3 Blank
test
Make a blank test (omitting only the sample) under the same conditions and
allow for this in the calculation of the final result.
7.4 Control
test
Before carrying out the analysis, check that the apparatus is working
properly and that the correct application of the method is used, by taking an
aliquot portion of a standard solution of potassium thiocyanate (4.13),
approximating to the concentration of nitrogen in the sample.
8. EXPRESSION
OF RESULT
The result of the analysis must be expressed as the percentage of nitrogen
(N) contained in the fertiliser as received for analysis.
Variant
(a): N%=(50 - A) × 0.7
Variant
(b): N%=(50 - A) × 0.7
Variant
(c): N%=(35 - A) × 0.875
Where
A = millilitres of sodium or potassium hydroxide used for the titration.
4b.
DETERMINATION
OF TOTAL NITROGEN IN CALCIUM CYANAMIDE — IN THE PRESENCE OF NITRATE
1. SCOPE
This method is for the determination of total nitrogen in calcium cyanamide.
2. FIELD
OF APPLICATION
The method is applicable to calcium cyanamide containing nitrates.
3. PRINCIPLE
The direct application of Kjeldahl's method cannot be applied to calcium
cyanamides containing nitrates. For this reason the nitric nitrogen is
reduced to ammonia with metallic iron and stannous chloride before Kjeldahl
digestion. The ammoniacal nitrogen is then determined as in Method 4a.
4. REAGENTS
4.1
|
Sulfuric
acid (p=1.84 pg/ml).
|
4.2
|
Powdered
iron reduced in hydrogen.
|
4.3
|
Potassium
sulfate, finely pulverised.
|
4.4
|
Sulfuric
acid, 0.05 M solution
|
for variant (a) (see page 16)
|
4.5
|
Sodium
or potassium hydroxide, 0.1 M solution, carbonate free
|
|
4.6
|
Sulfuric
acid, 0.1 M solution
|
for variant (b) (see page16)
|
4.7
|
Sodium
or potassium hydroxide, 0.2 M solution, carbonate free
|
|
4.8
|
Sulfuric
acid, 0.25 M solution
|
for variant (c) (see page 16)
|
4.9
|
Sodium
or potassium hydroxide, 0.5 M solution, carbonate free
|
|
4.10
|
Indicator
solutions:
|
|
4.10.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1
volume of A with 2 volumes of B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.
|
|
4.10.2
Methyl red indicator: Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make
up to 100 ml with water and filter if necessary. This indicator (4 to 5
drops) may be used instead of the preceding one.
|
4.11
|
Solution
of stannous chloride:
|
Dissolve 120 g of stannous chloride (SnCl2.2H2O) in 400 ml
concentrated hydrochloric acid (p=1.18 g/ml) and make up to 1 litre with
water. The solution must be completely clear and prepared immediately
before use.
|
It is essential to check the reducing power of the stannous
chloride. Dissolve 0.5 g of stannous chloride in 2 ml concentrated
hydrochloric acid (p=1.18 g/ml) and make up to 50 ml with water. Then add 5
g of Rochelle salt (potassium sodium tartrate) and a sufficient quantity of
sodium bicarbonate for the solution to show an alkaline reaction to a
litmus paper test.
|
Titrate with 0.1 M iodine solution in the presence of a starch
solution as an indicator.
|
1 ml of 0.1 M iodine solution corresponds to 0.01128 g SnCl2.2H2O.
|
At least 80% of the total tin present in the solution thus prepared
must be in the bivalent form. For the titration at least 35 ml of 0.1 M
iodine solution should be used.
|
4.12
|
Sodium
hydroxide solution, 30 g per 100 ml, ammonia free.
|
4.13
|
Standard
nitrate-ammoniacal solution:
|
Weigh out 2.500 g of potassium nitrate and 10.160 g of ammonium
sulfate into a 250 ml graduated flask. Dissolve in water and make up to 250
ml. 1 ml of this solution contains 0.010 g of nitrogen.
|
4.14
|
Anti-bump
granules of pumice stone, washed in hydrochloric acid and ignited.
|
5. APPARATUS
Distillation apparatus. See Method 2.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution
Weigh to the nearest 0.001 g,1 g of the prepared sample into the Kjeldahl
flask. Add 0.5 g of powdered iron (4.2) and 50 ml of the stannous chloride
solution (4.11), stir and leave standing for half an hour. During the time it
is left standing, stir again after 10 and 20 minutes. Then add 10 g of
potassium sulfate (4.3) and 30 ml of sulfuric acid (4.1). Boil and continue
for an hour after the appearance of white fumes. Leave to cool and dilute
with 100-150 ml of water. Transfer the suspension quantitatively into a 250
ml graduated flask, cool and make up to volume with water, mix and filter
through a dry paper into a dry container. Discard the first portion of the
filtrate.
7.2 Determination
According to the variant chosen (see Method 2) transfer with a pipette 50,
100 or 200 ml of the solution to the distillation apparatus and add
sufficient sodium hydroxide solution (4.12) to ensure a considerable excess.
Distil the ammonia and titrate the excess acid as described in Method 2.
7.3 Blank
test
Make a blank test (omitting only the sample) under the same conditions and
allow for this in the calculation of the final result.
7.4 Control
test
Before carrying out the analysis, check that the apparatus is working
properly and that the correct application of the method is used with a
standard solution containing quantities of ammoniacal and nitrate nitrogen
comparable to the quantities of cyanamide and nitrate nitrogen contained in
nitrated calcium cyanamide.
8. EXPRESSION
OF RESULT
The result of the analysis must be expressed as the percentage of total
nitrogen (N) contained in the fertiliser as received for analysis.
Variant (a): N%=(50 - A) × 0.7
Variant (b): N%=(50 - A) × 0.7
Variant (c): N%=(35 - A) × 0.875
Where A = millilitres of sodium or potassium hydroxide used for the
titration.
5.
DETERMINATION
OF TOTAL NITROGEN IN UREA
1. SCOPE
This method is for the determination of total nitrogen in urea.
2. FIELD
OF APPLICATION
The method is applicable exclusively to urea fertilisers which are nitrate
free.
3. PRINCIPLE
Urea is transformed quantitatively into ammonia by boiling in the presence of
sulfuric acid. The ammonia thus obtained is distilled from an alkaline medium
and collected in an excess of standard sulfuric acid. The excess acid is
titrated by means of a standard alkaline solution.
4. REAGENTS
4.1
|
Sulfuric
acid, concentrated (p = 1.84 g/ml).
|
4.2
|
Sodium
hydroxide solution, 30 g per 100 ml, ammonia free.
|
4.3
|
Sulfuric
acid, 0.05 M solution
|
for variant (a) (see page 16)
|
4.4
|
Sodium
or potassium hydroxide, 0.1 M solution, carbonate free
|
|
4.5
|
Sulfuric
acid, 0.1 M solution
|
for variant (b) (see page 16)
|
4.6
|
Sodium
or potassium hydroxide, 0.2 M solution, carbonate free
|
|
4.7
|
Sulfuric
acid, 0.25 M solution
|
for variant (c) (see page 16)
|
4.8
|
Sodium
or potassium hydroxide, 0.5 M solution, carbonate free
|
|
4.9
|
Indicator
solutions:
|
|
4.9.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1
volume of A with 2 volumes of B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops).
|
|
4.9.2
Methyl red indicator:
|
|
Dissolve
0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water. Filter
if necessary. This indicator (4 to 5 drops) may be used instead of the
preceding one.
|
4.10
|
Anti-bump
granules of pumice stone, washed in hydrochloric acid and ignited.
|
4.11
|
Urea.
|
5. APPARATUS
5.1 Distillation
apparatus. See Method 2.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution
Weigh to the nearest 0.001 g, 2.5 g of the prepared sample into a 300 ml
Kjeldahl flask and moisten with 20 ml water. Add with care 20 ml concentrated
sulfuric acid (4.1) and a few anti-bump granules (4.10). To prevent
splashing, place a long-stemmed glass funnel in the neck of the flask. Heat
slowly at first, then increase the heat until white fumes are observed (30 -
40 minutes).
Cool
and dilute with 100 - 150 ml water. Transfer quantitatively to a 500 ml
graduated flask, discarding any sediment. Allow to cool to room temperature.
Make up to volume with water, mix and, if necessary, filter through a dry
paper into a dry receptacle. Discard the first portion of the filtrate.
7.2 Determination
According to the variant chosen (see Method 2) transfer with a pipette 25, 50
or 100 ml of the solution to the distillation apparatus and add sufficient
sodium hydroxide solution (4.2) to ensure a considerable excess. Distil the
ammonia and titrate the excess acid as described in Method 2.
7.3 Blank
test
Carry out a blank test (omitting only the sample) under the same conditions
and allow for this in the calculation of the final result.
7.4 Control
test
Before carrying out the analysis, check that the apparatus is working
properly and that the correct application of the method is used, with an
aliquot portion of a freshly prepared solution of urea (4.11).
8. EXPRESSION
OF RESULT
Express the result as the percentage of total nitrogen (N) contained in the
fertiliser as received for analysis.
Variant (a): N%=(50 - A) × 1.12
Variant (b): N%=(50 - A) × 1.12
Variant (c): N%=(35 - A) × 1.40
Where A = millilitres of sodium or potassium hydroxide used for the
titration.
6.
DETERMINATION
OF CYANAMIDE NITROGEN
1. SCOPE
This method is for the determination of cyanamide nitrogen.
2. FIELD
OF APPLICATION
Calcium cyanamide and calcium cyanamide/nitrate mixtures.
3. PRINCIPLE
Cyanamide nitrogen is precipitated as a silver complex and estimated in the
precipitate by Kjeldahl's method.
4. REAGENTS
4.1
|
Glacial
acetic acid.
|
4.2
|
Ammonia
solution: dilute one volume of ammonia (p=0.88 pg/ml) with 3 volumes of
water.p
|
4.3
|
Ammoniacal
silver solution, according to Tollens, freshly prepared: mix 500 ml silver
nitrate solution (10 g per 100 ml) with 500 ml ammonia solution (4.2).
|
Do not expose unnecessarily to light, heat or air.
|
Safety precaution: when handling ammoniacal silver nitrate solution,
safety goggles must be worn.
|
4.4
|
Concentrated
sulfuric acid (p=1.84 g/ml).
|
4.5
|
Potassium
sulfate.
|
4.6
|
Copper
oxide (CuO), 0.3 - 0.4 g for each determination or an equivalent quantity of
copper sulfate pentahydrate (0.95 - 1.25 g) for each determination.
|
4.7
|
Sodium
hydroxide solution, 30 g per 100 ml, ammonia free.
|
4.8
|
Sulfuric
acid, 0.05 M solution.
|
4.9
|
Sodium
or potassium hydroxide, 0.1 M solution.
|
4.10
|
Indicator
solutions:
|
|
4.10.1
Mixed indicator:
|
|
Solution
A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and
make up to 1 litre with water.
|
|
Solution
B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1
volume of A with 2 volumes of solution B.
|
|
This
indicator is violet in acid solution, grey in neutral solution and green in
alkaline solution. Use 0.5 ml (10 drops).
|
4.10.2 Methyl red indicator:
|
|
|
Dissolve
0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water. Filter
if necessary. This indicator (4 to 5 drops) may be used instead of the
preceding one.
|
4.11
|
Anti-bump
granules of pumice stone, washed in hydrochloric acid and ignited.
|
4.12
|
Potassium
thiocyanate.
|
5. APPARATUS
5.1 Distillation
apparatus. See Method 2.
5.2
500
ml graduated flask (e.g. Stohmann).
5.3
Rotary
shaker, 35 - 40 turns per minute.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the solution for analysis
Weigh, to the nearest 0.001 g, 2.5 g of the prepared sample into a small
glass mortar. Grind the sample three times with water, pouring off the water
after each grinding into the 500 ml graduated flask (5.2). Transfer the
sample quantitatively into the flask, washing the mortar, pestle and funnel
with water. Make up with water to approximately 400 ml. Add 15 ml acetic acid
(4.1). Shake on the rotary shaker (5.3) for two hours.
Make up to 500 ml with water, mix and filter. Discard the first portion of
the filtrate.
Proceed immediately to 7.2.
7.2 Determination
Transfer 50.0 ml of the filtrate to a 250 ml beaker. Add ammonia solution
(4.2) until slightly alkaline and add 30 ml warm ammoniacal silver nitrate
(4.3) to precipitate the yellow silver complex of cyanamide. Leave overnight,
filter and wash the precipitate with cold water until completely free of
ammonia.
Place the filter paper and the precipitate, still moist, in a Kjeldahl flask,
add 10 - 15 g potassium sulfate (4.5), the catalyst (4.6) in the prescribed
proportion, then 50 ml water and 25 ml concentrated sulfuric acid (4.4). Warm
the flask slowly, whilst shaking it gently until the contents come to the
boil. Increase the heat, boil until the contents of the flask become either
colourless or pale green. Continue boiling for one hour, then leave to cool.
Transfer the liquid quantitatively from the Kjeldahl flask to the
distillation flask, add a few anti-bump granules of pumice stone (4.11) and
make up with water to a total volume of approximately 350 ml. Mix and cool.
Add sufficient sodium hydroxide solution (4.7) to ensure a considerable
excess.
Distil the ammonia and titrate the excess acid as described in Method 2
(variant (a)).
7.3 Blank
test
Make a blank test (omitting only the sample) under the same conditions and
allow for this in the calculation of the final result.
7.4 Control
test
Before carrying out the analysis, check that the apparatus is working
properly and that the correct application of the method is used, with an
aliquot portion of a standard solution of potassium thiocyanate (4.12),
corresponding to 0.05 g of nitrogen.
8. EXPRESSION
OF RESULT
Express the result as the percentage of cyanamide nitrogen contained in the
fertiliser as received for analysis.
N%=(50 - A) × 0.56
Where A = millilitres of sodium or potassium hydroxide used for the
titration.
7.
DETERMINATION
OF BIURET IN UREA
1. SCOPE
This method is for the determination of biuret in urea.
2. FIELD
OF APPLICATION
The method is applied exclusively to urea.
3. PRINCIPLE
In an alkaline medium, in the presence of potassium sodium tartrate, biuret
and bivalent copper form a violet cupric compound, the absorbance of which is
measured at 546 nm.
4. REAGENTS
4.1
|
Methanol.
|
4.2
|
Sulfuric
acid solution, approximately 0.05 M.
|
4.3
|
Sodium
hydroxide solution, approximately 0.1 M.
|
4.4
|
Alkaline
solution of potassium sodium tartrate:
|
In a 1 litre graduated flask dissolve 40 g of sodium hydroxide in
500 ml of water and leave to cool. Add 50 g of potassium sodium tartrate
(KNaC4H4O6.4H2O). Make up to the mark and mix. Leave standing 24 hours
before use.
|
4.5
|
Copper
sulfate solution:
|
In a 1 litre graduated flask dissolve 15 g of copper sulfate
(CuSO4.5H2O) in 500 ml of water. Make up to the mark and mix.
|
4.6
|
Biuret
standard solution:
|
In a 250 ml graduated flask, dissolve 0.250 g of pure biuret[8]
in water. Make up to the mark and mix. 1 ml of this solution contains 0.001
g of biuret. This solution should be freshly prepared.
|
4.7
|
Methyl
red indicator solution:
|
Dissolve 0.1 g methyl red in 50 ml 95% ethanol and make up to 100 ml
with water. Filter if necessary.
|
5. APPARATUS
5.1 Spectrophotometer.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of the standard curve
Transfer 2, 5, 10, 20, 25 and 50 ml aliquot portions of biuret standard
solution (4.6) into a series of six 100 ml graduated flasks. Make up the
volumes to about 50 ml with water, add one drop of indicator solution (4.7)
and neutralise, if necessary, with 0.05 M sulfuric acid (4.2). Add the
swirling 20.0 ml of the alkaline tartrate solution (4.4) and then 20.0 ml
copper sulfate solution (4.5). Make up to the mark with water, mix and allow
to stand at 30+ 2 C for fifteen minutes.
At the same time prepare a reagent blank as follows. Place 50 ml water in a
100 ml graduated flask and proceed as described above from "... add one
drop of indicator solution ...".
Measure the absorbance of each solution at 546 nm against the reagent blank
as reference, using cells of suitable path length. Plot the calibration
curve, using the absorbances as the ordinates and the corresponding
quantities of biuret in milligrams, as the abscissae.
7.2 Preparation
of solution for analysis
Weigh to the nearest 0.001g, 10 g of the prepared sample; dissolve in about
150 ml of water in a 250 ml graduated flask and make up to the mark and mix.
Filter if necessary.
Note
1: If the sample for analysis contains more than 0.015 g of
ammoniacal nitrogen, dissolve in 50 ml methanol (4.1) in a 250 ml beaker.
Reduce by evaporation to a volume of about 25 ml. Transfer quantitatively to
a graduated 250 ml flask. Make up to the mark with water. Filter, if
necessary, through a dry fluted paper into a dry receiver.
Note
2: Elimination of the opalescence: if any colloidal substance
is present difficulties may arise during filtration. In that case the
solution for analysis is prepared as follows: dissolve the sample in 150 ml
of water, add 2 ml 1 M hydrochloric acid, and filter the solution into a 250
ml graduated flask. Wash the filters with water and make up to volume.
Continue the process according to the method described in 7.3.
7.3 Determination
According to the presumed biuret content, transfer with a pipette 25 or 50 ml
from the solution prepared in 7.2, to a 100 ml graduated flask and neutralise
if necessary with 0.05 M sulfuric acid or sodium hydroxide solution (4.2 or
4.3) as required, using methyl red indicator (4.7). Add 20.0 ml of the
alkaline solution of potassium sodium tartrate (4.4) and 20.0 ml of the
copper solution (4.5). Make up to volume, mix thoroughly and leave standing
for 15 minutes at 30 C+2. Measure the absorbance of the solution as described
in 7.1.
8. EXPRESSION
OF RESULTS
|
where:
C = mass, in mg, of biuret read from the standard curve;
V = volume of the aliquot used for the determination.
|
|
8a.
DETERMINATION
OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE PRESENCE OF
CYANAMIDE NITROGEN
1. SCOPE
This method is for the determination of any one form of nitrogen in the
presence of any other form.
2. FIELD
OF APPLICATION
Any fertiliser in Group 1(a) of Section A, and Groups 1, 2 and 3 of Section B
of the Table in Schedule 1 of the Fertilisers Regulations 1991 containing
nitrogen in various forms.
3. PRINCIPLE
3.1 Total
soluble and insoluble nitrogen
3.1.1 In the absence of nitrates,
the sample is subjected to direct Kjeldahl digestion.
3.1.2 In the presence of nitrates,
the sample is subjected to Kjeldahl digestion after reduction with the aid of
metallic iron and stannous chloride. In both cases, the ammonia is determined
according to Method 2.
Note: If
analysis shows an insoluble nitrogen content of more than 0.5%, it is
presumed that the fertiliser contains other forms of insoluble nitrogen not
specified for fertilisers covered by the list in paragraph 2.
3.2 Forms
of soluble nitrogen
The following are determined from different aliquot parts taken from the same
solution of the sample:
3.2.1 Total soluble nitrogen
3.2.1.1 In
the absence of nitrates, by direct Kjeldahl digestion.
3.2.1.2 In
the presence of nitrates, by Kjeldahl digestion on an aliquot portion
taken from the solution after reduction according to Ulsch, the ammonia being
determined in both cases as described in Method 2.
3.2.2 Total soluble nitrogen with the
exception of nitric nitrogen, by Kjeldahl digestion after elimination in
an acid medium of nitric nitrogen with ferrous sulfate, the ammonia being
determined as described in Method 2.
3.2.3 Nitric nitrogen by difference
3.2.3.1 In
the absence of calcium cyanamide, between (3.2.1.2) and (3.2.2) or
between total soluble nitrogen (3.2.1.2) and the sum of ammoniacal nitrogen
and ureic nitrogen (3.2.4+3.2.5).
3.2.3.2 In
the presence of calcium cyanamide, between (3.2.1.2) and (3.2.2) and
between (3.2.1.2) and the sum of (3.2.4+3.2.5+3.2.6).
3.2.4 Ammoniacal nitrogen
3.2.4.1 Solely
in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen,
by applying Method 2.
3.2.4.2 In
the presence of ureic nitrogen and/or cyanamide nitrogen, by cold
distillation after making slightly alkaline, the ammonia being absorbed in a
standard solution of sulfuric acid and determined as described in Method 2.
3.2.5 Ureic nitrogen
Either
3.2.5.1 By
conversion using urease into ammonia which is titrated with a standard
solution of hydrochloric acid,
or:
3.2.5.2 By
gravimetry with xanthydrol, although biuret will also be precipitated by
xanthydrol, this should not give rise to a significant error in the
determination since its level is generally low in absolute value in compound
fertilisers.
or:
3.2.5.3 By
difference, according to the following table:
Case
|
Nitric
Nitrogen
|
Ammoniacal Nitrogen
|
Cyanamide Nitrogen
|
Difference
|
1
|
Absent
|
Present
|
Present
|
(3.2.1.1)-(3.2.4.2+3.2.6)
|
2
|
Present
|
Present
|
Present
|
(3.2.2)-(3.2.4.2+3.2.6)
|
3
|
Absent
|
Present
|
Absent
|
(3.2.1.1)-(3.2.4.2)
|
4
|
Present
|
Present
|
Absent
|
(3.2.2)-(3.2.4.2)
|
3.2.6 Cyanamide nitrogen, by
precipitation as a silver compound, the nitrogen being estimated in the
precipitate by the Kjeldahl method.
4. REAGENTS
4.1 Potassium
sulfate.
4.2 Iron
powder, reduced with hydrogen (the prescribed quantity of iron must be able
to reduce at least 50 mg of nitric nitrogen).
4.3 Potassium
thiocyanate.
4.4 Potassium
nitrate.
4.5 Ammonium
sulfate.
4.6 Urea.
4.7 Sulfuric
acid solution: dilute an appropriate volume of sulfuric acid (p=1.84 g/ml)
with an equal volume of water.
4.8 Sulfuric
acid, 0.1 M solution.
4.9 Sodium
hydroxide solution, 30 g per 100 ml, ammonia free.
4.10 Sodium
or potassium hydroxide, 0.2 M solution, free from carbonates.
4.11 Stannous
chloride solution:
Dissolve 120 g of stannous chloride (SnCl2.2H2O) in 400 ml of concentrated
hydrochloric acid (p=1.18 g/ml) and make up to 1 litre with water. The solution
must be perfectly clear and prepared immediately before use.
It is essential to check the reducing power of the stannous chloride:
dissolve 0.5 g of stannous chloride in 2 ml of concentrated hydrochloric acid
(p=1.18 g/ml) and make up to 50 ml with water. Then add 5 g of Rochelle salt
(potassium sodium tartrate) and a sufficient quantity of sodium bicarbonate
for the solution to be alkaline to litmus paper.
Titrate with 0.1 M iodine solution in the presence of a starch solution as an
indicator.
1 ml of 0.1 M iodine solution corresponds to 0.01128 g of SnCl2.2H2O.
At least 80% of the total tin present in the solution thus prepared must be
in bivalent form. For the titration, at least 35 ml of 0.1 M iodine solution
must therefore be used.
4.12 Sulfuric
acid, concentrated (p=1.84 g/ml).
4.13 Hydrochloric
acid solution: dilute an appropriate volume of hydrochloric acid (p=1.18
g/ml) with an equal volume of water.
4.14 Glacial
acetic acids.
4.15 Sulfuric
acid solution, approximately 30% (W/V) H2SO4.
4.16 Ferrous
sulfate, crystalline, FeSO4.7H2O
4.17 Sulfuric
acid, 0.05 M solution.
4.18 Octan-1-ol.
4.19 Potassium
carbonate, saturated solution.
4.20 Sodium
or potassium hydroxide, 0.1 M solution, free from carbonate.
4.21 Barium
hydroxide, saturated solution.
4.22 Sodium
carbonate solution, 10 g per 100 ml.
4.23 Hydrochloric
acid, 2 M solution.
4.24 Hydrochloric
acid, 0.1 M solution.
4.25 Urease
solution: Suspend 0.5 g of active urease in 100 ml of distilled water. Using
0.1 M hydrochloric acid (4.24), adjust the pH to 5.4, measured by pH meter.
4.26 Xanthydrol
solution, 5 g per 100 ml in ethanol or methanol (4.31) (do not use products
giving a high proportion of insoluble matter). The solution may be kept for
three months in a well-stoppered bottle, away from the light.
4.27 Copper
oxide (CuO): 0.3 to 0.4 g per determination or an equivalent quantity of
copper sulfate pentahydrate (0.95 to 1.25 g) per determination.
4.28 Anti-bump
granules washed in hydrochloric acid and ignited.
4.29 Indicator
solutions:
4.29.1 Mixed indicator solution: Solution
A: dissolve 1 g of methyl red in 37 ml of 0.1 M sodium hydroxide solution and
make up to one litre with water. Solution B: dissolve 1 g of methylene blue
in water and make up to one litre. Mix one volume of solution A and 2 volumes
of solution B. This indicator is violet in acid solution, grey in neutral
solution and green in alkaline solution. Use 0.5 ml (10 drops) of this
indicator solution.
4.29.2 Methyl red indicator solution:
Dissolve 0.1 g of methyl red in 50 ml of 95% ethanol, make up to 100 ml with
water and filter if necessary. This indicator (4 to 5 drops) can be used instead
of the previous one.
4.30 Indicator
papers: Litmus, bromothymol blue (or other papers sensitive in the range pH 6
to 8).
4.31 Ethanol
or methanol: solution 95%.
5. APPARATUS
5.1 Distillation
apparatus. See Method 2.
5.2 Apparatus
for the determination of ammoniacal nitrogen 7.2.5.3. An example of the
recommended apparatus is reproduced in Figure 6 in the Appendix.
The apparatus is made up of a specially shaped receptacle with a ground glass
neck, a side neck, a connecting tube with a splash head and a perpendicular
tube for the introduction of air. The tubes can be connected to the
receptacle by means of a simple perforated rubber bung. It is important to
give a suitable shape to the end of the tubes introducing air, since the
bubbles of gas must be evenly distributed throughout the solutions contained
in the receptacle and the absorber. The best arrangement consists of small
mushroom-shaped pieces with an external diameter of 20 mm and six openings of
1 mm around the periphery.
5.3 Apparatus
for the estimation of urea nitrogen (7.2.6.1).
It consists of a 300 ml Erlenmeyer flask, with a separating funnel and a
small absorber. An example of the recommended apparatus is reproduced in
Figure 7 in the Appendix.
5.4 Rotary
shaker, 35 - 40 turns per minute.
5.5 pH
meter.
5.6 Laboratory
oven.
5.7 Sintered
glass crucibles, diameter of pores 5 to 15 microns.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Total
soluble and insoluble nitrogen
7.1.1 In the absence of nitrate
7.1.1.1 Digestion
Weigh
to the nearest 0.001 g, a quantity of the prepared sample containing not more
than 100 mg of nitrogen. Place in the flask of the distillation apparatus
(5.1). Add 10 to 15 g of potassium sulfate (4.1), the prescribed quantity of
catalyst (4.27), and a few anti-bump granules (4.28). Then add 50 ml of
dilute sulfuric acid (4.7), and mix thoroughly. First heat gently, mixing
from time to time, until foaming ceases. Then heat so that the liquid boils
steadily and keep it boiling for one hour after the solution has become
clear, preventing any organic matter from sticking to the sides of the flask.
Allow to cool. Carefully add about 350 ml of water, with mixing. Ensure that
the dissolution is as complete as possible. Allow to cool and connect the
flask to the distillation apparatus (5.1).
7.1.1.2 Distillation
of ammonia
Transfer
with a pipette 50 ml of standard 0.1 M sulfuric acid (4.8) into the receiver
of the apparatus. Add the indicator (4.29.1 or 4.29.2). Ensure that the tip
of the condenser is at least 1 cm below the level of the solution.
Taking
the necessary precautions to avoid any loss of ammonia, carefully add to the
distillation flask enough of the concentrated sodium hydroxide solution (4.9)
to make the liquid strongly alkaline (120 ml is generally sufficient: check
by adding a few drops of phenolphthalein. At the end of the distillation the
solution in the flask must still be clearly alkaline). Adjust the heating of
the flask so as to distil 150 ml in half an hour. Test with indicator paper
(4.30) that the distillation has been completed. If it has not, distil a
further 50 ml and repeat the test until the supplementary distillate reacts
neutrally to the indicator paper (4.30). Then lower the receiver, distil a
few ml more and rinse the tip of the condenser. Titrate the excess acid with
a standard solution of potassium or sodium hydroxide 0.2 M (4.10) to the end
point of the indicator.
7.1.1.3 Blank
test
Make
a blank test under the same conditions (omitting only the sample) and use
this value in the calculation of the final result.
7.1.14 Expression of the result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the analysis.
M = mass of the sample in grams.
|
|
7.1.2 In the presence of nitrate
7.1.2.1 Test
sample
Weigh
to the nearest 0.001g, a quantity of the sample containing not more than 40
mg of nitric nitrogen.
7.1.2.2 Reduction
of the nitrate
Mix
the sample in a small mortar with 50 ml of water. Transfer with the minimum
amount of distilled water into a 500 ml Kjeldahl flask. Add 5 g of reduced
iron (4.2) and 50 ml of stannous chloride solution (4.11). Shake and leave to
stand for half an hour. During this time shake again after 10 and 20 minutes.
7.1.2.3 Kjeldahl
digestion
Add
30 ml of sulfuric acid (4.12), 5 g of potassium sulfate (4.1), the prescribed
quantity of catalyst (4.27) and some anti-bump granules (4.28). Heat gently
with the flask slightly tilted. Increase the heat slowly and swirl the
solution frequently to keep the mixture suspended; the liquid darkens and
then clears with the formation of a yellow-green anhydrous iron sulfate
suspension. After obtaining a clear solution simmer for one hour. Leave to
cool. Cautiously take up the contents of the flask in a little water and add
little by little 100 ml of water. Mix and transfer the contents of the flask
into a 500 ml graduated flask. Rinse the flask several times with distilled
water. Make up the volume with water and mix. Filter through a dry paper into
a dry receiver. Discard the first portion of the filtrate.
7.1.2.4 Distillation
of ammonia
Transfer
into the flask of the distillation apparatus (5.1), an aliquot part
containing not more than 100 mg of nitrogen. Dilute to about 350 ml with
distilled water, add a few anti-bump granules (4.28), connect the flask to
the distillation apparatus and continue the determination as described in
paragraph 7.1.1.2.
7.1.2.5 Blank
test
See
7.1.1.3.
7.1.2.6 Expression
of the result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the analysis.
M = mass of the sample, expressed in grams, present in the aliquot part
taken for a analysis.
|
|
7.2 Forms
of soluble nitrogen
7.2.1 Preparation of the solution to be
analysed
Weigh to the nearest 0.001 g, 10 g of
the sample and place it in a 500 ml graduated flask.
7.2.1.1 In
the case of fertilisers not containing cyanamide nitrogen
Add
to the flask 50 ml of water and then 20 ml of dilute hydrochloric acid
(4.13). Shake and leave it to stand until the evolution of carbon dioxide
ceases. Then add 400 ml of water and shake for half an hour on the rotary
shaker (5.4).
Make
up to the volume with water, mix and filter through a dry filter into a dry
receiver. Discard the first portion of the filtrate.
7.2.1.2 In
the case of fertilisers containing cyanamide nitrogen
Add
to the flask 400 ml of water and a few drops of methyl red (4.29.2). If
necessary make the solution acidic by using acetic acid (4.14). Add 15 ml of
acetic acid (4.14). Shake on the rotary shaker (5.4) for 2 hours. If
necessary, re-acidify the solution during the operation, using acetic acid
(4.14). Make up to the volume with water, mix, filter immediately through a
dry filter into a dry receiver and immediately determine the cyanamide
nitrogen.
In
both cases, determine the various soluble forms of nitrogen the same day
the solution is made up, starting with cyanamide nitrogen and urea nitrogen,
if they are present.
7.2.2 Total soluble nitrogen
7.2.2.1 In
the absence of nitrate
Transfer
by pipette into a 300 ml Kjeldahl flask, an aliquot portion of the filtrate
(7.2.1.1 or 7.2.1.2), containing not more than 100 mg of nitrogen. Add 15 ml
of concentrated sulfuric acid (4.12), 0.4 g of copper oxide or 1.25 g of
copper sulfate (4.27) and a few anti-bump granules (4.28). First heat gently
to begin the digestion and then at a higher temperature until the liquid
becomes colourless or slightly greenish and white fumes are clearly apparent.
After cooling, quantitatively transfer the solution into the distillation
flask, dilute to about 500 ml with water and add a few anti-bump granules
(4.28). Connect the flask to the distillation apparatus (5.1) and continue the
distillation as described in paragraph 7.1.1.2.
7.2.2.2 In
the presence of nitrate
Transfer
by pipette into a 500 ml Erlenmeyer flask, an aliquot portion of the filtrate
(7.2.1.1 or 7.2.1.2) containing not more than 40 mg of nitric nitrogen. At
this stage of the analysis the total quantity of nitrogen is not important.
Add 100 ml of 30% sulfuric acid (4.15), 5 g of reduced iron (4.2) and
immediately cover the Erlenmeyer flask with a watch glass. Heat gently until
the reaction is steady but not vigorous. At this juncture stop the heating
and allow the flask to stand for at least three hours at ambient temperature.
With water, quantitatively transfer the liquid into a 250 ml graduated flask,
leaving behind the undissolved iron and make up to the mark with water. Mix
thoroughly, and transfer by pipette into a 300 ml Kjeldahl flask, an aliquot
part containing not more than 100 mg of nitrogen. Add 15 ml of concentrated
sulfuric acid (4.12), 0.4 g of copper oxide or 1.25 g of copper sulfate
(4.27) and some anti-bump granules (4.28). First heat gently to begin the
digestion and then at a higher temperature until the liquid becomes
colourless or slightly greenish and white fumes are clearly apparent. After
cooling transfer the solution quantitatively into the distillation flask,
dilute to approximately 500 ml with water and add some anti-bump granules
(4.28). Connect the flask to the distillation apparatus (5.1) and continue
the determination as described in paragraph 7.1.1.2.
7.2.2.3 Blank
test
See
7.1.1.3.
7.2.2.4 Expression
of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for analysis.
M = mass of the sample, expressed in grams, present in the aliquot part
taken for analysis.
|
|
7.2.3 Total soluble nitrogen with the
exception of nitric nitrogen
Transfer by pipette into a 300 ml
Kjeldahl flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2)
containing not more than 50 mg of nitrogen. Dilute to 100 ml with water, add
5 g of ferrous sulfate (4.16), 20 ml of concentrated sulfuric acid (4.1) and
some anti-bump granules (4.28). First heat gently and then increase the heat
until white fumes appear. Continue the digestion for 15 minutes. Stop the
heating, introduce the copper oxide (4.27) as a catalyst and keep it at a
temperature such that white fumes are emitted for a further 10 to 15 minutes.
After cooling, quantitatively transfer the contents of the Kjeldahl flask
into the distillation flask of the apparatus (5.1). Dilute to approximately
500 ml with water and add a few anti-bump granules (4.28). Connect the flask
to the distillation apparatus and continue the determination as described in
paragraph 7.1.1.2.
7.2.3.1 Blank
test
See
7.1.1.3
7.2.3.2 Expression
of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for analysis.
