Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996

• Dissolve 120 g of stannous chloride (SnCl₂.2H₂O) in 400 ml of concentrated hydrochloric acid (ρ = 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 (ρ = 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 (ρ = 1.84 g/ml).

• (4.13) Hydrochloric acid solution: dilute an appropriate volume of hydrochloric acid (ρ = 1.18 g/ml) with an equal volume of water.

• (4.14) Glacial acetic acid.

• (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-l-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 methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to one litre with water.

• Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of solution 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) of this indicator solution.

• (4.29.2) 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 (4 to 5 drops) may be used instead of the preceding 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%.

APPARATUS

5

• (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.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Total soluble and insoluble nitrogen 7.1 In the absence of nitrate 7.1.1 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. 7.1.1.4 Expression of result $%N=(a-A)×0.28M$ 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. In the presence of nitrate 7.1.2 7.1.2.1 Test sample Weigh to the nearest 0.001 g, 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 result $%N=(a-A)×0.28M$ 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 analysis.

Forms of soluble nitrogen 7.2 Preparation of the solution to be analysed 7.2.1 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. Total soluble nitrogen 7.2.2 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 $%N=(a-A)×0.28M$ 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. Total soluble nitrogen with the exception of nitric nitrogen 7.2.3 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 $%N=(a-A)×0.28M$ 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 cyanamid 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. Ammoniacal nitrogen 7.2.5 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 $%N(ammoniacal)=(a-A)×0.28M$ 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 nitroge 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-l-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 $%N=(a-A)×0.14M$ 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. Ureic nitrogen 7.2.6 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 $%N(ureic)=(a-A)×0.14M$ 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 a 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 $%(ureic+biuret)N=6.67×mM$ 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:— CaseNitric NitrogenAmmoniacal NitrogenCyanamide NitrogenUreic Nitrogen 1AbsentPresentPresent(7.2.2.4)-(7.2.5.5 + 7.2.7)2PresentPresentPresent(7.2.3.2)-(7.2.5.5 + 7.2.7)3AbsentPresentAbsent(7.2.2.4)-(7.2.5.5)4PresentPresentAbsent(7.2.3.2)-(7.2.5.5) Cyanamide Nitrogen 7.2.7 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.

VERIFICATION OF RESULTS

8

• (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

SCOPE

1

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.

FIELD OF APPLICATION

2

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 to the Fertilisers Regulations (Northern Ireland) 1992[^f00009] which contain exclusively nitric, ammoniacal or ureic nitrogen.

PRINCIPLE

3

The following determinations are made on different portions of a single sample solution.

Total soluble nitrogen 3.1 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)

REAGENTS

4

• (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 (ρ = 1.84 g/ml).

• (4.10) Hydrochloric acid solution: dilute an appropriate volume of hydrochloric acid (ρ = 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-l-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).

APPARATUS

5

• (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.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Preparation of solution for analysis 7.1 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.

Total nitrogen 7.2 In the absence of nitrates 7.2.1 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. In the presence of nitrates 7.2.2 Transfer by pipette into a 500 ml Erlenmeyer flask an 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. Blank test 7.2.3 Carry out a blank test under the same conditions (omitting only the sample) and use this value in the calculation of the final result. Expression of result 7.2.4 $%N(total)=(a-A)×0.28M$ 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.

Total nitrogen excluding nitric nitrogen 7.3 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 (4.25). 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. Blank test 7.3.2 See 7.2.3. Expression of result 7.3.3 $%N(total)=(a-A)×0.28M$ 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

$(7.2.4)-(7.5.3+7.6.3)or(7.2.4)-(7.5.3+7.6.5)or(7.2.4)-(7.5.3+7.6.6)$

Ammoniacal nitrogen 7.5 In the presence of ureic nitrogen 7.5.1 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-l-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). Blank test 7.5.2 See 7.2.3. Expression of result 7.5.3 $%N(ammoniacal)=(a-A)×0.14M$ 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.

Ureic nitrogen 7.6 Urease method 7.6.1 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.

Blank test 7.6.2 See 7.2.3.

Expression of result 7.6.3 $%N(ureic)=(a-A)×0.14M$ 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.

Gravimetric method using xanthydrol 7.6.4 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.

Expression of result 7.6.5 $%N(ureic)6.67×mM$ 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. 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.

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.

Difference method 7.6.6 Ureic N can also be calculated as indicated in the following table: CaseNitric NAmmoniacal NUreic N 1AbsentPresent(7.2.4)-(7.5.3)2PresentPresent(7.3.3)-(7.5.3)

VERIFICATION OF RESULTS

8

• (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

SCOPE

1

This method is for the determination of phosphorus soluble in mineral acids.

FIELD OF APPLICATION

2

Subject to regulation 5(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 to the Fertilisers Regulations (Northern Ireland) 1992[^f00010], 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”.

PRINCIPLE

3

Extraction of the phosphorus in the fertiliser with a mixture of nitric acid and sulfuric acid.

REAGENTS

4

• (4.1) Sulfuric acid (ρ = 1.84 g/ml).

