The Fertilisers (Sampling and Analysis) Regulations 1991

• (4.1) 500 ml graduated flask (for example Stohmann).

• (4.2) Rotary shaker, 35-40 turns per minute.

PREPARATION OF THE SAMPLE

5

See Method 1.

PROCEDURE

6

Extraction 6.1 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 to the flask 450 ml of water, the temperature of which must be between 20° and 25°C. Shake on the rotary shaker (4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly by shaking the filter through a dry fluted filter, into a dry container.

Determination 6.2 Determine the phosphorus according to Method 10, on an aliquot part of the clear filtrate.

10. — DETERMINATION OF EXTRACTED PHOSPHORUS (Gravimetric method using quinoline phosphomolybdate)

SCOPE

1

This method is for the determination of phosphorus in the extracts from fertilisers.

FIELD OF APPLICATION

2

The method is applicable to all extracts of fertilisers[^f01012], for the determination of the different forms of phosphorus.

PRINCIPLE

3

After hydrolysis, phosphorus is precipitated in an acid solution in the form of quinoline phosphomolybdate. The precipitate is collected, washed, dried at 250°C and weighed.

REAGENTS

4

• (4.1) Concentrated nitric acid (d = 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 add 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 35 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.

APPARATUS

5

• (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.

PROCEDURE

6

Treatment of the solution 6.1 With a pipette take an aliquot part of fertiliser extract (see the Table) containing about 0.01 g of P₂O₅ and put it in a 500 ml Erlenmeyer flask. Add 15 ml concentrated nitric acid[^f01013] (4.1) and dilute with water to about 100 ml.

Hydrolysis 6.2 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.

Weighing the crucible 6.3 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.

Precipitation 6.4 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)[^f01014] drop by drop, stirring continuously. Place the Erlenmeyer flask in a steam bath, leave it there for 15 minutes, shaking it from time to time. The solution can be filtered immediately or after it has cooled down.

Filtering and Washing 6.5 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.

Drying and weighing 6.6 Wipe the outside of the crucible with a filter paper. Place the crucible in the drying oven (5.5) and keep it there until its weight remains constant at a temperature of 250°C (usually 15 minutes); leave it to cool in a desiccator to ambient temperature and weigh rapidly.

Blank test 6.7 For each series of determination, make a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test 6.8 Carry out the determination using an aliquot part of a potassium dihydrogen phosphate solution containing 0.01 g of P₂O₅. TABLE FOR METHOD 10 %P205 in the fertiliser%P in the fertiliserSample for analysis gDilution to mlSampl mlDilution to mlSample to be precipitated mlQuinoline phosphomolybdate conversion factor (F) in percentage P₂0₅Quinoline phosphomolybdate conversion factor (F) in percentage P 1500——10016.0376.9921-50.44-2.22.5500——5012.8305.5945500——2512.8305.5941500——5032.07413.9845-102.2-4.42.5500——2525.66011.1883500——2521.3839.3235500——1032.07413.9841500——2564.14827.96810-254.4-11.02.5500——1064.14827.9683500——1053.45723.3075500——5064.14827.9681500——10160.37069.921+25+112.55005050050128.29655.93735005050050106.91346.61455005050025128.29655.937

EXPRESSION OF RESULTS

7

If the samples for analysis and diltutions shoen in the Table are used the following formulae apply:

• % P in the fertiliser = (A − a) × F’

• % P₂O₅ in the fertiliser = (A − a) × F

• where:

• A = weight in g of the quinoline phosphomolybdate

• a = weight 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: $%P2O5 in the fertiliser(A-a)×f×D×100M$

• $%P in the fertiliser(A-a)×f’×D×100M$ where: f = conversion factor, quinoline phosphomolybdate into P₂O₅ = 0.032074 f’ = conversion factor, quinoline phosphomolybdate into P = 0.013998 D = dilution factor M = weighing of the sample analysed.

11. — DETERMINATION OF WATER-SOLUBLE POTASSIUM

SCOPE

1

This method is for the determination of water-soluble potassium.

FIELD OF APPLICATION

2

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 1990[^f01015].

PRINCIPLE

3

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).

REAGENTS

4

• (4.1) Formaldehyde, 25-30% solution, filter if necessary before use.

• (4.2) Potassium chloride.

• (4.3) Sodium hydroxide, 10 N solution. Care should be taken to ensure that the sodium hydroxide is free from potassium.

• (4.4) Indicator solution: dissolve 0.5 g phenolphtalein 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. Store this reagent in a plastic container.

• (4.7) Liquid for washing: dilute 20 ml of the STPB solution (4.6) to 1 litre with water.

• (4.8) Bromine water: saturated bromine solution in water.

APPARATUS

5

• (5.1) Filter crucibles with a porosity of 5 to 20 microns.

• (5.2) Oven regulated at 120±10°C.

PREPARATION OF THE SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001g, 10 g of the prepared sample (5 g for potassium salts containing more than 50% of potassium oxide or 20 g for fetilisers 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 allow it to boil 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 part containing at the most 100 mg of K₂O and place in a 100 ml graduated flask, add bromine water and bring to the boil to eliminate any surplus bromine. After cooling make up the volume, filter and quantitatively determine the potassium in an aliquot part of the filtrate.