M = mass of the sample, expressed in grams, present in the aliquot part
taken for analysis.
|
|
7.2.4 Nitric nitrogen is obtained:
7.2.4.1 In
the absence of calcium cyanamide
By
the difference between the results obtained in paragraphs 7.2.2.4 and 7.2.3.2
and/or the result obtained in paragraph 7.2.2.4 and the sum of the results
obtained in paragraphs 7.2.5.2 or 7.2.5.5 and 7.2.6.3 or 7.2.6.5 or 7.2.6.6.
7.2.4.2 In
the presence of calcium cyanamide
By
the difference between the results obtained in paragraphs 7.2.2.4 and 7.2.3.2
and between the result obtained in paragraph 7.2.2.4 and the sum of the
results obtained in paragraphs 7.2.5.5 and 7.2.6.3 or 7.2.6.5 or 7.2.6.6 and
7.2.7.
7.2.5 Ammoniacal nitrogen
7.2.5.1 Solely
in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen
Transfer
by pipette into the flask of the distillation apparatus (5.1) an aliquot
portion of the filtrate (7.2.1.1) containing not more than 100 mg of ammoniacal
nitrogen. Add water to obtain a total volume of about 350 ml and some
anti-bump granules (4.28) to facilitate boiling. Connect the flask to the
distillation apparatus, add 20 ml of sodium hydroxide solution (4.9) and
distil as described in paragraph 7.1.1.2.
7.2.5.2 Expression
of result
|
where:
a = ml of standard solution or potassium hydroxide (0.2 M) used for the
blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the analysis.
M = mass of the sample, expressed in grams, present in the aliquot part
taken for analysis.
|
|
7.2.5.3 In
the presence of urea and/or cyanamide nitrogen
Transfer
by pipette into the dry flask of the apparatus (5.2), an aliquot portion of
the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 20 mg of
ammoniacal nitrogen. Then assemble the apparatus. Transfer by pipette into
the 300 ml Erlenmeyer flask 50 ml of the standard sulfuric acid solution 0.1
M (4.17) and enough distilled water for the level of the liquid to be
approximately 5 cm above the opening of the delivery tube; add the indicator
(4.29.1). Introduce, through the side neck of the reaction flask, distilled
water to make up the volume to about 50 ml and mix. To avoid foaming during
aeration, add a few drops of octan-1-ol (4.18). Make the solution alkaline by
adding 50 ml of saturated potassium carbonate solution (4.19) and immediately
begin to expel the ammonia thus liberated from the cold suspension. A strong
current of air is necessary (flow of approximately 3 litres per minute) and
should be purified beforehand by passing it through washing flasks containing
dilute sulfuric acid and dilute sodium hydroxide. Instead of using
pressurised air, it is also possible to use a vacuum (water pump) provided
that the inflow tube is connected in a sufficiently airtight manner to the
receiver used to collect the ammonia. The liberation of the ammonia is
generally complete after three hours. It is nevertheless advisable to verify
this by changing the receiving flask. When the operation is finished,
disconnect the flask from the apparatus, rinse the tip of the tube and the
sides of the flask with a little distilled water. Titrate the excess acid
with standard sodium hydroxide solution (0.1 M) (4.20) to the end point of
the indicator (4.29.1).
7.2.5.4 Blank
test
See
7.1.1.3.
7.2.5.5 Expression
of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 M) used
for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.1 M) used
for the analysis.
M = mass of the sample, expressed in grams, present in the aliquot part
taken for analysis.
|
|
7.2.6 Ureic nitrogen
7.2.6.1 Urease
method
Transfer
by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate
(7.2.1.1 or 7.2.1.2) containing not more than 250 mg of ureic nitrogen. To
remove phosphates add saturated barium hydroxide solution (4.21) until no
further precipitation occurs. Eliminate the excess of barium ions and any
dissolved calcium ions by adding 10% sodium carbonate solution (4.22). Allow
the precipitate to settle and check whether total precipitation has occurred.
Make up to the mark, mix and filter through a pleated filter. Transfer by pipette
50 ml of the filtrate into the 300 ml Erlenmeyer flask of the apparatus
(5.3). Acidify the filtrate with 2 M hydrochloric acid (4.23), until a pH of
3.0 measured by the pH meter (5.5) is obtained. Then raise the pH to 5.4 with
0.1 M sodium hydroxide solution (4.20).
To
avoid losses of ammonia during reaction with urease, close the Erlenmeyer
flask with a stopper provided with a separating funnel and a small bubble
trap containing exactly 2 ml of standard 0.1 M hydrochloric acid (4.24).
Introduce through the separating funnel 20 ml of urease solution (4.25), and
allow to stand for one hour at 20 - 25 C. Transfer by pipette 25 ml of
standard 0.1 M hydrochloric acid (4.24) into the separating funnel, allow it
to run through into the solution and then rinse with a little water. In the
same way transfer quantitatively the contents of the bubble trap into the
solution contained in the Erlenmeyer flask. Titrate the excess acid with the
standard solution of sodium hydroxide (0.1 M) (4.20), until a pH of 5.4 is obtained,
measured by the pH meter.
7.2.6.2 Blank
test
See
7.1.1.3.
7.2.6.3 Expression
of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 M) used
for the blank, carried out exactly under the same conditions as the
analysis.
A = ml of standard solution of sodium or potassium hydroxide (0.1 M) used
for the analysis.
M = mass of the sample, expressed in grams, present in the aliquot part
taken for analysis.
|
|
Remarks
(1)
|
After
precipitation by the solutions of barium hydroxide and sodium carbonate,
make up to the mark, filter and neutralise as rapidly as possible.
|
(2)
|
The
titration may also be carried out with the indicator (4.29.2), but the end
point is then more difficult to observe.
|
7.2.6.4 Gravimetric
method with xanthydrol
Transfer
by pipette into a 250 ml beaker, an aliquot portion of the filtrate (7.2.1.1
or 7.2.1.2) containing not more than 20 mg of urea. Add 40 ml of acetic acid
(4.14). Stir with a glass rod for one minute, allow any precipitate to settle
for five minutes. Filter into a 100 ml beaker, wash with several ml of acetic
acid (4.14), then add to the filtrate drop by drop, 10 ml of xanthydrol
solution (4.16), stirring continuously with a glass rod. Allow to stand until
the precipitate appears, then stir again for one or two minutes. Allow to
stand for one and half hours. Filter through a sintered glass crucible (5.7)
which has been previously dried and weighed, using a slight reduction in
pressure. Wash three times with 5 ml ethanol (4.31) without trying to remove
all the acetic acid. Place it in the oven (5.6) at a temperature of 130 C for
one hour (do not exceed 145 C). Allow to cool in a desiccator and weigh.
7.2.6.5 Expression
of result
|
where:
m = mass of the precipitate obtained, in grams.
M = mass of the sample, in grams, present in the aliquot part taken for
analysis. Correct for the blank.
|
|
Note: although
biuret will also be precipitated by xanthydrol, this should not give rise to
a significant error in the determination since its level is generally low.
7.2.6.6 Method
of difference
Ureic
nitrogen may also be calculated according to the following table: —
Case
|
Nitric
Nitrogen
|
Ammoniacal Nitrogen
|
Cyanamide Nitrogen
|
Ureic Nitrogen
|
1
|
Absent
|
Present
|
Present
|
(7.2.2.4) - (7.2.5.5+7.2.7)
|
2
|
Present
|
Present
|
Present
|
(7.2.3.2) - (7.2.5.5+7.2.7)
|
3
|
Absent
|
Present
|
Absent
|
(7.2.2.4) - (7.2.5.5)
|
4
|
Present
|
Present
|
Absent
|
(7.2.3.2) - (7.2.5.5)
|
7.2.7 Cyanamide Nitrogen
Take
an aliquot part of the filtrate (7.2.1.2), containing 10 to 30 mg of
cyanamide nitrogen and place it in a 250 ml beaker. Continue the analysis
according to Method 6.
8. VERIFICATION
OF RESULTS
8.1 In
certain cases, a difference may be found between the total nitrogen obtained
directly from a weighed out sample (paragraph 7.1) and total soluble nitrogen
(paragraph 7.2.2). Nevertheless, the difference should not be greater than
0.5%. If this is not the case, the fertiliser contains forms of insoluble
nitrogen not specified for fertilisers covered by the list in paragraph 2.
8.2 Before
each analysis, check that the apparatus is working properly and that the
correct application of the method is used, with a standard solution including
the various forms of nitrogen in proportions similar to those of the test
sample. This standard solution is prepared from solutions of potassium
thiocyanate (4.3), potassium nitrate (4.4), ammonium sulfate (4.5) and urea
(4.6).
8b.
DETERMINATION
OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE ABSENCE OF
CYANAMIDE NITROGEN
1. SCOPE
This method is for the determination of any one form of nitrogen in the
presence of any other form, but in the absence of cyanamide nitrogen.
2. FIELD
OF APPLICATION
This method is applicable to all fertilisers in Group 1(a) of Section A and
Groups 1, 2 and 3 of Section B of the Table in Schedule 1 of the Fertilisers
Regulations 1991 which contain exclusively nitric, ammoniacal or ureic
nitrogen.
3. PRINCIPLE
The following determinations are made on different portions of a single
sample solution.
3.1 Total
soluble nitrogen
3.1.1 In the absence of nitrates,
by direct Kjeldahl digestion of the solution.
3.1.2 In the presence of nitrates,
by Kjeldahl digestion of a portion of the solution after reduction by the
Ulsch method; ammonia is determined in both cases as described in Method 2.
3.2 Total
soluble nitrogen except nitric nitrogen, by Kjeldahl digestion after elimination
of nitric nitrogen in acid medium by means of ferrous sulfate; ammonia is
determined as described in Method 2.
3.3 Nitric
nitrogen, by difference: between 3.1.2 and 3.2 and/or between total
soluble nitrogen (3.1.2) and the sum of ammoniacal and ureic nitrogen
(3.4+3.5).
3.4 Ammoniacal
nitrogen, by cold distillation of a weak alkaline solution; the ammonia
is absorbed in a solution of sulfuric acid and determined as described in
Method 2.
3.5 Ureic
nitrogen, either:
3.5.1 By conversion using urease,
into ammonia, which is determined by titration with a standard solution of
hydrochloric acid;
or,
3.5.2 By gravimetry using xanthydrol:
although biuret will also be precipitated by xanthydrol, this should not give
rise to a significant error in the determination since its level is generally
low in absolute value in compound fertilisers,
or,
3.5.3 By difference, according to
the following table:
Case
|
Nitric
nitrogen
|
Ammoniacal nitrogen
|
Difference
|
1
|
Absent
|
Present
|
(3.1.1) - (3.4)
|
2
|
Present
|
Present
|
(3.2) - (3.4)
|
4. REAGENTS
4.1 Potassium
sulfate.
4.2 Iron
powder, reduced with hydrogen (the prescribed quantity of iron must be able
to reduce at least 50 mg nitric nitrogen).
4.3 Potassium
nitrate.
4.4 Ammonium
sulfate.
4.5 Urea.
4.6 Sulfuric
acid, 0.1 M solution.
4.7 Sodium
hydroxide solution 30 g per 100 ml, ammonia free.
4.8 Sodium
or potassium hydroxide, 0.2 M solution, free of carbonates.
4.9 Sulfuric
acid (p=1.84 g/ml).
4.10 Hydrochloric
acid solution: dilute an appropriate volume of hydrochloric acid (p=1.18
g/ml) with an equal volume of water.
4.11 Glacial
acetic acid.
4.12 Sulfuric
acid solution, approximately 30% (W/V) H2SO4.
4.13 Ferrous
sulfate, crystalline FeSO4.7H2O.
4.14 Sulfuric
acid, 0.05 M solution.
4.15 Octan-1-ol.
4.16 Potassium
carbonate, saturated solution.
4.17 Sodium
or potassium hydroxide, 0.1 M solution.
4.18 Barium
hydroxide, saturated solution.
4.19 Sodium
carbonate solution, 10 g per 100 ml.
4.20 Hydrochloric
acid, 2 M solution.
4.21 Hydrochloric
acid, 0.1 M solution.
4.22 Urease
solution: suspend 0.5 g active urease in 100 ml distilled water. Using 0.1 M
hydrochloric acid (4.21), adjust to pH 5.4, measured with pH meter.
4.23 Xanthydrol
solution, 5 g per 100 ml in ethanol or methanol (4.28) (do not use products
giving a high proportion of insoluble material). The solution can be kept for
3 months in a carefully stoppered bottle in the dark.
4.24 Catalyst:
copper oxide (CuO), 0.3 to 0.4 g per determination, or an equivalent amount
of copper sulfate pentahydrate, (0.95 to 1.25 g).
4.25 Anti-bump
granules of pumice stone washed with hydrochloric acid and ignited.
4.26 Indicator
solutions:
4.26.1 Mixed indicator: Solution A:
dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up
to 1 litre with water. Solution B: dissolve 1 g methylene blue in water and
make up to 1 litre. Mix 1 volume of solution A and 2 volumes of solution B.
This indicator is violet in acid solution, grey in neutral solution and green
in alkaline solution; use 0.5 ml (10 drops) of this indicator.
4.26.2 Methyl red indicator solution:
Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water
and filter if necessary; 4 - 5 drops of this indicator can be used instead of
the previous one.
4.27 Indicator
papers: litmus, bromothymol blue (or other papers sensitive in the range pH 6
- 8).
4.28 Ethanol
or methanol, 95% (V/V).
5. APPARATUS
5.1 Distillation
apparatus. See Method 2.
5.2 Apparatus
for determination of ammoniacal nitrogen. An example of the recommended
apparatus is reproduced in Figure 6 in the Appendix.
5.3 Apparatus
for determination of ureic nitrogen by the urease method (7.6.1). An example
of the recommended apparatus is reproduced in Figure 7 in the Appendix.
5.4 Rotary
shaker: 35 - 40 turns per minute.
5.5 pH
meter.
5.6 Sintered
glass crucibles, diameter of pores 5 to 15 microns.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Preparation
of solution for analysis
Weigh to the nearest 0.001 g, 10 g of the prepared sample and transfer to a
500 ml graduated flask. Add 50 ml water and then 20 ml dilute hydrochloric
acid (4.10) and mix. Allow to stand until the evolution of carbon dioxide
ceases. Add 400 ml water, shake for half an hour; make up to volume with
water, mix, filter through a dry filter into a dry container.
7.2 Total
nitrogen
7.2.1 In the absence of nitrates
Transfer
by pipette into a 300 ml Kjeldahl flask an aliquot portion of the filtrate
(7.1) containing a maximum of 100 mg nitrogen. Add 15 ml concentrated
sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a
few glass beads to control boiling. Heat moderately at first in order to
initiate the reaction, then more strongly until the liquid becomes colourless
or slightly greenish and white fumes appear. After cooling, transfer the
solution into the distillation flask, dilute to about 500 ml with water and
add a few granules of pumice stone (4.25). Connect the flask to the
distillation apparatus (5.1) and carry out the determination as described in
Method 8a, 7.1.1.2.
7.2.2 In the presence of nitrates
Transfer
by pipette into a 500 ml Erlenmeyer flask a aliquot portion of the filtrate
(7.1) containing not more than 40 mg nitric nitrogen. At this stage of the
analysis, the total quantity of nitrogen is unimportant. Add 10 ml of 30%
sulfuric acid (4.12), 5 g reduced iron (4.2) and immediately cover the
Erlenmeyer flask with a watch glass. Heat gently until the reaction becomes
strong but not violent. Stop heating and allow to stand for at least 3 hours
at ambient temperature. Transfer the liquid quantitatively to a 250 ml
graduated flask, ignoring undissolved iron. Make up to the mark with water
and mix carefully. Transfer by pipette a portion containing a maximum of 100
mg nitrogen into a 300 ml Kjeldahl flask. Add 15 ml concentrated sulfuric
acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few
glass beads.
Heat
moderately at first in order to initiate the reaction, then more strongly
until the liquid becomes colourless or slightly greenish and white fumes
appear. After cooling, transfer the solution quantitatively to the
distillation flask, dilute to about 500 ml with water and add a few granules
of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1)
and continue the determination as described in Method 8a, 7.1.1.2.
7.2.3 Blank test
Carry
out a blank test under the same conditions (omitting only the sample), and
use this value in the calculation of the final result.
7.2.4 Expression of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the blank, carried out under the same conditions as the analysis.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for
analysis.
|
|
7.3 Total
nitrogen excluding nitric nitrogen
7.3.1
Transfer by pipette into a 300 ml Kjeldahl flask an aliquot portion of the
filtrate (7.1) containing not more than 50 mg of nitrogen. Dilute to 100 ml
with water, add 5 g ferrous sulfate (4.13), 20 ml concentrated sulfuric acid
(4.9) and a few glass beads to control boiling (425). Heat moderately at
first then more strongly until white fumes appear. Continue the reaction for
15 minutes. Stop heating, introduce 0.4 g copper oxide or 1.25 g copper
sulfate (4.24) as catalyst, resume heating and maintain production of white
fumes for 10 - 15 minutes. After cooling, transfer the contents of the
Kjeldahl flask quantitatively to the distillation flask (5.1). Dilute to
about 500 ml with water and add a few granules of pumice stone (4.25).
Connect the flask to the distillation apparatus and continue the
determinations as in Method 8a, 7.1.1.2.
7.3.2 Blank test
See
7.2.3.
7.3.3 Expression of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used
for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for
analysis.
|
|
7.4 Nitric
nitrogen is obtained: by difference between
(7.2.4)
- (7.5.3+7.6.3)
or
(7.2.4) - (7.5.3+7.6.5)
or
(7.2.4) - (7.5.3+7.6.6)
7.5 Ammoniacal
nitrogen
7.5.1 In the presence of ureic nitrogen
Transfer
by pipette into the dry flask of the apparatus (5.2) an aliquot portion of
the filtrate (7.1) containing a maximum of 20 mg ammoniacal nitrogen. Connect
up the apparatus. Place in the 300 ml Erlenmeyer flask 50.0 ml standard 0.05
M sulfuric acid solution (4.14) and an amount of distilled water such that
the level of the liquid is about 5 cm above the opening of the intake tube.
Introduce through the side neck of the reaction flask distilled water so as
to bring the volume to about 50 ml and mix. To avoid foaming during aeration
add several drops of octan-1-ol (4.15). Add 50 ml saturated potassium carbonate
solution (4.16) and immediately begin to expel the ammonia thus released from
the cold suspension. A strong current of air is necessary (flow rate of about
3 litres per minute) and should be purified beforehand by passing it through
washing flasks containing dilute sulfuric acid and dilute sodium hydroxide.
Instead of using air under pressure, a vacuum may be used (water pump)
provided that the connections between the apparatus are air tight. The
liberation of ammonia is generally complete after three hours. However, it is
desirable to make certain of this by changing the Erlenmeyer flask. When the
process is finished, disconnect the Erlenmeyer flask from the apparatus,
rinse the end of the intake tube and the walls of the Erlenmeyer flask with a
little distilled water and titrate the excess acid against standard 0.1 M
sodium hydroxide solution (4.17).
7.5.2 Blank test
See
7.2.3.
7.5.3 Expression of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 M)
(4.17) used for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.1 M)
(4.17) used for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for
analysis.
|
|
7.6 Ureic
nitrogen
7.6.1 Urease method
Transfer
by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate
(7.1) containing not more than 250 mg of ureic nitrogen. To remove
phosphates, add a suitable quantity of saturated barium hydroxide solution
(4.18) until further addition does not cause the production of more
precipitate. Eliminate excess barium ions (and any dissolved calcium ions)
with 10% sodium carbonate solution (4.19). Allow to settle and check whether
precipitation is complete. Make up to the mark, mix and filter through a
fluted filter paper. Transfer by pipette 50 ml of filtrate into the 300 ml
Erlenmeyer flask of the apparatus (5.3). Acidify with 2 M hydrochloric acid
(4.20) to pH 3.0, measured by means of the pH meter (5.5). Raise the pH to
5.4 by the addition of 0.1 M sodium hydroxide (4.17). To avoid ammonia losses
when hydrolysis by urease occurs, close the Erlenmeyer flask by means of a
stopper provided with a dropping funnel and a small bubble trap containing
exactly 2 ml standard 0.1 M hydrochloric acid solution (4.21). Introduce
through the separating funnel, 20 ml urease solution (4.22). Allow to stand
for one hour at 20 - 25 C. Place 25.0 ml of the standard 0.1 M
hydrochloric acid solution (4.20) in the dropping funnel, allow to run into
the solution, then rinse with a little water. Transfer quantitatively the
contents of the bubble trap to the solution contained in the Erlenmeyer
flask. Titrate the excess acid using standard 0.1 M sodium hydroxide solution
(4.17), until a pH of 5.4 is obtained, measured on the pH meter.
Remarks
1.
|
After
precipitation by barium hydroxide and sodium carbonate solutions, make up
to the mark, filter and neutralise as quickly as possible.
|
2.
|
The
titration may also be carried out using an indicator (4.26), although the
change of colour is more difficult to observe.
|
7.6.2 Blank test
See
7.2.3.
7.6.3 Expression of result
|
where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 M)
(4.17) used for the blank, carried out in exactly the same conditions as
the analysis.
A = ml of standard solution of sodium or potassium hydroxide (0.1 M)
(4.17) used for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for
analysis.
|
|
7.6.4 Gravimetric method using
xanthydrol
Transfer
by pipette into a 100 ml beaker an aliquot portion of the filtrate (7.1)
containing not more than 20 mg urea. Add 40 ml acetic acid (4.11). Stir with
a glass rod for one minute. Allow any precipitate to settle for five minutes.
Filter, wash with a few ml acetic acid (4.11). Add 10 ml xanthydrol solution
(4.23) to the filtrate drop by drop, stirring continuously with a glass rod.
Allow to stand until the precipitate appears, then stir again for one or two
minutes. Allow to stand for one and a half hours. Filter, using a slight
reduction in pressure, through a sintered glass crucible (5.6) which has been
previously dried and weighed. Wash three times with 5 ml ethanol (4.28),
without trying to remove all the acetic acid. Place in an oven at a
temperature of 130°C for one hour (do not exceed 145 C). Allow to cool in a
desiccator and weigh.
7.6.5 Expression of result
|
where:
m = mass of the precipitate in grams.
M = mass of the sample, in grams, present in the aliquot part taken for
analysis.
|
|
Correct
for the blank.
Note:
Although biuret will also be precipitated by xanthydrol, this should not give
rise to a significant error in the determination since its level is generally
low in absolute value in compound fertilisers.
7.6.6 Difference method
Ureic
N can also be calculated as indicated in the following table:
Case
|
Nitric
N
|
Ammoniacal N
|
Ureic N
|
1
|
Absent
|
Present
|
(7.2.4) - (7.5.3)
|
2
|
Present
|
Present
|
(7.3.3) - (7.5.3)
|
8. VERIFICATION
OF RESULTS
8.1 Before
each analysis, check the functioning of the apparatus and the correct
application of the methods used with a standard solution containing the
different forms of nitrogen in proportions similar to those in the sample.
This standard solution is prepared from solutions of potassium nitrate (4.3),
ammonium sulfate (4.4) and urea (4.5).
9a.
EXTRACTION
OF TOTAL PHOSPHORUS BY MINERAL ACIDS
1. SCOPE
This method is for the determination of phosphorus soluble in mineral acids.
2. FIELD
OF APPLICATION
Subject to regulation 6(3), applicable only to the phosphatic fertilisers
listed in Group 2(a) of Section A and Groups 1, 2 and 4 of Section B of the
Table in Schedule 1 of the Fertilisers Regulations 1991, and to phosphatic
fertilisers listed in Groups 1 (a), 1 (b) and 2 of Section C of that table
which are not designated as "EEC fertiliser".
3. PRINCIPLE
Extraction of the phosphorus in the fertiliser with a mixture of nitric acid
and sulfuric acid.
4. REAGENTS
4.1 Sulfuric
acid (p=1.84 g/ml).
4.2 Nitric
acid (p=1.40 g/ml).
5. APPARATUS
5.1 A
Kjeldahl flask, with a capacity of at least 500 ml, or a 250 ml round-bottomed
flask with a glass tube forming a reflux condenser.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001g 2.5 g of the prepared sample and place it in a
dry Kjeldahl flask. Add 15 ml water and swirl to suspend the substance. Add
20 ml nitric acid (4.2) and carefully add 30 ml sulfuric acid (4.1). When the
initial violent reaction has ceased, slowly bring the contents of the flask
to boiling and boil for 30 minutes. Allow to cool and then carefully add with
mixing about 150 ml water and boil for 15 minutes.
Cool completely and transfer the liquid quantitatively to a 500 ml graduated
flask. Make up to volume, mix and filter through a dry fluted filter,
discarding the first portion of the filtrate.
7.2 Determination
Determine the phosphorus using Method 10 on an aliquot portion of the clear
filtrate.
Note:
If the sample contains cellulose matter, the following procedure is suggested
to avoid excessive frothing during digestion:
Weigh
to the nearest 0.001 g, 2.5 g of the prepared sample and place it in a dry
Kjeldahl flask. Add 30 ml sulfuric acid (4.1) and carefully boil until most
of the organic matter has been destroyed. Allow to cool, add 15 ml water and
20 ml nitric acid (4.2); bring to the boil and continue boiling for 30
minutes. Continue as described in 7.1 from "Allow to cool and then
...".
9b.
EXTRACTION
OF PHOSPHORUS BY 2% FORMIC ACID
1. SCOPE
This method is for the determination of phosphorus soluble in 2% formic acid.
2. FIELD
OF APPLICATION
Applicable only to soft natural phosphate.
3. PRINCIPLE
To differentiate between hard natural phosphates and soft natural phosphates,
phosphorus soluble in formic acid is extracted under specified conditions.
4. REAGENTS
4.1 Formic
acid, 2% (20 g per litre): dilute 82 ml formic acid (concentration 98 - 100%
p = 1.22 g/ml) to 5 litres with distilled water.
5. APPARATUS
5.1 500
ml graduated flask with a wide neck (eg Stohmann).
5.2 Rotary
shaker, 35 - 40 turns per minute.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a
dry 500 ml graduated flask (5.1). While continuously rotating the flask by
hand, add the formic acid (4.1) (at 20+1 C) until it is approximately 1 cm
below the graduation mark. Then make up to the volume. Close the flask with a
rubber stopper and shake for 30 minutes (5.2). Filter the solution through a
dry fluted filter, into a dry receiver, discarding the first portion of the
filtrate.
7.2 Determination
Determine the phosphorus using Method 10 on an aliquot portion of the clear
filtrate.
9c.
EXTRACTION
OF PHOSPHORUS BY 2% CITRIC ACID
1. SCOPE
This method is for the determination of phosphorus soluble in 2% citric acid.
2. FIELD
OF APPLICATION
Subject to regulation 6(3) only applicable to basic slag fertilisers in Group
2(a) of Section A and Groups 1, 2 and 4 of Section B of the Table in Schedule
1 of the Fertilisers Regulations 1991.
3. PRINCIPLE
Extraction of the phosphorus in the fertiliser with a 2% citric acid solution
under specified conditions.
4. REAGENT
4.1 2%
citric acid solution (20 g per litre), prepared from citric acid monohydrate.
Note:
Verify the concentration of this citric acid solution by titrating 10 ml with
a 0.1M sodium hydroxide standard solution using phenolphthalein as an
indicator. If the concentration is correct, the titre should be 28.55 ml.
5. APPARATUS
5.1 Rotary
shaker: 35 - 40 turns per minute.
6. PREPARATION
OF THE SAMPLE
The analysis is carried out on the product as received, without grinding,
after carefully mixing the original sample to ensure it is homogeneous. See
Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001 g, 5 g of the mixed sample and place it in a dry
flask with a sufficiently wide neck, with a capacity of 600 ml, to allow the
liquid to be shaken thoroughly. Add 500 ml+1 ml of the citric acid solution
(4.1) at 20+1 C. When adding the first portion of the reagent shake
vigorously by hand to stop the formation of lumps and to prevent the sample
sticking to the sides. Close the flask with a rubber stopper and shake it on
the rotary shaker (5.1) for exactly 30 minutes at a temperature of 20+2 C.
Filter immediately through a dry fluted filter, into a dry glass receiver and
discard the first 20 ml of the filtrate. Continue the filtration until a
sufficient quantity of filtrate is obtained to carry out the phosphorus
determination.
7.2 Determination
Determine the phosphorus using Method 10 on an aliquot portion of the clear
filtrate.
9d.
EXTRACTION
OF PHOSPHORUS BY NEUTRAL AMMONIUM CITRATE
1. SCOPE
This method is for the determination of phosphorus soluble in neutral
ammonium citrate.
2. FIELD
OF APPLICATION
Applicable to all fertilisers in Group 2(a) of Section A and Groups 1, 2 and
4 of Section B and Group 2 of Section C of the Table in Schedule 1 of the
Fertilisers Regulations 1991 for which the declaration of the solubility in
neutral ammonium citrate is prescribed.
3. PRINCIPLE
Extraction of phosphorus at a temperature of 65 C using a neutral ammonium
citrate solution (pH=7.0) under specified conditions.
4. REAGENTS
4.1 Neutral
ammonium citrate solution (pH=7.0).
This solution must contain 185 g of citric acid monohydrate per litre and
must have a specific gravity of 1.09 at 20°C and a pH of 7.0. The reagent is
prepared as follows:
Dissolve 370 g citric acid monohydrate in about 1.5 litres of water and make
an approximately neutral solution by adding 345 ml of ammonia solution (28 -
29% of NH3). If the NH3 concentration is lower than 28% add a correspondingly
larger quantity of ammonia solution and dilute the citric acid in
correspondingly smaller quantities of water.
Cool and make exactly neutral by adding the ammonia solution (28 - 29% of
NH3) drop by drop, stirring continuously (with a mechanical stirrer) until a
pH of exactly 7.0 at 20°C is obtained, keeping the electrodes of the pH meter
(5.1) immersed in the solution.
At this point make up the volume to 2 litres and test the pH again. Keep the
reagent in a closed container and check the pH at regular intervals.
5. APPARATUS
5.1 pH
meter.
5.2 Water
bath which can be set thermostatically at 65°C, equipped with a mechanically
operated shaking tray (see Figure 8 in the Appendix).
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Transfer 1[9] or 3[10] grams, as appropriate, of the
fertiliser to be analysed into a 200 or 250 ml Erlenmeyer flask containing
100 ml of ammonium citrate solution previously heated at 65°C. Stopper the
Erlenmeyer flask and shake in order to suspend the fertiliser without forming
lumps. Remove the stopper for an instant in order to balance the pressure and
close the Erlenmeyer flask again. Place the flask in the water-bath (5.2) set
to maintain the contents of the flask at exactly 65°C. Shake mechanically for
one hour so as to ensure complete suspension of the sample.[11] The level of suspension in the
flask must stay constantly below that of the water in the bath. After exactly
one hour remove the Erlenmeyer flask from the water-bath. Cool immediately
under running water to ambient temperature and transfer the contents
quantitatively from the Erlenmeyer flask into a graduated 500 ml flask with a
jet of water. Make up the volume with water. Mix thoroughly and filter through
a dry fluted filter (medium speed) into a dry container, discarding the first
part of the filtrate (about 50 ml).
About 100 ml of clear filtrate should be collected.
7.2 Determination
Determine the phosphorus using Method 10 in an aliquot portion of the clear
filtrate.
9e.
EXTRACTION
OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (PETERMANN'S METHOD) AT 65°C
1. SCOPE
This method is for the determination of phosphorus soluble in alkaline
ammonium citrate.
2. FIELD
OF APPLICATION
Applicable only to precipitated dihydrated dicalcium phosphate (CaHPO4.2H2O).
3. PRINCIPLE
Extraction of phosphorus at a temperature of 65°C with an alkaline solution
of ammonium citrate (Petermann) under specified conditions.
4. REAGENTS
4.1 Petermann's
solution
Characteristics:
Citric acid monohydrate, 173 g per litre.
Ammonia, 42 g per litre ammoniacal nitrogen.
pH, between 9.4 and 9.7.
Preparation from diammonium citrate:
Dissolve 941 g diammonium citrate in about 3,500 ml water in a 5 litre
graduated flask. Stand the flask in a bath of running water, mix and cool.
Add, in small amounts, 430 ml of ammonia solution (p=0.880 g/ml), from a
freshly opened bottle (or an equivalent amount of diluted ammonia, for
example if p=0.906 g/ml then 502 ml are required). Adjust the temperature to
20°C, make up to volume with water and mix.
Preparation from citric acid and ammonia:
Dissolve 865 g citric acid monohydrate in about 2,500 ml distilled water in a
container of about 5 litres capacity. Place the container in an ice bath and
add in small amounts, shaking continually, 966 ml of ammonia solution
(p=0.880 g/ml), from a freshly opened bottle (or an equivalent amount of
diluted ammonia, for example if p=0.906 g/ml, then, 1,114 ml are required) . Adjust
the temperature to 20°C, transfer to a 5 litre graduated flask, make up to
the mark with distilled water and mix.
Check the ammoniacal nitrogen content as follows:
Transfer 25 ml of the solution into a 250 ml graduated flask, make up to
volume with distilled water and mix. Determine the ammoniacal nitrogen
content on 25 ml of this solution using Method 2. If the solution is correct,
15 ml 0.25 M H2SO4 are required — Calculate the concentration of ammoniacal
nitrogen in the reagent solution (1 ml 0.25 M H2SO4=0.007g nitrogen).
If the concentration of ammoniacal nitrogen is greater than 42 g/litre,
ammonia can be expelled by a stream of inert gas or by moderate heating to
bring back the pH to 9.7. Carry out a second determination.
If the concentration of ammoniacal nitrogen is less than 42 g/litre,
calculate the volume of ammonia solution required to achieve this level (1 ml
ammonia solution, p=0.880 g/ml contains approximately 0.22g ammoniacal
nitrogen). For each ml of ammonia solution required add 0.173 g of citric
acid.
Whenever corrections are made to this reagent solution, it is imperative that
the final concentration of both the citric acid and ammoniacal nitrogen are
as specified.
5. APPARATUS
5.1 Water
bath which can be maintained at a temperature of 65 +1 C.
5.2 500
ml graduated flask with a wide neck (eg Stohmann).
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001g, 1 g of the prepared sample and transfer to the
500 ml graduated flask (5.2). Add 200 ml alkaline ammonium citrate solution
(4.1). Stopper the flask and shake vigorously by hand to avoid the formation
of lumps and to prevent any adherence of the sample to the sides.
Place the flask in the water bath at 65 C and shake every 5 minutes during
the first half an hour. After each shaking, raise the stopper to equilibrate
the pressure. The level of water in the water bath should be above the level
of solution in the flask. Allow the flask to remain in the water bath a
further hour at 65 C and shake every ten minutes. Remove the flask, cool to a
temperature of about 20 C, make up to volume of 500 ml with water. Mix and
filter through a dry fluted filter paper, rejecting the first portion of
filtrate.
7.2 Determination
Determine the phosphorus using Method 10 on an aliquot portion of the clear
filtrate.
9f.
EXTRACTION
OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (PETERMANN'S) METHOD AT AMBIENT
TEMPERATURE
1. SCOPE
This method is for the determination of phosphorus soluble in alkaline
ammonium citrate.
2. FIELD
OF APPLICATION
Applicable only to disintegrated phosphates.
3. PRINCIPLE
Extraction of phosphorus at a temperature of 20°C with an alkaline solution
of ammonium citrate (Petermann's solution) under specified conditions.
4. REAGENT
See Method 9e.
5. APPARATUS
5.1 250
ml graduated flask with a wide neck (eg Stohmann).