Determination 7.2 Transfer by pipette an aliquot part of the filtrate containing 25-50 mg of potassium (see Table on page 53) 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, sdoium hydroxide solution (4.3) until it 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). 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 (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.

Weighing the crucible 7.3 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 then weigh it.

Precipitation 7.4 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 at least 10 minutes before filtering.

Filtering and washing 7.5 Filter under vacuum into the weighed crucible, rinse the beaker with the liquid for washing (4.7), wash the precipitate three times with the liquid for washing (60 ml in all of the liquid for washing) and twice with 5 to 10 ml of water.

Drying and weighing 7.6 Wipe the outside of the crucible with a filter paper and place in the oven (5.2) for one and a half hours at temperature of 120°C. Allow the crucible to cool in a desiccator to ambient temperature and weigh rapidly.

Blank test 7.7 Make a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test 7.8 Carry out the determination of an aliquot part of an aqueous solution of potassium chloride, containing at the most 40 mg of K₂O.

EXPRESSION OF RESULTS

8

Method of calculation and formulae 8.1 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) × F’ where: A = weight in grams of the precipitate from the sample a = weight in grams of the precipitate from the blank F and F’ = factors—see Table. % of K₂O in the fertiliser% of K in the fertiliserSample for analysis (g)Aliquot part to be taken as a sample for precipitation (ml)Conversion factor F % K₂O g KTPBConversion factor F % K g KTPB 1 — 50.8 — 4.2205013.14010.9065 — 104.2 — 8.3105026.28021.81210 — 208.3 — 16.6102552.56043.62420 — 5016.6 — 41.51010131.400109.060more than 50more than 41.5510262.800218.120 With samples and dilutions which differ from those shown in the Table use the following formulae: $%K2O(A-a)×f×D×100M$ or $%K2O(A-a)×f’×D×100M$ where: f = conversion factor, KTPB into K₂O = 0.1314 f’ = conversion factor, KTPB into K = 0.109 D = dilution factor M = weight in grams of sample for analysis

12a. — DETERMINATION OF WATER-SOLUBLE MAGNESIUM—ATOMIC ABSORPTION SPECTROPHOTOMETRIC METHOD

SCOPE

1

This method is for the determination of water-soluble magnesium.

FIELD OF APPLICATION

2

Exclusively to fertilisers in Groups 1(a) and 3(a) of Section A of the Table in Schedule 1 of the Fertilisers Regulations 1990[^f01016], in respect of which the declaration of water-soluble magnesium is required.

PRINCIPLE

3

Solution of magnesium by boiling the test sample in water, and determination by atomic absorption spectrophotometry.

REAGENTS

4

• (4.1) Hydrochloric acid, N solution (approximately).

• (4.2) Hydrochloric acid, 0.5 N solution.

• (4.3) Magnesium standard solution: dissolve 1.013 g magnesium sulphate (MgSO₄.7H₂O) in 0.5 N hydrochloric acid solution (4.2) and dilute to 100 ml with this acid.

• 1 ml of this solution contains 1 mg of magnesium (Mg).

• or

• weigh out 1.658 g of magnesium oxide, previously calcined at 600° for 2 hours, place in a beaker with 100 ml of water and 120 ml of approximately N hydrochloric acid (4.1). After dissolution, transfer quantitively into a one litre graduated flask, make up the volume with water and mix.

• 1 ml of this solution contains 1 mg of magnesium (Mg).

• (4.4) Strontium chloride solution: dissolve 15 g strontium chloride (SrCl₂.6H₂O) in 0.5 N hydrochloric acid solution (4.2) and dilute to 100 ml with the same solvent.

APPARATUS

5

• (5.1) Atomic absorption spectrophotometer with a magnesium lamp (285.2 nm).

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample and place in a 500 ml graduated flask. Add about 300 ml water and boil for half an hour. Allow to cool, dilute to the mark with water, mix and filter.

Preparation of the sample solution 7.2 7.2.1 If the fertiliser has a declared magnesium oxide (MgO) content greater than 10%, transfer by pipette 25 ml of the filtrate (7.1) into a 100 ml graduated flask, make up to the mark with water and mix. 7.2.2 Transfer by pipette 10 ml of the filtrate (7.1) or the diluted filtrate (7.2.1) into a 200 ml graduated flask and make up to the mark with 0.5 N hydrochloric acid solution (4.2). 7.2.3 Dilute solution (7.2.2) with 0.5 N hydrochloric acid solution (4.2) to a concentration within the working range of the spectrophotometer. The final solution must contain 10% V/V of the strontium chloride solution (4.4).

Blank solution 7.3 Prepare a blank solution from which only the sample has been omitted.

Standard solutions for calibration 7.4 By diluting the standard solution (4.3) with 0.5 N hydrochloric acid solution (4.2), prepare at least 5 standard solutions of increasing concentration corresponding to the optimal measuring range of the spectrophotometer. The final solutions must contain 10% V/V of the strontium chloride solution (4.4).