5.2 Rotary
shaker, 35 - 40 turns per minute.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and transfer to a
250 ml graduated flask (5.1). Add a little of Petermann's solution (4) at
20°C, shake very hard in order to stop the formation of lumps and to prevent
any of the sample adhering to the side of the flask. Make up to the mark with
Petermann's solution and close the flask with a rubber stopper.
Shake for two hours on the rotary shaker (5.2). Filter immediately through a
dry fluted filter into a dry container, discarding the first portion of the
filtrate.
7.2 Determination
Determine the phosphorus using Method 10 on an aliquot portion of the clear
filtrate.
9g.
EXTRACTION
OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (JOULIE'S METHOD)
1. SCOPE
This method is for the determination of phosphorus soluble in Joulie's
alkaline ammonium citrate.
2. FIELD
OF APPLICATION
Applicable to all the straight and compound phosphatic fertilisers, in which
the phosphate occurs in an aluminocalcic form.
3. PRINCIPLE
Extraction by shaking vigorously with an alkaline solution of ammonium
citrate of defined specification (and where appropriate in the presence of
oxine), at about 20°C.
4. REAGENTS
4.1 Joulie's
alkaline solution of ammonium citrate:
This solution contains 400 g of citric acid monohydrate and 153 g of NH3 per
litre. Its free ammonia content is approximately 55 g per litre. It is
prepared by one of the methods described below:
4.1.1 In a 1 litre graduated flask,
dissolve 400 g of citric acid monohydrate in approximately 600 ml ammonia
solution (p=0.925 g/ml), containing 200 g NH3 per litre; this may be prepared
by diluting 760 ml ammonia solution (p=0.880 g/ml) from a freshly opened
bottle with water to 1 litre. The citric acid is added successively in
quantities of 50 to 80 g maintaining the temperature below 50 C. Make up the
volume to 1 litre with ammonia solution (p=0.925 g/ml).
4.1.2 In a litre graduated flask, dissolve
432 g of diammonium citrate in 300 ml of water. Add 440 ml of ammonia
solution (p=0.925 g/ml) (see 4.1.1 above). Make up the volume to 1 litre with
water.
Verification
of the total ammonia content:
Transfer
a 10 ml sample of the citrate solution to a 250 ml flask. Make up the volume
with distilled water. Determine the ammoniacal nitrogen content on 25 ml of
this solution using Method 2. In these conditions the reagent is considered
to be correct when the volume of 0.25 M sulfuric acid required is between
17.7 and 18.0 ml (1 ml 0.25 M H2SO4=0.008516g NH3). If the titre is too low
add 4.25 ml of ammonia (p=0.925 g/ml) per 0.1 ml below the 18 ml indicated
above.
4.2 8-Hydroxyquinoline
(oxine), powdered.
5. APPARATUS
5.1 Rotary
shaker, 35 - 40 turns per minute.
5.2 500
ml graduated flask with a wide neck (Stohmann).
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.0005 g, 1 g of the prepared sample and place in a
small glass or porcelain mortar. Add about ten drops of ammonium citrate
solution (4.1) to moisten it and then break it up very carefully with a
pestle. Add 20 ml ammonium citrate solution (4.1), mix to a paste and leave
to settle for about 1 minute.
Decant the liquid into a 500 ml graduated flask (5.2). Add 20 ml ammonium
citrate solution (4.1) to the residue, grind as above and decant the liquid
into the graduated flask. Repeat the process four times, so that by the end
of the fifth time all the product can be poured into the flask. The total
quantity of ammonium citrate solution used for these processes must be
approximately 100 ml.
Rinse the residue from the pestle and mortar into the graduated flask with 40
ml of distilled water.
Stopper the flask and shake for three hours on the rotary shaker (5.1).
Leave the flask standing for fifteen to sixteen hours and then shake it again
under the same conditions for three hours. The temperature during the whole
process should be kept at 20°+2°C.
Make up to volume with distilled water and mix. Filter through a dry filter,
discard the first portion of the filtrate and collect the clear filtrate in a
dry flask.
7.2 Determination
Determine the phosphorus using Method 10 on an aliquot portion of the clear
filtrate.
8. NOTE
The use of oxine makes it possible to apply this method to fertilisers
containing magnesium. This is recommended when the ratio of magnesium to
phosphorus pentoxide is higher than 0.03 (Mg/P205>0.03). If this is the
case, add 3 g of oxine to the moistened sample for analysis. The use of oxine
in the absence of magnesium is not, moreover, likely to interfere
subsequently with the determination. In the known absence of magnesium, oxine
may be omitted.
9h.
EXTRACTION
OF PHOSPHORUS BY WATER
1. SCOPE
This method is for the determination of water-soluble phosphorus.
2. FIELD
OF APPLICATION
Applicable to all fertilisers where water-soluble phosphorus is to be
determined.
3. PRINCIPLE
Extraction in water by shaking under specified conditions.
4. APPARATUS
4.1 500
ml graduated flask with a wide neck (eg Stohmann).
4.2 Rotary
shaker, 35 - 40 turns per minute.
5. PREPARATION
OF THE SAMPLE
See Method 1.
6. PROCEDURE
6.1 Extraction
Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a
500 ml graduated flask (4.1). Add 450 ml of water, the temperature of which
must be between 20°C and 25°C. Close the flask and shake on the rotary shaker
(4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly and
filter through a dry fluted paper into a dry container.
6.2 Determination
Determine the phosphorus using Method 10, on an aliquot portion of the clear
filtrate.
10.
DETERMINATION
OF EXTRACTED PHOSPHORUS (Gravimetric method using quinoline phosphomolybdate)
1. SCOPE
This method is for the determination of phosphorus in extracts from
fertilisers.
2. FIELD
OF APPLICATION
This method is applicable to all extracts of fertilisers[12] for the determination of the
different forms of phosphorus.
3. PRINCIPLE
After hydrolysis, phosphorus is precipitated in an acidic solution in the
form of quinoline phosphomolybdate. The precipitate is collected, washed,
dried at 250°C and weighed.
In the above conditions, compounds likely to be found in the solution
(mineral and organic acids, ammonium ions, soluble silicates, etc...) will
not interfere provided that a reagent based on sodium molybdate or ammonium
molybdate is used in the precipitation.
4. REAGENTS
4.1 Concentrated
nitric acid (p = 1.40 g/ml).
4.2 Molybdate
reagent:
4.2.1 Preparation of the reagent based on
sodium molybdate:
Solution
A: dissolve 70 g sodium molybdate dihydrate in 100 ml water
Solution
B: dissolve 60 g citric acid monohydrate in 100 ml water and 85 ml
concentrated nitric acid (4.1).
Solution
C: stir solution A into solution B to obtain solution C.
Solution
D: to 50 ml water add 25 ml concentrated nitric acid (4.1), add 5 ml freshly
distilled quinoline. Add this solution to solution C, mix thoroughly and
leave standing overnight in the dark. Make up to 500 ml with water, mix again
and filter through a sintered glass funnel (5.3).
4.2.2 Preparation of the reagent based on
ammonium molybdate:
Solution
A: dissolve 100 g ammonium molybdate in 300 ml water, heating gently and
stirring from time to time.
Solution
B: dissolve 120 g citric acid monohydrate in 200 ml water and add 170 ml of
concentrated nitric acid (4.1).
Solution
C: add 10 ml freshly distilled quinoline to 70 ml of concentrated nitric acid
(4.1).
Solution
D: slowly pour, stirring well, solution A into solution B. After thoroughly
mixing, add solution C to this mixture and make up to 1 litre with water.
Leave standing for two days in a dark place and filter through a sintered
glass funnel (5.3).
The
reagents 4.2.1 and 4.2.2 can be used in the same way; both must be kept in
the dark in stoppered polyethylene bottles.
5. APPARATUS
5.1 Filter
crucible with porosity of 5 to 20 microns.
5.2 Drying
oven regulated at 250°C+10°C.
5.3 Sintered
glass funnel with porosity of 5 to 20 microns.
6. PROCEDURE
6.1 Treatment
of the solution
Using a pipette take an aliquot portion of fertiliser extract (see the Table)
containing about 0.01 g of P2O5 and transfer to a 500 ml Erlenmeyer flask.
Add 15 ml concentrated nitric acid[13] (4.1) and dilute with water to
about 100 ml.
6.2 Hydrolysis
Bring the contents of the Erlenmeyer flask to the boil slowly and keep at
this temperature until hydrolysis is completed (this usually takes 1 hour).
Care must be taken to avoid losses by splashing and excessive evaporation
which would reduce the initial volume by more than half, by fitting a reflux
condenser. After hydrolysis make up to the initial volume with distilled
water.
6.3 Weighing
the crucible
Dry the filter crucible (5.1) for at least 15 minutes in the drying oven
(5.2). Cool the crucible in a desiccator and weigh.
6.4 Precipitation
Heat the acid solution in the Erlenmeyer flask until it begins to boil and
then precipitate the quinoline phosphomolybdate by adding 40 ml of the
precipitating reagent (4.2.1 or 4.2.2)[14] drop by drop, stirring
continuously. Place the Erlenmeyer flask in a steam bath for 15 minutes,
shaking from time to time. The solution can be filtered immediately or after
it has cooled down.
6.5 Filtering
and Washing
Filter the solution under vacuum by decantation. Wash the precipitate in the
Erlenmeyer flask with 30 ml water. Decant and filter the solution. Repeat
this process five times. Quantitatively transfer the rest of the precipitate
into the crucible washing it with water. Wash four times with 20 ml water,
allowing the liquid to drain from the crucible before each addition.
6.6 Drying
and weighing
Wipe the outside of the crucible with a filter paper. Place the crucible in
the drying oven (5.2) for approximately 15 minutes. Cool in a desiccator and
weigh rapidly, repeat this process until a constant mass is attained.
6.7 Blank
test
For each series of determinations, make a blank test under the same
conditions (omitting only the sample) and allow for this in the calculation
of the final result.
6.8 Control
test
Carry out the determination using an aliquot portion of a potassium
dihydrogen phosphate solution containing 0.01 g of P2O5.
7. EXPRESSION
OF RESULTS
If the samples for analysis and dilutions shown in the Table are used the
following formulae apply:
% P2O5 in the fertiliser = (A-a) × f
% P in the fertiliser = (A-a) × f'
where:
A = weight in g of the quinoline phosphomolybdate
a = mass in g of the quinoline phosphomolybdate obtained in the blank test
f and f'= factors given in the last two columns of the Table.
With samples for analysis and dilutions which differ from those of the Table
the following formulae apply:
% P2O5 in the fertiliser =
|
|
|
|
where:
F = conversion factor, quinoline phosphomolybdate into P2O5 = 0.0321
F'= conversion factor, quinoline phosphomolybdate into P=0.0140.
D = dilution factor
M = mass of the sample analysed.
|
|
TABLE FOR METHOD 10
%P2O5 in the
fertiliser
|
%
in the fertiliser
|
Sample for analysis g
|
Dilution to ml
|
Sample ml
|
Dilution to ml
|
Sample to be precipitated ml
|
Quinoline phosphomolybdate
conversion factor (f) in percentage P2O5
|
Quinoline phosphomolybdate
conversion factor (f1) in percentage P
|
1 - 5
|
0.44
- 2.2
|
|
1
|
500
|
-
|
-
|
100
|
16.04
|
7.00
|
2.5
|
500
|
-
|
-
|
50
|
12.83
|
5.60
|
5
|
500
|
-
|
-
|
25
|
12.83
|
5.60
|
|
|
|
|
|
|
5 - 10
|
2.2
- 4.4
|
|
1
|
500
|
-
|
-
|
50
|
32.07
|
14.00
|
2.5
|
500
|
-
|
-
|
25
|
25.66
|
11.20
|
3
|
500
|
-
|
-
|
25
|
21.38
|
9.33
|
5
|
500
|
-
|
|
10
|
32.07
|
14.00
|
|
|
|
|
|
|
10 - 25
|
4.4
- 11.0
|
|
1
|
500
|
-
|
-
|
25
|
64.15
|
28.00
|
2.5
|
500
|
-
|
-
|
10
|
64.15
|
28.00
|
3
|
500
|
-
|
-
|
10
|
53.46
|
23.33
|
5
|
500
|
50
|
500
|
50
|
64.15
|
28.00
|
|
|
|
|
|
|
+ 25
|
+:
11
|
|
1
|
500
|
-
|
-
|
10
|
160.40
|
70.01
|
2.5
|
500
|
50
|
500
|
50
|
128.30
|
55.99
|
3
|
500
|
50
|
500
|
50
|
106.90
|
46.66
|
5
|
500
|
50
|
500
|
25
|
128.30
|
55.92
|
|
|
|
|
|
|
11.
DETERMINATION
OF WATER-SOLUBLE POTASSIUM
1. SCOPE
This method is for the determination of water-soluble potassium.
2. FIELD
OF APPLICATION
All the potassium fertilisers listed in Group 3(a) of Section A and Groups 1,
3 and 4 of Section B and Group 2 of Section C of the Table in Schedule 1 of
the Fertilisers Regulations 1991.
3. PRINCIPLE
The potassium is extracted with water and after the removal of interfering
substances, the potassium is precipitated in a slightly alkaline medium in
the form of potassium tetraphenylborate (KTPB).
4. REAGENTS
4.1 Formaldehyde,
25 - 35% solution, filter if necessary before use.
4.2 Potassium
chloride.
4.3 Sodium
hydroxide, 10 M solution. Care should be taken to ensure that the sodium
hydroxide is free from potassium.
4.4 Indicator
solution: dissolve 0.5 g phenolphthalein in 100 ml 90% ethanol.
4.5 EDTA
solution: 4 g of the dihydrated disodium salt of ethylenediaminetetra-acetic
acid (EDTA) per 100 ml. Store this reagent in a plastic container.
4.6 STPB
solution: dissolve 32.5 g sodium tetraphenylborate in 480 ml of water, add 2
ml sodium hydroxide solution (4.3) and 20 ml of a magnesium chloride solution
(100 g of MgCl2.6H2O per litre). Stir for fifteen minutes and filter through
a fine, ashless filter paper. Store this reagent in a plastic container.
4.7 Wash
liquid: dilute 20 ml of the STPB solution (4.6) to 1 litre with water.
4.8 Bromine
water: saturated bromine solution in water.
5. APPARATUS
5.1 Filter
crucibles with a porosity of 5 to 20 microns.
5.2 Oven
regulated at 120°+ 10° C.
6. PREPARATION
OF THE SAMPLE
See Method 1.
In
the case of potassium salts the sample must be ground finely enough to ensure
that a representative sample is obtained for analysis. For these products,
Method 1, paragraph 6(a) must be used.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001 g, 10 g of the prepared sample (5 g for potassium
salts containing more than 50% of potassium oxide or 20 g for fertilisers
containing less than 5% of potassium oxide) and place in a 600 ml beaker with
approximately 400 ml of water. Bring to the boil and maintain heat for 30
minutes. Cool, transfer quantitatively into a 1 litre graduated flask, make
up the volume, mix and filter into a dry receiver. Discard the first 50 ml of
the filtrate.
Note: If
the filtrate is dark in colour, transfer by pipette, an aliquot portion
containing at the most 100 mg of K20 and place in a 100 ml beaker, add
bromine water and bring to the boil to eliminate any surplus bromine. After
cooling transfer quantitatively to a 100 ml graduated flask, make up to the
volume, filter and determine the potassium in an aliquot portion of the
filtrate.
7.2 Determination
Transfer by pipette an aliquot portion of the filtrate containing 25-50 mg of
potassium (see Table on page 50) into a 250 ml beaker; make up to 50 ml with
water.
To remove interferences, add 10 ml of the EDTA solution (4.5), several drops
of the phenolphthalein solution (4.4) and stir in, drop by drop, sodium
hydroxide solution (4.3) until a red colour persists. Finally add a few more
drops of sodium hydroxide to ensure an excess (usually 1 ml of sodium
hydroxide is sufficient to neutralise the sample and ensure an excess).
Boil gently for 15 minutes to eliminate most of the ammonia. Add water to
make the volume up to 60 ml.
Bring the solution to the boil, remove the beaker from the heat and add 10 ml
formaldehyde (4.1). Add several drops of phenolphthalein solution (4.4) and
if necessary, more sodium hydroxide solution until a distinct red colour
appears. Cover the beaker with a watch glass and place it on a steam bath for
fifteen minutes.
7.3 Weighing
the crucible
Dry the filter crucible (5.1) to constant weight in the oven at 120° C (5.2)
(about 15 minutes). Allow the crucible to cool in a desiccator and weigh it.
7.4 Precipitation
Remove the beaker from the steam bath, stir in drop by drop 10 ml of the STPB
solution (4.6). This addition should take about 2 minutes; allow to stand for
a least 10 minutes before filtering.
7.5 Filtering
and washing
Filter under vacuum into the weighed crucible, rinse the beaker with the wash
liquid (4.7), wash the precipitate three times with the wash liquid (60 ml in
all of the wash liquid) and twice with 5 to 10 ml of water.
7.6 Drying
and weighing
Wipe the outside of the crucible with a filter paper and place in the oven
(5.2) for one and half hours at a temperature of 120° C. Allow the crucible
to cool in a desiccator to ambient temperature and weigh rapidly.
7.7 Blank
test
Carry out a blank test under the same conditions (omitting only the sample)
and allow for this in the calculation of the final result.
7.8 Control
test
Carry out the determination on an aliquot portion of an aqueous solution of
potassium chloride, containing at the most 40 mg of K2O.
8. EXPRESSION
OF RESULTS
8.1 Method
of calculation and formulae
If the quantities and the dilutions shown in the Table are used, the
following formulae apply:
% K2O in the fertiliser = (A - a) × f
or
% K in the fertiliser = (A - a) × f1
where:
A = mass in grams of the precipitate from the sample
a = mass in grams of the precipitate from the blank
f and f1 = factors — see Table.
With samples and dilutions which differ from those shown in the Table use the
following formulae:
or
|
where:
F = conversion factor, KTPB into K2O = 0.1314
F1 = conversion factor, KTPB into K = 0.109
D = dilution factor
M = mass in grams of sample for analysis.
|
|
TABLE FOR METHOD 11
% of K2O in the
fertiliser
|
%
of K in the fertiliser
|
Sample for analysis (g)
|
Aliquot portion to be taken as a
sample for precipitation (ml)
|
Conversion factor f % K2O
g KTPB
|
Conversion factor f1 % K g KTPB
|
1 - 5
|
0.8
- 4.2
|
20
|
50
|
13.14
|
10.91
|
5 - 10
|
4.2
- 8.3
|
10
|
50
|
26.28
|
21.81
|
10 - 20
|
8.3
- 16.6
|
10
|
25
|
52.56
|
43.62
|
20 - 50
|
16.6
- 41.5
|
10
|
10
|
131.40
|
109.10
|
more than 50
|
more
than 41.5
|
5
|
10
|
262.80
|
218.10
|
12.
DETERMINATION
OF CHLORIDES IN THE ABSENCE OF ORGANIC MATERIAL
1. SCOPE
This method is for the determination of chloride, in the absence of organic
material.
2. FIELD
OF APPLICATION
All fertilisers which are free from organic material, except ammonium nitrate
fertilisers of a nitrogen content greater than 28% by weight.
3. PRINCIPLE
The chlorides, dissolved in water, are precipitated in an acid medium by an
excess of standard solution of silver nitrate. The excess is titrated with a
solution of ammonium thiocyanate in the presence of ferric ammonium sulfate
(Volhard's method).
4. REAGENTS
4.1 Nitrobenzene
or diethyl ether.
4.2 Nitric
acid, 10 M solution.
4.3 Indicator
solution: dissolve 40 g of ferric ammonium sulfate
[Fe2(SO4)3.(NH4)2SO4.24H2O] in water and make up to 1 litre.
4.4 Silver
nitrate, 0.1 M solution.
4.5 Ammonium
thiocyanate, 0.1 M solution.
Preparation:
since this salt is hygroscopic and cannot be dried without risk of
decomposition, it is advisable to weigh out approximately 9g, dissolve in
water and make up the volume to one litre. Standardise by titration against
0.1 M silver nitrate solution.
4.6 Potassium
Chloride solution: Dissolve 2.103g of potassium chloride, previously dried at
130°C for one hour, in water and make up to 500ml.
5. APPARATUS
5.1 Rotary
shaker, 35 - 40 turns per minute.
6. PREPARATION
OF SAMPLE
See Method 1.
7. PROCEDURE
7.1 Extraction
Weigh to the nearest 0.001 g, 5 g of the prepared sample and place in a 500
ml graduated flask and add 450 ml water. Shake for half an hour on the rotary
shaker (5.1); make up to 500 ml with distilled water, mix and filter into a
beaker, discarding the first part of the filtrate.
7.2 Determination
Take an aliquot portion of the filtrate containing not more than 0.150 g of
chloride. If the portion taken is smaller than 50 ml it is necessary to make
up the volume to 50 ml with distilled water. Add 5 ml 10 M nitric acid (4.2),
20 ml indicator solution (4.3), and two drops of ammonium thiocyanate
standard solution (taken from a burette adjusted to zero). From a burette
then add silver nitrate solution (4.4) until there is an excess of 2
to 5 ml. Add 5 ml nitrobenzene or 5 ml
diethyl ether (4.1) and shake well to agglomerate the precipitate. Titrate
the excess silver nitrate with 0.1 M ammonium thiocyanate (4.5) until a
red-brown colour just appears which remains after the flask has been shaken
slightly.
Note: Nitrobenzene
or diethyl ether (especially the former) prevents the silver chloride from
reacting with thiocyanate ions, thus a clear colour change is obtained.
7.3 Blank
test
Carry out a blank test under the same conditions (omitting only the sample)
and allow for this in the calculation of the final result.
7.4 Control
test
Carry out the determination using 50ml (equivalent to 0.100g of chloride) of
the potassium chloride solution (4.6).
8. EXPRESSION
OF RESULT
Express the result of the analysis as a percentage of chloride contained in
the sample as it has been received for analysis.
Calculation: calculate the percentage of chloride (Cl) with the formula:
% Cl = 0.003546 ×
|
(Vz - Vcz) - (Va - Vca) × 100
|
|
M
|
|
|
where:
Vz = number of millilitres of silver nitrate added
Vcz = number of millilitres of silver nitrate used in the blank test
Va = number of millilitres of ammonium thiocyanate used for the titration
of the sample
Vca = number of millilitres of ammonium thiocyanate used for the
titration of the blank
M = mass in grams of the sample in aliquot volume taken for titration.
|
|
13a.
DETERMINATION
OF FINENESS OF GRINDING — DRY METHOD
1. SCOPE
This method is for the determination of the fineness of grinding by the dry
method.
2. FIELD
OF APPLICATION
All fertilisers in Schedule 1 of the Fertilisers Regulations 1991 for which
requirements are given of fineness of grinding using 0.630 mm and 0.160 mm
sieves.
3. PRINCIPLE
By mechanical sieve shaking, the quantities of product with a granule size
greater than 0.63 mm and those with a granule size between 0.16 mm and 0.63
mm are determined and the percentage of fineness of grinding is calculated.
4. APPARATUS
4.1 Mechanical
sieve shaker.
4.2 Sieves
with apertures of 0.160 mm and 0.630 mm respectively of standard ranges
(diameter 20 cm, height 5 cm).
5. PROCEDURE
Weigh to the nearest 0.05 g, 50 g of the sample. Assemble the two sieves and
the collecting container on the shaker (4.1), the sieve with the larger
apertures being placed on top. Place the sample for analysis on the top.
Sieve for ten minutes and remove the part collected on the bottom. Sieve
again for one minute and check that the amount collected on the bottom during
this time is not more than 250 mg. Repeat the process (for one minute each
time) until the amount collected is less than 250 mg. Weigh the residual
material on both sieves separately.
6. EXPRESSION
OF RESULTS
Percentage of material passing sieve of 0.630 mm apertures = (50-M1) × 2
Percentage of material passing sieve of 0.160 mm apertures = [50-(Ml+M2)] × 2
where:
Ml = mass in g of residue on the sieve with 0.630 mm apertures
M2 = mass in g of residue on the sieve with 0.160 mm apertures
The results are to be rounded up to the nearest unit.
13b.
DETERMINATION
OF FINENESS OF GRINDING OF SOFT NATURAL PHOSPHATES
1. SCOPE
This method is for determining the fineness of grinding of soft natural
phosphates.
2. FIELD
OF APPLICATION
Soft natural phosphates.
3. PRINCIPLE
For samples of fine particle size, agglomeration may occur thus making dry
sieving difficult. For this reason, wet sieving is normally used.
4. REAGENTS
Sodium hexametaphosphate solution, 1 g per 100 ml.
5. APPARATUS
5.1 Sieves
with apertures of 0.063 mm and 0.125 mm respectively of standard ranges
(diameter 20 cm, height 5 cm) and collecting containers.
5.2 Glass
funnel of 20 cm diameter mounted on a stand.
5.3 Laboratory
oven.
6. PROCEDURE
Wash both sides of the sieves with water and place the sieve with 0.125 mm
apertures above the 0.063 mm sieve.
Weigh to the nearest 0.05 g, 50 g of the prepared sample and place on the top
sieve. Sieve under a small jet of cold water (tap water can be used) until
the water is practically clear when it passes through. Care should be taken
to ensure that the flow of water is such that the lower sieve never fills
with water. When the residue on the top sieve seems to remain more or less
constant, remove this sieve, and place on a collecting container (5.1) for
the time being.
Continue the wet sieving through the lower sieve for a few minutes, until the
water passing through is nearly clear. Replace the 0.125 mm sieve over the
0.063 mm sieve. Transfer any deposit from the collecting container to the top
sieve and begin sieving again under a small jet of water until this water
becomes almost clear once more.
Transfer each of the residues quantitatively into a separate 250 ml beaker by
means of the funnel. Suspend each residue by filling the beakers with water.
Allow to stand for about 1 minute and then decant as much water as possible.
Place the beakers in the oven (5.3) at 150° C for two hours. Allow them to
cool to room temperature in a desiccator, detach the residues with a brush
and weigh them.
7. EXPRESSION
OF RESULTS
Percentage of material passing sieve of 0.125 mm apertures = (50-Ml) × 2
Percentage of material passing sieve of 0.063 mm apertures = [50-(Ml+M2)] × 2
where:
M1 = mass in g of the residue on the 0.125 mm sieve
M2 = mass in g of the residue on the 0.063 mm sieve.
The results are to be rounded up to the nearest unit.
8. REMARK
If the presence of lumps is observed after sieving, the analysis should be
carried out again in the following way:
Slowly pour 50 g of the sample into a 1 litre flask containing 500 ml of the
sodium hexametaphosphate solution, stirring continuously. Stopper the flask
and shake vigorously by hand to break up the lumps. Transfer the whole
suspension into the top sieve and wash the flask thoroughly. Continue the
analysis as described under paragraph 6.
14.
METHODS
OF ANALYSIS AND TEST PROCEDURES FOR AMMONIUM NITRATE FERTILISERS CONTAINING
MORE THAN 28% NITROGEN BY WEIGHT
14a.
METHOD
FOR THE APPLICATION OF THERMAL CYCLES
1. SCOPE
This method defines the procedure for the application of thermal cycles
before carrying out the oil retention test on straight ammonium nitrate
fertilisers containing more than 28% nitrogen by weight.
2. FIELD
OF APPLICATION
This procedure is for thermal cycling prior to determining the oil retention
value of the fertiliser.
3. PRINCIPLE
AND DEFINITION
Heat the sample in an Erlenmeyer flask by immersing the flask in a water bath
at 50° C and maintain at this temperature for two hours (phase at 50° C).
Then cool the flask in a water bath at 25° C and maintain at this temperature
for two hours (phase at 25° C). The combination of the two phases, first at
50° C then at 25° C, forms one thermal cycle.
4. APPARATUS
Normal laboratory apparatus, in
particular
4.1 Water
baths thermostated at 25 (+1) and 50 (+1)° C respectively.
4.2 Erlenmeyer
flasks with an individual capacity of 150 ml.
5. PROCEDURE
Place each test sample of 70(+5) grams into
an Erlenmeyer flask which is then closed with a stopper. Place the flask in
the 50<° C water bath for 2 hours, then transfer to the 25° C bath for a
further 2 hours. Transfer the flask back into 50° C water bath for a further
2 hours and then return to the 25° C bath.
Maintain the water in each bath at constant temperature, stir fairly rapidly
and ensure that the water level is above the level of the sample in the
flask. Protect the stopper from condensation by a rubber cap or aluminium
foil.
After two thermal cycles, keep the sample at 20+3° C for the determination of
the oil retention value.
14b.
DETERMINATION
OF THE OIL RETENTION VALUE
1. SCOPE
AND FIELD OF APPLICATION
This method defines the procedure for the determination of the oil retention
value of straight ammonium nitrate fertilisers containing more than 28%
nitrogen by weight.
The method is applicable to both prilled and granular fertilisers which do
not contain oil-soluble materials.
2. DEFINITION
Oil retention value of a fertiliser: the quantity of oil retained by the
fertiliser determined under the operating conditions specified and expressed
as a percentage by mass.
3. PRINCIPLE
Total immersion of the test portion in gas oil for a specified period,
followed by the draining away of surplus oil under specified conditions.
Measurement of the increase in mass of the test portion.
4. REAGENT
Gas oil
|
Viscosity max:
|
5
mPas at 40° C
|
Density:
|
0.8
to 0.85 g/ml at 20° C
|
Sulfur content:
|
<1.0%
(m/m)
|
Ash: <0.1% (m/m)
|
|
5. APPARATUS
5.1 Balance,
capable of weighing to the nearest 0.01 gram.
5.2 Beakers,
of capacity 500 ml.
5.3 Funnel,
plastic, preferably with a cylindrical wall at the upper end, diameter
approximately 200 mm.
5.4 Test
sieve, aperture 0.5 mm, fitting into the funnel (5.3).
Note: The
size of the funnel and sieve is such as to ensure that only a few granules
lie one above another and the oil is able to drain away.
5.5 Filter
paper, rapid filtering grade, creped, soft, weight 150 g/m2.
5.6 Absorbent
tissue (laboratory grade).
6. PROCEDURE
6.1 Carry
out two individual determinations in quick succession on separate portions of
the same test sample.
6.2 Remove
particles smaller than 0.5 mm using the test sieve (5.4). Weigh to the
nearest 0.01 gram approximately 50 grams of the sample into the beaker (5.2).
Add sufficient gas oil (Section 4) to cover the prills completely and stir
carefully to ensure that the surfaces of all the prills are fully wetted.
Cover the beaker with a watch glass and leave to stand for one hour at 25
(+2)° C.
6.3 Filter
the entire contents of the beaker through the funnel (5.3) containing the
test sieve (5.4). Allow the portion retained by the sieve to remain there for
one hour so that most of the excess oil can drain away.
6.4 Lay
two sheets of filter paper (5.5) (about 500 × 500mm) on top of each other on
a smooth surface; fold the four edges of both filter papers upwards to a
width of about 40 mm to prevent the prills from rolling away. Place two
layers of absorbent tissue (5.6) in the centre of the filter papers. Pour the
entire contents of the sieve (5.4) over the absorbent tissues and spread the
prills evenly with a soft, flat brush. After two minutes lift one side of the
tissues to transfer the prills to the filter papers beneath and spread them
evenly over these with the brush. Lay another sheet of filter paper,
similarly with its edges turned upward, on the sample and roll the prills
between the filter papers with circular movements while exerting a little
pressure. Pause after every eight circular movements to lift the opposite
edges of the filter papers and return to the centre the prills that have
rolled to the periphery. Keep to the following procedure: make four complete
circular movements, first clockwise and then anticlockwise. Then roll the
prills back to the centre as described above. This procedure to be carried
out three times (24 circular movements, edges lifted twice). Carefully insert
a new sheet of filter paper between the bottom sheet and the one above it and
allow the prills to roll onto the new sheet by lifting the edges of the upper
sheet. Cover the prills with a new sheet of filter paper and repeat the same
procedure as described above. Immediately after rolling, pour the prills into
a tared dish and reweigh to the nearest 0.01 gram to determine the mass of
the gas oil retained.
6.5 Repeating
the rolling procedure and reweighing.
If the mass of gas oil retained in the portion is found to be greater than
2.00 grams, place the portion on a fresh set of filter papers and repeat the
rolling procedure, lifting the corners in accordance with Section 6.3 (two
times eight circular movements, lifting once). Then reweigh the portion.
7. EXPRESSION
OF RESULTS
7.1 Method
of calculation and formula
The oil retention, from each determination (6.1) expressed as a percentage by
mass of the sieved test portion, is given by the equation:
|
where:
ml is the mass, in grams, of the sieved test portion (6.2);
m2 is the mass, in grams, of the test portion according to Section 6.4 or
6.5 respectively as the result of the last weighing.
Take as the result the arithmetic mean of the two individual
determinations.
|
|
14c.
DETERMINATION
OF COMBUSTIBLE INGREDIENTS
1. SCOPE
AND FIELD OF APPLICATION
This method defines the procedure for the determination of the combustible
content of straight ammonium nitrate fertilisers containing more than 28%
nitrogen by weight.
2. PRINCIPLE
The carbon dioxide produced by inorganic fillers is removed in advance with
an acid. The organic compounds are oxidised by means of a chromic
acid/sulfuric acid mixture. Carbon dioxide formed is absorbed in a barium
hydroxide solution. The precipitate is dissolved in a solution of hydrochloric
acid and measured by back-titration with sodium hydroxide solution.
3. REAGENTS
3.1 Analytical-grade
chromium VI oxide; CrVlO3.
3.2 Sulfuric
acid diluted to 60% by volume: pour 360 ml of water into a one litre beaker
and carefully add 640 ml of sulfuric acid, density at 20° C p=1.83 g/ml.
3.3 Silver
nitrate: 0.1 M solution.
3.4 Barium
hydroxide:
weigh
out 15 grams of barium hydroxide (Ba(OH)2.8H2O), and dissolve completely in
hot water. Allow to cool and transfer to a one-litre flask. Fill up to the
mark and mix. Filter through a pleated filter paper.
3.5 Hydrochloric
acid: 0.1 M standard solution.
3.6 Sodium
hydroxide: 0.1 M standard solution.
3.7 Bromophenol
blue: solution of 0.4 grams per litre in water.
3.8 Phenolphthalein:
solution of 2 grams per litre in 60% by volume ethanol.
3.9 Soda
lime: particle dimensions, about 1.0 to 1.6 mm.
3.10 Demineralised
water, freshly boiled to remove carbon dioxide.
4. APPARATUS
Standard laboratory equipment, in particular:
4.1 filter
crucible with a plate of sintered glass and a capacity of 15 ml, plate
diameter: 20 mm, total height: 50 mm, porosity 4 (pore diameter from 5 to 15
μm);
4.2 Compressed
nitrogen supply.
4.3 Apparatus
made up of the following parts and assembled, if possible, by means of
spherical ground joints (see Figure 9).
4.3.1 Absorption tube (A) about 200 mm
long and 30 mm in diameter filled with soda lime (3.9) kept in place by
fibreglass plugs.
4.3.2 500 ml reaction flask (B) with side
arm and a round bottom.
4.3.3 Vigreux fractioning column about 150
mm long (C').
4.3.4 Double-surface condenser (C), 200 mm
long.
4.3.5 Drechsel bottle (D) acting as a trap
for any excess acid which may distil over.
4.3.6 Ice bath (E) to cool the Drechsel
bottle.
4.3.7 Two absorption vessels (F1)
and (F2), 32 to 35 mm in diameter, the gas distributor of which
comprises a 10 mm disc of low-porosity sintered glass.