Measurement 7.5 Set up the spectrophotometer (5.1), at a wavelength of 28.25 nm using an oxidising air-acetylene flame. Spray successively, in triplicate, the standard solutions (7.4), the sample solution (7.2) and the blank solution (7.3), washing the instrument through with distilled water between each spraying. Plot the calibration curve using the mean absorbances as the ordinates and the corresponding concentrations of magnesium in Ö as the abscissae. Determine the concentration of magnesium in the sample and blank by reference to the claibration curve.

EXPRESSION OF RESULTS

8

Calculate the quantity of magnesium (Mg) or magnesium oxide (MgO) (conversion factor Mg to MgO = 1.66) in the sample taking into consideration the blank. Express the result as a percentage of the sample.

12b. — DETERMINATION OF WATER-SOLUBLE MAGNESIUM—EDTA METHOD

SCOPE

1

This method is for the determination of water-soluble magnesium.

FIELD OF APPLICATION

2

Exclusively to straight fertilisers in Groups 1(a) and 3(a) of Section A of the Table in Schedule 1 of the Fertilisers Regulations 1990[^f01017] in respect of which the indication of water-soluble magnesium, expressed as magnesium oxide, is required.

PRINCIPLE

3

Solution of magnesium by boiling a test sample in water. Titration with EDTA of calcium and magnesium in the presence of eriochrome black-T, followed by titration with EDTA of calcium in the presence of calcein or of calcon carbonic acid. Determination of magnesium by difference.

REAGENTS

4

• (4.1) Magnesium solution, 0.05 M: weigh out 2.016 g magnesium oxide, previously calcined at 600°C for 2 hours, place in a beaker with 100 ml water and stir in 120 ml of approximately N hydrochloric acid. After dissolution, transfer quantitatively into a 1 litre graduated flask, make up the volume with water and mix. Check the strength of the solution gravimetrically by precipitation as magnesium ammonium phosphate.

• 1 ml of the solution should contain 1.216 mg of Mg (= 2.016 mg of MgO).

• (4.2) EDTA solution, 0.05 M: dissolve 18.61 g of the dihydrated disodium salt of ethylenediaminetetra-acetic acid in 600-800 ml water contained in a 1 litre beaker. Transfer the solution quantitatively to a 1 litre graduated flask, make up to volume with water and mix. Check this solution (4.1) by taking a sample of 20 ml of the latter and titrating as described under 7.3.1.

• 1 ml of the EDTA solution should correspond to 1.216 mg of Mg or 2.016 mg of MGO and to 2.004 mg of Ca or 2.804 mg of CaO.

• (4.3) Calcium solution 0.05 M: weigh out 5.004 g of dry calcium carbonate and place in a beaker with 100 ml water. Progressively stir in 120 ml approximately N hydrochloric acid. Bring to the boil in order to drive off the carbon dioxide, cool, transfer quantitatively into a 1 litre graduated flask, make up to volume with water and mix. Check the solution against the EDTA solution (4.2) following analytical procedure 7.3.2. One 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 molar EDTA solution.

• (4.4) Calcein indicator: carefully mix in a mortar 1 g calcein with 100 g sodium chloride. Use 10 mg of this mixture. The indicator changes from green to orange. Titration must be carried out until an orange colour is obtained which is free from green tinges.

• (4.5) Calcon carbonic acid indicator: dissolve 400 mg calcon carbonic acid in 100 ml methanol. Use three drops of this solution. The indicator changes from red to blue. Titration must be carried out until a blue colour is obtained which is free from red tinges.

• (4.6) Eriochrome black-T indicator: dissolve 300 mg eriochrome black-T in a mixture of 25 ml propan-1-ol and 15 ml triethanolamine. Use three drops of this solution. This indicator turns from red to blue and titration must be carried out until a blue colour is obtained which is free from rred tinges. It changes colour only when magnesium is present. If necessary add 0.1 ml of standard solution 4.1.

• (4.7) Potassium cyanide solution, 2 g per 100 ml.

• (4.8) Solution of potassium hydroxide and potassium cyanide: dissolve 280 g potassium hydroxide and 66 g potassium cyanide in water, make up the volume to 1 litre and mix.

• (4.9) pH 10 buffer solution: dissolve 33 g ammonium chloride in 200 ml water, add 207 ml ammonia solution (d = 0.880 g/ml) from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if d = 0.91 g/ml, use 250 ml). Make up the volume to 500 ml with water and mix. Check the pH of this solution regularly.

APPARATUS

5

• (5.1) Magnetic or mechanical stirrer.

• (5.2) pH meter.

PREPARATION OF THE SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample and place in a 500 ml graduated flask. Add about 300 ml water and boil for half an hour. Cool, make up the volume, mix and filter.

Control test 7.2 Carry out a determination on aliquot parts of solutions (4.1) and (4.3) such that the Ca/Mg ratio is equal to that expected from the sample. For this purpose take (a) ml of standard solution (4.3) and (b — a) ml standard solution (4.1), where (a) and (b) are the numbers of ml EDTA solution used in the two titrations when analysing the sample. This procedure is correct only if the standard solutions of EDTA, calcium and magnesium are exactly equivalent. If this is not the case, it is necessary to make the appropriate corrections.

Determination 7.3 Titration in the presence of eriochrome black-T 7.3.1 Place an aliquot part of the solution to be analysed (see the Table) in a 300 ml beaker and dilute with water to about 100 ml. Add 5 ml buffer solution (4.9). The pH measured by the meter (5.2) must be 10.5±0.1. Add 2 ml potassium cyanide solution (4.7) and 3 drops of the eriochrome black-T indicator (4.6). Stir gently and titrate with the EDTA solution (4.2). Let “b” be the number of ml of 0.05 molar EDTA solution. Note: For titration with eriochrome black-T, the titration must not exceed 25 ml of EDTA, otherwise the volume of the aliquot part must be reduced. Titration in the presence of calcein or of calcon carbonic acid 7.3.2 Place an aliquot part of the solution to be analysed equal to that taken for the above titration in a beaker. Dilute with water to about 100 ml. Add 10 ml potassium hydroxide-potassium cyanide solution (4.8) and the indicator (4.4) or (4.5). Stir gently and titrate with the EDTA solution (4.2). Let “a” be the number of ml of 0.05 molar EDTA solution.

EXPRESSION OF RESULTS

8

$%MgO(b-a)×0.2016M$

13a. — DETERMINATION OF TOTAL MAGNESIUM—ATOMIC ABSORPTION SPECTROPHOTOMETRIC METHOD

SCOPE

1

This method is for the determination of total magnesium.

FIELD OF APPLICATION

2

Exclusively to the fertiliser magnesium ammonium nitrate in Group 1(a) of Section A of the Table in Schedule 1 of the Fertilisers Regulations 1990[^f01018] in respect of which the declaration of total magnesium is required.

PRINCIPLE

3

Solution of magnesium by boiling the test sample in dilute acid, and determination by atomic absorption spectrophotometry.

REAGENTS

4

• (4.1) Hydrochloric acid solution 50% (V/V): dilute an appropriate volume of hydrochloric acid (d = 1.18 g/ml) with an equal volume of water.

• (4.2) Hydrochloric acid, N solution (approximately).

• (4.3) Hydrochloric acid, 0.5 N solution.

• (4.4) Magnesium solution: dissolve 1.013 g magnesium sulphate (MgSO₄.7H₂O) in 0.5 N hydrochloric acid solution (4.3) and dilute to 100 ml with this acid.

• 1 ml of this solution contains 1 mg of magnesium (Mg).

• or

• weigh out 1.658 g of magnesium oxide, previously calcined at 600°C for 2 hours, place in a beaker with 100 ml of water and 120 ml of approximately N hydrochloric acid (4.2). After dissolution, transfer quantitatively into a one litre graduated flask, make up the volume with water and mix.

• 1 ml of this solution contains 1 mg of magnesium (Mg).

• (4.5) Strontium chloride solution: dissolve 75 g strontium chloride (SrCl₂.6H₂O) in 0.5 N hydrochloric acid solution (4.3) and dilute to 500 ml with this acid.

APPARATUS

5

• (5.1) Atomic absorption spectrophotometer with a magnesium lamp (285.2 nm).

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample and place in a 500 ml graduated flask. Add about 200 ml water, 20 ml hydrochloric acid solution (4.1) and boil for half an hour. Allow to cool, dilute to the mark with water, mix and filter.

Preparation of the sample solution 7.2 7.2.1 If the fertiliser has a declared magnesium oxide (MgO) content greater than 10%, transfer by pipette 25 ml of the filtrate (7.1) into a 100 ml graduated flask, make up to the mark with water and mix. 7.2.2 Transfer by pipette 10 ml of the filtrate (7.1) or the diluted filtrate (7.2.1), into a 200 ml graduated flask and make up to the mark with 0.5 N hydrochloric acid solution (4.3). 7.2.3 Dilute solution (7.2.2) with 0.5 N hydrochloric acid solution (4.3) to a concentration within working range of the spectrophotometer. The final solution must contain 10% V/V strontium chloride solution (4.5).

Blank solution 7.3 Prepare a blank solution from which only the sample has been omitted.

Standard solutions for calibration 7.4 By diluting the standard solution (4.4) with 0.5 hydrochloric acid solution (4.3), prepare at least 5 standard solutions of increasing concentration corresponding to the optimal measuring range of the spectrophotometer. The final solutions must contain 10% V/V of the strontium chloride solution (4.5).

Measurement 7.5 Set up the spectrophotometer (5.1), at a wavelength of 285.2 nm using an oxidising air-acetylene flame. Spray successively, in triplicate, the standard solutions (7.4), the sample solution (7.2) and the blank solution (7.3), washing the instrument through with distilled water between each spraying. Plot the calibration curve using the mean absorbances as the ordinates and the corresponding concentrations of magnesium in Ö as the abscissae. Determine the concetration of magnesium in the sample and blank by reference to the calibration curve.

EXPRESSION OF RESULTS

8

Calculate the quantity of magnesium (Mg) or magnesium oxide (MgO) (conversion factor Mg to MgO = 1.66) in the sample, taking into consideration the blank. Express the result as a percentage of the sample.

13b. — DETERMINATION OF TOTAL MAGNESIUM—EDTA METHOD

SCOPE

1

This method is for the determination of total magnesium.