4.3.8 Suction pump and suction regulating
device (G) comprising a T-shaped glass piece inserted into the circuit, the
free arm of which is connected to a fine capillary tube by a short rubber
tube fitted with a screw clamp.
Caution:
the
use of boiling chromic acid solution in an apparatus under reduced pressure
is a hazardous operation and requires appropriate precautions.
5. PROCEDURE
5.1 Sample
for analysis
Weigh approximately 10 grams of ammonium nitrate to the nearest 0.001 gram.
5.2 Removal
of carbonates
Place the sample for analysis in the reaction flask (B). Add 100 ml of
sulfuric acid (3.2). The prills dissolve in about 10 minutes at ambient
temperature. Assemble the apparatus as indicated in the diagram: connect one
end of the absorption tube (A) to the nitrogen source (4.2) via a non-return
flow device containing 5 to 6 mm of mercury and the other end to the feed
tube which enters the reaction flask. Place the Vigreux fractioning column
(C') and the condenser (C) with cooling water supply in position. Adjust the
nitrogen to provide a moderate flow through the solution, bring the solution
to boiling point and heat for two minutes. At the end of this time there
should be no more effervescence. If effervescence is seen, continue heating
for 30 minutes. Allow the solution to cool for at least 20 minutes with the
nitrogen flowing through it.
Complete
assembly of the apparatus as indicated in the diagram by connecting the
condenser tube to the Drechsel bottle (D) and the bottle to the absorption
vessel F1 and F2. The nitrogen must continue to pass
through the solution during the assembly operation. Rapidly introduce 50 ml
of barium hydroxide solution (3.4) into each of the absorption vessels (F1
and F2).
Bubble
a stream of nitrogen through for about 10 minutes. The solution in the
absorbers must remain clear. If this does not happen, the carbonate removal
process must be repeated with a fresh barium hydroxide solution.
5.3 Oxidation
and absorption
After withdrawing the nitrogen feed tube, rapidly introduce 20 grams of
chromium trioxide (3.1) and 6 ml of silver nitrate solution (3.3) via the
side arm of the reaction flask (B). Connect the apparatus to the suction pump
and adjust the nitrogen flow so that a steady stream of gas bubbles passes
through the sintered-glass absorbers (F1) and (F2).
Heat
the reaction flask (B) until the liquid boils and keep it boiling for 90
minutes.[15] It may be necessary to adjust the
suction-regulating valve (G) to control the nitrogen flow since it is
possible that the barium carbonate precipitated during the test may block the
sintered glass discs. The operation is satisfactory when the barium hydroxide
solution in the absorber (F2) remains clear. Otherwise repeat the
test. Stop heating and dismantle the apparatus. Wash each of the distributors
both inside and outside to remove barium hydroxide and collect the washings
in the corresponding absorber. Place the distributors one after the other in
a 600 ml beaker which will subsequently be used for the determination.
Rapidly
filter under vacuum firstly the contents of absorber F2 and then
absorber F1 using the sintered glass crucible. Collect the
precipitate by rinsing the absorbers with water (3.10) and wash the crucible
with 50 ml of the same water. Place the crucible in the 600 ml beaker and add
about 100 ml of boiled water (3.10). Introduce 50 ml of boiled water into
each of the absorbers and pass nitrogen through the distributors for five
minutes. Combine the water with that from the beaker. Repeat the operation
once to ensure that the distributors are rinsed thoroughly.
5.4 Measurement
of the carbonates originating from organic material
Add five drops of phenolphthalein (3.8) to the contents of the beaker. The
solution becomes red in colour. Add hydrochloric acid (3.5) drop by drop
until the pink colour just disappears. Stir the solution well in the crucible
to check the pink colour does not reappear. Add five drops of bromophenol
blue and titrate with hydrochloric acid until the solution turns yellow. Add
a further 10 ml of hydrochloric acid.
Heat
the solution to boiling point and continue boiling for a maximum of one
minute. Check carefully that no precipitate remains in the liquid.
Allow
to cool and titrate with the sodium hydroxide solution (3.6).
6. BLANK
TEST
Carry out a blank test following the same procedure, omitting the sample, and
using the same quantities of all reagents.
7. EXPRESSION
OF RESULTS
The content of combustible ingredients (C), expressed as carbon, as a
percentage by mass of the sample, is given by the formula:
|
where:
E = the mass in grams of the test portion:
V1 = the total volume in ml of 0.1 M hydrochloric acid added after the
change in colour of the phenolphthalein;
V2 = the volume in ml of the 0.1 M sodium hydroxide solution used in the
titration.
|
|
14d.
DETERMINATION
OF THE pH VALUE
1. SCOPE
AND FIELD OF APPLICATION
This method defines the procedure for measuring the pH value of a solution of
a straight ammonium nitrate fertiliser containing more than 28% nitrogen by
weight.
2. PRINCIPLE
Measurement of the pH of an ammonium nitrate solution by means of a pH meter.
3. REAGENTS
Distilled or demineralised water, free from carbon dioxide.
3.1 Buffer
solution, pH 6.88 at 20° C
Dissolve 3.40+0.01 grams of potassium dihydrogen orthophosphate (KH2PO4)
in approximately 400 ml of water. Then dissolve 3.55+0.01 gram of disodium
hydrogen orthophosphate (Na2HPO4) in approximately 400
ml of water. Transfer the two solutions without loss into a 1 litre graduated
flask, make up to the mark and mix. Keep the solution in an airtight vessel.
3.2 Buffer
solution, pH 4.00 at 20° C
Dissolve 10.21+0.01 grams of potassium hydrogen phthalate (KHC8O4H4)
in water, transfer without loss into a 1 litre standard flask, make up to the
mark and mix.
Keep
this solution in an airtight vessel.
3.3 Commercially
available pH standard solutions may be used.
4. APPARATUS
pH meter, equipped with glass and calomel electrodes or equivalent,
sensitivity of 0.05 pH unit.
5. PROCEDURES
5.1 Calibration
of the pH meter
Calibrate the pH meter (4) at a temperature of 20(±1)° C, using the buffer
solutions (3.1), (3.2) or (3.3). Pass a slow stream of nitrogen onto the
surface of the solution and maintain this throughout the test.
5.2 Determination
Pour 100.0 ml of water onto 10 (±0.01) grams of the sample in a 250 ml beaker.
Remove the insolubles by filtering, decanting or centrifuging the liquid.
Measure the pH value of the clear solution at a temperature of 20 (±1)° C,
according to the same procedure as for the calibration of the meter.
6. EXPRESSION
OF RESULTS
Express the result in pH units, to the nearest 0.1 unit and state the
temperature used.
14e.
DETERMINATION
OF THE PARTICLE SIZE
1. SCOPE
AND FIELD OF APPLICATION
This method defines the procedure for the test sieving of straight ammonium
nitrate fertilisers containing more than 28% nitrogen by weight.
2. PRINCIPLE
The test sample is sieved on a nest of three sieves, either by hand or by
mechanical means. The mass retained on each sieve is recorded and the
percentage of material passing the required sieves is calculated.
3. APPARATUS
3.1 200
mm diameter woven-wire test sieves to BS 410 (1986) with apertures of 2.0 mm,
1.0 mm and 0.5 mm respectively of standard ranges. One lid and one receiver
for these sieves.
3.2 Balance
to weigh to 0.1 gram.
3.3 Mechanical
sieve shaker (if available) capable of imparting both vertical and horizontal
motion to the test sample.
4. PROCEDURE
4.1 The
sample is divided representatively into portions of approximately 100 grams.
4.2 Weigh
one of these portions to the nearest 0.1 gram.
4.3 Arrange
the nest of sieves in ascending order (receiver, 0.5 mm, 1 mm, 2 mm) and
place the weighed test portion on the top sieve. Fit the lid to the top of
the nest of sieves.
4.4 Shake
by hand or machine, imparting both a vertical and horizontal motion and, if
by hand, tapping occasionally. Continue this process for 10 minutes or until
the quantity passing through each sieve in one minute is less than 0.1 gram.
4.5 Remove
the sieves from the nest in turn and collect the material retained, brush
gently from the reverse side with a soft brush, if necessary.
4.6 Weigh
the material retained on each sieve and that collected in the receiver, to
the nearest 0.1 gram.
5. EVALUATION
OF RESULTS
5.1 Convert
the fraction masses to a percentage of the total of the fraction masses (not
of the original charge).
Calculate
the percentage in the receiver (ie <0.5 mm): A%
Calculate
the percentage retained on the 0.5 mm sieve: B%
Calculate
the percentage passing 1.0 mm, ie (A+ B)%.
The
sum of the fraction masses should be within 2% of the initial mass taken.
5.2 At
least two separate analyses should be carried out and the individual results
for A should not differ by more than 1.0% absolute and for B by more than
1.5% absolute. Repeat the test if this is not the case.
6. EXPRESSION
OF RESULTS
Report the mean of the two values for A on the one hand and for A+ B on the
other hand.
14f.
DETERMINATION
OF THE CHLORINE CONTENT (AS CHLORIDE ION)
1. SCOPE
AND FIELD OF APPLICATION
This method defines the procedure for the determination of the chlorine
content (as chloride ion) of straight ammonium nitrate fertilisers containing
more than 28% nitrogen by weight.
2. PRINCIPLE
Chloride ions dissolved in water are determined by potentiometric titration
with silver nitrate in an acidic medium.
3. REAGENTS
Distilled or demineralised water, free from chloride ions.
3.1 Acetone
AR.
3.2 Concentrated
nitric acid (density at 20°C p=1.40 g/ml).
3.3 Silver
nitrate 0.1 M standard solution. Store this solution in a brown glass bottle.
3.4 Silver
nitrate 0.004 M standard solution — prepare this solution at the time of use.
3.5 Potassium
chloride 0.1 M standard reference solution. Weigh, to the nearest 0.1 mg,
3.7276 grams of analytical-grade potassium chloride, previously dried for one
hour in an oven at 130° C and cooled in a desiccator to ambient temperature.
Dissolve in a little water, transfer the solution without loss into a 500 ml
standard flask, dilute to the mark and mix.
3.6 Potassium
chloride 0.004 M standard reference solution — prepare this solution at the
time of use.
4. APPARATUS
4.1 Potentiometer
with silver indicating electrode and calomel reference electrode, sensitivity
2 mV, covering the range - 500 to +500 mV, or with silver and mercury (1)
sulfate electrodes.
4.2 Bridge,
containing a saturated potassium nitrate solution, connected to the calomel
electrode (4.1), fitted at the ends with porous plugs. This bridge is not
necessary if silver and mercury (1) sulfate electrodes are used.
4.3 etic
stirrer, with a Teflon-coated rod.
4.4 Microburette
with fine-pointed tip, graduated in 0.01 ml divisions.
5. PROCEDURE
5.1 Standardisation
of the silver nitrate solution
Take 5.00 ml and 10.00 ml of the standard reference potassium chloride
solution (3.6) and place in two low-form beakers of convenient capacity (for
example 250 ml). Carry out the following titration of the contents of each
beaker.
Add 5 ml of the nitric acid solution (3.2), 120 ml of acetone (3.1) and
sufficient water to bring the total volume to about 150 ml. Place the rod of
the magnetic stirrer (4.3) in the beaker and set the stirrer in motion.
Immerse the silver electrode (4.1) and the free end of the bridge (4.2) in
the solution. Connect the electrodes to the potentiometer (4.1) and, after
verifying the zero of the apparatus, note the value of the starting
potential.
Titrate, using the microburette (4.4), adding initially 4 or 9 ml
respectively of the silver nitrate solution corresponding to the standard
reference potassium chloride solution used. Continue the addition in 0.1 ml
portions for the 0.004 M solutions and in 0.05 ml portions for the 0.1 M
solutions. After each addition, await the stabilisation of the potential.
Record the volumes added and the corresponding value of the potential in the
first two columns of a table.
In a third column of the table, record the successive increments (Δ1E)
of the potential E. In a fourth column, record the differences (Δ2E)
positive or negative, between the potential increments (Δ1E).
The end of the titration corresponds to the addition of the 0.1 or 0.05 ml
portion V1) of the silver nitrate solution which gives the maximum
value of Δ1E.
In
order to calculate the exact volume (Veq) of the silver nitrate
solution corresponding to the end of the reaction, use the formula:
|
where:
Vo is the total volume, in ml, of the silver nitrate solution
immediately lower than the volume which gives the maximum increment of
Δ1E;
V1 is the volume, in ml, of the last portion of the silver
nitrate solution added (0.1 or 0.05 ml);
b is the last positive value of Δ2E;
B is the sum of the absolute values of the last positive value of 2E and
the first negative value of 2E (see example in Table 1).
|
|
5.2 Blank
test
Calculate the blank value using the equation below and take account thereof
when calculating the final result.
The result V4 of the blank test on the reagents is given, in ml,
by the formula:
V4=
2V3- V2
where:
V2
is the value, in ml, of the exact volume (Veq) of the silver
nitrate solution corresponding to the titration of 10 ml of the potassium
chloride standard reference solution used;
V3 is the value, in ml, of the exact volume (Veq) of
the silver nitrate solution corresponding to the titration of 5 ml of the
potassium chloride standard reference solutions used.
5.3 Check
test
The blank test can at the same time serve as a check that the apparatus is
functioning satisfactorily and that the test procedure is being implemented
correctly.
5.4 Determination
Take
a portion of sample in the range of 10 to 20 grams and weigh to the nearest
0.01 gram. Transfer quantitatively to a 250 ml beaker. Add 20 ml of water, 5
ml of nitric acid solution (3.2), 120 ml of acetone (3.1) and sufficient
water to bring the total volume to about 150 ml.
Place the rod of the magnetic stirrer (4.3) in the beaker, place the beaker
on the stirrer and set the stirrer in motion. Immerse the silver electrode
(4.1) and the free end of the bridge (4.2) in the solution, connect the
electrodes to the potentiometer (4.1) and, after having verified the zero of
the apparatus, note the value of the starting potential.
Titrate with the silver nitrate solution, by additions from the microburette
(4.4) in increments of 0.1 ml. After each addition, await the stabilisation
of the potential.
Continue the titration as specified in 5.1, starting from the fourth
paragraph: ‘Record the volumes added and the corresponding values of the
potential in the first two columns of a table...’
6. EXPRESSION
OF RESULTS
Express the result of the analysis as the percentage of chlorine contained in
the sample as received for analysis.
Calculate
the percentage of chlorine (Cl) content from the formula:
Cl% =
|
0.03545 × T × (V5- V4)
× 100
|
|
m
|
|
|
where:
T is the molarity of silver nitrate solution used;
V4 is the result, in ml, of the blank test (5.2);
V5 is the value, in ml, of Veq corresponding to the
determination (5.4);
m is the mass, in grams, of the test portion.
|
|
Table 1
EXAMPLE
Volume of the silver nitrate
solution V
|
Potential
E
|
Δ1E
|
Δ2E
|
ml
|
mv
|
|
|
4.80
|
176
|
|
|
|
|
35
|
|
4.90
|
211
|
|
+ 37
|
|
|
72
|
|
5.00
|
283
|
|
- 49
|
|
|
23
|
|
5.10
|
306
|
|
- 10
|
|
|
13
|
|
5.20
|
319
|
|
|
14g.
DETERMINATION
OF COPPER
1. SCOPE
AND FIELD OF APPLICATION
This method defines the procedure for the determination of the copper content
of straight ammonium nitrate fertilisers containing more than 28% nitrogen by
weight.
2. PRINCIPLE
The sample is dissolved in dilute hydrochloric acid and the copper content is
determined by atomic absorption spectrometry.
3. REAGENTS
3.1 Hydrochloric
acid (density at 20° C ρ= 1.18 g/ml).
3.2 Hydrochloric
acid, 6 M solution.
3.3 Hydrochloric
acid, 0.5 M solution.
3.4 Ammonium
nitrate.
3.5 Hydrogen
peroxide, 30%.
3.6 Copper
solution[16] (stock): weigh, to the nearest 0.001
gram, 1 gram of pure copper, dissolve in 25 ml of 6 M hydrochloric acid
solution (3.2), add 5 ml of hydrogen peroxide (3.5) in portions and dilute to
1 litre with water. 1 ml of this solution contains 1,000 μg of copper
(Cu).
3.6.1 Copper solution (dilute): dilute 10
ml of stock solution (3.6) to 100 ml with water and then dilute 10 ml of the
resulting solution to 100 ml with water. 1 ml of the final dilution contains
10 μg of copper (Cu).
Prepare
this solution at the time of use.
4. APPARATUS
Atomic absorption spectrometer with a copper lamp (324.8 nm).
5. PROCEDURE
5.1 Preparation
of the solution for analysis
Weigh 25 grams, to the nearest 0.001 gram, of the sample into a 400 ml
beaker, add carefully 20 ml of hydrochloric acid (3.1) (there may be a
vigorous reaction due to carbon dioxide formation). Add more hydrochloric
acid, if necessary. When effervescence has stopped, evaporate to dryness on a
steam bath, stirring occasionally with a glass rod. Add 15 ml 6 M
hydrochloric acid solution (3.2) and 120 ml of water. Stir with the glass
rod, which should be left in the beaker, and cover the beaker with a watch
glass. Boil the solution gently until dissolution is complete and then cool.
Transfer the solution quantitatively into a 250 ml graduated flask, by
washing the beaker with 5 ml 6 M hydrochloric acid (3.2), and twice with 5 ml
of boiling water, cool and make up to the mark with 0.5 M hydrochloric acid
(3.3) and mix carefully.
Filter
through a copper-free filter paper[17], discarding the first 50 ml.
5.2 Blank
solution
Prepare a blank solution from which only the sample has been omitted and
allow for this in the calculation of the final result.
5.3 Determination
5.3.1 Preparation of sample and blank
test solutions
Dilute
the sample solution (5.1) and the blank test solution (5.2) with 0.5 M
hydrochloric acid solution (3.3) to a concentration of copper within the
optimal measuring range of the spectrometer. Normally no dilution is needed.
5.3.2 Preparation of the calibration
solutions
By
diluting the standard solution (3.6.1) with 0.5 M hydrochloric acid solution
(3.3), prepare at least five standard solutions corresponding to the optimal
measuring range of the spectrometer (0 to 5.0 μg/l Cu). Before making up
to the mark, add ammonium nitrate (3.4) to every solution to give a final
concentration of 100 mg per ml.
5.4 Measurement
Set up the spectrometer (4) at a wavelength of 324.8 nm and use an oxidising
air-acetylene flame. Spray, in triplicate, the calibration solutions (5.3.2),
the sample solution and the blank solution (5.3.1), washing the instrument
through with distilled water between each spraying. Plot the calibration
curve using the mean absorbances of every standard used as the ordinates and
the corresponding concentrations of copper in μg/ml as the abscissae.
Determine the concentration of copper in the final sample and blank solutions
by reference to the calibration curve.
6. EXPRESSION
OF RESULTS
Calculate the copper content of the sample taking into account the weight of
the test sample, the dilutions carried out in the course of the analysis and
the value of the blank. Express the result as mg Cu/kg.
15.
EXTRACTION
OF TOTAL CALCIUM, TOTAL MAGNESIUM, TOTAL SODIUM AND TOTAL SULFUR IN THE FORM
OF SULFATES
1. SCOPE
This method is for the extraction of total calcium, total magnesium, total
sodium and total sulfur present in the form of sulfates.
2. FIELD
OF APPLICATION
This method applies to all fertilisers, for which a declaration of the total
calcium, total magnesium, total sodium and total sulfur in the form of
sulfates is required.
3. PRINCIPLE
Dissolution by boiling in dilute hydrochloric acid.
4. REAGENTS
4.1 Diluted
hydrochloric acid; One volume of hydrochloric acid (p = 1.18g/ml) plus one
volume of water.
5. APPARATUS
Electric hot plate with adjustable temperature.
6. PREPARATION
OF THE SAMPLE
See method 1.
7. PROCEDURE
7.1 Test
sample.
Calcium, magnesium, sodium and sulfur in the form of sulfates are extracted
from a test sample of 5 g weighed to within 1 mg. However, when the
fertiliser contains more than 15% of sulfur (S) i.e. 37.5% SO3, and more than
18.8% of calcium (Ca) i.e. 26.3% CaO, the extraction of calcium and sulfur is
carried out on a test sample of 1 g, weighed to within 1 mg. Place the test
sample in a 600 ml beaker.
7.2 Preparation
of the solution.
Add
approximately 400 ml of water and, taking care when the sample contains a
significant quantity of carbonates, 50 ml of dilute hydrochloric acid (4.1) a
small amount at a time. Bring to the boil and maintain for 30 minutes. Allow
to cool, stirring occasionally. Transfer quantitatively into a 500 ml
graduated flask. Make up to volume with water, and mix. Pass through a dry
filter into a dry container, discarding the initial portion. The extract must
be completely clear. Stopper if the filtrate is not used immediately.
16.
EXTRACTION
OF TOTAL SULFUR
1. SCOPE
This method is for the extraction of total sulfur contained in fertilisers in
elemental form and/or in other chemical combinations.
2. FIELD
OF APPLICATION
This method applies to all fertilisers for which a declaration of the total
sulfur present in various forms (elemental, thiosulfate, sulfite and sulfate)
is required.
3. PRINCIPLE
Elemental sulfur is converted in an alkaline medium into polysulfides and
thiosulfate; these, together with any sulfites which may be present, are then
oxidised with hydrogen peroxide. The various forms of sulfur are thus
converted into sulfate which is determined by precipitation as barium sulfate
(method 23).
4. REAGENTS
4.1 Diluted
hydrochloric acid:
One volume of hydrochloric acid (p = 1.18 g/ml) plus one volume of water.
4.2 Sodium
hydroxide solution, NaOH, 30% minimum (p = 1.33)
4.3 Hydrogen
peroxide solution, 30% w/w.
4.4 Aqueous
solution of barium chloride BaCl2.2H2O, 122 gram per
litre.
5. APPARATUS
Electric hot plate with adjustable temperature.
6. PREPARATION
OF THE SAMPLE
See method 1.
7. PROCEDURE
7.1 Test
sample.
Weigh out to within 1 mg a quantity of fertiliser containing between 80 and
350 mg of sulfur (S) or 200 and 875 mg SO3.
As a rule (where S<15%), weigh out 2.5 grams. Place the test sample in a
400 ml beaker.
7.2 Oxidation.
Add
20 ml of sodium hydroxide solution (4.2) and 20 ml of water. Cover with a
watch glass. Boil for five minutes on the hot plate (5). Remove from the hot
plate. Using a jet of hot water, collect any material sticking to the sides
of the beaker and boil for 20 minutes. Leave to cool.
Add 2 ml increments of hydrogen peroxide (4.3) until no reaction is observed.
Six to eight ml of hydrogen peroxide will be necessary. Allow oxidation to
continue for one hour, then bring to the boil for half an hour. Leave to
cool.
7.3 Preparation
of the solution to be analysed.
Add approximately 50 ml of water and 50 ml of the hydrochloric acid solution
(4.1).
— If the level of sulfer (S) is less than 5%:
filter into a 600 ml beaker. Wash the residue on the filter several times
with cold water. After washing, check for the absence of sulfate in the last
drops of the filtrate using the barium chloride solution (4.4). The filtrate
must be perfectly clear. Sulfate is determined on the whole of the filtrate
in accordance with method 23.
— If the level of sulfur (S) is at/above 5%:
transfer quantitatively into a 250 ml volumetric flask, make up to volume
with water and mix. Filter through a dry filter into a dry container; the
filtrate must be completely clear. Stopper if the solution is not to be used
immediately. Determine sulfates in an aliquot portion of this solution by
precipitation in the form of barium sulfate (method 23).
17.
EXTRACTION
OF WATER-SOLUBLE CALCIUM, MAGNESIUM, SODIUM AND SULFUR (IN THE FORM OF
SULFATES)
1. SCOPE
This method is for the extraction of water-soluble calcium, magnesium, sodium
and sulfur (in the form of sulfates), so that the same extract can be used to
determine each nutrient required.
2. FIELD
OF APPLICATION
This method applies solely to fertilisers for which a declaration of the
water-soluble calcium, magnesium, sodium and sulfur (in the form of sulfates)
is required.
3. PRINCIPLE
The nutrients are dissolved in boiling water.
4. REAGENTS
Distilled or demineralized water of equivalent quality.
5. APPARATUS
Electric hot plate with adjustable temperature.
6. PREPARATION
OF THE SAMPLE
See method 1.
7. PROCEDURE
7.1 Test
sample.
(a) Where
fertilisers contain no sulfur or where they contain, at the same time, no
more than 3% of sulfur (S) i.e. 7.5% SO3, and no more than 4% of calcium (Ca)
i.e. 5.6% CaO, weigh out 5 g of fertiliser to within 1 mg.
(b) Where
fertilisers contain more than 3% of sulfur (S) and more than 4% of calcium
(Ca), weigh out 1 g of fertiliser to within 1 mg.
Place
the test sample in a 600 ml beaker.
7.2 Preparation
of the solution.
Add
approximately 400 ml of water and boil for 30 minutes. Allow to cool,
stirring occasionally, and transfer quantitatively into a 500 ml graduated
flask. Make up to volume with water and mix.
Filter
through a dry filter into a dry container:
Discard
the initial portion of the filtrate. The filtrate must be completely clear.
Stopper
if the solution is not to be used immediately.
18.
EXTRACTION
OF WATER — SOLUBLE SULFUR
1. SCOPE
This method is for the extraction of water-soluble sulfur contained in
fertilisers, in various forms.
2. FIELD
OF APPLICATION
This method applies to all fertilisers for which a declaration of the
water-soluble sulfur trioxide is required.
3. PRINCIPLE
Soluble forms of sulfur are dissolved in cold water and converted into
sulfate by oxidation with hydrogen peroxide in an alkaline medium.
4. REAGENTS
4.1 Diluted
hydrochloric acid:
One volume of hydrochloric acid (p = 1.18 g/ml) plus one volume of water.
4.2 Sodium hydroxide solution containing at least 30% NaOH (p = 1.33g/ml).
5. APPARATUS
5.1 500
ml graduated Stohmann flask.
5.2 Rotary
shaker, 30 to 40 turns per minute.
5.3 Electric
hot plate with adjustable temperature.
6. PREPARATION
OF THE SAMPLE
See method 1.
7. PROCEDURE
7.1 Test
sample.
(a) Where
fertilisers contain a maximum of 3% of sulfur (S) i.e. 7.5% SO3,
together with a maximum of 4% of calcium (Ca) i.e. 5.6% CaO, weigh out 5 g of
fertiliser to within 1 mg.
(b) Where
fertilisers contain more than 3% of sulfur (S) together with more than 4% of
calcium (Ca), weigh out 1 g of fertiliser to within 1 mg.
Place
the test sample in a 500 ml flask (5.1).
7.2 Preparation
of the solution.
Add
approximately 400 ml of water. Stopper. Shake on the rotary shaker (5.2) for
30 minutes. Make up to volume with water and mix. Pass through a dry filter
into a dry container. Reject the first portion of the filtrate. Stopper if
the solution is not to be used immediately.
7.3 Oxidation
of the aliquot portion to be analysed.
Take an aliquot of the extraction solution not exceeding 50 ml and, if
possible, containing between 20 and 100 mg of sulfur (S).
Make up the volume to 50 ml with water, if necessary. Add 3 ml of sodium
hydroxide solution (4.2) and 2 ml of hydrogen peroxide solution (4.3). Cover
with a watch glass and boil gently for one hour on the hot plate (5.3). Keep
adding 1 ml increments of hydrogen peroxide solution for as long as the
reaction continues (maximum quantity 5 ml).
Then leave to cool. Remove the watch glass and wash the underside into the
beaker. Add approximately 20 ml of dilute hydrochloric acid (4.1). Make up to
approximately 300 ml with water.
Determine the content of sulfates on the whole of the oxidised solution in
accordance with method 23.
19.
EXTRACTION
AND DETERMINATION OF ELEMENTAL SULFUR
WARNING
This method of analysis involves the use of carbon disulfide (CS2). Special
safety measures must therefore be taken, in particular with regard to:
— the storage of CS2,
— protective equipment for staff,
— occupational hygiene,
— prevention of fires and explosions,
— disposal of the reagent.
This method requires highly skilled staff and a suitably equipped laboratory.
1. SCOPE
This method is for the extraction and determination of the elemental sulfur
content of fertilisers.
2. FIELD
OF APPLICATION
This method applies to all fertilisers for which a declaration of the total
sulfur in elemental form is required.
3. PRINCIPLE
After the removal of soluble compounds, elemental sulfur is extracted by
using carbon disulfide, followed by gravimetric determination of the sulfur
extracted.
4. REAGENTS
Carbon disulfide.
5. APPARATUS
5.1 100
ml extraction flask with ground glass stopper.
5.2 Soxhlet
apparatus.
5.3 Vacuum
rotary evaporator.
5.4 Electric
oven, fan assisted, set at 90+2° C.
5.5 Petri
dishes, five to seven centimetres in diameter, not exceeding five centimetres
in height.
5.6 Electric
hot plate with adjustable temperature.
6. PREPARATION
OF THE SAMPLE
See method 1.
7. PROCEDURE
7.1 Test
sample. Weigh out 5 - 10 g of the sample to an accuracy of 1 mg and place in
the thimble of the Soxhlet apparatus (5.2).
7.2 Extraction
of the sulfur.
Wash thoroughly the contents of the thimble with hot water to remove all
soluble compounds. Dry in the oven at 90°C (5.4) for at least one hour. Place
the thimble in the Soxhlet apparatus (5.2).
Place a few glass beads in the flask of the apparatus (5.1) and weigh (P0),
then add 50 ml of carbon disulfide (4.1).
Connect the apparatus, switch on and leave for six hours. Switch off the heat
and, after cooling, disconnect the flask. Connect the flask to the rotary
evaporator (5.3) and evaporate until the contents of the flask have
solidified in a spongy mass.
Dry the flask in the oven at 90° C (5.4) (generally one hour if necessary)
until a constant weight is obtained (P1).
7.3 Determination
of the purity of the elemental sulfur.
Certain
substances may have been extracted by the carbon disulfide at the same time
as the elemental sulfur. The purity of the elemental sulfur is determined as
follows:
homogenize the contents of the flask as
thoroughly as possible and remove 2 - 3 g, weigh to an accuracy of 1 mg (n).
Place in the petri dish (5.5). Weigh dish and contents together (P2).
Place on the hot plate (5.6), set at a temperature not exceeding 220° C so as
not to cause combustion of the sulfur. Continue sublimation for three to four
hours until a constant weight is obtained (P3).
Note: For
some fertilisers, it may not be necessary to determine how pure the sulfur
is. In this case, omit step 7.3.
8. EXPRESSION
OF RESULTS
The percentage elemental sulfur (S) content of the fertiliser is as follows:
Impure S (%) of the fertiliser =
|
|
× 100
|
|
Purity of S extracted (%) =
|
|
× 100
|
|
Pure S (%) of the fertiliser =
|
|
× 100
|
|
Where:
m = the mass of the test sample of fertiliser in grams,
P0= the mass of the Soxhlet flask in grams,
P1= the mass of the Soxhlet flask and the impure sulfur after
drying,
n = the mass of impure sulfur to be purified in grams,
P2= the mass of the Petri dish and the sample,
P3= the mass of the Petri dish after sublimation of the
sulfur.
|
|
20.
MANGANIMETRIC
DETERMINATION OF EXTRACTED CALCIUM FOLLOWING PRECIPITATION IN THE FORM OF
OXALATE
1. SCOPE
This method is for the determination of calcium in fertiliser extracts.
2. FIELD
OF APPLICATION
This method applies to all fertilisers for which a declaration of the total
and/or water-soluble calcium is required.
3. PRINCIPLE
Precipitation of the calcium contained in an aliquot portion of the
extraction solution in the form of an oxalate, which is determined by
titration using potassium permanganate.
4. REAGENTS
4.1 Diluted
hydrochloric acid: One volume of hydrochloric acid (ρ= 1.18 g/ml) plus
one volume of water.
4.2 1:10
dilute sulfuric acid:
One
volume of sulfuric acid (ρ= 1.84 g/ml) in ten volumes of water.
4.3 1:1
dilute ammonia solution: One volume of ammonia (ρ= 0.88 g/ml) and one
volume of water.
4.4 Saturated
solution of ammonium oxalate [(NH4)2C2O4.H2O]
at ambient temperature (approximately 40 g per litre).
4.5 Citric
acid solution, 30% (m/v).
4.6 Ammonium
chloride solution, 5% (m/v).
4.7 Solution
of bromothymol blue in 95% ethanol, 0.1% (m/v).
4.8 Solution
of bromocresol green in 95% ethanol, 0.04% (m/v).
4.9 Standard
solution of potassium permanganate, 0.02 M.
5. APPARATUS
5.1 Filter
crucible with 5 to 20μ porosity sintered glass.
5.2 Hot
water bath.
6. PREPARATION
OF THE ALIQUOT PORTION TO BE ANALYSED
Using a pipette, take an aliquot portion of the extraction solution obtained
by method 15 or 17, containing between 15 and 50 mg of Ca (= 21 to 70 mg of
CaO). Let the volume of this aliquot be v2. Pour into a 400 ml
beaker. If necessary, neutralise (change of indicator (4.7) from green to
blue) with a few drops of the ammonia solution (4.3).
Add
1 ml of the citric acid solution (4.5) and 5 ml of ammonium chloride solution
(4.6).
7. PRECIPITATION
OF THE CALCIUM OXALATE
Add approximately 100 ml of water. Bring to the boil, add 8 to 10 drops of
indicator solution (4.8) and, slowly, 50 ml of the hot ammonium oxalate
solution (4.4), stirring constantly. If a precipitate forms, dissolve by
adding a few drops of hydrochloric acid (4.1). Neutralise very slowly with
ammonia solution (4.3) while stirring continuously to a pH of 4.4 to 4.6
(change of indicator (4.8) from green to blue). Place the beaker in a boiling
hot water bath (5.2) for approximately 30 minutes.
Remove the beaker from the bath, leave standing for an hour and filter
through the crucible (5.1).
8. TITRATION
OF THE OXALATE PRECIPITATE
Wash the beaker and crucible until
the excess ammonium oxalate has been completely removed (this can be checked
by the absence of chloride in the washing water). Place the crucible in the
400 ml beaker and dissolve the precipitate with 50 ml of hot sulfuric acid
(4.2). Add water to the beaker in order to obtain a volume of approximately
100 ml. Bring to a temperature of 70 to 80° C and titrate drop by drop with
the permanganate solution (4.9) until the pink colour lasts for a minute. Let
this volume be n.
9. EXPRESSION
OF RESULTS
The calcium (Ca) content of the fertiliser is as follows:
|
Where:
n = the volume of 0.2 M permanganate used, in millilitres,
m = the mass of the test sample in grams,
v2= the aliquot volume in millilitres,
v1= the volume of the extraction solution in millilitres,
t = the molarity of the permanganate solution in moles per litre.
CaO(%) = Ca (%) × 1.400.
|
|
21.
DETERMINATION
OF MAGNESIUM BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method is for the determination of magnesium in fertiliser extracts.
2. FIELD
OF APPLICATION
This method applies to all fertiliser extracts obtained by methods 15 and 17,
for which a declaration of the total magnesium and/or water-soluble magnesium
is required, with the exception of kieserite, magnesium sulfate, magnesium
chloride solution and kieserite with potassium sulfate to which method 22
applies.
3. PRINCIPLE
Determination of magnesium by atomic absorption spectrometry after appropriate
dilution of the extract.
4. REAGENTS
4.1 Hydrochloric
acid, 1 M solution.