FIELD OF APPLICATION

2

Exclusively to the fertiliser magnesium ammonium nitrate in Group 1(a) of Section A of the Table in Schedule 1 of the Fertilisers Regulations 1990[^f01019] in respect of which the indication of total magnesium is required.

PRINCIPLE

3

Solution of magnesium by boiling a test sample in dilute acid. Titration of calcium and magnesium with EDTA in the presence of eriochrome black-T, followed by titration with EDTA of calcium in the presence of calcein or of calcon carbonic acid. Determination of magnesium by difference.

REAGENTS

4

• (4.1) Magnesium solution, 0.05 M: weigh out 2.016 g of magnesium oxide previously calcined at 600°C for 2 hours, place in a beaker with 100 ml of water and stir in 120 ml of approximately 1 N hydrochloric acid. After dissolution, transfer quantitatively into a 1 litre graduated flask, make up the volume with water and mix. Check the strength of the solution gravimetrically by precipitation as ammonium-magnesium phosphate.

• 1 ml of the solution should contain 1.216 mg of magnesium (Mg) (= 2.016 mg of magnesium oxide (MgO)).

• (4.2) EDTA solution 0.05 M: dissolve 18.61 g of the dihydrated disodium salt of ethylenediaminetetra-acetic acid in 600-800 ml water contained in a 1 litre beaker. Transfer the solution quantitatively into a 1 litre graduated flask, make up to volume with water and mix. Check this solution with solution (4.1) by taking a sample of 20 ml of the latter and titrating following analytical procedure 7.3.1.

• 1 ml of the EDTA solution should correspond to 1.216 mg of Mg or 2.016 mg of MgO and to 2.004 mg of Ca or 2.804 mg of CaO.

• (4.3) Calcium solution 0.05 M: weigh out 5.004 g of dry calcium carbonate and place in a beaker with 100 ml of water. Progressively stir in 120 ml of approximately N hydrochloric acid. Bring to the boil in order to drive off the carbon dioxide, cool, transfer quantitatively into a 1 litre graduated flask, make up to volume with water and mix. Check this solution against the EDTA solution (4.2) following analytical procedure 7.3.2.

• One 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 molar EDTA solution.

• (4.4) Calcein indicator: carefully mix in a mortar 1 g of calcein with 100 g of sodium chloride. Use 10 mg of this mixture. The indicator changes from green to orange. Titration must be carried out until an orange colour is obtained which is free from green tinges.

• (4.5) Calcon carbonic acid indicator: dissolve 400 mg of calcon carbonic acid in 100 ml of methanol. Use three drops of this solution. The indicator changes from red to blue. Titration must be carried out until a blue colour is obtained which is free from red tinges.

• (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. Use three drops of this solution. This indicator turns from red to blue and titration must be carried out until a blue colour is obtained which is free from red tinges. It changes colour only when magnesium is present. If necessary add 0.1 ml of standard solution (4.1).

• (4.7) Potassium cyanide solution, 2 g per 100 ml.

• (4.8) Solution of potassium hydroxide and potassium cyanide: dissolve 280 g potassium hydroxide and 66 g potassium cyanide in water, make up the volume to one litre and mix.

• (4.9) pH 10.5 buffer solution: dissolve 33 g ammonium chloride in 200 ml of water, add 207 ml ammonia solution (d = 0.880 g/ml) from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if d = 0.91 g/ml, use 250 ml). Make up to volume to 500 ml with water and mix. Check the pH of this solution regularly.

• (4.10) Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (d = 1.18 g/ml) with an equal volume of water.

• (4.11) Sodium hydroxide solution, 5N.

APPARATUS

5

• (5.1) Magnetic or mechanical stirrer.

• (5.2) pH meter.

PREPARATION OF THE SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample and place in a 500 ml graduated flask. Add about 200 ml water and 20 ml hydrochloric acid (4.10) and boil for half an hour. Cool, make up to volume with water, mix and filter.

Control test 7.2 Carry out a determination on aliquot parts of solutions (4.1) and (4.3) such that the Ca/Mg ratio is equal to that expected from the sample. For this purpose take (a) ml of standard solution (4.3) and (b — a) ml standard solution (4.1), where (a) and (b) are the numbers of ml EDTA solution used in the two titrations when analysiing the sample. This procedure is correct only if the standard solutions of EDTA, calcium and magnesium are exactly equivalent. If this is not the case, it is necessary to make the appropriate corrections.

Determination 7.3 Titration in the presence of eriochrome black-T 7.3.1 Transfer by pipette 50 ml of the solution to be analysed into a 300 ml beaker. Neutralise the excess acid with the 5 N sodium hydroxide solution (4.11) using the pH meter (5.2). Dilute with water to 100 ml. Add 5 ml buffer solution (4.9). The pH measured by the meter must be 10.5±0.1. Add 2 ml potassium cyanide solution (4.7) and three drops eriochrome black-T indicator (4.6). Titrate with the EDTA solution (4.2), stirring gently with the stirrer (5.1). Let “b” be the number of ml of 0.05 molar EDTA solution. Note: For titration with eriochrome black-T, the titration must not exceed 25 ml of EDTA otherwise the volume of the aliquot part must be reduced. Titration in the presence of calcein or of calcon carbonic acid 7.3.2 Place an aliquot part of the solution to be analysed equal to that taken for the above titration in a 300 ml beaker. Neutralise the excess acid with 5 N sodium hydroxide solution (4.11) using the pH meter (5.2). Dilute with water to about 100 ml. Add 10 ml potassium hydroxide—potassium cyanide solution (4.8) and the indicator (4.4) or (4.5). Stir gently and titrate with the EDTA solution. Let “a” be the number of ml of 0.05 molar EDTA solution.

EXPRESSION OF RESULTS

8

$%MgO(b-a)×0.2016M$

14. — DETERMINATION OF CHLORIDES IN THE ABSENCE OF ORGANIC MATERIAL

SCOPE

1

This method is for the determination of chloride, in the absence of organic material.

FIELD OF APPLICATION

2

All fertilisers which are free from organic material, except ammonium nitrate fertilisers of a nitrogen content greater than 28% by weight.

PRINCIPLE

3

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 sulphate (Volhard’s method).

REAGENTS

4

• (4.1) Nitrobenzene or diethyl ether.

• (4.2) Nitric acid, 10 N solution.

• (4.3) Indictaor solution: dissolve 40 g of ferric ammonium sulphate [Fe₂(SO₄)₃.(NH₄)₂SO₄.24H₂O] in water and make up to 1 litre.

• (4.4) Silver nitrate, 0.1 N solution.

• (4.5) Ammonium thiocyanate, 0.1 N solution.

• Preparation: since this salt is hygroscopic and cannot be dried without risk of decomposition, it is advisable to weigh out approximately 9 g, dissolve in water and make up the volume to one litre. Standardise by titration against 0.1 N silver nitrate solution.

APPARATUS

5

• (5.1) Rotary shaker, 35-40 turns per minute.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 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. Mix for half an hour on the shaker (5.1); make up to 500 ml with distilled water, mix and filter into a beaker.

Determination 7.2 Take an aliquot part of the filtrate containing not more than 0.150 g of chloride. If the sample taken is smaller than 50 ml it is necessary to make up the volume to 50 ml with distilled water. Add 5 ml 10 N nitric acid (4.2), 20 ml indicator solution (4.3), and two drops ammonium thiocyanate standard solution (taken from a burette adjusted to zero). From a burette than 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 N ammonium thiocyanate (4.5) until a red-brown colour 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.

Blank test 7.3 Make a blank test under the same conditions (omitting only the sample) and allow for it when calculating the final result.

Control test 7.4 Carry out the determination on an aliquot part of a freshly prepared solution of potassium chloride, containing 0.100 g as chloride.

EXPRESSION OF RESULT

8

Express the result of the analysis as a percentage of chloride contained in the sample as it has been received for analysis.

15a. — DETERMINATION OF FINENESS OF GRINDING—DRY METHOD

SCOPE

1

This method is for the determination of the fineness of grinding by the dry method.

FIELD OF APPLICATION

2

All fertilisers in Schedule 1 of the Fertilisers Regulations 1990[^f01020] for which requirements are given of fineness of grinding using 0.630 mm and 0.160 mm sieves.

PRINCIPLE

3

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 are calculated.

APPARATUS

4

• (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).

PROCEDURE

5

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 seperately.

EXPRESSION OF RESULTS

6

Percentage of material passing sieve of 0.630 mm apertures = (50 — M₁) × 2

15b. — DETERMINATION OF THE FINENESS OF GRINDING OF SOFT NATURAL PHOSPHATES

SCOPE

1

This method is for determining the fineness of grinding of soft natural phosphates.

FIELD OF APPLICATION

2

Soft natural phosphates.

PRINCIPLE

3

For samples of fine particle size, agglomeration may occur thus making dry sieving difficult. For this reason, wet sieving is normally used.

REAGENTS

4

Sodium hexametaphosphate solution, 1 g per 100 ml.

APPARATUS

5

• (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.

PROCEDURE

6

Wash both sides of the sieves with water and place the sieve with 0.125 mm apertures above the 0.063 mm sieve.

EXPRESSION OF RESULTS

7

Percentage of material passing sieve of 0.125 mm apertures = (50 − M₁) × 2

REMARK

8

If the presence of lumps is observed after sieving the analysis should be carried out again in the following way:

16. — METHODS OF ANALYSIS AND TEST PROCEDURES FOR AMMONIUM NITRATE FERTILISERS CONTAINING MORE THAN 28% NITROGEN BY WEIGHT

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedures for the application of thermal cycles prior to the execution of the oil retention test in straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

THERMAL CYCLES

2

Field application 2.1 This procedure is for thermal cycling prior to determining the oil retention of the fertiliser.

Principle and definition 2.2 In an Erlenmeyer flask, heat the sample from ambient temperature to 50°C and maintain at this temperature for a period of two hours (phase at 50°C). Thereupon, cool the sample until a temperature of 25°C is acheived and maintain at that temperature for two hours (phase at 25°C). The combination of the successive phases at 50°C and 25°C forms one thermal cycle. After being subjected to two thermal cycles, the test sample is held at a temperature of 20±3°C for the determination of the oil retention value.

Apparatus 2.3 Normal laboratory apparatus, in particular Water baths thermostated at 25 (±1) and 50 (±1)°C respectively. Erlenmeyer flasks with an individual capacity of 150 ml.