4.2 Hydrochloric
acid, 0.5 M solution.
4.3 Standard
solution of magnesium, 1.00 mg per ml.
4.3.1 Dissolve 1.013 g of magnesium
sulfate (MgSO4.7H2O) in 0.5 M hydrochloric acid
solution (4.2).
or:
4.3.2 weigh out 1.658 g of magnesium oxide
(MgO), previously ashed to remove all traces of carbonate. Place in a beaker
with 100 ml of water and 120 ml of 1 M hydrochloric acid (4.1). When it has
dissolved, transfer quantitatively into a 1 litre graduated flask. Make up to
the volume and mix.
or:
4.3.3 Commercial standard solution.
The
laboratory is responsible for testing such solutions.
4.4 Strontium
chloride solution.
Dissolve
75 g of strontium chloride (SrCl2.6H2O) in the
hydrochloric acid solution (4.2) and make up to 500 ml with the same acid
solution.
5. APPARATUS
5.1 Spectrometer
fitted for atomic absorption, with a magnesium lamp, set at 285.2 nm.
5.2 Air-acetylene
flame.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
See methods 15 and 17.
7. PROCEDURE
7.1 If
the fertiliser has a declared magnesium (Mg) content of more than 6% (i.e.
10% as MgO), take 25 ml (V1) of the extraction solution (6).
Transfer into a 100 ml graduated flask, and make up to volume with water and
mix. The solution factor is D1= 100/V1.
7.2 Using
a pipette, take 10 ml of the extraction solution (6) or the solution (7.1).
Transfer into a 200 ml graduated flask. Make up to the volume with the 0.5 M
hydrochloric acid solution (4.2) and mix. The dilution factor is 200/10.
7.3 Dilute
this solution (7.2) with the 0.5 M hydrochloric acid solution (4.2) so as to
obtain a concentration in the optimum working field of spectrometer (5.1). V2
is the volume of the sample in 100 ml. The dilution factor is D2=
100/V2.
7.4 Preparation
of blank solution.
Prepare a blank solution by repeating the whole procedure from the extraction
(method 15 or 17), omitting only the test sample of fertiliser.
7.5 Preparation
of calibration solutions.
By diluting the standard solution (4.3) with 0.5 M hydrochloric acid, prepare
at least five calibration solutions in increasing concentration within the
optimum measuring range of the apparatus (5.1).
These solutions should contain 10% v/v of the strontium chloride solution
(4.4).
7.6 Measurement.
Set
up the spectrometer (5.1) at a wavelength of 285.2 nm.
Spray,
successively, the calibration solutions (7.5), the sample solution (7.3) and
the blank solution (7.4), washing the instrument through with the solution to
be measured next. Repeat this operation three times. Plot the calibration
curve using the mean absorbances of each of the calibration solutions (7.5) as
the ordinates and the corresponding concentration of magnesium in μg/ml
as the abscissae. Determine the concentration of magnesium in the sample
(7.3), xs and blank (7.4), xb, by reference to the
calibration curve.
8. EXPRESSION
OF RESULTS
Calculate the amount of magnesium (Mg) or magnesium oxide (MgO) in the sample
by reference to the calibration solutions and taking into consideration the
blank.
The
percentage of magnesium (Mg) in the fertiliser is equal to:
Mg (%) =
|
(xs- xb) × D1×
(200/10) × D2× 500 × 100
|
|
1,000 × 1,000 M
|
|
|
Where:
xs= the concentration of the solution as calculated from the
calibration curve, in μg/ml.
xb= the concentration of the blank solution as calculated from
the calibration curve, in μg/ml.
D1= the dilution factor if the solution is diluted (7.1). It
is equal to four if 25 millilitres are taken. It is equal to one when the
solution is not diluted.
D2= the dilution factor in 7.3.
M = the mass of the test sample taken for the extraction.
|
|
22.
DETERMINATION
OF MAGNESIUM BY COMPLEXOMETRY
1. SCOPE
This method is for the determination of magnesium in fertiliser extracts.
2. FIELD
OF APPLICATION
This method applies to the determination of total magnesium and/or
water-soluble magnesium in the following fertilisers:
— Straight
nitrogenous fertilisers (calcium magnesium nitrate, magnesium sulphonitrate,
nitrogenous fertiliser with magnesium) and straight potassic fertilisers
(enriched kainite, potassium chloride containing magnesium, potassium sulfate
containing magnesium salt), kieserite, magnesium sulfate, magnesium chloride
solution, and kieserite with potassium sulfate.
3. PRINCIPLE
The magnesium is extracted by methods 15 and/or 17. First titration: with
EDTA of Ca and Mg in the presence of Eriochrome black T. Second titration:
with EDTA of Ca in the presence of calcein or of calcon carbonic acid.
Determination of magnesium by difference.
4. REAGENTS
4.1 Standard
0.05 M solution of magnesium:
4.1.1 Dissolve 1.232 g of magnesium
sulfate (MgSO4.7H2O) in the 0.5 M hydrochloric acid solution (4.11) and make
up to 100 ml with the same acid.
or:
4.1.2 Weigh out 2.016 g of magnesium
oxide, previously calcined to remove all traces of carbonation. Place it in a
beaker with 100 ml of water.
Stir
in approximately 120 ml of approximately 1 M hydrochloric acid (4.12).
After
dissolution, transfer quantitatively into a graduated 1 litre flask. Make up
to volume and mix.
1
ml of these solutions should contain 1.216 mg of Mg (= 2.016 mg of MgO).
The laboratory is responsible for testing the strength of this standard
solution.
4.2 0.05
M solution of EDTA.
Weigh out 18.61 g of the dihydrated disodium salt of
ethylenediaminetetraacetic (C10H14.Na2O82H2O),
place it in a 1,000 ml beaker and dissolve in 600 to 800 ml of water.
Transfer the solution quantitatively into a graduated 1 litre flask. Make up
the volume and mix. Check this solution with the standard solution (4.1) by
taking a sample of 20 ml of the latter and by titration according to the analytical
procedure described at 7.2.
4.3 0.05
molar standard solution of calcium.
Weigh
out 5.004 g of dry calcium carbonate. Place it in a beaker with 100 ml of
water. Progressively stir in 120 ml of approximately 1 M hydrochloric acid
(4.12).
Bring to the boil in order to drive off the carbon dioxide, cool, transfer
quantitatively into a graduated one-litre flask, make up the volume with
water and mix. Check this solution against the EDTA solution (4.2) following
analytical procedure (8.3). 1 ml of this solution should contain 2.004 mg of
Ca (=2.804 mg of CaO) and should correspond to 1 ml of the 0.05 M EDTA
solution (4.2).
4.4 Calcein
indicator.
Carefully
mix in a mortar one gram of calcein with 100 g of sodium chloride. Use 10 mg
of this mixture. This indicator changes colour from green to orange.
Titration must be carried out until an orange colour free from green tinges
is obtained.
4.5 Calcon
carbonic acid indicator.
Dissolve
400 mg of calcon carbonic acid in 100 ml of methanol. This solution may only
be kept for approximately four weeks. Use three drops of this solution. The
indicator changes colour from red to blue. Titration must be carried out
until a blue colour free from red tinges is obtained.
4.6 Eriochrome
black — T indicator.
Dissolve 300 mg of Eriochrome black-T in a mixture of 25 ml of propan-1-ol
and 15 ml of triethanolamine. This solution may only be kept for
approximately four weeks. Use three drops of this solution. This indicator
changes colour from red to blue and titration must be carried out until a
blue colour free from red tinges is obtained. It changes colour only when
magnesium is present. If necessary add one millilitre of the standard
solution (4.1).
When both calcium and magnesium are present the EDTA first forms a complex
with the calcium and then the magnesium. In that case the two elements are
determined concurrently.
4.7 Potassium
cyanide solution.
Aqueous
solution of KCN at 2%. (CAUTION: potassium cyanide is extremely poisonous,
take suitable precautions and do not pipette by mouth. See also 10.7).
4.8 Solution
of potassium hydroxide and potassium cyanide.
Dissolve 280 g of KOH and 66 g of KCN in water, make up the volume to one
litre and mix.
4.9 Buffer
solution, pH 10.5.
In
a 500 ml graduated flask, dissolve 33 g of ammonium chloride in 200 ml of
water, add 250 ml of ammonia (ρ= 0.91) make up the volume with water and
mix. Check the pH of the solution regularly.
4.10 Diluted
hydrochloric acid:
One
volume of hydrochloric acid (ρ= 1.18 g/ml) plus one volume of water.
4.11 Hydrochloric
acid solution approximately 0.5 M.
4.12 Hydrochloric
acid solution approximately 1 M.
4.13 Sodium
hydroxide solution 5 M.
5. APPARATUS
5.1 Magnetic
or mechanical stirrer.
5.2 pH
meter.
6. CONTROL
TEST
Carry out a determination on aliquot portions of solutions (4.1 and 4.3) such
that the Ca/Mg ratio is approximately equal to that of the solutions to be
analysed. To this end take (a) of standard solution (4.3) and (b - a) of
standard solution (4.1). (a) and (b) are the volumes of EDTA solution in
millilitres used in the two titrations performed on the solution to be
analysed. This procedure is correct only if the solutions of EDTA, calcium
and magnesium are exactly equivalent. If this is not the case, it is
necessary to make corrections.
7. PREPARATION
OF THE SOLUTION TO BE ANALYSED
See methods 15 and 17.
8. DETERMINATION
8.1 Aliquot
portions to be taken.
Take aliquot portions of the extracts which contain between 9 and 18 mg of
magnesium (= 15 to 30 mg of MgO).
8.2 Titration
in the presence of Eriochrome black-T.
Pipette an aliquot portion (8.1) of the solution to be analysed into a 400 ml
beaker. Neutralise the excess acid with the 5 M sodium hydroxide solution
(4.12) and check the pH. Dilute with water to approximately 100 ml. Add 5 ml
of the buffer solution (4.9). The pH measured by meter must be 10.5 +0.1. Add
2 ml of the potassium cyanide solution (4.7) and three drops of the
Eriochrome black-T indicator (4.6). Titrate with the EDTA solution (4.2).
Stirring gently with the stirrer (5.1) (see 10.2, 10.3 and 10.4). Let ‘b’ be
the volume in millilitres of 0.05 molar EDTA solution used.
8.3 Titration
in the presence of calcein or of calcon carbonic acid.
Pipette
an aliquot portion of the solution to be analysed equal to that taken for the
above titration and place it in a 400 ml beaker. Neutralise the excess acid
with the 5 M sodium hydroxide solution (4.13) using the pH meter. Dilute with
water to about 100 ml. Add 10 ml of KOH/KCN solution (4.8) and three drops of
the indicator (4.4 or 4.5). Stirring gently with the stirrer (5.1) titrate
with the EDTA solution (4.2) (see 10.2, 10.3 and 10.4). Let ‘a’ be the volume
in millilitres of 0.05 M EDTA solution.
9. EXPRESSION
OF RESULTS
For the EEC fertilisers to which the method is applicable (5 g of fertiliser
in 500 ml of extract), the percentage content of the fertiliser is:
MgO (%) in the fertiliser =
|
|
|
Mg (%) in the fertiliser =
|
|
|
Where:
a = the volume in millilitres of 0.05 M EDTA solution used for the
titration in the presence of calcein or calcon carbonic acid.
b = the volume in millilitres of 0.05 M EDTA solution used for the
titration in the presence of Eriochrome black-T.
M = the mass of the sample present in the aliquot taken (in grams).
T = 0.2016 × molarity of the EDTA solution/0.05 (see 4.2).
T1 = 0.1216 × molarity of the EDTA solution/0.05 (see 4.2).
|
|
10. REMARKS
10.1 The stoichiometric EDTA-metal ratio in the complexometric analyses is
always 1:1 whatever the valency of the metal and in spite of the fact that
EDTA is quadrivalent. The EDTA titration solution and the standard solutions
will therefore be molar and not normal.
10.2
Complexometric indicators are often sensitive to air. The solution may lose
colour during titration. In this case, one or two drops of indicator must be
added. This is true particularly in the case of Eriochrome black-T and calcon
carbonic acid.
10.3
The metal-indicator complexes are often relatively stable and it may take
some time for the colour to change. The last drops of EDTA must therefore be
added slowly and a drop of 0.05 molar solution of magnesium (4.1) or calcium
(4.3) added to ensure that the colour change has not already taken place.
This is particularly true in the case of the Eriochrome-magnesium complex.
10.4
The colour change of the indicator must not be observed vertically, but
horizontally across the solution and the beaker must be placed against a
white background in a well-lit position. The colour change of the indicator
may also be observed easily by placing the beaker on frosted glass lit
moderately from below (25 watt lamp).
10.5
This analysis requires a certain amount of experience. The task will involve,
among other things, observing the colour changes of standard solutions 4.1
and 4.3. It is recommended that the determinations be carried out by the same
laboratory chemist.
10.6
If an EDTA solution of guaranteed strength is used (Titrisol, Normex, for
example) this may simplify the control of the equivalence of standard
solutions 4.1, 4.2 and 4.3.
10.7
The solutions containing potassium cyanide must not be poured down the
sink until the cyanide has been converted into a harmless compound, for
example, by oxidation with sodium hypochlorite after having been made
alkaline.
23.
DETERMINATION
OF SULFATES
1. SCOPE
This method is for the determination of sulfur present in fertiliser extracts
in the form of sulfates.
2. FIELD
OF APPLICATION
This method applies to the determination of sulfates present in the
extractions performed in methods 15, 16, 17 and 18.
3. PRINCIPLE
Gravimetric determination as barium sulfate.
4. REAGENTS
4.1 Diluted
hydrochloric acid:
One volume of hydrochloric acid (ρ= 1.18 g/ml) and one volume of water.
4.2 Barium
chloride solution BaCl2.2H2O:122 grams per litre.
4.3 Silver
nitrate solution: 5 grams per litre.
5. APPARATUS
5.1 Crucibles.
5.2 Hot
water bath.
5.3 Drying
oven set at 105° C ± 1° C.
5.4 Electric
furnace set at 800° C ± 50° C.
6. PROCEDURE
6.1 Sampling
of the solution.
Pipette an aliquot portion of one of the extraction solutions indicated at
(2) containing between 20 and 100 mg of S or 50 and 250 mg of SO3.
Place
this aliquot portion in a beaker of suitable capacity. Add 20 ml of dilute
hydrochloric acid (4.1). Make up to about 300 ml with water.
6.2 Preparation
of the precipitate.
Bring
the solution to the boil. Add, drop by drop, about 20 ml of the hot barium
chloride solution (4.2) while stirring the solution vigorously. Boil for a
few minutes.
Place
the beaker, covered with a watch glass, in a boiling water bath (5.2) for an
hour. Then leave standing hot (approximate60 C) until the supernatant liquor
is clear. Decant the clear solution through a slow filtration ash-free
filter. Wash the precipitate several times with hot water. Continue to wash
the precipitate on the filter until the filtrate is chloride free. This can
be checked by using silver nitrate solution (4.3).
6.3 Incineration
and weighing of the precipitate.
Place
the filter paper and precipitate in a crucible (5.1) previously weighed to
the nearest 0.1 mg. Dry in the oven (5.3) and ash at approximately 800° C for
half an hour (5.4). Allow to cool in a desiccator and weigh to within 0.1 mg.
7. EXPRESSION
OF RESULTS
One mg of barium sulfate corresponds to 0.137 mg of S or to 0.343 mg of SO3.
The
percentage S content of the fertiliser is obtained as follows:
|
Where:
w = the mass of the barium sulfate precipitate in milligrams,
v1= the volume of the extraction solution in millilitres,
v2= the aliquot volume in millilitres,
m = the mass of the test sample in grams.
|
|
24.
DETERMINATION
OF THE SODIUM EXTRACTED
1. SCOPE
This method is for the determination of sodium in fertiliser extracts.
2. FIELD
OF APPLICATION
This method applies to fertilisers for which a declaration of sodium is
required.
3. PRINCIPLE
Following suitable dilution of the extract obtained via method 15 and/or 17
the sodium content of the solution is determined by flame-emission
spectrometry.
4. REAGENTS
4.1 Diluted
hydrochloric acid:
One volume of hydrochloric acid (ρ= 1.18 g.ml) plus one volume of water.
4.2 Aluminium
nitrate Al(NO3)3.9H2O.
4.3 Caesium
chloride, CsCl.
4.4 Anhydrous
sodium chloride, NaCl.
4.5 Caesium
chloride and aluminium nitrate solution.
Dissolve
in water 50 g of caesium chloride (4.3) and 250 g of aluminium nitrate (4.2)
in a 1 litre graduated flask. Make up to volume with water and mix.
4.6 Standard
sodium solution of 1 mg/ml of Na.
Dissolve
in water 2.542 g of sodium chloride (4.4) in a 1 litre graduated flask. Add
10 ml of hydrochloric acid (4.1). Make up to volume with water and mix.
5. APPARATUS
Spectrometer equipped for flame emission, set at 589.3 nm.
6. CALIBRATION
SOLUTIONS
6.1 Pipette
10 ml of standard solution (4.6) into a 250 ml graduated flask. Make up to
volume and mix. Concentration of solution: 40 μg/ml of Na.
6.2 Using
a burette place 0, 5, 10, 15, 20, 25 ml of the intermediate solution (6.1) in
100 ml graduated flasks. Add 10 ml of the solution (4.5). Make up to volume and
mix. Concentration of solutions: 0, 2, 4, 6, 8, 10 μg/ml of Na.
7. PREPARATION
OF SOLUTIONS TO BE MEASURED
Depending upon the expected sodium content of the extraction solution as in
method 15 or 17 (5 g of fertiliser in 500 ml), carry out the dilutions in
accordance with the following table:
|
|
Intermediate dilution
|
Final dilution
|
Na2O (%)
|
Na
(%)
|
Sample (ml) (v2)
|
Dilution to ml (v3)
|
Sample (ml) (v4)
|
Dilution to ml
|
Degree of dilution
|
3 - 5
|
2.2
- 3.7
|
10
|
50
|
10
|
100
|
50
|
5 - 10
|
3.7
- 7.4
|
10
|
100
|
10
|
100
|
100
|
10 - 20
|
7.4
- 15
|
10
|
100
|
5
|
100
|
200
|
20 - 38
|
15
- 28
|
5
|
100
|
5
|
100
|
400
|
Make
up the intermediate dilution with water. For the final dilution add 10 ml of
the solution (4.5) to the 100 ml graduated flask.
For
a test sample of 1 g multiply the volume of the final dilution (v4)
by five.
8. DETERMINATION
Prepare the spectrometer (5) for the measurements at 589.3nm. Calibrate the
instrument by measuring the response of the calibration solutions (6.2). Then
adjust the sensitivity of the instrument to use its entire scale when the
most concentrated calibration solution is used. Then measure the response of
the sample solution to be analysed (7). Repeat this operation twice.
9. CALCULATION
OF RESULTS
Draw a calibration curve by plotting the average response for each
calibration solution along the ordinate and the corresponding concentrations,
expressed in μg per ml on the abscissa. Determine from this the sodium
concentration of the test solution. Calculate the quantity of sodium from the
standard solutions taking account of the levels of dilution. Express the
results as a percentage of the sample.
The
percentage sodium (Na) content of the fertiliser is as follows:
Na2O (%) = Na (%) × 1.348
|
|
Where:
X = the concentration of the solution introduced into the spectrometer in
μg/ml,
v1= the volume of the extraction solution in millilitres,
v2= the aliquot volume in the intermediate dilution in
millilitres,
v3= the volume of intermediate dilution in millilitres,
v4= the aliquot volume in ml of the final dilution (in 100
millilitres),
m = the mass of the test sample in grams.
|
|
25.
TRACE
ELEMENTS AT A CONCENTRATION LESS THAN 10%
25a.
EXTRACTION
OF TOTAL TRACE ELEMENTS
1. SCOPE
This method defines the procedure for extracting the following trace
elements: total boron, total cobalt, total copper, total iron, total
manganese, total molybdenum and total zinc. The aim is to carry out the
minimum number of extractions, making use wherever possible of the same
extract to determine the total level of each of the trace elements listed
above.
2. FIELD
OF APPLICATION
This procedure concerns fertilisers containing one or more of the following
trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc.
It is applicable to each trace element the declared content of which is less
than or equal to 10%.
3. PRINCIPLE
Dissolution in boiling dilute hydrochloric acid.
Note: The
extraction is empirical and may not be quantitative depending on the product
or the other constituents of the fertiliser. In particular, in the case of
certain manganese oxides, the quantity extracted may be substantially smaller
than the total quantity of manganese which the product contains. It is the
responsibility of the fertiliser manufacturer to ensure that the declared
content actually corresponds to the quantity extracted under the conditions
pertaining to the method.
4. REAGENTS
4.1. Dilute
hydrochloric acid (HCI) solution, about 6 M:
Mix
1 volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of water.
4.2. Concentrated
ammonia solution (NH4OH, p = 0.9g/ml)
5. APPARATUS
Electric hot plate with variable temperature control.
Note: Where
the boron content of an extract is to be determined, do not use borosilicate
glassware. As the method involves boiling, teflon or silica is preferable.
Rinse the glassware thoroughly if it has been washed in detergents containing
borates.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1. Test
sample
Take a quantity of fertiliser weighing between 2 and 10 g depending on the
declared content of the element in the product. The following table shall be
used to obtain a final solution which, after appropriate dilution, will be
within the measuring range for each method. Samples should be weighed to
within 1 mg.
Declared content of trace element in the fertiliser (%)
|
<0.01
|
0.01 - <5
|
>=5 - 10
|
Mass of test sample (g)
|
10
|
5
|
2
|
Mass of element in the sample (mg)
|
1
|
0.5 - 250
|
100 - 200
|
Volume of extract V (ml)
|
250
|
500
|
500
|
Concentration of element in extract (mg/l)
|
4
|
1 - 500
|
200 - 400
|
Place
the sample in a 250 ml beaker.
7.2. Preparation
of the solution
If
necessary moisten the sample with a little water, add 10 ml of dilute
hydrochloric acid (4.1) per gram of fertiliser carefully, in small amounts,
then add about 50 ml of water. Cover the beaker with a watch glass and mix.
Bring to the boil on the hot plate and boil for 30 minutes. Allow to cool,
stirring occasionally. Transfer quantitatively to a 250 or 500 ml volumetric
flask (see Table). Make up to volume with water and mix thoroughly. Filter
through a dry filter into a dry container. Discard the first portion. The
extract must be perfectly clear.
It is recommended that the
determinations be carried out without delay on aliquot portions of the clear
filtrate, if not the containers should be stoppered.
Note: Extracts
in which the boron content has to be determined: Adjust the pH to between 4
and 6 with concentrated ammonia (4.2).
8. DETERMINATION
The determination of each trace element is to be carried out on the aliquot
portions indicated in the method for each individual trace element.
If
necessary, remove organic chelating or complexing substances from an aliquot
portion of the extract by using Method 25c. In the case of determination by
atomic absorption spectrometry, such removal may not be necessary.
25b.
EXTRACTION
OF WATER-SOLUBLE TRACE ELEMENTS
1. SCOPE
This method defines the procedure for extracting water-soluble forms of the
following trace elements: boron, cobalt, copper, iron, manganese, molybdenum
and zinc. The aim is to carry out the minimum number of extractions, making
use wherever possible of the same extract to determine the level of each of
the trace elements listed above.
2. FIELD
OF APPLICATION
This procedure concerns fertilisers containing one or more of the following
trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc.
It is applicable to each trace element the declared content of which is less
than or equal to 10%.
3. PRINCIPLE
The trace elements are extracted by shaking the fertiliser in water at 20°
C±2°: C.
Note: The
extraction is empirical and may or may not be quantitative.
4. REAGENTS
4.1. Dilute
hydrochloric acid (HCl) solution, above 6 M:
Mix
1 volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of water.
5. APPARATUS
5.1. Rotary
shaker set at about 35 to 40 rpm.
5.2. pH-meter.
Note: Where
the boron content of the extract is to be determined, do not use borosilicate
glassware. Teflon or silica is preferable for this extraction. Rinse the
glassware thoroughly if it has been washed in detergents containing borates.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1. Test
sample
Take a quantity of fertiliser weighing between 2 and 10 g depending on the
declared content of the element in the product. The following table shall be
used to obtain a final solution which, after appropriate dilution, will be
within the measuring range for each method. The samples should be weighed to
within 1 mg.
Declared content of trace element in the fertiliser(%)
|
<0.01
|
0.01 - <5
|
>=5 - 10
|
Mass of test sample (g)
|
10
|
5
|
2
|
Mass of element in the sample (mg)
|
1
|
0.5-250
|
100 - 200
|
Volume of extract V (ml)
|
250
|
500
|
500
|
Concentration of element in extract (mg/l)
|
4
|
1 - 500
|
200 - 400
|
Place
the sample in a 8 250 or 500 ml flask (according to the Table).
7.2. Preparation
of the solution
Add
about 200 ml of water to the 250 ml flask or 400 ml of water to the 500 ml
flask.
Stopper
the flask well. Shake vigorously by hand to disperse the sample, then place
the flask on the shaker and shake for 30 minutes.
Make
up to volume with water and mix thoroughly.
7.3. Preparation
of the test solution
Filter immediately into a
clean, dry flask. Stopper the flask. Carry out the determination immediately
after filtering.
Note: If
the filtrate gradually becomes cloudy, make another extraction following 7.1
and 7.2 in a flask of volume Ve. Filter into a calibrated flask of volume W
which has previously been dried and has received 5.00 ml of dilute
hydrochloric acid (4.1). Stop the filtration at the exact moment when the
calibration mark is reached. Mix thoroughly.
Under
these conditions the value of V in the expression of results is:
The
dilutions in the expression of results depend on this value of V.
8. DETERMINATION
The determination of each trace element is carried out on the aliquot
portions indicated in the method for each individual trace element.
If
necessary, remove organic chelating or complexing substances from an aliquot
portion by using Method 25c. In the case of determination by atomic absorption
spectrometry, such removal may not be necessary.
25c.
REMOVAL
OF ORGANIC COMPOUNDS FROM FERTILISER EXTRACTS
1. SCOPE
This method defines a procedure for removing organic compounds from
fertiliser extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
element is required.
Note: The
presence of small quantities of organic matter usually does not affect
determination by means of atomic absorption spectrometry.
3. PRINCIPLE
The organic compounds in an aliquot proportion of the extract are oxidised
with hydrogen peroxide.
4. REAGENTS
4.1. Dilute
hydrochloric acid (HCl) solution, about 0.5 M:
Mix 1 volume of hydrochloric acid (ρ= 1.18 g/m) with 20 volumes of
water.
4.2. Hydrogen
peroxide solution (30% H2O2ρ= 1.11 g/ml), free
from trace elements.
5. APPARATUS
Electric hot plate with variable temperature control.
6. PROCEDURE
Take 25 ml of the extract solution obtained by Method 25a or Method 25b and
place in a 100 ml beaker. In the case of Method 25b add 5 ml of the dilute
hydrochloric acid solution (4.1). Then add 5 ml of the hydrogen peroxide
solution (4.2). Cover with a watch glass. Allow oxidation to occur at room
temperature for about one hour, then bring gradually to boiling and boil for
half an hour. If necessary, add a further 5 ml of the hydrogen peroxide to
the solution once it has cooled. Then boil to remove the excess hydrogen
peroxide. Allow to cool and transfer quantitatively to a 50 ml volumetric
flask and make up to volume. Filter where necessary.
Account should be taken of this dilution when taking aliquot portions and
calculating the amount of trace element in the product.
25d.
DETERMINATION
OF TRACE ELEMENTS IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
(GENERAL PROCEDURE)
1. SCOPE
This method defines a general procedure for determining the levels of certain
trace elements in fertiliser extracts by atomic absorption spectrometry.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertiliser extracts
obtained by Methods 25a and 25b for which a declaration of total and/or
water-soluble element is required.
Adaptations of this procedure
for the various trace elements are detailed in the methods defined
specifically for each element.
Note: In
most cases the presence of small quantities of organic matter will not affect
determinations by atomic absorption spectrometry.
3. PRINCIPLE
After the extract has been treated where necessary to reduce or eliminate
interfering chemical species, the extract is diluted so that its
concentration is in the optimum range of the spectrometer at a wave-length
suitable for the trace element to be determined.
4. REAGENTS
4.1. Dilute
hydrochloric acid solution (HCl), about 6 M:
Mix
one volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of water.
4.2. Dilute
hydrochloric acid solution (HCl), about 0.5 M:
Mix
one volume of hydrochloric acid (ρ= 1.18 g/ml) with 20 volumes of water.
4.3. Lanthanum
salt solutions (10 g of La per litre).
This reagent is used for
determinations of cobalt, iron, manganese and zinc. Lanthanum is added to the
extract to eliminate chemical interferences in the air-acetylene flame. It
can be prepared either:
(a) with
lanthanum oxide dissolved in hydrochloric acid (4.1). Place 11.73 g of
lanthanum oxide (La2O3) in 150 ml of water in a 1 litre
volumetric flask and add 120 ml of 6 M hydrochloric acid (4.1). Allow to
dissolve and then make up to 1 litre with water and mix thoroughly. This solution
is approximately 0.5 M in hydrochloric acid: or
(b) with
solutions of lanthanum chloride, sulfate or nitrate. Place 26.7 g of
lanthanum chloride heptahydrate (LaCl3.7H2O) or 31.2 g
of lanthanum nitrate hexahydrate [La(NO3)3.6H2O]
or 26.2 g of lanthanum sulfate nonahydrate La2 (SO4)3.9H2O]
in 150 ml of water in a 1 litre volumetric flask, then add 85 ml of 6 M
hydrochloric acid (4.1). Allow to dissolve and then make up to 1 litre with
water. Mix thoroughly. This solution is approximately 0.5 M in hydrochloric
acid.
4.4. Calibration
solutions
For the preparation of these, see the individual method of determination for
each trace element.
5. APPARATUS
Atomic absorption spectrometer fitted with sources emitting radiation
characteristic of the trace elements to be determined.
The analyst must follow the manufacturer's instructions and be familiar with
the apparatus. The apparatus must allow background correction so that it can
be used whenever necessary (Co and Zn). The gases to be used are air and
acetylene.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Preparation
of extract solutions of the trace elements to be determined
See
Method 25a and/or 25b and, if appropriate 25c.
6.2. Treatment
of the test solution
Dilute an aliquot portion of the extract obtained by Method 25a, 25b or 25c
with water and/or hydrochloric acid (4.1 or 4.2) so as to obtain, in the
final solution for measurement, a concentration of the element to be
determined that is appropriate to the calibration range used (7.2) and a
hydrochloric acid concentration of at least 0.5 M and not more than 2.5 M.
This operation may require one or more successive dilutions.
Take an aliquot portion of the final solution obtained by dilution of the
extract, let (a) be its volume in ml, and pour into a 100 ml volumetric
flask. When determining the cobalt, iron, manganese or zinc content, add 10
ml of the lanthanum salt solution (4.3). Make up to volume with the 0.5 M
hydrochloric acid solution (4.2) and mix thoroughly. This is the final
solution for measurement. Let D be the dilution factor.
7. PROCEDURE
7.1. Preparation
of a blank solution
Prepare a blank solution by repeating the whole procedure from the extraction
stage, omitting only the test sample of fertiliser.
7.2. Preparation
of calibration solutions
From the working calibration solution prepared using the method given for
each individual trace element, prepare in 100 ml volumetric flasks a series
of at least five calibration solutions of increasing concentration within the
optimum measuring range of the spectrometer. If necessary, adjust the
concentration of hydrochloric acid to bring it as close as possible to that
of the diluted test solution (6.2). For determining cobalt, iron, manganese
or zinc add 10 ml of the same lanthanum salt solution (4.3) as used in 6.2.
Make up to volume with the 0.5 M hydrochloric acid solution (4.2) and mix
thoroughly.
7.3 Determination
Prepare the spectrometer (5) for the determination and adjust to the
wavelength given in the method for the individual trace element concerned.
Spray three times in succession the calibration solutions (7.2), and the test
solution (6.2) and the blank solution (7.1), noting each result and flushing
the instrument with distilled water between individual sprayings.
Construct the calibration curve by plotting the average spectrometer reading
for each calibration solution (7.2) along the ordinate and the corresponding
concentration of the element, expressed in μg per ml, along the
abscissa.
From this curve, determine the concentrations of relevant trace element in
the test solution xs (6.2) and in the blank solution xb (7.1), expressing
these concentrations in μg per ml.
8. EXPRESSION
OF RESULTS
The percentage of trace element (E) in the fertiliser is equal to:
E (%) = [(xs- xb) × V × D]/(M ×
104).
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|
If
method (25c) has been used:
E (%) = [(xs- xb) × V × 2D]/(M
× 104),
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|
where:
E is the amount of the trace element determined, expressed as a
percentage of the fertiliser;
xs is the concentration of the test solution (6.2), in
μg/ml;
xb is the concentration of the blank solution (7.1), in
μg/ml;
V is the volume of the extract obtained by Method 25a or 25b, in ml;
D is the factor corresponding to the dilution carried out in (6.2);
M is the mass of the test sample taken in accordance with Method 25a or
25b in grams.
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|
Calculation
of dilution factor D:
If
(a1), (a2), (a3), . . ., (ai) and
(a) are the aliquot portions and (v1), (v2), (v3),
. . ., (vi) and (100) are the volumes in ml corresponding to their
respective dilutions, the dilution factor D will be equal to:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/ai) ×
(100/a).
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25e.
DETERMINATION
OF BORON IN FERTILISER EXTRACTS BY MEANS OF SPECTROMETRY WITH AZOMETHINE-H
1. SCOPE
This method describes a procedure for determining boron in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
boron is required.
3. PRINCIPLE
In an azomethine — H solution, borate ions form a yellow complex the
concentration of which is determined by molecular absorption spectrometry at
410 nm. Interfering ions are masked with EDTA.
4. REAGENTS
4.1. EDTA
buffer solution
Place in a 500 ml volumetric flask containing 300 ml of water:
—
75 g of ammonium acetate (NH4OOCCH3);
—
10 g of disodium salt of ethylene diamine tetraacetic acid (Na2EDTA);
—
40 ml of acetic acid (CH3COOH, p = 1.05 g/ml).
Make
up to volume with water and mix thoroughly. The pH of the solution, checked
by means of a glass electrode, must be 4.8 0.1.
4.2. Azomethine-H
solution
Place
in a 200 ml volumetric flask
—
10 ml of the buffer solution (4.1);
—
400 mg of azomethine-H (C17H12NNaO8S2);
—
2 g of ascorbic acid (C6H8O6).
Make
up to volume and mix thoroughly. Do not prepare large quantities of this
reagent as it is stable for only a few days.
4.3. Boron
calibration solutions
4.3.1. Boron stock solution (100
μg/ml)
Dissolve
0.5719 g of boric acid (H3BO3) in water in a 1,000 ml
volumetric flask. Make up to volume with water and mix thoroughly. Transfer
to a plastic bottle for storage in a refrigerator.
4.3.2. Boron working solution (10
μg/ml)
Place
50 ml of stock solution (4.3.1) in a 500 ml volumetric flask. Make up to
volume with water and mix thoroughly.
5. APPARATUS
Spectrometer fitted for molecular absorption with cells having a 10 mm
optical path and set to a wavelength of 410 nm.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Preparation
of the boron solution
See
Methods 25a and/or 25b and, if appropriate, 25c.
6.2. Preparation
of the test solution
Dilute
an aliquot portion of extract (6.1) to obtain a boron concentration as
specified in 7.2. Two successive dilutions may be necessary. Let D be the
dilution factor.
6.3. Preparation
of the correction solution.
If
the test solution (6.2) is coloured, prepare a corresponding correction
solution by placing in a plastic flask 5 ml of test solution (6.2), 5 ml of
EDTA buffer solution (4.1) and 5 ml of water and mix thoroughly.
7. PROCEDURE
7.1. Preparation
of the blank solution
Prepare a blank solution by repeating the whole procedure from the extraction
stage, omitting only the test sample of fertiliser.
7.2. Preparation
of the calibration solutions
Transfer 0, 5, 10, 15, 20 and 25 ml of the working calibration solution
(4.3.2) to a series of 100 ml volumetric flasks. Make up to 100 ml with water
and mix thoroughly. These solutions contain between 0 and 2.5 μg/ml of
boron.
7.3. Colour
development
Transfer
5 ml of the calibration solutions (7.2), test solutions (6.2) and blank (7.1)
to a series of plastic flasks. Add 5 ml of the EDTA buffer solution (4.1).
Add 5 ml of the azomethine-H solution (4.2).
Mix thoroughly and allow the colour to develop in the dark for 2½ to 3 hours.
7.4. Determination
Measure
the absorbance of the solutions obtained at 7.3 and if appropriate the
correction solution (6.3) against water at a wavelength of 410 nm. Rinse the
cells with water before each new reading.
8. EXPRESSION
OF RESULTS
Plot a calibration curve of the concentration of the calibration solutions
(7.2) along the abscissa and the absorbance given by the spectrophotometer
(7.4) along the ordinate.
Read off the calibration curve the concentration of boron in the blank (7.1),
the concentration of boron in the test solution (6.2) and, if the test
solution is coloured, the corrected concentration of the test solution. To
calculate the latter, subtract the absorbance of the correction solution
(6.3) from the absorbance of the test solution (6.2) and determine the
corrected concentration of the test solution. Note the concentration of the
test solution (6.2), with or without correction, (xs) and of the
blank (xb).
The percentage of boron in the fertiliser is given by:
B%= [(xs- xb) × V × D] / (M ×
104)
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If
Method 25c is used:
B%=[(xs- xb) × V × 2D] / (M ×
104)
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|
where:
B is the quantity of boron expressed as a percentage of the fertiliser;
xs is the concentration μg/ml) in the test solution (6.2)
with or without correction;
Xb is the concentration (μg/ml) in the blank (7.1);
V is the volume in ml of extract obtained in accordance with Method 25a
or 25b;
D is the factor corresponding to the dilution carried out in 6.2;
M is the mass in grams of the test sample taken in accordance with Method
25a or 25b.
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Calculation
of the dilution factor D: if (a1) and (a2) are
successive aliquot portions and (v1) and (v2) are the
volumes corresponding to their respective dilutions, the dilution factor is
given by:
25f.
DETERMINATION
OF COBALT IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining cobalt in fertilisers
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
cobalt is required.
3. PRINCIPLE
After suitable treatment and dilution of the extracts, the cobalt content is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1. Hydrochloric
acid solution, about 6 M.
See Method 25d (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M.
See Method 25d (4.2).
4.3. Lanthanum
salt solutions (10 g of La per litre)
See Method 25d (4.3).
4.4. Cobalt
calibration solutions.
4.4.1. Cobalt stock solution (1,000
μg/ml)
In
a 250 ml beaker, weigh to the nearest 0.1 mg, 1 g of cobalt, add 25 ml of 6 M
hydrochloric acid (4.1) and heat on a hot plate until the cobalt is
completely dissolved. When cool, transfer quantitatively to a 1,000 ml
volumetric flask. Make up to volume with water and mix thoroughly.
4.4.2. Cobalt working solution (100
μg/ml)
Place
10 ml of the stock solution (4.4.1) in a 100 ml volumetric flask. Make up to
volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
5. APPARATUS
Atomic absorption spectrometer: see Method 25d (5). The instrument must be
equipped with a source of rays characteristic of cobalt (240.7 nm). The
spectrometer must allow background correction to be made.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Cobalt
extract solution
See Methods 25a and/or 25b and, if appropriate 25c.
6.2. Preparation
of the test solution
See Methods 25d (6.2). The test solution must contain 10% (v/v) of a
lanthanum salt solution (4.3).
7. PROCEDURE
7.1. Preparation
of blank solution
See Method 25d (7.1). The blank must contain 10% (v/v) of the lanthanum salt
solution used in 6.2.
7.2. Preparation
of calibration solutions
See Method 25d (7.2).
For an optimum determination range of 0 to 5 μg/ml of cobalt, place 0,
0.5, 1, 2, 3, 4, and 5 ml respectively of working solution (4.4.2) in a
series of 100 ml volumetric flasks. If necessary adjust the hydrochloric acid
concentration as closely as possible to that of the test solution. Add to
each flask 10 ml of the lanthanum salt solution used in 6.2. Make up to 100
ml with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These
solutions contain 0, 0.5, 1, 2, 3, 4, and 5 μg/ml respectively of
cobalt.
7.3. Determination
See
Method 25d (7.3). Prepare the spectrometer (5) for measurement at a
wavelength of 240.7 nm.
8. EXPRESSION
OF RESULTS
See Method 25d (8).
The
percentage of cobalt in the fertiliser is given by:
Co %= [(xs- xb) × V × D] / (M ×
104)
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If
Method 25c is used:
Co %= [(xs- xb) × V × 2D] / (M
× 104)
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|
where:
Co is the quantity of cobalt expressed as a percentage of the fertiliser;
xs is the concentration in μg/ml of the Co in the test
solution (6.2);
xb is the concentration in μg/ml of the Co in the blank
solution (7.1);
V is the volume in ml of extract obtained in accordance with Method 25a
or 25b;
D is the factor corresponding to the dilution carried out in 6.2;
M is the mass in grams of the test sample taken in accordance with Method
25a or 25b.
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Calculation
of the dilution factor D: if (a1), (a2), (a3),
. . ., (ai) and (a) are aliquot portions and (vl), (v2),
(v3), . . ., (vi) and (100) are the volumes in ml
corresponding to their respective dilutions, the dilution factor D is given
by:
D = (vl/al) × (v2/a2)
× (v3/a3) x. . . × (vi/ai) ×
(100/a).
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25g.
DETERMINATION
OF COPPER IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining copper in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
copper is required.
3. PRINCIPLE
After suitable treatment and dilution of the extracts, the copper content is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1. Hydrochloric
acid solution, about 6 M
See Method 25d (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M
See Method 25d (4.2).
4.3. Hydrogen
peroxide solution (30% H2O, p = 1.11 g/ml), free from trace
elements.
4.4. Copper
calibration solutions
4.4.1. Copper stock solution (1,000
μg/ml)
In
a 250 ml beaker weigh to the nearest 0.1 mg, 1 g of copper, add 25 ml of 6M
hydrochloric acid (4.1) add 5 ml hydrogen peroxide solution (4.3) and heat on
a hotplate until the copper is completely dissolved. Transfer quantitatively
to a 1 litre volumetric flask. Make up to volume with water and mix
thoroughly.
4.4.2. Copper working solution (100
μg/ml)
Place
20 ml of the stock solution (4.4.1) in a 200 ml volumetric flask. Make up to
volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
5. APPARATUS
Spectrometer equipped for atomic absorption: see Method 25.d (5). The
instrument must be fitted with a source of rays characteristic of copper
(324.8 nm).
6. PREPARATION
FOR THE SOLUTION TO BE ANALYSED
6.1. Copper
extract solution
See Methods 25a and/or 25b and, if appropriate, 25c.
6.2. Preparation
of the test solution
See Method 25d (6.2).
7. PROCEDURE
7.1. Preparation
of blank solution
See Method 25d (7.1).
7.2. Preparation
of calibration solutions
See Method 25d (7.2).
For an optimum determination range of 0 to 5 μg/ml of copper, place 0,
0.5, 1, 2, 3, 4 and 5 ml respectively of working solution (4.4.2) in a series
of 100 ml volumetric flasks. If necessary adjust the hydrochloric acid
concentration as closely as possible to that of the test solution (6.2). Make
up to 100 ml with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
These solutions contain 0, 0.5, 1, 2, 3, 4, and 5 μg/ml respectively of
copper.
7.3. Determination
See
Method 25d (7.3). Prepare the spectrometer (5) for measurement at a
wavelength of 324.8 nm.
8. EXPRESSION
OF RESULTS
See Method 25d (8)
The percentage of copper in the fertiliser is given by:
Cu %= [(xs- xb) × V × D] / M ×
104)
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If
Method 25c is used:
Cu %= [(xs- xb) × V × 2D] / M ×
104)
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|
where:
Cu is the quantity of copper expressed as percentage of the fertiliser;
xs is the concentration in Ug/ml of Cu in the test solution
(6.2);
xb is the concentration in μg/ml of Cu in the blank
solution (7.1);
V is the volume in ml of extract obtained in accordance with Method 25a
or 25b;
D is the factor of the dilution carried out in 6.2;
M is the mass in grams of the test sample taken in accordance with Method
25a or 25b.
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Calculation
of the dilution factor D: if (a1), (a2), (a3),
. . ., (ai) and (a) are aliquot portions and (v1), (v2),
(v3), . . ., (vi) and (100) are the volumes in ml
corresponding to their respective dilution, the dilution factor D is given
by:
D = (v1/a1) × (v2/a2)
× (v3/a3) x. . . × (vi/ai) ×
(100/a)
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25h.
DETERMINATION
OF IRON IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining iron in fertiliser extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
iron is required.
3. PRINCIPLE
After suitable treatment and dilution of the extract, the iron content is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1 Hydrochloric
acid solution, about 6M.
See Method 25d (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M
See Method 25d (4.2).
4.3. Hydrogen
peroxide solution (30% H2O2 p = 1.11 g/ml) free from
trace element.
4.4. Lanthanum
salt solutions (10 g of La per litre)
See Method 25d (4.3).
4.5. Iron
calibration solutions
4.5.1. Iron stock solution (1,000 μg/ml)
In
a 500 ml beaker, weigh to the nearest 0.1 mg, 1 g of pure iron wire, add 200
ml of 6 M hydrochloric acid (4.1) and 15 ml of hydrogen peroxide solution
(4.3). Heat on a hotplate until the iron is completely dissolved. When cool,
transfer quantitatively to a 1 litre volumetric flask. Make up to volume with
water and mix thoroughly.
4.5.2. Iron working solution (100
μg/ml)
Place
20 ml of the stock solution (4.5.1) in a 200 ml volumetric flask. Make up to
volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
5. APPARATUS
Atomic absorption spectrometer: see Method 25d (5). The instrument must be
fitted with a source of rays characteristic of iron (248.3 nm).
6. PREPARATION
FOR THE SOLUTION TO BE ANALYSED
6.1. Iron
extract solution
See Methods 25a and/or 25b and, if appropriate, 25c.
6.2. Preparation
of the test solution
See Method 25d (6.2). The test solution must contain 10% (v/v) of a lanthanum
salt solution.
7. PROCEDURE
7.1. Preparation
of blank solution
See Method 25d (7.1). The test solution must contain 10% (v/v) of the
lanthanum salt solution used in 6.2.
7.2 Preparation
of calibration solutions
See Method 25d (7.2).
For an optimum determination range of 0 to 10 μg/ml of iron, place 0, 2,
4, 6, 8 and 10 ml respectively of working solution (4.5.2) in a series of 100
ml volumetric flasks. If necessary adjust the hydrochloric acid concentration
as closely as possible to that of the test solution. Add 10 ml of the lanthanum
salt solution used in 6.2. Make up to volume with 0.5 M hydrochloric acid
solution (4.2) and mix thoroughly. These solutions contain 0, 2, 4, 6, 8 and
10 μg/ml respectively of iron.
7.3. Determination
See Method 25d (7.3). Prepare the spectrometer (5) for measurement at a
wavelength of 248.3nm.
8. EXPRESSION
OF RESULTS
See Method 25d (8).
The percentage of iron in the fertiliser is given by:
Fe %= [(xs- xb) × V × D] / (M ×
104)
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If
Method 27d is used:
Fe %= [(xs- xb) × V × 2D] / M ×
104)
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|
where:
Fe is the quantity of iron expressed as a percentage of the fertiliser;
xs is the concentration in μg/ml of Fe in the test
solution (6.2);
xb is the concentration in μg/ml of Fe in the blank
solution (7.1);
V is the volume in ml of extract obtained in accordance with Method 25a
or 25b;
D is the factor of the dilution carried out in 6.2;
M is the mass in grams of the test sample taken in accordance with Method
25a or 25b
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Calculation
of the dilution factor D: if (a1), (a2), (a3),
. . ., (ai) and (a) are aliquot portions and (v1), (v2),
(v3), . . ., (vi) and (100) are the volumes in ml
corresponding to their respective dilutions, the dilution factor D is given
by:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/ai) ×
(100/a).
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25i DETERMINATION OF
MANGANESE IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining manganese in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
manganese is required.
3. PRINCIPLE
After suitable treatment and dilution of the extracts, the manganese level is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1. Hydrochloric
acid solution, about 6 M
See Method 25d (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M
See
Method 25d (4.2).
4.3. Lanthanum
salt solutions (10 g of La per litre)
See Method 25d (4.3).
4.4. Manganese
calibration solutions
4.4.1. Manganese stock solution (1,000
μg/ml)
In a 250
ml beaker, weigh to the nearest 0.1 mg, 1 g of manganese, add 25 ml of 6 M
hydrochloric acid solution (4.1). Heat on a hotplate until the manganese is
completely dissolved. When cool, transfer quantitatively to a 1,000 ml
volumetric flask. Make up to volume with water and mix thoroughly.
4.4.2. Manganese working solution (100
μg/ml)
Place 20
ml of the stock solution (4.4.1) in a 200 ml volumetric flask. Make up to
volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
5. APPARATUS
Atomic absorption spectrometer: see Method 25d (5). The apparatus must be
fitted with a source of rays characteristic of manganese (279.6 nm).
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Manganese
extract solution
See Methods 25a and/or 25b and, if appropriate 25c.
6.2. Preparation
of the test solution
See Method 25d (6.2). The test solution must contain 10% by volume of
lanthanum salt solution (4.3).
7. PROCEDURE
7.1. Preparation
of the blank solution
See Method 25d (7.1). The blank solution must contain 10% by volume of the
lanthanum salt solution used in 6.2.
7.2. Preparation
of the calibration solutions
See Method 25d (7.2).
For an optimum interval of 0 to 5 μg/ml manganese, place 0, 0.5, 1, 2,
3, 4 and 5 ml, respectively, of the working solution (4.4.2) in a series of
100 ml volumetric flasks. Where necessary, adjust the hydrochloric acid
concentration to bring it as close as possible to that of the test solution.
To each flask add 10 ml of the lanthanum salt solution used in 6.2. Make up
to 100 ml with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
These solutions contain 0, 0.5, 1, 2, 3, 4 and 5 μg/ml manganese
respectively.
7.3. Determination
See Method 25d (7.3). Prepare the spectrometer (5) for measurements at a
wavelength of 279.6 nm.
8. EXPRESSION
OF RESULTS
See Method 25d (8).
The percentage of manganese in the fertiliser is as follows:
Mn %= [(xs- xb) × V × D ] / (M
× 104)
|
|
If Method 25c has been used:
Mn %= [(xs- xb) × V × 2D] / (M
× 104)
|
|
where:
Mn is the quantity of manganese expressed as a percentage of the
fertiliser;
xs is the concentration in μg/ml of Mn in the test
solution (6.2);
xb is the concentration in μg/ml of Mn in the blank
solution (7.1);
V is the volume in ml of the extract obtained using Method 25a or 25b;
D is the factor corresponding to the dilution performed in 6.2;
M is the mass in g of the test sample taken using Method 25a or 25b.
|
|
Calculation of dilution factor
D: where (a1), (a2), (a3), . . ., (ai)
and (a) are aliquot portions and (v1), (v2), (v3),
. . ., (vi) and (100) the volumes in ml corresponding to their
respective dilutions, dilution factor D will be equal to:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/ai) ×
(100/a).
|
|
25j.
DETERMINATION
OF MOLYBDENUM IN FERTILISER EXTRACTS BY SPECTROMETRY OF A COMPLEX WITH
AMMONIUM THIOCYANATE
1. SCOPE
This method describes a procedure for determining molybdenum in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
molybdenum is required.
3. PRINCIPLE
Molybdenum(v) forms a complex [MoO(SCN)5] -- in an acid medium with SCN -
ions. The complex is extracted with n-butyl acetate. Interfering ions such as
those of iron remain in the aqueous phase. The yellow-orange colour is
determined by molecular absorption spectrometry at 470 nm.
4. REAGENTS
4.1. Dilute
hydrochloric acid solution (HCl), about 6 M
See method 25d (4.1).
4.2. Copper
solution (70 mg/l) in 1.5 M hydrochloric acid
Dissolve 275 mg of copper sulfate (CuSO4.5H2O) weighed
to within 0.1 mg in 250 ml of the 6 M hydrochloric acid solution (4.1) in a
1,000 ml volumetric flask. Make up to volume with water and mix thoroughly.
4.3. Ascorbic
acid solution (50 g/l)
Dissolve 50 g of ascorbic acid (C6H8O6) in
water in a 1,000 ml volumetric flask. Make up to volume with water, mix
thoroughly and keep in a refrigerator.
4.4. n-butyl
acetate
4.5. Ammonium
thiocyanate solution, 0.2 M
Dissolve 15.224 g of NH4SCN in water in a 1,000 ml volumetric
flask. Make up to volume with water; mix thoroughly and store in a
dark-coloured bottle.
4.6. Stannous
chloride solution (50 g/l) in 2 M hydrochloric acid
This solution must be perfectly clear and prepared immediately before use.
Very pure stannous chloride must be used otherwise the solution will not be
clear.
To prepare 100 ml of solution, dissolve 5 g of SnCl2.2H2O
in 35 ml of 6 M HCl solution (4.1). Add 10 ml of the copper solution (4.2).
Make up to volume with water and mix thoroughly.
4.7. Molybdenum
calibration solutions
4.7.1. Molybdenum stock solution (500
μg/ml)
Dissolve
0.920 g of ammonium molybdate [(NH4)6 Mo7O24.4H2O]
weighed to within 0.1 mg in the 6 M hydrochloric acid (4.1) in a 1 litre
volumetric flask. Make up to volume with that solution and mix thoroughly.
4.7.2. Molybdenum intermediate solution
(25 μg/ml)
Place
25 ml of the stock solution (4.7.1) in a 500 ml volumetric flask. Make up to
volume with 6 M hydrochloric acid (4.1) and mix thoroughly.
4.7.3. Molybdenum working solution (2.5
μg/ml)
Place
10 ml of the intermediate solution (4.7.2) in a 100 ml volumetric flask. Make
up to volume with 6 M hydrochloric acid (4.1) and mix thoroughly.
5. APPARATUS
5.1. Spectrometer
fitted for molecular absorption with cells having a 20 mm optical path and
set to a wavelength of 470 nm.
5.2. 200
or 250 ml separating funnels.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Molybdenum
extract solution
See Methods 25a and/or 25b and, if appropriate, 25c.
6.2. Preparation
of the test solution
Dilute an aliquot portion of the extract (6.1) with 6 M hydrochloric acid
solution (4.1) so as to obtain an appropriate molybdenum concentration. Let D
be the dilution factor.
Take an aliquot portion (a) from the extract solution containing 1 to 12
μg molybdenum and place it in the separating funnel (5.2). Make up to 50
ml with the 6 M hydrochloric acid solution (4.1).
7. PROCEDURE
7.1. Preparation
of the blank solution
Prepare a blank solution by repeating the whole procedure from the extraction
stage, omitting only the test sample of fertiliser.
7.2. Preparation
of the series of calibration solutions
Prepare a series of at least six calibration solutions of increasing
concentration corresponding to the optimum response range of the
spectrometer.
For the interval 0 - 12.5 μg molybdenum, place 0, 1, 2, 3, 4, and 5 ml,
respectively, of the working solution (4.7.3) in the separating funnels
(5.2). Make up to 50 ml with 6 M hydrochloric acid (4.1). The funnels
contain, respectively, 0, 2.5, 5, 7, 5, 10 and 12.5 μg molybdenum.
7.3. Development
and separation of the complex
To each separating funnel (6.2, 7.1 and 7.2), add in the following order:
—
10 ml of the copper solution (4.2)
—
20 ml of the ascorbic acid solution (4.3);
mix
thoroughly and wait for two or three minutes. Then add:
—
10 ml of n-butyl acetate (4.4), using a precision pipette;
—
20 ml of the thiocyanate solution (4.5).
Shake
for one minute to extract the complex into the organic phase; allow to
separate; after the separation of the two phases, draw off the entire aqueous
phase and discard it; then wash the organic phase with:
—
10 ml of the stannous chloride solution (4.6).
Shake
for one minute. Allow to separate and draw off the entire aqueous phase.
Remove the organic phase in a test tube; this will make it possible to
collect the drops of water in suspension.
7.4. Determination
Measure the absorbencies of the solutions obtained at 7.3 at a wavelength of
470 nm using the 0 μg/ml molybdenum calibration solution (7.2) as a
reference.
8. EXPRESSION
OF RESULTS
Construct the calibration curve by plotting the corresponding masses of
molybdenum in the calibration solutions (7.2) expressed in μg along the
abscissa and the corresponding values of the absorbencies (7.4) given by the
spectrometer reading along the ordinate.
From this curve determine the mass of molybdenum in the test solution (6.2)
and the blank solution (7.1). These masses are designated (xs) and
(xb) respectively.
The percentage of molybdenum in the fertiliser is:
Mo %= [(xs- xb) × V/a × D] / (M
× 104)
|
|
If
Method 25c has been used:
Mo %= [(xs- xb) × V/a × 2D] /
(M × 104)
|
|
where:
Mo is the quantity of molybdenum expressed as a percentage of the
fertiliser;
a is the volume in ml of the aliquot taken from the last dilute solution
(6.2);
xs is the mass in μg of Mo in the test solution (6.2);
xb is the mass in μg of Mo in the blank solution (7.1)
the volume of which corresponds to the volume (a) of the aliquot of the
test solution (6.2);
V is the volume in ml of the extract solution obtained in accordance with
Method 25a or 25b;
D is the factor corresponding to the dilution performed in 6.2;
M is the mass in g of the test sample taken in accordance with Method 25a
or 25b.
|
|
Calculation
of the dilution factor D: where (a1), (a2) are
successive aliquot portions and (v1), (v2) are the
volumes corresponding to their respective dilutions, the dilution factor D
will be:
25k.
DETERMINATION
OF ZINC IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining zinc in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 25a and 25b for which a declaration of total and/or water-soluble
zinc is required.
3. PRINCIPLE
After suitable treatment and dilution of the extracts, the zinc level is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1. Hydrochloric
acid solution, about 6 M
See Method 25d (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M
See Method 25d (4.2).
4.3. Lanthanum
salt solutions (10 g of La per litre)
See Method 25d (4.3).
4.4. Zinc
calibration solutions
4.4.1. Zinc stock solution (1,000
μg/ml)
In
a 1 litre volumetric flask dissolve 1 g of zinc powder or flakes weighed to
within 0.1 mg in 25 ml of 6 M hydrochloric acid (4.1). When completely
dissolved, make up to volume with water and mix thoroughly.
4.4.2. Zinc working solutions (100
μg/ml)
Place
20 ml of the stock solution, (4.4.1) in a 200 ml volumetric flask. Make up to
volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
5. APPARATUS
Atomic absorption spectrometer: See Method 25d (5). The apparatus must be
fitted with a source of rays characteristic of zinc (213.8 nm). The
spectrometer must allow background correction to be made.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Zinc
extract solution
See Methods 25a and/or 25b and, if appropriate, 25c.
6.2. Preparation
of the test solution
See Method 25d (6.2). The test solution must contain 10% by volume of
lanthanum salt solution.
7. PROCEDURE
7.1. Preparation
of the blank solution
See Method 25d (7.1). The blank solution must contain 10% by volume of the
lanthanum salt solution used in 6.2.
7.2. Preparation
of the calibration solutions
See Method 25d (7.2).
For an optimum interval of 0 to 5 μg/ml of zinc, place 0, 0.5, 1, 2, 3,
4 and 5 ml, respectively, of the working solution (4.4.2) in a series of 100
ml volumetric flasks. Where necessary, adjust the concentration of
hydrochloric acid to bring it as close as possible to that of the test
solution. Add 10 ml of the lanthanum salt solution used in (6.2) to each
volumetric flask. Make up to 100 ml with the 0.5 M hydrochloric acid solution
(4.2) and mix thoroughly. These solutions contain, respectively: 0, 0.5, 1,
2, 3, 4, and 5 μg/ml of zinc.
7.3. Determination
See Method 25d (7.3). Prepare the spectrometer (5) for measurements at a
wavelength of 213.8 nm.
8. EXPRESSION
OF RESULTS
See Method 25d (8).
The percentage of zinc in the fertiliser is:
Zn %= [(xs- xb) × V × D] / (M ×
104)
|
|
If
Method 25c has been used:
Zn %= [(xs- xb) × V × 2D] / (M
× 104)
|
|
where:
Zn is the quantity of zinc expressed as a percentage of the fertiliser;
xs is the mass in μg of Zn in the test solution (6.2);
xb is the mass in μg of Zn in the blank solution (7.1);
V is the volume in ml of the extract solution obtained in accordance with
Method 25a or 25b;
D is the factor corresponding to the dilution performed in 6.2;
M is the mass in g of the test sample taken in accordance with Method 25a
or 25b
|
|
Calculation
of the dilution factor D: where (a1), (a2), (a3),
. . ., (ai) and (a) are successive aliquot portions and (v1),
(v2), (v3), . . ., (vi) and (100) are
volumes corresponding to their respective dilutions, the dilution factor D
will be:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/ai) ×
(100/a).
|
|
26.
TRACE
ELEMENTS AT A CONCENTRATION GREATER THAN 10%
26a.
EXTRACTION
OF TOTAL TRACE ELEMENTS
1. SCOPE
This method defines the procedure for extracting the following trace
elements: total boron, total cobalt, total copper, total iron, total
manganese, total molybdenum and total zinc. The aim is to carry out the
minimum number of extractions, making use wherever possible of the same
extract to determine the total level of each of the trace elements listed
above.
2. FIELD
OF APPLICATION
This procedure concerns fertilisers containing one or more of the following
trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc.
It is applicable to each trace element, the declared content of which is more
than 10%.
3. PRINCIPLE
Dissolution in boiling diluted hydrochloric acid.
Note: The
extraction is empirical and may not be quantitative depending on the product
or the other constituents of the fertiliser. In particular, in the case of
certain manganese oxides, the quantity extracted may be substantially smaller
than the total quantity of manganese which the product contains. It is the
responsibility of the fertiliser manufacturers to ensure that the declared
content actually corresponds to the quantity extracted under the conditions
pertaining to the method.
4. REAGENTS
4.1. Diluted
hydrochloric acid (HCI) solution, about 6M
Mix 1 volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of water.
4.2. Concentrated
ammonia solution (NH4OH, p = 0.9 g/ml)
5. APPARATUS
5.1. Electric
hotplate with variable temperature control.
5.2. pH
meter
Note: Where
the boron content of an extract is to be determined, do not use borosilicate
glassware. As the method involves boiling, teflon or silica is preferable.
Rinse the glassware thoroughly if it has been washed in detergents containing
borates.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1. Test
sample
Take a quantity of fertiliser weighing 1 or 2g depending on the declared
content of element in the product. The following table shall be used to
obtain a final solution which, after appropriate dilution, will be within the
measuring range for each method. Samples should be weighed to within 1 mg.
Declared content of trace element in the fertiliser (%)
|
<10 - <25
|
<25
|
Mass of test sample (g)
|
2
|
1
|
Mass of element in the sample (mg)
|
<200 - <500
|
<250
|
Volume of extract V (ml)
|
500
|
500
|
Concentration of element in extract (mg/l)
|
<400 - <1 000
|
<500
|
Place
the sample in a 250ml beaker.
7.2. Preparation
of the solution
If
necessary moisten the sample with a little water, add 10 ml of dilute
hydrochloric acid (4.1) per gram of fertiliser carefully, in small amounts,
then add about 50 ml of water. Cover the beaker with a watchglass and mix.
Bring to the boil on the hotplate and boil for 30 minutes. Allow to cool,
stirring occasionally. Transfer quantitatively to a 500 ml volumetric flask. Make
up to volume with water and mix thoroughly. Filter through a dry filter into
a dry container. Discard the first portion. The extract must be perfectly
clear.
It
is recommended that the determinations be carried out without delay on
aliquot portions of the clear filtrate, if not the containers should be
stoppered.
Note: Extracts
in which the boron content has to be determined.
Adjust
the pH to between 4 and 6 with concentrated ammonia solution (4.2).
8. DETERMINATION
The determination of each trace element is to be carried out on the aliquot
portions indicated in the method for each individual trace element.
Methods 26e, 26f, 26g, 26i and 26j cannot be used to determine elements
present in a chelated or complexed form. In such cases Method 26c must be
used prior to the determination.
In case of determinations by atomic absorption spectrometry (Methods 26h and
26k) such treatment may not be necessary.
26b.
EXTRACTION
OF WATER — SOLUBLE TRACE ELEMENTS
1. SCOPE
This method defines the procedure for extracting water-soluble forms of the
following trace elements: boron, cobalt, copper, iron, manganese, molybdenum
and zinc. The aim is to carry out the minimum number of extractions, making
use wherever possible of the same extract to determine the level of each of
the elements listed above.
2. FIELD
OF APPLICATION
This procedure concerns fertilisers containing one or more of the following
trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc.
It is applicable to each trace element, the declared content of which is more
than 10%.
3. PRINCIPLE
The trace elements are extracted by shaking the fertiliser in water at 20±°C.
Note: The
extraction is empirical and may not be quantitative.
4. REAGENTS
4.1. Diluted
hydrochloric acid (HCl) solution, about 6 M
Mix
1 volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of water.
5. APPARATUS
5.1. Rotary
shaker set at about 35 to 40 rpm.
Note: Where
the boron content of the extract is to be determined, do not use borosilicate
glassware. Teflon or silica is preferable for this extraction. Rinse the
glassware thoroughly if it has been washed in detergents containing borates.
6. PREPARATION
OF THE SAMPLE
See Method 1.
7. PROCEDURE
7.1. Test
sample
Take a quantity of fertiliser weighing 1 or 2g depending on the declared
content of the product. The following table shall be used to obtain a final
solution which, after appropriate dilution, will be within the measuring
range for each method. The samples should be weighed to within 1mg.
Declared content of trace element in the fertiliser (%)
|
<10 -<25
|
<25
|
Mass of test sample (g)
|
2
|
1
|
Mass of element in the sample (mg)
|
<200 -<500
|
<250
|
Volume of extract V (ml)
|
500
|
500
|
Concentration of element in extract (mg/l)
|
<400 -<1000
|
<500
|
Place
the sample in a 500 ml flask.
7.2. Preparation
of the solution
Add about 400 ml of water.
Stopper the flask well. Shake vigorously by hand to disperse the sample, then
place the flask on the shaker and shake for 30 minutes.
Make up to volume with water and mix thoroughly.
7.3. Preparation
of the test solution
Filter immediately into a clean, dry flask. Stopper the flask. Carry out the
determination immediately after filtering.
Note: If
the filtrate gradually becomes cloudy, make another extraction following 7.1
and 7.2 in a flask of volume Ve. Filter into a calibrated flask of volume W
which has previously been dried and has received 5 ml of dilute hydrochloric
acid (4.1). Stop the filtration at the exact moment when the calibration mark
is reached. Mix thoroughly.
Under
these conditions the value of V in the expression of results is:
The
dilutions in the expression of results depend on this value of V.
8. DETERMINATION
The determination of each trace element is carried out on the aliquot
portions indicated in the method for each individual trace element.
Methods 26e, 26f, 26g, 26i and 26j cannot be used to determine elements
present in a chelated or complexed form. In such cases Method 26c must be
used prior to the determination.
In the case of determinations by atomic absorption spectrometry (Methods 26h
and 26k) such treatment may not be necessary.
26c.
REMOVAL
OF ORGANIC COMPOUNDS FROM FERTILISER EXTRACTS
1. SCOPE
This method defines a procedure for removing organic compounds from
fertiliser extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertilisers extracted by
Methods 26a and 26b for which a declaration of total and/or water — soluble
element is required.
Note: The
presence of small quantities of organic matter usually does not affect
determinations by means of atomic absorption spectrometry.
3. PRINCIPLE
The organic compounds in an aliquot portion of the extract are oxidized with
hydrogen peroxide.
4. REAGENTS
4.1. Diluted
hydrochloric acid solution, about 0.5 M
Mix 1 volume of hydrochloric acid (ρ= 1.18 g/ml) with 20 volumes of
water.
4.2. Hydrogen
peroxide solution (30% H2O2, p = 1.11 g/ml), free from
trace elements.
5. APPARATUS
Electric hotplate with variable temperature control.
6. PROCEDURE
Take 25 ml of extract solution obtained by Method 26a or 26b and place in a
100 ml beaker. In the case of Method 26b, add 5 ml of the dilute hydrochloric
acid solution (4.1). Then add 5 ml of the hydrogen peroxide solution (4.2).
Cover with a watchglass. Allow oxidation to occur at room temperature for
about one hour, then bring gradually to boiling and boil for half an hour. If
necessary, add a further 5 ml of the hydrogen peroxide to the solution once
it has cooled. Then boil to remove the excess hydrogen peroxide. Allow to
cool and transfer quantitatively to a 50 ml volumetric flask and make up to
volume. Filter where necessary.
Account should be taken of this dilution when taking aliquot portions and
calculating the percentage of trace element in the product.
26d.
DETERMINATION
OF TRACE ELEMENTS IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
(GENERAL PROCEDURE)
1. SCOPE
This method defines a general procedure for determining the levels of iron
and zinc in fertiliser extracts by atomic absorption spectrometry.
2. FIELD
OF APPLICATION
This procedure is applicable to analysing samples of fertiliser extracts
obtained by Methods 26a and 26b for which a declaration of total and/or water
— soluble iron or zinc is required. Adaptations of this procedure for the various
trace elements are detailed in the methods defined specifically for each
element.
Note: In
most cases the presence of small quantities of organic matter will not affect
determinations by means of atomic absorption spectrometry.
3. PRINCIPLE
After the extract has been treated where necessary to reduce or eliminate
interfering chemical species, the extract is diluted so that its
concentration is in the optimum range of the spectrometer at a wavelength
suitable for the trace element to be determined.
4. REAGENTS
4.1. Diluted
hydrochloric acid solution (HCl), about 6 M
Mix one volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of
water.
4.2. Diluted
hydrochloric acid solution (HCl), about 0.5 M
Mix one volume of hydrochloric acid (ρ= 1.18 g/ml) with 20 volumes of
water.
4.3. Lanthanum
salt solutions (10 g of La per litre)
This reagent is used for determinations of iron and zinc. Lanthanum is added
to the extract to eliminate chemical interferences in the air-acetylene
flame. It can be prepared either:
(a) with
lanthanum oxide dissolved in hydrochloric acid (4.1). Place 11.73g of
lanthanum oxide (La2O3) in 150 ml of water in a 1 litre
volumetric flask and add 120 ml of 6 M hydrochloric acid (4.1). Allow to
dissolve and then make up to 1 litre with water and mix thoroughly. This
solution is approximately 0.5 M in hydrochloric acid; or
(b) with
solutions of lanthanum chloride, sulfate or nitrate.