Procedure 2.4 Put each test sample of 70(±5) grams into an Erlenmeyer flask which is then sealed with a stopper. Move each flask every two hours from the 50°C bath to the 25°C bath and vice versa. Maintain the water in each bath at constant temperature and keep in motion by rapid stirring to ensure the water level comes above the level of the sample. Protect the stopper from condensation by a foam rubber cap.

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedure for the determination of oil retention of straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

DEFINITION

2

Oil retention of a fertiliser: the quantity of oil retained by the fertiliser determined under the operating conditions specified and expressed as a percentage by mass.

PRINCIPLE

3

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.

REAGENT

4

Gas oil
Viscosity max:	5 mPas at 40°C
Density:	0.8 to 0.85 g/ml at 20°C
Sulphur content:	≤1.0% (m/m)
Ash:	≤0.1% (m/m)

APPARATUS

5

Ordinary laboratory apparatus and:

• (5.1) Balance, capable of weighing to the nearest 0.01 gram.

• (5.2) Beakers, of capacity 500 ml.

• (5.3) Funnel, of plastic materials, 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 150g/m².

• (5.6) Absorbent tissue (laboratory grade).

PROCEDURE

6

• (6.1) Two individual determinations are carried out in quick succession on seperate 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 galss 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 × 500 mm) 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 sof 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 weight of the quantity of gas oil retained.

Repeating the rolling procedure and reweighing 6.5 If the quantity 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.

EXPRESSION OF RESULTS

7

Method of calculation and formula 7.1 The oil retention, from each determination (6.1) expressed as a percentage by mass of the sieved test portion, is given by the equation: $Oil retention=100×m2-m1m1$ where: m₁ is the mass, in grams, of the sieved test portion (6.2); m₂ is the mass, in grmas, of the test portion accodring 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.

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedure for the determination of the combustible content of straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

PRINCIPLE

2

The carbon dioxide produced by inorganic filters is removed in advance with an acid. The organic compounds are oxidised by means of a chromic acid/sulphuric 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.

REAGENTS

3

• (3.1) Analytical-grade chromium VI oxide; Cr-(VI)-)3.

• (3.2) Sulphuric acid diluted to 60% by volume:

• pour 360 ml of water into a one-litre beaker and carefully add 640 ml of sulphuric acid, density at 20°C=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 1.5 mm.

• (3.10) Demineralised water, freshly boiled to remove carbon dioxide.

APPARATUS

4

• (4.1) Standard laboratory equipment, in particular:

• 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 15μm);

• 600 ml beaker.

• (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 1).

• (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 fractionating 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.

PROCEDURE

5

Sample for analysis 5.1 Weigh approximately 10 grams of ammonium nitrate to the nearest 0.001 grams.

Removal of carbonates 5.2 Place the sample for analysis in the reaction flask (B). Add 100 ml of H₂So₄ (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 fractionating column (C’) and the condenser (C) with coolinhg 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 effervesence, if effervesence is seen, continue heating for 30 minutes. Allow 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 vessels 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 must remain clear in the absorbers. If this does not happen, the carbonate removal process must be adjusted.

Oxidation and absorption 5.3 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 one-and-a-half hours[^f01021]. 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 of 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 fro the beaker. Repeat the operation once to ensure that the distributors are rinsed thoroughly.

Measurement of the carbonates originating from organic material 5.4 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 that 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 back titrate with the sodium hydroxide solution (3.6).

BLANK TEST

6

Carry out a blank test following the same procedure and using the same quantities of all reagents.

EXPRESSION OF RESULTS

7

The content of combustible ingredients (C), expressed as carbon, as a percentage by mass of the sample, is given by the formula:

$$C%=0.06xV1-V2E$ 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 for back titration.$

SCOPE AND FIELD OF APPLICATION

1

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.

PRINCIPLE

2

Measurement of the pH of an ammonium nitrate solution by means of a pH meter.

REAGENTS

3

Distilled or demineralised water, free from carbon dioxide.

Buffer solution, pH 6.88 at 20°C 3.1 Dissolve 3.40±0.01 grams of potassium dihydrogen orthophosphate (KH₂PO₄) in approximately 400 ml of water. The 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 1,00 ml standard flask, make up to the mark and mix. Keep the solution in an airtight vessel.

Buffer solution, pH 4.00 at 20°C 3.2 Dissolve 10.21±0.01 grams of potassium hydrogen phthalate (KHC₈O₄H₄) in water, transfer without loss into a 1,00 ml 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.

APPARATUS

4

pH meter, equipped with glass and calomel electrodes or equivalent, sensitivity 0.05 pH unit.

APPARATUS

5

Calibration of the pH meter 5.1 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.

Determination 5.2 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.

EXPRESSION OF RESULTS

6

Express the result in pH units, to the nearest 0.1 unit and state the temperature used.

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedure for the test sieving of straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

PRINCIPLE

2

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 are calculated.

APPARATUS

3

• (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.

PROCEDURE

4

• (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.

EVALUATION OF RESULTS

5

• (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 seperate 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.

EXPRESSION OF RESULTS

6

Report the mean of the two values for A on the one hand and for A + B on the other hand.