Place
26.7 g of lanthanum chloride heptahydrate (LaCl3.7H2O)
or 31.2 g of lanthanum nitrate hexahydrate (La(NO3)3.6H2O)
or 26.2 g of lanthanum sulfate nonahydrate (La2(SO4)3.9H2O)
in 150 ml of water in a 1 litre volumetric flask, then add 85 ml of 6 M
hydrochloric acid (4.1). Allow to dissolve and then make up to 1 litre with
water. Mix thoroughly. This solution is approximately 0.5 M in hydrochloric
acid.
4.4. Calibration
solutions
For the preparation of these, see the individual methods of determination for
each trace element.
5. APPARATUS
Atomic absorption spectrometer fitted with sources emitting radiation
characteristic of trace elements to be determined.
The analyst must follow the manufacturer's instructions and be familiar with
the apparatus. The apparatus must allow background correction so that it can
be used whenever necessary (e.g. Zn). The gases to be used are air and
acetylene.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Preparation
of extract solutions containing the elements to be determined.
See Method 26a and/or 26b and, if appropriate, 26c.
6.2. Treatment
of the test solution
Dilute an aliquot portion of the extract obtained by Method 26a, 26b or 26c
with water and/or hydrochloric acid (4.1) or (4.2) so as to obtain, in the
final solution for measurement, a concentration of the element to be determined
that is appropriate to the calibration range used (7.2) and a hydrochloric
acid concentration of at least 0.5 M and not more than 2.5 M. This operation
may require one or more successive dilutions.
The final solution has to be obtained by placing an aliquot portion of the
diluted extract in a 100 ml volumetric flask. Let the volume of this aliquot
portion be (a) ml. Add 10 ml of the lanthanum salt solution (4.3). Make up to
volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. Let D
be the dilution factor.
7. PROCEDURE
7.1. Preparation
of a blank solution.
Prepare a blank solution by repeating the whole procedure from the extraction
stage, omitting only the test sample of fertiliser.
7.2. Preparation
of calibration solutions
From the working calibration solution prepared using the method given for
each individual trace element, prepare in 100 ml volumetric flasks a series
of at least five calibration solutions of increasing concentration within the
optimum measuring range of the spectrophotometer. If necessary, adjust the
concentration of hydrochloric acid to bring it as close as possible to that
of the diluted test solution (6.2). Add 10 ml of the same lanthanum salt
solution (4.3) as used in (6.2). Make up to volume with the 0.5 hydrochloric
acid solution (4.2) and mix thoroughly.
7.3. Determination
Prepare the spectrometer (5) for the determination and adjust to the
wavelength given in the method for the individual trace element concerned.
Spray three times in succession the calibration solutions (7.2), the test
solution (6.2) and the blank solution (7.1), noting each result and flushing
the instrument with distilled water between individual sprayings.
Construct the calibration curve by plotting the average spectrometer reading
for each calibration solution (7.2) along the ordinate and the corresponding
concentration of the element, expressed in μg/ml, along the abscissa.
From this curve, determine the concentrations of the relevant trace element in
the test solution xs, (6.2) and in the blank solution xb
(7.1), expressing these concentrations in μg per ml.
8. EXPRESSION
OF RESULTS
The percentage of trace element (E) in the fertiliser is given by:
E(%) = [(xs- xb) × V × D] / (M
× 104)
|
|
If
method 26c has been used:
E(%) = [(xs- xb) × V × 2D] / (M
× 104)
|
|
where:
E is the amount of the trace element determined, expressed as a
percentage of the fertiliser;
xs is the concentration of the Fe or Zn in the test solution
(6.2), in μg/ml;
xb is the concentration of the Fe or Zn in the blank solution
(7.1) in μ/ml;
V is the volume of the extract obtained by Method 26a or 26b, in ml;
D is the factor corresponding to the dilution carried out in (6.2);
M the mass of the test sample taken in accordance with Method 26a or 26b,
in grams.
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|
Calculation
of dilution factor D:
If
(a1), (a2), (a3), . . . . . , (ai)
and (a) are the aliquot portions and (v1), (v2), (v3),
. . . . . , (vi) and (100) are the volumes in ml corresponding to
their respective dilutions, the dilution factor D will be equal to:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/ai) ×
(100/a)
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26e.
DETERMINATION
OF BORON IN FERTILISER EXTRACTS BY MEANS OF ACIDIMETRIC TITRATION
1. SCOPE
This method defines a procedure for determining the boron content of
fertiliser extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Method 26a or Method 26b and for which a declaration for the total and/or
water — soluble boron content is required.
3. PRINCIPLE
A mannitoboric complex is formed by the following reaction of the borate with
mannitol:
C6H8(OH)6+ H3BO3>
C6H15O8B + H2O
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|
The
complex is titrated with sodium hydroxide solution to a pH of 6.3.
4. REAGENTS
4.1. Methyl
red indicator solution
Dissolve 0.1 g of methyl red (C15H15N3O2)
in 50 ml of ethanol (95% in a 100 ml volumetric flask. Make up the volume to
100 ml with water. Mix thoroughly.
4.2. Diluted
hydrochloric acid solution, about 0.5 M
Mix
1 volume of hydrochloric acid HCl, (ρ= 1.18 g/ml) with 20 volumes of
water.
4.3. Sodium
hydroxide solution, about 0.5 M
Must
be free of carbon dioxide. Dissolve 20 g of sodium hydroxide (NaOH) in pellet
form in a 1 litre volumetric flask containing about 800 ml of boiled water.
When the solution has cooled, make up to 1000 ml with boiled water and mix
thoroughly.
4.4. Standard
sodium hydroxide solution, about 0.025 M
Must be free of carbon dioxide. Dilute the 0.5 M sodium hydroxide solution (4.3)
20 times with boiled water and mix thoroughly. The value of the solution
expressed as boron (B) is to be determined (see paragraph 9).
4.5. Boron
calibration solution (100 μg/ml B)
Dissolve 0.5719 g of boric acid (H3BO3), weighed to the
nearest 0.1 mg, in water in a 1 litre volumetric flask. Make up to volume
with water and mix thoroughly. Transfer to a plastic bottle for storage in a
refrigerator.
4.6. D-mannitol
(C6H14O6) powder.
4.7. Sodium
chloride (NaCl).
5. APPARATUS
5.1. pH
meter with glass electrode
5.2. Magnetic
stirrer
5.3. 400
ml beaker with teflon rod
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Preparation
of the boron solution
See Methods 26a, 26b and, where appropriate, 26c.
7. PROCEDURE
7.1. Determination
Place in a 400 ml beaker (5.3) an aliquot portion (a) of the extract (6.1)
containing 2 to 4 mg B. Add 150 ml of water.
Add several drops of the methyl red indicator solution (4.1).
In the case of extraction with Method 26b, acidify by adding 0.5 M
hydrochloric acid (4.2) up to the point of change of the indicator solution,
then add a further 0.5 ml of 0.5 M hydrochloric acid (4.2).
After adding 3 g of sodium chloride (4.7), bring to boiling to drive off the
carbon dioxide. Allow to cool. Place the beaker on the magnetic stirrer (5.2)
and insert the precalibrated pH meter electrodes (5.1).
Adjust the pH to exactly 6.3, first with the 0.5 M sodium hydroxide solution
(4.3), then with the 0.025 M solution (4.4).
Add 20 g of D-mannitol (4.6), dissolve completely and mix thoroughly. Titrate
with the 0.025 M sodium hydroxide solution (4.4) to pH 6.3 (at least 1 minute
stability). Let x1, be the volume required.
8. BLANK
SOLUTION
Prepare a blank solution by repeating the whole procedure from the
preparation of solution stage, omitting only the fertiliser. Let x0
be the volume required.
9. BORON
(B) VALUE OF THE SODIUM HYDROXIDE SOLUTION (4.4)
Transfer by pipette 20 ml (2.0 mg B) of the calibration solution (4.5), into
a 400 ml beaker and add several drops of methyl red indicator solution (4.1).
Add 3g of sodium chloride (4.7) and the hydrochloric acid solution (4.2) up
to the point of change of the indicator solution (4.1).
Make up the volume to about 150 ml and bring gradually to the boil so as to
eliminate carbon dioxide. Allow to cool. Place the beaker on the magnetic
stirrer (5.2), and insert the precalibrated pH meter electrodes (5.1). Adjust
the pH to exactly 6.3, first with the 0.5 M sodium hydroxide solution (4.3),
then with the 0.025 M solution (4.4).
Add 20 g of D - mannitol (4.6), dissolve completely and mix thoroughly.
Titrate with the 0.025 M sodium hydroxide solution (4.4) to pH 6.3 (at least
1 minute stability). Let V1 be the volume required.
Prepare a blank solution in the same way, substituting 20 ml of water for the
calibration solution. Let V0 be the volume required.
The boron value (F) in mg/ml of the standard NaOH solution (4.4) is as
follows:
F (in mg/ml) = 2/(V1- V0)
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|
1
ml of exactly 0.025 M sodium hydroxide solution corresponds to 0.27025 mg B.
10. EXPRESSION
OF RESULTS
The percentage of boron in fertiliser is given by:
B (%) =
|
(x1- x0) × F ×
V
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10 × a × M
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where:
B(%) is the percentage of boron in the fertiliser;
x1 is the volume, in ml, of the 0.025 M sodium hydroxide
solution (4.4);
x0 is the volume, in ml, of the 0.025 M sodium hydroxide
solution M (4.4);
F is the boron (B) value, in mg/ml, of the 0.025 M sodium hydroxide
solution (4.4);
V is the volume, in ml, of the extract solution obtained in accordance
with Method 26a or 26b;
a is the volume, in ml, of the aliquot portion (7.1) taken from the
extract solution (6.1);
M is the mass, in grams, of the test sample taken in accordance with
Method 26a or 26b.
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26f.
DETERMINATION
OF COBALT IN FERTILISER EXTRACTS BY THE GRAVIMETRIC METHOD WITH
1-NITROSO-2-NAPHTHOL
1. SCOPE
This method defines a procedure for determining cobalt in fertiliser extracts
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Method 26a or Method 26b for which a declaration of cobalt content is
required.
3. PRINCIPLE
CobaltIII combines with 1-nitroso-2-naphthol to give a red
precipitate Co (Cl0H6ONO)3.2H2O.
After the cobalt present in the extract has been brought to the cobalt 111
state, the cobalt is precipitated in an acetic acid medium by a solution of
1-nitroso-2-naphthol. After filtration, the precipitate is washed and dried
to constant weight and then weighed as Co (C10H6ONO)3.2H2O.
4. REAGENTS
4.1. Hydrogen
peroxide solution (H2O2ρ= 1.11 g/ml) 30%
4.2. Sodium
hydroxide solution, about 2 M
Dissolve 8 g of sodium hydroxide in pellet form in 100 ml of water.
4.3. Diluted
hydrochloric acid solution, about 6 M
Mix one volume of hydrochloric acid (ρ= 1.18 g/ml) with 1 volume of
water.
4.4. Acetic
acid (99.7% CH3COOH) (ρ= l.05 g/ml).
4.5. Acetic
acid solution (1:2), about 6 M
Mix one volume of acetic acid (4.4) with 2 volumes of water.
4.6. Solution
of l-nitroso-2-naphthol in 100 ml of acetic acid (4.4). Add 100 ml of
lukewarm water. Mix thoroughly. Filter at once. The solution obtained must be
used immediately.
5. APPARATUS
5.1. Filter
crucible P 16/ISO 4793, porosity 4, capacity 30 or 50 ml
5.2. Drying
oven at 130 2° C
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Preparation
of the cobalt solution
See Methods 26a or 26b.
6.2. Preparation
of the solution to be analysed
Place the aliquot portion of the extract containing not more than 20 mg Co in
a 400 ml beaker. If the extract is obtained according to Method 26b, acidify
with five drops of hydrochloric acid (4.3). Add about 10 ml of the hydrogen
peroxide solution (4.1). Allow the oxidant to react in the cold state for 15
minutes, then make up to about 100 ml with water. Cover the beaker with a
watchglass. Bring the solution to boiling point and allow to boil for about
10 minutes. Cool. Make alkaline with the sodium hydroxide solution (4.21)
drop by drop until black cobalt hydroxide begins to precipitate.
7. PROCEDURE
Add 10 ml of acetic acid (4.4) and make up the solution with water to about
200 ml. Heat until boiling. Using a burette, add 20 ml of the
1-nitroso-2-naphthol solution (4.6) drop by drop, stirring constantly.
Complete by vigorous stirring to make the precipitate coagulate.
Filter through a previously weighed filter crucible (5.1), taking care not to
clog up the crucible. With this in mind, ensure that liquid is left above the
precipitate throughout the filtration process.
Wash the beaker with dilute acetic acid (4.5) to remove all the precipitate,
wash the precipitate on the filter with dilute acetic acid (4.5) and then
three times with hot water.
Dry in a oven (5.2) at 130±2° C until constant weight is achieved.
8. EXPRESSION
OF RESULTS
1 mg of Co (C10H6ONO)3.2H2O
precipitate corresponds to 0.096381 mg Co.
The percentage of Cobalt (Co) in the fertiliser is given by:
|
where:
X is the mass in mg of the precipitate;
V is the volume in ml of the extract solution obtained in accordance with
Method 26a or Method 26b;
a is the volume in ml of the aliquot taken from the last dilution;
D is the dilution factor of this aliquot;
M is the mass in g of the test sample.
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26g.
DETERMINATION
OF COPPER IN FERTILISER EXTRACTS BY THE TITRIMETRIC METHOD
1. SCOPE
This method defines a procedure for determining copper in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Method 26a or Method 26b for which a declaration of copper content is
required.
3. PRINCIPLE
The cupric ions are reduced in an acidic medium with potassium iodide:
The
iodine released in this way is titrated with a standard sodium thiosulfate
solution in the presence of starch as an indicator in accordance with:
I2+ 2 Na2S2O3>
2 NaI + Na2S4O6
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4. REAGENTS
4.1. Nitric
acid (HNO3, ρ= 1.40 g/ml).
4.2. Urea
[(NH2)2 C O].
4.3. Ammonium
bifluoride (NH4HF2) solution (10 % w/v)
Keep the solution in a plastic container.
4.4. Ammonium
hydroxide solution (1 + 1)
Mix 1 volume of ammonia (NH4OH, p =: 0.9 g/ml) with 1 volume of
water.
4.5. Sodium
thiosulfate standard solution
Dissolve 7.812 g of sodium thiosulfate pentahydrate (Na2S2O3.5H2O)
with water in a litre volumetric flask. This solution must be prepared so
that 1 ml = 2 mg Cu. For stabilization, add several drops of chloroform. The
solution must be kept in a glass container and protected from direct light.
4.6. Potassium
iodide (KI).
4.7. Potassium
thiocyanate (KSCN) solution (25 % w/v)
Keep this solution in a plastic flask.
4.8. Starch
solution (about 0.5 %)
Place 2.5 g of starch in a 600 ml beaker. Add about 500 ml of water. Boil
while stirring. Cool to ambient temperature. The solution has a short
preservation period. Its preservation can be extended by adding about 10 mg
of mercury iodide.
5. PREPARATION
OF THE SOLUTION TO BE ANALYSED
Preparation of the copper solution
See Methods 26a and 26b.
6. PROCEDURE
6.1. Preparation
of the solution for titration
Place an aliquot portion of the solution containing not less than 20 mg Cu in
a 500 ml Erlenmeyer flask.
Drive off any excess oxygen present by boiling briefly. Make up to volume of
about 100 ml water. Add 5 ml of nitric acid (4.1), bring to boiling and allow
to boil for about half a minute.
Remove the Erlenmeyer flask from the heating apparatus, add about 3 g of urea
(4.2) and resume boiling for about half a minute.
Remove from the heating apparatus and add 200 ml of cold water. Where
necessary, cool the contents of the Erlenmeyer flask to ambient temperature.
Gradually add ammonium hydroxide solution (4.4) until the solution becomes
blue, then add 1 ml in excess.
Add 50 ml of ammonium bifluoride solution (4.3) and mix.
Add 10 g of potassium iodide (4.6) and allow it to dissolve.
6.2. Titration
of the solution
Place the Erlenmeyer flask on a magnetic stirrer. Insert the rod into the
Erlenmeyer flask and adjust the stirrer to the desired speed.
Using a burette, add standard sodium thiosulfate solution (4.5) until the
brown colour of the iodine released from the solution becomes less intense.
Add 10 ml of the starch solution (4.8).
Continue to titrate with the sodium thiosulfate solution (4.5) until the
purple colour has almost disappeared.
Add 20 ml of the potassium thiocyanate solution (4.7) and continue titration
until the violet blue colour has completely disappeared.
Note the volume of thiosulfate solution employed.
7. EXPRESSION
OF RESULTS
1 ml of standard sodium thiosulfate solution (4.5) corresponds to 2 mg Cu.
The percentage of copper in the fertiliser is given by:
|
where:
X is the volume in ml of the sodium thiosulfate solution used;
V is the volume in ml of the extract solution in accordance with Methods
26a and 26b;
a is the volume in ml of the aliquot portion;
M is the mass in g of the test sample treated in accordance with Methods
26a and 26b.
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26h.
DETERMINATION
OF IRON IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining iron in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Methods 26a and 26b for which a declaration of total and/or water -
soluble iron is required.
3. PRINCIPLE
After suitable treatment and dilution of the extract, the iron content is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1. Hydrochloric
acid solution, about 6 M
See Method 26d, (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M
See Method 26d, (4.2).
4.3. Hydrogen
peroxide solution (30% H2O2 p = 1.11 g/ml) free from
trace elements.
4.4. Lanthanum
salt solutions (10 g of La per litre)
See Method 26d, (4.3).
4.5. Iron
calibration solution
4.5.1. Iron stock solution (1,000
μg/ml)
In
a 500 ml beaker, weigh to the nearest 0.1 mg, 1 g of pure iron wire, add 200
ml of 6 M hydrochloric acid (4.1) and 15 ml of hydrogen peroxide solution
(4.3). Heat on a hotplate until the iron is completely dissolved. When cool,
transfer quantitatively to a 1 litre volumetric flask. Make up to volume with
water and mix thoroughly.
4.5.2. Iron working solution (100
μg/ml)
Place
20 ml of the stock solution (4.5.1) in a 200 ml volumetric flask. Make up to
volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.
5. APPARATUS
Atomic absorption spectrometer: see Method 26d, (5). The instrument must be
fitted with a source of rays characteristic of iron (248.3 nm).
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Iron
extract solution
See Methods 26a and/or 26b and, if appropriate, 26c.
6.2. Preparation
of the test solution
See Method 26d, (6.2). The test solution must contain 10% (v/v) of a
lanthanum salt solution.
7. PROCEDURE
7.1. Preparation
of the blank solution
See Method 26d (7.1). The blank solution must contain 10 % (v/v) of the
lanthanum salt solution used in 6.2.
7.2. Preparation
of calibration solutions
See Method 26d, (7.2).
For an optimum determination range of 0 to 10 μg/ml of iron, place 0, 2,
4, 6, 8 and 10 ml respectively of working solution (4.5.2) in a series of 100
ml volumetric flasks. If necessary adjust the hydrochloric acid concentration
as closely as possible to that of the test solution. Add 10 ml of the
lanthanum salt solution used in 6.2. Make up to volume with 0.5 M
hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain
0, 2, 4, 6, 8 and 10 μg/ml respectively of iron.
7.3. Determination
See Method 26d, (7.3). Prepare the spectrometer (5) for measurement at a
wavelength of 248.3 nm.
8. EXPRESSION
OF RESULTS
See Method 26d, (8).
The percentage of iron in the fertiliser is given by:
Fe (%) = [(Xs- Xb) × V × D] /
(M × 104)
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If
Method 26c is used:
Fe (%) = [(Xs- Xb) × V × 2D] /
(M × 104)
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|
where:
Fe is the quantity of iron expressed as a percentage of the fertiliser;
Xs is the concentration in μg/ml of the test solution
(6.2);
Xb is the concentration in μg/ml of the blank solution
(7.1);
V is the volume in ml of extract obtained in accordance with Method 26a
or 26b;
D is the factor of the dilution carried out in 6.2;
M is the mass in grams of the test sample taken in accordance with Method
26a or 26b.
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Calculation
of the dilution factor D: if (a1), (a2), a3),
. . ., (ai) and (a) are aliquot portions and (v1), (v2),
(v3), . . ., (vi) and (100) are the volumes in ml
corresponding to their respective dilutions, the dilution factor D is given
by:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/ai) ×
(100/a)
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26i.
DETERMINATION
OF MANGANESE IN FERTILISER EXTRACTS BY TITRATION
1. SCOPE
This method describes a procedure for determining manganese in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Methods 26a and 26b for which a declaration of manganese is required.
3. PRINCIPLE
If chloride ions are present in the extract, they are driven off by boiling
with sulfuric acid. The manganese is oxidized by sodium bismuthate in a
nitric acid medium. The permanganate formed is reduced by an excess of
ferrous sulfate. This excess is titrated with a potassium permanganate
solution.
4. REAGENTS
4.1. Concentrated
sulfuric acid (H2SO4, ρ= 1.84 g/ml).
4.2. Sulfuric
acid, about 9 M
Carefully
mix 1 volume of concentrated sulfuric acid (4.1) with 1 volume of water.
4.3. Nitric
acid, 6 M
Mix
3 volumes of nitric acid (HNO3, ρ= 1.40 g/ml) with 4 volumes
of water.
4.4. Nitric
acid, 0.3 M
Mix
1 volume of 6 M nitric acid with 19 volumes of water.
4.5. Sodium
bismuthate (NaBiO3) (85 %).
4.6. Kieselguhr.
4.7. Orthophosphoric
acid, 15 M (H3PO4, ρ= 1.71 g/ml).
4.8. Ferrous
sulfate solution, 0.15 M
Dissolve 41.6 g of ferrous sulfate heptahydrate (FeSO4. 7 H2O)
in a 1-litre volumetric flask.
Add 25 ml of concentrated sulfuric acid (4.1) and 25 ml phosphoric acid
(4.7). Make up to 1000 ml. Mix.
4.9. Potassium
permanganate solution, 0.02 M
Weigh out 3.160 g of potassium permanganate (KMnO4) to within 0.1
mg. Dissolve and make up 1000 ml with water.
4.10. Silver nitrate solution, 0.1 M
Dissolve 1.7 g of silver nitrate (AgNO3) in water and make up to
100 ml.
5. APPARATUS
5.1. Filter
crucible P16/ISO 4793, porosity 4, capacity 50 ml, mounted on a
500 ml filtration flask.
5.2. Magnetic
stirrer.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Manganese
extract solution
See Methods 26a and 26b. If it is not known whether chloride ions are
present, perform a test on the solution with one drop of the silver nitrate
solution (4.10).
6.2. In
the absence of chloride ions, place an aliquot portion of the extract
containing 10 to 20 mg of manganese in a tall form 400 ml beaker. Bring to a
volume of about 25 ml either by evaporation or by adding water. Add 2 ml of
concentrated sulfuric acid (4.1).
6.3. If
chloride ions are present, it is necessary to remove them as follows:
Place an aliquot portion of the extract containing 10 to 20 mg of manganese
in a tall form 400 ml beaker. Add 5 ml of 9 M sulfuric acid (4.2). Under a
fume hood, bring to boiling on a hotplate and allow to boil until copious
white fumes are released. Continue until the volume is reduced to about 2 ml
(thin film of syrupy liquid at the bottom of the beaker). Allow to cool to
ambient temperature.
Carefully add 25 ml of water and once again test for the presence of
chlorides with one drop of the silver nitrate solution (4.10). If chlorides
still remain, repeat the operation after adding 5 ml of 9 M sulfuric acid
(4.2).
7. PROCEDURE
Add 25 ml of 6 M nitric acid (4.3) and 2.5 g of sodium bismuthate (4.5) to the
400 ml beaker containing the test solution. Stir vigorously for three minutes
on the magnetic stirrer (5.2).
Add 50 ml of 0.3 M nitric acid (4.4) and stir again. Filter in vacuo through
a crucible (5.1), the bottom of which is covered with Keiselguhr (4.6). Wash
the crucible several times with the 0.3 M nitric acid (4.4) until a
colourless filtrate is obtained.
Transfer the filtrate and the washing solution into a 500 ml beaker. Mix and
add 25 ml of 0.15 M ferrous sulfate solution (4.8). If the filtrate turns
yellow after the addition of ferrous sulfate, add 3 ml of 15 M
orthophosphoric acid (4.7).
Using a burette, titrate the excess ferrous sulfate with 0.02 M potassium
permanganate solution (4.9) until the mixture turns pink, the colour
remaining stable for one minute. Perform a blank test under the same
conditions, omitting only the test sample.
Note: The
oxidized solution must not come into contact with rubber.
8. EXPRESSION
OF RESULTS
1 ml of 0.02 M potassium permanganate solution corresponds to 1.099 mg of
manganese (Mn). The percentage of manganese in the fertiliser is given by:
Mn (%) = (xb- xs) × 0.1099 x
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|
|
where:
xb is the volume in ml of the permanganate used for the blank;
xs is the volume in ml of the permanganate used for the test
sample;
V is the volume in ml of the extract solution in accordance with Methods
26a and 26b;
a is the volume in ml of the aliquot portion taken from the extract (6.2)
or (6.3);
M is the mass in g of the test sample.
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|
26j.
DETERMINATION
OF MOLYBDENUM IN FERTILISER EXTRACTS BY THE GRAVIMETRIC METHOD WITH
8-HYDROXYQUINOLINE
1. SCOPE
This method describes a procedure for determining molybdenum in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Methods 26a and 26b for which a declaration of molybdenum is required.
3. PRINCIPLE
The molybdenum level is determined by precipitation as molybdenyl oxinate
under specific conditions.
4. REAGENTS
4.1. Sulfuric
acid solution, approximately 1 M
Carefully pour 55 ml of sulfuric acid (H2SO4, ρ
=1.84 g/ml) into a 1-litre volumetric flask containing 800 ml of water. Mix.
After cooling, make up to one litre. Mix again.
4.2. Diluted
ammonia solution (1:3)
Mix
1 volume of concentrated ammonia solution (NH4OH, ρ= 0.9
g/ml) with 3 volumes of water.
4.3. Diluted
acetic acid solution (1:3)
Mix 1 volume of concentrated acetic acid (99.7% CH3COOH, ρ=
1.049 g/ml) with 3 volumes of water.
4.4. Solution
of disodium salt of ethylene diamine tetraacetic acid (EDTA)
Dissolve
5 g of Na2EDTA in water in a 100 ml volumetric flask. Make up to
the calibration mark and mix.
4.5. Buffer
solution
In a 100 ml volumetric flask, dissolve 15 ml of concentrated acetic acid and
30 g of ammonium acetate in water. Make up to 100 ml.
4.6. 8-hydroxyquinoline
(oxine) solution
In a 100 ml volumetric flask dissolve 3 g of 8-hydroxyquinoline in 5 ml of
concentrated acetic acid. Add 80 ml of water. Add the ammonia solution (4.2)
drop by drop until the solution becomes cloudy and then add the acetic acid
(4.3) until the solution becomes clear again.
Make up to 100 ml with water.
5. APPARATUS
5.1. Filter
crucible P16/ISO 4793, porosity 4, capacity 30 ml.
5.2. pH
meter with glass electrode.
5.3. Drying
oven at 130 to 135°C.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Preparation
of the molybdenum solution. See Methods 26a and 26b.
7. PROCEDURE
7.1. Preparation
of the test solution
Place an aliquot portion containing 25 to 100 mg Mo in a 250 ml beaker. Make
up the volume to 50 ml with water.
Adjust this solution to pH 5 by adding the sulfuric acid solution (4.1) drop
by drop. Add 15 ml of EDTA solution (4.4) and then 5 ml of buffer solution
(4.5). Make up to about 80 ml with water.
7.2. Obtaining
and washing the precipitate
Obtaining the precipitate
Heat the solution slightly. Stirring constantly, add the oxine solution
(4.6). Continue the precipitation until formation of a deposit is no longer
observed. Add further reagent until the supernatant solution turns slightly
yellow. A quantity of 20 ml should normally be sufficient. Continue to heat
the precipitate slightly for two to three minutes.
Filtration and washing
Filter through a filter crucible (5.1). Rinse several times with 20 ml of hot
water. The rinse water should gradually become colourless indicating that
oxine is no longer present.
7.3. Weighing
the precipitate
Dry the precipitate at 130 to 135°C to constant weight (at least one hour).
Allow to cool in a desiccator and then weigh.
8. EXPRESSION
OF RESULTS
1 mg of molybdenyl oxinate, MoO2(C9H6ON)2,
corresponds to 0.02305 mg Mo.
The
percentage of molybdenum in the fertiliser is given by:
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where:
X is the mass in mg of the molybdenyl oxinate precipitate;
V is the volume in ml of the extract solution in accordance with Methods
26a or 26b;
a is the volume in ml of the aliquot portion taken from the last
dilution;
D is the dilution factor of the aliquot portion;
M is the mass in g of the test sample.
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26k.
DETERMINATION
OF ZINC IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY
1. SCOPE
This method describes a procedure for determining zinc in fertiliser
extracts.
2. FIELD
OF APPLICATION
This procedure is applicable to extracts from samples of fertilisers obtained
by Methods 26a and 26b for which a declaration of zinc is required.
3. PRINCIPLE
After suitable treatment and dilution of the extracts, the zinc level is
determined by atomic absorption spectrometry.
4. REAGENTS
4.1. Hydrochloric
acid solution, about 6 M
See Method 26d (4.1).
4.2. Hydrochloric
acid solution, about 0.5 M
See Method 26d (4.2).
4.3. Lanthanum
salt solutions (10 g of La per litre)
See Method 26d (4.3).
4.4. Zinc
calibration solutions
4.4.1. Zinc stock solution (1000
μg/ml)
In
a 1 litre volumetric flask dissolve 1 g of zinc powder or flakes weighed to
within 0.1 mg in 25 ml of 6 M hydrochloric acid (4.1). When completely
dissolved, make up to volume with water and mix thoroughly.
4.4.2. Zinc working solution (100
μg/ml)
In
a 200 ml volumetric flask, dilute 20 ml of the stock solution (4.4.1) in 0.5
M hydrochloric acid solution (4.2). Make up to volume with the 0.5 M
hydrochloric acid solution and mix thoroughly.
5. APPARATUS
Atomic absorption spectrometer
See Method 26d (5). The apparatus must be fitted with a source of rays
characteristic of zinc (213.8 nm). The spectrometer must allow background
correction to be made.
6. PREPARATION
OF THE SOLUTION TO BE ANALYSED
6.1. Zinc
extract solution
See Methods 25a and/or 26b.
6.2. Preparation
of the test solution
See Method 26d, (6.2). The test solution must contain 10% by volume of
lanthanum salt solution (4.3).
7. PROCEDURE
7.1. Preparation
of the blank solution.
See Method 26d. (7.1). The blank solution must contain 10 % by volume of the
lanthanum salt solution used in 6. 2.
7.2. Preparation
of the calibration solutions
See Method 26d (7.2). For an optimum interval of 0 to 5 μg/ml of zinc,
place 0, 0.5, 1, 2, 3, 4 and 5 ml, respectively, of the working solution
(4.4.2) in a series of 100 ml volumetric flasks. Where necessary, adjust the
concentration of hydrochloric acid to bring it as close as possible to that
of the test solution. Add 10 ml of the lanthanum salt solution used in (6.2)
to each volumetric flask. Make up to 100 ml with the 0.5 M hydrochloric acid
solution (4.2) and mix thoroughly.
These solutions contain, respectively: 0, 0.5, 1, 2, 3, 4 and 5 μg/ml of
zinc.
7.3. Determination
See Method 26d (7.3). Prepare the spectrometer (5) for measurements at a
wavelength of 213.8 nm.
8. EXPRESSION
OF RESULTS
See Method 26d (8).
The percentage of zinc in the fertiliser is given by:
Zn (%) = [(xs- xb) × V × D] /
(M × 104)
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If
method 26c has been used:
Zn (%) = [(xs- xb) × V × 2D] /
(M × 104)
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where:
Zn is the quantity of zinc expressed as a percentage of the fertiliser;
xs is the concentration in μg/ml of the test solution;
xb is the concentration in μg/ml of the blank solution;
V is the volume in ml of the extract solution obtained in accordance with
Methods 26a or 26b;
D is the factor corresponding to the dilution performed in (6.2);
M is the mass in g of the test sample taken in accordance with Methods
26a or 26b.
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Calculation
of the dilution factor D: where (a1), (a2), (a3),
. . . , (ai) and (a) are successive aliquot portions and (v1),
(v2), (v3), . . . , (vi) and (100) are the
volumes in ml corresponding to their respective dilutions, the dilution
factor D will be:
D = (v1/a1) × (v2/a2)
× (v3/a3) × . . . × (vi/a) × (100/a).'
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PART II
1. General
When two or more methods are prescribed in this part of this Schedule to
determine a component of a fertiliser the choice of the method shall, except
where otherwise indicated, be left to the agricultural analyst concerned; the
method used must, however, be indicated in the certificate of analysis.
2. Reagents
Except where otherwise specified in the method of analysis, all reagents
shall be of analytical quality. Where trace elements are to be determined,
the purity of the reagents used shall be checked by means of a blank test.
3. Water
(a) Except
where otherwise specified, a reference in this Part of this Schedule to water
shall be a reference to demineralized or distilled water.
(b) For
the determination of any form of nitrogen, water shall be free of all
nitrogenous compounds and carbon dioxide.
(c) Except
where the method of analysis specifies a particular solvent or diluent, all
dissolution, dilution, rinsing and washing operations mentioned in the
methods of analysis shall be carried out using water.
4. Apparatus
(a) Only
special instruments and apparatus and specifically required apparatus and
equipment are mentioned in the methods of analysis.
(b) Apparatus
and equipment shall be clean.
(c) The
accuracy of graduated glassware shall be assured by reference to the
appropriate standards.
5. Methods
of Analysis
1. Preparation
of the sample for analysis
2. Determination
of moisture
3. Determination
of total nitrogen — chromium powder reduction method
4. Determination
of urea
5. Determination
of potassium — gravimetric method
6. Determination
of the neutralising value in liming materials
7. Determination
of fineness of products other than potassic basic slag
8. Determination
of fineness of potassic basic slag
9. Determination
of fineness of certain lime products by wet sieving.
1.
PREPARATION
OF THE SAMPLE FOR ANALYSIS
1. INTRODUCTION
The preparation of a sample for analysis from the final sample received at
the laboratory is a series of operations, usually sieving, grinding and
mixing, carried out in such a way that the smallest amount weighed, as
prescribed by the method of analysis chosen, is representative of the final
sample. The sample should be ground to the fineness required by the method of
analysis. (Over grinding must be avoided in cases where this will affect the
solubility in various reagents). With some materials, fine grinding may lead
to loss or gain of moisture and allowance for this must be made.
2. SCOPE
AND FIELD OF APPLICATION
This method is applicable to fertilisers in Groups 1(b), l(c), 2(b), 2(c),
2(d), 3(b), 3(c), 4(a), 4(b), 4(c) and 5(b) of Section A and Group 5 and 6 of
Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991.
This method is also applicable to fluid fertilisers.
The determination of the fineness of fertilisers is carried out on the sample
as received.
3. PRINCIPLE
3.1 Solid
fertilisers:
the whole final sample is ground to the required fineness. All the ground
sample is thoroughly mixed before each test portion is taken.