SCOPE AND FIELD OF APPLICATION

1

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.

PRINCIPLE

2

Chloride ions dissolved in water are determined by potentiometric titration with silver nitrate in an acidic medium.

REAGENTS

3

Distilled or demineralised water, free from chloride ions.

• (3.1) Acetone AR.

• (3.2) Concentrated nitric acid (density at 20°C = 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.

APPARATUS

4

• (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) sulphate 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) sulphate electrodes are used.

• (4.3) Magnetic stirrer, with a Teflon-coated rod.

• (4.4) Microburette with a fine-pointed tip, graduated in 0.01 ml divisions.

PROCEDURE

5

Standardisation of the silver nitrate solution 5.1 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 the 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 elctrodes 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 values 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: $Veq=V0+(V1×bB)$ where: V₀ 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 values of Δ₂E and the first negative value of Δ₂E (see example in Table 1).

Blank test 5.2 Carry out a blank test and take account thereof when calculating the final result. The result V₄ of the blank test and take account thereof when calculating the final result. $V4=2V3-V2$ 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 solution used.

Check test 5.3 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.

Determination 5.4 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 potentiometler (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….”.

EXPRESSION OF RESULTS

6

Express the result of the analysis as the percentage of chlorine contained in the sample as received for analysis.

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedure for the determination of copper content of straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

PRINCIPLE

2

The sample is dissolved in dilute hydrochloric acid and the copper content is determined by atomic absorption spectrophotometry.

REAGENTS

3

• (3.1) Hydrochloric acid (density at 20°C=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[^f01022] (stock): weigh, to the nearest 0.001 gram, 1 gram of pure copper, dissolve in 25 ml 6 M hydrochloric acid solution (3.2), add 5 ml of hydrogen peroxide (3.5) in portions and dilute to I 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 10μg of copper (Cu).

• Prepare this solution at the time of use.

APPARATUS

4

Atomic absorption spectrophotometer with a copper lamp (324.8 nm).

PROCEDURE

5

Preparation of the solution for analysis 5.1 Weigh, to the nearest O.OO1 gram, 25 grams of the sample, place it in 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, make up to the mark with 0.5 M hydrochloric acid (3.3) and mix carefully. Filter through a copper-free filter paper[^f01023], discarding the first 50 ml.

Blank solution 5.2 Prepare a blank solution from which only the sample has been omitted and allow for this in the calculation of the final result.

Determination 5.3 Preparation of sample and blank test solutions 5.3.1 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 spectrophotometer. Normally no dilution is needed. Preparation of the calibration solutions 5.3.2 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 spectrophotometer (0 to 5.0 μ/l Cu). Before making up to the mark, add to every solution ammonium nitrate (3.4) to give a final concentration of 100 mg per ml.

Measurement 5.4 Set up the spectrophotometer (4) at a wavelength of 324.8 nm using an oxidising air-acetylene flame. Spray successively, 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 μ/ml as the abscissae. Determine the concentration of copper in the final sample and blank solutions by reference to the calibration curve.

EXPRESSION OF RESULTS

6

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.

PART II

General

1

• (a) 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 the analysis.

• (b) Any reference to water in this Schedule means purified water as defined in the European Pharmacopeia.

Reagents and Apparatus

2

• (a) All reagents used shall be of analytical quality.

• (b) For the determination of any form of nitrogen, water must be free of all nitrogeneous compounds and carbon dioxide.

• (c) Solutions for which no solvents are prescribed must be aqueous.

• (d) Only special instruments or apparatus requiring special standards are mentioned in the descriptions of the methods of analysis.

Methods of Analysis

3

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.a

Extraction of phosphorus—by mineral acids (total phosphorus)

b

Extraction of phosphorus—by 2% citric acid

6

Determination of extracted phosphorus—spectrophotometric method

7.a

Determination of potassium—gravimetric method

b

Determination of potassium—flame photometric method

8

Determination of total magnesium

9.a

Determination of boron—titrimetric method

b

Determination of boron—spectrophotometric method

10

Determination of cobalt

11

Determination of molybdenum

12

Determination of copper

13

Determination of iron

14

Determination of manganese

15

Determination of the nuetralising value in limiting materials

16

Determination of fineness of products other than potassic bag slag

17

Determination of fineness of potassic basic slag.

1. — PREPARATION OF THE SAMPLE FOR ANALYSIS

INTRODUCTION

1

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. (Overgrinding must be avoided in cases where this will affect the solubility in various reagents.) With some materials, fine grinding may lead to loss of gain or moisture and allowance for this must be made.

SCOPE AND FIELD OF APPLICATION

2

This method is applicable to fertilisers in Groups 1(b), 1(c), 2(d), 3(b), 3(c), 4(a), 4(b), 4(c) of Section A and Group 5 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1990[^f01024]. It is also applicable to products in Group 5(a) of Section A in the said table when the determination of total magnesium is required.

PRINCIPLE

3

• (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.

APPARATUS

4

• (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; 1976 are suitable.

• (4.4) Sample containers of non-corrodible materials, with air tight closures.

PROCEDURE

5

WARNING

All operations connected with this procedure should be carried out as quickly as possible to minimise absorbtion 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.