3.2 Fluid
fertilisers:
the final sample is thoroughly mixed before each test portion is taken.
4. APPARATUS
4.1 Sample
grinder capable of grinding the fertiliser to pass the specified sieve.
4.2 Mortar
and pestle of suitable material and size.
4.3 Sieves
having square apertures of 0.18 mm, 0.5 mm and 1.0 mm. Test sieves conforming
to British Standard 410: 1986 are suitable.
4.4 Sample
containers of non-corrodible materials, with air-tight closures.
5. PROCEDURE
WARNING
All operations connected with this procedure should be carried out as quickly
as possible to minimise absorption or loss of water. Care should be taken
during grinding that the temperature of the fertiliser does not rise above
45°C to avoid loss of volatile constituents. Grinding beyond the fineness
required must in all cases be avoided.
5.1 Grinding
and sieving
The procedure in 5.1.1 should be followed except when a grinding machine is
not available, in which case 5.1.2 is applicable.
5.1.1 Grind the final sample until all the
sample has passed through, or for the specified time, depending on the type
of grinder (4.1). To check that the grinding has been adequate, sieve a small
portion of the ground sample through a 0.5 mm sieve (4.3) and discard it. If
the whole of this portion does not pass the sieve, return the remainder of
the sample to the grinder and repeat the grinding until satisfactory grinding
is achieved.
5.1.2 Sieve the whole final sample through
the 0.5 mm sieve (4.3). Grind the residue on the sieve, using the pestle and
mortar (4.2), until all the material passes through the sieve. Carefully mix
the sample.
5.2 Place
the prepared sample in a clean container (4.4) and seal it until required for
analysis.
5.3 Before
taking each test portion for analysis, the whole sample must be well mixed.
Form the material into a flattened cone and using a spatula take the required
test portion at random in small increments.
5.4 If
the sample contains foreign matter which cannot be ground this shall be
removed, weighed and allowed for in the results of the analysis. This
material shall be retained and if possible its nature recorded.
6. SPECIAL
CASES
6.1 Samples
not to be ground
For those samples where the fineness of grinding is to be determined it shall
be carried out on an unground sample. The sample should be well mixed (soft
lumps may be disintegrated by lightly crushing) and divided into two parts,
which are as identical as possible. All other determinations shall be carried
out on the sample prepared in accordance with the directions in paragraph
5.1.
6.2 Products
which may be difficult to grind mechanically, including products with
abnormal moisture or products which become doughy through grinding
Some products such as superphosphate may become doughy if ground
mechanically. In these cases crush the sample in a mortar (4.2) so that all
the material passes through a 1.0 mm sieve (4.3). Place the material so
crushed in a clean container (4.4) and seal it until required for analysis.
6.3 Organic
materials
Some organic materials may be of such a nature that the procedures given
above cannot be used (for example fresh guano, leather, wool and animal
residues). In these cases the analyst should use the best practicable means
to obtain a representative sample.
6.4 Fertilisers
comprising several different materials
These fertilisers include materials with marked differences in texture or
mechanical properties (hardness, density, etc). They may be difficult to
grind entirely (for example mixtures of organic and inorganic materials) or
they may segregate during handling (for example "Kalimagnesia").
Special procedures are necessary in these cases:
6.4.1 for mixtures other than those in
6.4.2, follow the procedure in 5.1.1, replacing the 0.5 mm sieve by one with
apertures of 0.18 mm. A grinding machine, capable of grinding the whole of
the sample to the required fineness in one pass, is strongly recommended;
6.4.2 in the case of mixtures containing
one or more very hard components, or mixtures containing organic materials,
it may be difficult to grind and homogenise all the components. To avoid
overgrinding some of the softer components proceed as follows: —
grind
the sample as in 5.1.1 or 5.1.2 to pass a 0.5 mm sieve. Re-sieve the sample
through a 0.18 mm sieve and reduce the residue to a convenient size by
further grinding or other practical means. Thoroughly remix the sample and
place in a clean container (4.4).
7. FLUID
FERTILISERS
Mix thoroughly by shaking, ensuring that any insoluble matter, particularly
crystalline material, is thoroughly dispersed, immediately before drawing a
portion of the sample for analysis.
2.
DETERMINATION
OF MOISTURE
1. SCOPE
AND FIELD OF APPLICATION
This method is applicable to fertilisers where a correction for moisture is
necessary.
2. PRINCIPLE
The sample is dried to constant weight in an oven at 100°C. The loss in
weight corresponds to the moisture content of the sample.
3. APPARATUS
3.1 Suitable
containers with lids ensuring air-tight closure; the dimensions should allow
the sample to be spread at about 0.3 g per cm2.
3.2 Electrically
heated oven, suitably ventilated and capable of being maintained at 100°C.
4. PREPARATION
OF SAMPLE
See Method 1.
5. PROCEDURE
Weigh to the nearest 0.001 g, 5 g of the prepared sample and transfer to a
previously weighed container (3.1). Place the uncovered container and the lid
in the oven (3.2) for 2 to 3 hours. Replace the lid on the container, remove
from the oven and allow to cool in a desiccator and weigh. Reheat for another
hour, cool and reweigh. If the difference in weight exceeds 0.01 g continue
the heating and cooling procedure until a weight constant within 0.01 g is
attained.
6. EXPRESSION
OF RESULT
Calculate the total loss of weight and express it as a percentage of the
original weight.
3.
DETERMINATION
OF TOTAL NITROGEN CHROMIUM POWDER REDUCTION METHOD
1. SCOPE
AND FIELD OF APPLICATION
This method is applicable to fertilisers in Groups 1(b), 1(c), 3(b), 4(a) and
4(c) of Section A, Group 5 and 6 of Section B and Groups 1(c) and 1(d) of
Section C of the Table in Schedule 1 of the Fertilisers Regulations 1991 in
respect of which a declaration of total nitrogen is required.
2. PRINCIPLE
The nitrate is reduced to ammonia by chromium powder in an acid medium.
Organic and ureic nitrogen are converted into ammonium sulfate by digestion
with concentrated sulfuric acid using a catalyst. The ammonia is distilled
from an alkaline solution and absorbed in a standard acid. The excess acid is
titrated with standard alkali.
3. REAGENTS
3.1 Sodium
hydroxide solution: 40 g per 100 ml, ammonia free.
3.2 Sulfuric
acid, 0.05 M solution.
3.3 Sulfuric
acid, 0.1 M solution.
3.4 Sulfuric
acid, 0.25 M solution.
3.5 Sodium
hydroxide, 0.2 M solution, carbonate free.
3.6 Chromium
metal powder, 100 mesh, low nitrogen content.
3.7 Anti-bump
granules of pumice stone, washed in hydrochloric acid and ignited.
3.8 Anti-foaming
agent, paraffin wax.
3.9 Sulfuric
acid (ρ= 1.84 g/ml).
3.10 Hydrochloric
acid (ρ= 1.18 g/ml).
3.11 Catalyst
mixture: 1,000 g potassium sulfate and 50 g copper sulfate pentahydrate. The
ingredients must be ground and thoroughly mixed.
3.12 Indicator
solutions:
3.12.1 Mixed indicator:
mix
50 ml of 2 g/litre ethanolic solution of methyl red with 50 ml of 1 g/litre
ethanolic solution of methylene blue.
3.12.2 Methyl red indicator:
dissolve
0.1 g methyl red in 50 ml ethanol . This indicator may be used instead of the
preceding one.
3.13 pH
indicator paper, wide range.
4. APPARATUS
Apparatus for mineral acid digestion and distillation according to Kjeldahl's
method.
5. PREPARATION
OF SAMPLE
See Method 1.
6. PROCEDURE
6.1 Reduction
Weigh, to the nearest 0.001 g, between 0.5 and 2.0 g of the prepared sample,
containing not more than 0.06 g nitric nitrogen and 0.235 g total nitrogen
and transfer to a Kjeldahl flask. Add sufficient water to make the total
volume 35 ml. Allow the flask to stand for 10 minutes with occasional gentle
swirling to ensure solution of all nitrate salts.
Add 1.2 g chromium powder (3.6) and 7 ml hydrochloric acid (3.10), mix well
and allow the flask to stand for at least 5 minutes but not more than 10
minutes at ambient temperature. Heat the flask gently so that the contents
just begin to boil in about 7 minutes. Continue boiling gently for 10
minutes. Remove the flask from the heat and allow to cool.
6.2 Hydrolysis,
when the fertiliser is known not to contain organic matter
Place the flask (6.1) in a fume cupboard, add a small quantity of anti-bump
granules (3.7) and then carefully add 25 ml sulfuric acid (3.9). Mix the
contents of the flask and heat gently until boiling. Continue heating until
dense white fumes of sulfuric acid are evolved for at least 15 minutes. Allow
the mixture to cool and then carefully add 250 ml water. Allow to cool to
room temperature and continue as described in 6.4.
6.3 Digestion,
when the fertiliser is known to contain organic matter
Add a small quantity of anti-bump granules (3.7), 10 g of the catalyst
mixture (3.11) and then carefully add 25 ml sulfuric acid (3.9) (see Note).
Add 0.5 g paraffin wax (3.8) to reduce foaming and mix. Heat the flask
moderately at first, shaking from time to time until frothing ceases and the
liquid is practically colourless. Continue the digestion for at least a further
60 minutes. Allow the mixture to cool and then carefully add 250 ml water.
Allow to cool to room temperature, and continue as described in 6.4.
Note: If
organic matter other than urea exceeds 1.0 g add an additional 1.0 ml
sulfuric acid for each 0.1 g organic matter in excess of 1.0 g.
6.4 Distillation
Transfer an appropriate volume of 0.1 M, 0.2 M or 0.5 M sulfuric acid (3.2,
3.3, 3.4) to the collecting flask of the distillation apparatus, according to
the presumed level of nitrogen; add a few drops of indicator solution (3.12.1
or 3.12.2). Taking precautions against the loss of ammonia, carefully add to
the contents of the Kjeldahl flask (6.2 or 6.3) 100 ml sodium hydroxide
solution (3.1). Mix well and connect immediately to the distillation apparatus.
Heat the flask so that approximately 150 ml of the liquid are distilled in 30
minutes. At the end of this time, lower the collecting flask so that the tip
of the condenser is above the surface of the liquid. Test the subsequent
distillate by means of the indicator paper (3.13) to ensure that all the
ammonia is completely distilled. Remove the source of heat. Titrate the
excess acid with 0.2 M sodium hydroxide solution (3.5) to the end point of
the indicator.
6.5 Blank
test
Carry out a blank test (omitting only the sample) under the same conditions
and allow for this in the calculation of the final results.
7. EXPRESSION
OF RESULTS
Determine the quantity of sulfuric acid consumed.
1 ml 0.05 M sulfuric acid, = 0.0014 g nitrogen.
1 ml 0.1 M sulfuric acid, = 0.0028 g nitrogen.
1 ml 0.25 M sulfuric acid, = 0.0070 g nitrogen.
Express the result as the percentage of nitrogen (N) contained in the
fertiliser as received for analysis.
4.
DETERMINATION
OF UREA
1. SCOPE
AND FIELD OF APPLICATION
This method is applicable to fertilisers in Group 1(c) of Section A, Group 5
and 6 of Section B and Group 1(d) of Section C of the Table in Schedule 1 of
the Fertilisers Regulations 1991.
2. PRINCIPLE
The sample is suspended in acid solution with a clarifying agent and
filtered. The urea content of the filtrate is determined after the addition
of 4-dimethylaminobenzaldehyde (4-DMAB) by measuring the absorbance at 435
nm.
3. REAGENTS
3.1 Activated
charcoal.
3.2 Carrez
solution I:
dissolve 21.9 g zinc acetate dihydrate in water, add 3 ml glacial acetic acid
and dilute to 100 ml with water.
3.3 Carrez
solution II: 10.6 g potassium ferrocyanide per 100 ml.
3.4 Hydrochloric
acid solution, 0.02 M.
3.5 Sodium
acetate solution: 136 g sodium acetate trihydrate per litre.
3.6 4-dimethylaminobenzaldehyde
solution:
dissolve 1.6 g of 4-dimethylaminobenzaldehyde (4-DMAB) in 100 ml 96% ethanol
and add 10 ml of hydrochloric acid (ρ= 1.18 g/ml)
3.7 Urea
standard solution: 1.0 g per 100 ml (1 ml of this solution = 10 mg urea).
4. APPARATUS
4.1 Mechanical
shaker.
4.2 Spectrometer
with 10 mm cells.
5. PREPARATION
OF SAMPLE
See Method 1.
6. PROCEDURE
6.1 Preparation
of the solution for analysis
Weigh to the nearest 0.001 g, 2 g of the prepared sample, or a suitable
amount expected to contain between 50 and 500 mg of urea and transfer it to a
500 ml graduated flask. Add 150 ml 0.02 M hydrochloric acid solution (3.4),
shake for 30 minutes using a mechanical shaker (4.1) then add 10 ml sodium
acetate solution (3.5) and mix well. Add 2 g activated charcoal (3.1) to the
flask, shake well and allow to stand for a further 15 minutes. Add 5 ml
Carrez solution I (3.2), followed by 5 ml Carrez solution II (3.3), mixing
well between additions. Dilute to volume with water and mix well. Filter a
portion of the solution through a dry filter paper into a clean dry 250 ml
beaker.
6.2 Determination
Transfer 10 ml of the filtrate (6.1) to a 50 ml graduated flask, add 10 ml
4-DMAB solution (3.6), dilute to 50 ml with water, mix well and allow to
stand for 10 minutes. Measure the absorbance of the solution at 435 nm, in a
10 mm cell against a reference solution prepared by diluting 10 ml 4-DMAB
solution (3.6) to 50 ml with water.
6.3 Calibration
curve
Transfer amounts of standard urea solution (3.7) corresponding to 50, 100,
150 and 250 mg of urea into a series of 250 ml graduated flask; add 75 ml
0.02 M hydrochloric acid solution (3.4) and proceed as described above (6.1)
commencing at ". . . shake for 30 minutes . . .". Measure the
absorbance of the solutions and construct a calibration graph relating the
absorbances to the amounts of urea present.
7. EXPRESSION
OF RESULTS
Determine the amount of urea in the sample by reference to the calibration
graph. Express the result in terms of percentage ureic nitrogen of the
sample:
(mg urea × 0.4665 = mg ureic nitrogen).
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5.
DETERMINATION OF POTASSIUM — GRAVIMETRIC METHOD
1. SCOPE
AND FIELD OF APPLICATION
This method is applicable to fertilisers in Groups 3(b), 3(c), 3(d) and 4(c)
of Section A and Group 5 and 6 of Section B of the Table in Schedule 1 of the
Fertilisers Regulations 1991 in respect of which an indication of total
potassium is required.
2. PRINCIPLE
The sample is ashed and dissolved in dilute hydrochloric acid or, if it
contains no organic substances, it is dissolved directly in dilute
hydrochloric acid. After the removal of interfering substances the potassium
is precipitated in a slightly alkaline medium in the form of potassium
tetraphenylborate (KTPB).
3. REAGENTS
3. <1
Formaldehyde, 25 - 35% solution, filtered if necessary before use.
3.2 Potassium
chloride.
3.3 Sodium
hydroxide, 10 M solution. Care should be taken to ensure that the sodium
hydroxide is free from potassium.
3.4 Indicator
solution: dissolve 0.5 g phenolphthalein in 100 ml 90% ethanol.
3.5 EDTA
solution: 4 g of the dihydrated disodium salt of ethylenediaminetetraacetic
acid (EDTA) per 100 ml. Store this reagent in a plastic container.
3.6 STPB
solution: dissolve 32.5 g sodium tetraphenylborate in 480 ml of water, add 2
ml of sodium hydroxide solution (3.3) and 20 ml of a magnesium chloride
solution (100 g of MgCl2.6H2O per litre). Stir for
fifteen minutes and filter through a fine, ashless filter. Store this reagent
in a plastic container.
3.7 Liquid
for washing: dilute 20 ml of the STPB solution (3.6) to 1 litre with water.
3.8 Hydrochloric
acid (ρ =1.18 g/ml).
4. APPARATUS
4.1 Filter
crucibles with a porosity of 5 to 20 microns.
4.2 Oven
regulated to 120°C10°C.
5. PREPARATION
OF SAMPLE
See Method 1.
6. PROCEDURE
6.1 Preparation
of the solution for analysis
6.1.1 Fertilisers containing little or
no organic matter
Weigh to the nearest 0.001 g, 2.5 g of the
prepared sample and transfer to a 400 ml beaker. Add 50 ml water and 5 ml
hydrochloric acid (3.8) and evaporate to dryness on a steam bath. Add 5 ml
hydrochloric acid (3.8) and 50 ml water. Bring the contents to the boiling
point, breaking down any crystals or lumps with a glass rod. Dilute the
solution with water to about 100 ml and boil gently for a few minutes. Allow
to cool, transfer to a 250 ml graduated flask, dilute to the mark with water
and mix; filter through a dry paper.
6.1.2 Fertilisers containing organic
matter
Weigh to the nearest 0.01 g, 10 g of the
prepared sample into a suitable crucible and place in a cold muffle furnace.
Gradually raise the temperature to about 475°C (do not exceed 500°C).
Maintain at this temperature for at least 16 hours and then open the furnace
and allow the crucible to cool. Grind the residue to eliminate any lumps, add
50 ml water and 10 ml hydrochloric acid (3.8) and evaporate to dryness on a
steam bath. Proceed as in 6.1.1, commencing "Add 5 ml hydrochloric acid
(3.8) and 50 ml water.".
6.2 Determination
6.2.1 Transfer by pipette an aliquot
portion of the filtrate (6.1.1 or 6.1.2), containing 25-50 mg of potassium
(30 - 60 mg K2O) into a 250 ml beaker; make up to 50 ml with
water.
6.2.2 To remove interferences, add 10 ml
of the EDTA solution (3.5), several drops of the phenolphthalein solution
(3.4) and stir in sodium hydroxide solution (3.3), drop by drop, until the
solution turns red, then finally add a few more drops of sodium hydroxide to
ensure an excess (usually 1 ml of sodium hydroxide is sufficient to
neutralise the sample and ensure an excess).
6.2.3 To eliminate most of the ammonia
boil gently for 15 minutes. Add water to make the volume up to 60 ml. Bring
the solution to the boil, remove the beaker from the heat and add 10 ml
formaldehyde (3.1). Add several drops of phenolphthalein solution (3.4), and
if necessary, more sodium hydroxide solution until a distinct red colour
appears. Cover the beaker with a watch glass and place it on a steam bath for
fifteen minutes.
6.3 Weighing
the crucible
Dry the filter crucible (4.1) to constant weight in the oven at 120°C (4.2)
(about 15 minutes).
Allow the crucible to cool in a desiccator and weigh.
6.4 Precipitation
Remove the beaker from the steam bath and stir in drop by drop 10 ml of the
STPB solution (3.6). This addition should take about 2 minutes; allow to
stand for at least 10 minutes before filtering.
6.5 Filtering
and washing
Filter under vacuum into the weighed crucible; rinse the beaker with the
liquid for washing (3.7), wash the precipitate three times with the liquid
for washing (60 ml in all) and twice with 5 to 10 ml of water.
6.6 Drying
and weighing
Wipe the outside of the crucible with a filter paper and place in the oven
(4.2) for one and a half hours at a temperature of 120°C. Allow the crucible
to cool in a desiccator to ambient temperature and weigh rapidly.
6.7 Blank
test
Make a blank test under the same conditions (omitting only the sample) and
allow for this in the calculation of the final result.
6.8 Control
test
Carry out the determination on an aliquot portion of an aqueous solution of
potassium chloride, containing at the most 40 mg of K2O.
7. EXPRESSION
OF RESULTS
Calculate the percentage potassium content of the samples as K2O,
taking into account the weight of the test sample, the volume of the aliquot
portion taken for the determination and the value of the blank determination.
(Conversion factor, KTPB to K2O = 0.1314.)
6.
DETERMINATION OF THE NEUTRALISING VALUE IN LIMING
MATERIALS
1. SCOPE
AND FIELD OF APPLICATION
This method is applicable to products in Groups 5(a) and 5(b) of Section A of
the Table in Schedule 1 of the Fertilisers Regulations 1991.
2. PRINCIPLE
The sample is dissolved in a measured quantity of standard hydrochloric acid,
the excess of which is titrated with standard solution of sodium hydroxide.
3. REAGENTS
3.1 Hydrochloric
acid, 0.5 M solution.
3.2 Sodium
hydroxide, 0.5 M solution (carbonate free).
3.3 Phenolphthalein
indicator solution: dissolve 0.25 g phenolphthalein in 150 ml 95% ethanol and
dilute with water to 250 ml.
4. PREPARATION
OF SAMPLE
Rapidly grind 50 g of the representative lime sample to pass through a 1 mm
sieve.
5. PROCEDURE
5.1 Determination
Weigh to the nearest 0.001 g, 0.5 g of the prepared sample and transfer to a
300 ml conical flask. Add 50 ml of 0.5 M hydrochloric acid (3.1), cover the
flask with a watch glass and boil the contents gently for five minutes. Cool
the mixture to room temperature, add two or three drops of the phenolphthalein
indicator (3.3) and titrate with 0.5 M sodium hydroxide solution (3.2) to the
end point of the indicator.
6. EXPRESSION
OF RESULTS
Determine the amount of hydrochloric acid consumed by the sample. 1 ml 0.5 M
hydrochloric acid = 0.01402 g calcium oxide (CaO).
The neutralising value is expressed as a percentage by weight of calcium
oxide (CaO) and refers to the undried sample as received.
7.
DETERMINATION OF FINENESS OF PRODUCTS OTHER THAN
POTASSIC BASIC SLAG
1. SCOPE
AND FIELD OF APPLICATION
This method is applicable to "Rock phosphate" in Group 2(b) and to
products in Groups 4(c), 5(a) and 5(b) of Section A of the Table in Schedule
1 of the Fertilisers Regulations 1991.
2. PRINCIPLE
By hand sieve shaking, the proportion of material passing through the
prescribed sieve is determined.
3. APPARATUS
Sieves having square apertures of 45 mm, 6.7 mm, 6.3 mm, 5 mm, 3.35 mm, l.0
mm and 150 microns; lower receiver to fit sieve. Test sieves conforming to
British Standard 410: 1986 are suitable.
4. PROCEDURE
4.1 For
sieving through 3.5 mm, 1.0 mm and 150 micron sieves
Thoroughly mix the sample and quarter down until a portion of about 100 g is
obtained. Heat this portion at 100°C until dry and thoroughly mix. Weigh to
the nearest 0.01 g, 20 g and transfer to the sieve with the lower receiver
attached. Proceed as described in 4.4.
4.2 For
sieving through 6.7 mm, 6.3 mm and 5 mm sieves
Oven dry the sample of 100°C for 24 hours and thoroughly mix. Weigh to the
nearest 0.1 g, 200 g and transfer to the sieve with the lower receiver
attached. Proceed as described in 4.4.
4.3 For
sieving through a 45 mm sieve
If the sample appears moist or damp, oven dry at 100°C for 24 hours, but if
the sample appears dry, heating is not necessary. Thoroughly mix the sample
and weigh to the nearest 0.1 g, 500 g and transfer to the sieve with the
lower receiver attached. Proceed as in 4.4.
4.4 Sieving
Shake the sieve for 5 minutes, frequently tapping the side. Disintegrate soft
lumps such as can be caused to crumble by the application of the fibres of a
soft brush, taking care that the hard part of the brush does not make contact
with the sieve and that the brush is not used to brush particles through the
sieve. Brush out the powder in the lower receiver and weigh. Replace the
receiver and repeat the shaking and tapping procedure for 2 minutes. Add the
powder in the receiver to the first portion and weigh. Repeat the process
until not more than 0.04 g passes through the sieve during 2 minutes.
5. EXPRESSION
OF RESULTS
Calculate the fineness by expressing the weight of the material passing
through the sieve as a percentage of the weight of the portion of the dried
(or as the case may be, undried) sample taken for sieving.
8.
DETERMINATION OF FINENESS OF POTASSIC BASIC SLAG
1. SCOPE
AND FIELD OF APPLICATION
Exclusively to "Potassic basic slag" in Group 3(b) of Section A of
the Table in Schedule 1 of the Fertilisers Regulations 1991.
2. PRINCIPLE
By hand sieve shaking and dissolution of the soluble salts, the proportion of
slag passing through the prescribed sieve is determined.
3. APPARATUS
Sieve having square apertures of 0.5 mm (500 microns); lower receiver to fit
sieve. Test sieves conforming to British Standard 410: 1986 are suitable.
4. PROCEDURE
4.1 Preparation
of the sample
Thoroughly mix the sample and quarter down until a portion of about 100 g is
obtained. Heat this portion at 100°C until dry and thoroughly mix.
4.2 Sieving
Weigh to the nearest 0.1 g, 20 g of the dry sample and transfer to the sieve
with the lower receiver attached. Shake the sieve for five minutes,
frequently tapping the sides. Disintegrate soft lumps that can be caused to
crumble by the application of a soft brush, taking care that the hard part of
the brush does not make contact with the sieve and that the brush is not used
to brush particles through the sieve.
Transfer the finer portion from the
container into a 500 ml beaker and add 200 ml of previously boiled water.
Stir and then filter through a weighed glass sintered crucible. Thoroughly
wash the residue with water, dry and re-weigh the crucible. Calculate the
weight of slag in the mixture with a particle size of less than 0.5 mm (A).
Weigh to the nearest 0.01 g, about 20 g of
the dry sample and transfer to a 500 ml conical flask. Add 200 ml previously
boiled water and shake for 30 minutes. Filter through a weighed, sintered
glass crucible, wash the residue thoroughly with water, dry and re-weigh the
crucible. Calculate the total weight of slag in the mixture (B).
5. EXPRESSION
OF RESULTS
Express the fineness of the slag as
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x 100.
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9.
DETERMINATION OF FINENESS OF CERTAIN LIME PRODUCTS BY
WET SIEVING
1. SCOPE
This method is applicable to products in Group 5(b) of Section A of the Table
in Schedule 1 of the Fertilisers Regulations 1991 which are susceptible to
clogging, caking, electrostatic changes or agglomeration on pre-drying. The
method is not applicable to burnt and hydrated lime products.
2. PRINCIPLE
The liming material is suspended in water. The suspension is sieved under
continuous water spraying or using a mechanical wet-sieving machine. The
fractions retained on the sieves are collected and dried.
3. APPARATUS
Usual laboratory apparatus and in particular:
3.1 Balance,
capable of weighing to the nearest 0.01 g
3.2 Stainless
steel woven wire test sieves 100 mm diameter, complying with ISO 3310 - 1,
with nominal apertures of 5.00 mm, 3.35 mm and 150 microns
3.3 Stainless
steel woven wire test sieves complying with ISO 3310 - 1, with nominal
apertures of 10.00 mm
3.4 Oven
capable of being controlled at 105°C2
3.5 Rotating
end over end shaker: 35 - 40 turns per minute.
4. SAMPLING
4.1 Procedure
for samples with dry matter content <60%
Pass the laboratory sample through a sieve
with nominal apertures of 10.00 mm (3.3). If necessary, lightly crush any
lumps by means of a soft brush. Remove any lumps which cannot be crushed in
this way and record the weight of the residue and the weight of the lumps.
Take account of these lumps when recording the final results. Thoroughly mix
the sieved sample and quarter down until a representative sample portion of
about 50 g is obtained.
4.2 Procedure
for samples with dry matter content<60% which cannot be treated as per 4.1
due to the nature of the material.
Empty the whole of the sample onto a clean
dry surface and flatten to form a regular shape about 25 mm thick. Divide
into four approximately equal portions and reject two opposite quarters. Take
small portions from random places on all the exposed surfaces to give a
sample portion of about 50 g.
5. PROCEDURE
Weigh the sample portion (4.1 or 4.2) to the nearest 0.01 g and transfer to a
500 ml flask. Add approximately 300 ml of de-mineralized water, stopper and
shake vigorously by hand for 30 seconds. Remove the stopper for an instant to
relieve the pressure and replace the stopper. Place the flask in the rotating
end over end shaker (3.5) and shake for 60 minutes to ensure the complete
suspension of the sample.
Assemble the three sieves (3.2) in ascending order of aperture size on top of
the receiver.
Rinse the sample quantitatively onto the top sieve and wash under a flow of
water up to 2.5 litres/min until no more material passes each sieve, or up to
a maximum time period of 10 minutes.
Remove the sieves and rinse the residue on each sieve quantitatively into a
separate 250 ml beaker. Decant most of the water from the top of the material
and dry each of the oversize fractions in an oven set at 105 C and weigh each
fraction separately.
6. DRY
MATTER CONTENT
Determine the dry matter content of a portion of the original sample using
the method given in Method 2.
7. EXPRESSION
OF RESULTS
7.1 Original
dry mass
Calculate the original dry mass (Md) of material, using the following
formula:
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where:
M is the mass of the test portion taken for the sieving test
DM is the percentage dry matter obtained in 6.
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7.2 Sieve
fraction
Calculate the percentage of material
retained on each sieve, using the following formula:
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where:
Xn is the percentage by mass retained on sieve n
Mn is the dry mass retained on sieve n
Md is the dry mass of the test portion
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Report the percentages of material (100 -
Xn) which will pass through each sieve.
Carry out two single test on separate test
portions prepared from the same original sample. Record the mean of the two
individual results for each sieve as the result (corrected if necessary for
the presence of lumps (4.1)).
APPENDIX TO
SCHEDULE 2
PART 1,
METHOD 2
figure 1
FIGURE 1
KEY
TO FIGURE 1
(a) A round-bottom, long-necked
flask of l,000 ml capacity.
(b) Distillation tube with a
splash head, connected to the condenser by means of a spherical joint (the
spherical joint for the connection to the condenser may be replaced by an appropriate
rubber connection).
(c) Funnel with teflon tap for
the addition of sodium hydroxide (the tap may likewise be replaced by a
rubber connection with a clip).
(d) A six-bulb condenser with a
spherical joint, fitted with a glass extension tube. (The connection to the
distillation tube may be effected by means of a rubber bung instead of a
spherical joint.)
(e) A 500 ml flask in which the
distillate is collected.
The equipment is made of borosilicate
glass.
figure 2
FIGURE 2
KEY
TO FIGURE 2
(a) A round-bottomed,
short-necked flask of 1,000 ml capacity with a spherical joint.
(b) Distillation tube with a
splash head, fined with spherical joints, connected at the side to a funnel
with a teflon tap for the addition of sodium hydroxide.
(c) A six-bulb condenser with a
spherical joint, fined with a glass extension tube.
(d) A 500 ml flask in which the
distillate is collected.
The equipment is made of borosilicate
glass.
figure 3
FIGURE 3
KEY
TO FIGURE 3
(a) A round-bottomed,
long-necked flask of 750 or 1,000 ml capacity with a bell mouth.
(b) Distillation tube with a
splash head and a spherical joint.
(c) An elbow tube with a
spherical joint and a drip cone (the connection to the distillation tube may
be affected by means of a rubber tube instead of a spherical joint).
(d) A six-bulb condenser with a
glass extension tube.
(e) A 500 ml flask for the
collection of the distillate.
The equipment is made of borosilicate
glass.
figure 4
FIGURE 4
KEY
TO FIGURE 4
(a) A round-bottomed,
long-necked flask of 1,000 ml capacity with a bell mouth.
(b) Distillation tube with a
splash head and a spherical joint connected at the side to a funnel with a
teflon tap for the addition of sodium hydroxide (a suitable rubber bung may
be used instead of the spherical joint; the tap may be replaced by a rubber
connection with an appropriate clip).
(c) A six-bulb condenser with a
spherical joint, fitted with a glass extension tube. (The connection to the
distillation tube may be effected by means of a rubber bung instead of a
spherical joint.)
(d) A 500 ml flask for the
collection of the distillate.
The equipment is made of borosilicate
glass.
PART 1,
METHOD 3c
figure 5
FIGURE 5
KEY
TO FIGURE 5
(a) A round-bottomed,
long-necked flask of 750 or 1,000 ml capacity with a bell mouth.
(b) Distillation tube with a
splash head and a spherical joint.
(c) Elbow tube with a spherical
joint and drip cone. (A suitable connection may be used instead of the
spherical joint.)
(d) A six-bulb condenser with an
extension tube mounted on a rubber bung holding a bubble trap.
(e) 1 750 ml receiving flask.
(f) A bubble trap to prevent
loss of ammonia.
The equipment is made of borosilicate
glass.
PART 1,
METHOD 8a & b
figure 6
FIGURE 6
KEY
TO FIGURE 6
(a) Reaction vessel, 350 - 400
ml capacity.
(b) Tube for introduction of
air.
(c) Delivery tube with splash
head.
(d) Conical flask. 300 ml
capacity.
figure 7
FIGURE 7
KEY
TO FIGURE 7
(a) Separating funnel.
(b) Bubble trap.
(c) Conical flask. 300 ml
capacity.
PART 1,
METHOD 9d
figure 8
FIGURE 8
KEY
TO FIGURE 8
(a) Tray for flask.
(b) Tray support.
(c) Heater.
(d) Stirrer
(e) Controls for heater, stirrer
and electric motor.
(f) Electric motor.
PART 1,
METHOD 14c
figure 9
FIGURE 9
KEY
TO FIGURE 9
(a) Absorption tube with soda
lime.
(b) Reaction flask.
(c) Vigreux fractionating column
150 mm long.
(c) Double surface condenser 200
mm long.
(d) Dreschel bottle 250 ml.
(e) Ice bath.
(f1 and f2) Absorption
vesels 32 to 35 mm diameter assembled with spherical ground joints. Gas
distributor with 10 mm disc of low-porosity sintered glass.
(g) Suction-regulating device.
Notes:
[8] Biuret
can be purified beforehand by washing with 10% ammonia solution, then with
acetone and drying under vacuum at room temperature.
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[9] Where
the fertiliser is normal superphosphate or concentrated superphosphate in
Group 2(a) of Section A, or NPK fertiliser in Group 1, NP fertiliser in Group
2, or PK fertiliser in Group 4 of Section B or NPK fertiliser suspension, NP
fertiliser suspension or PK fertiliser suspension in Section C of the Table
in Schedule 1 of the Fertilisers Regulations 1991.
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[10] Where
the fertiliser is triple superphosphate in Group 2(a) of Section A, or NPK
fertiliser containing soft ground rock phosphate or partially solubilised
rock phosphate in Group 1, or NP fertiliser containing soft ground rock
phosphate or partially solubilised rock phosphate in Group 2, or PK
fertiliser containing soft ground rock phosphate or partially solubilised
rock phosphate in Group 4 of Section B of the Table in Schedule 1 of the
Fertilisers Regulations 1991.
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[11] If
no mechanical shaker is available, the flask may be shaken by hand every 5
minutes.
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[12] Phosphorus
soluble in mineral acids, water soluble phosphorus, phosphorus soluble in
solutions of ammonium citrate, phosphorus soluble in 2% citric acid and
phosphorus soluble in 2% formic acid.
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[13] 21
ml when the solution to be precipitated contains more than 15 ml of citrate
solution (neutral citrate, Petermann or Joulie alkaline citrate).
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[14] To
precipitate phosphate solutions containing more than 15 ml citrate solution
(neutral, Petermann or Joulie) which have been acidified with 21 ml
concentrated nitric acid (see footnote to paragraph 6.1) use 80 ml of the
precipitating reagent.
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[15] A
reaction time of 90 minutes is sufficient in the case of most of the organic
substances in the presence of silver nitrate catalyst.
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[16] Commercially
available standard copper solution may be used.
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[17] Whatman
541 or equivalent.
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