• (4.2) Nitric acid (ρ = 1.40 g/ml).

APPARATUS

5

• (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.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001 g, 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.

Determination 7.2 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 TOTAL PHOSPHORUS BY MINERAL ACIDS

SCOPE

1

This method is for the determination of phosphorus soluble in 2% formic acid.

FIELD OF APPLICATION

2

Applicable only to soft natural phosphate.

PRINCIPLE

3

To differentiate between hard natural phosphates and soft natural phosphates, phosphorus soluble in formic acid is extracted under specified conditions.

REAGENTS

4

• (4.1) Formic acid, 2% (20 g per litre): dilute 82 ml formic acid (concentration 98-100%; ρ = 1.22 g/ml) to 5 litres with distilled water.

APPARATUS

5

• (5.1) 500 ml graduated flask with a wide neck (eg Stohmann).

• (5.2) 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 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.

Determination 7.2 Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

9c. — EXTRACTION OF PHOSPHORUS BY 2% CITRIC ACID

SCOPE

1

This method is for the determination of phosphorus soluble in 2% citric acid.

FIELD OF APPLICATION

2

Subject to regulation 5(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 to the Fertilisers Regulations (Northern Ireland) 1992.

PRINCIPLE

3

Extraction of the phosphorus in the fertiliser with a 2% citric acid solution under specified conditions.

REAGENT

4

• (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 0.1 M sodium hydroxide standard solution using phenolphthalein as an indicator. If the concentration is correct, the titre should be 28.55 ml.

APPARATUS

5

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

PREPARATION OF SAMPLE

6

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.

PROCEDURE

7

Extraction 7.1 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.

Determination 7.2 Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

9d. — EXTRACTION OF PHOSPHORUS BY NEUTRAL AMMONIUM CITRATE

SCOPE

1

This method is for the determination of phosphorus soluble in neutral ammonium citrate.

FIELD OF APPLICATION

2

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 to the Fertilisers Regulations (Northern Ireland) 1992 for which the declaration of the solubility in neutral ammonium citrate is prescribed.

PRINCIPLE

3

Extraction of phosphorus at a temperature of 65°C using a neutral ammonium citrate solution (pH = 7.0) under specified conditions.

REAGENTS

4

Neutral ammonium citrate solution (pH = 7.0)

4.1

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:

APPARATUS

5

• (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).

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Transfer 1[^f00011] or 3[^f00012] 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[^f00013]. 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 of 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.

Determination 7.2 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

SCOPE

1

This method is for the determination of phosphorus soluble in alkaline ammonium citrate.

FIELD OF APPLICATION

2

Applicable only to precipitated dihydrated dicalcium phosphate (CaHPO₄.2H₂O).

PRINCIPLE

3

Extraction of phosphorus at a temperature of 65°C with an alkaline solution of ammonium citrate (Petermann) under specified conditions.

REAGENTS

4

Petermann’s solution 4.1

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 (ρ = 0.880 g/ml), from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if ρ = 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 (ρ = 0.880 g/ml), from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if ρ = 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 = 0.007 g 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, ρ = 0.880 g/ml contains approximately 0.22 g 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.

APPARATUS

5

• (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).

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.001 g, 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.

Determination 7.2 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

SCOPE

1

This method is for the determination of phosphorus soluble in alkaline ammonium citrate.

FIELD OF APPLICATION

2

Applicable only to disintegrated phosphates.

PRINCIPLE

3

Extraction of phosphorus at a temperature of 20°C with an alkaline solution of ammonium citrate (Petermann’s solution) under specified conditions.

REAGENT

4

See Method 9e.

APPARATUS

5

• (5.1) 250 ml graduated flask with a wide neck (eg Stohmann).

• (5.2) 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, 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.

Determination 7.2 Determine the phoshorus using Method 10 on an aliquot portion of the clear filtrate.

9g. — EXTRACTION OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (JOULIE'S METHOD)

SCOPE

1

This method is for the determination of phosphorus soluble in Joulie’s alkaline ammonium citrate.

FIELD OF APPLICATION

2

Applicable to all the straight and compound phosphatic fertilisers, in which the phosphate occurs in an aluminocalcic form.

PRINCIPLE

3

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.

REAGENTS

4

Joulie’s alkaline solution of ammonium citrate: 4.1 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 (ρ = 0.925 g/ml), containing 200 g NH₃ per litre; this may be prepared by diluting 760 ml ammonia solution (ρ = 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 (ρ = 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 (ρ = 0.925 g/ml) (see 4.1.1 above). Make up the volume to 1 litre with water. 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 = 0.008516 g NH₃). If the titre is too low add 4.25 ml of ammonia (ρ = 0.925 g/ml) per 0.1 ml below the 18 ml indicated above. 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 = 0.008516 g NH₃). If the titre is too low add 4.25 ml of ammonia (ρ = 0.925 g/ml) per 0.1 ml below the 18 ml indicated above.

• (4.2) 8-Hydroxyquinoline (oxine), powdered.

APPARATUS

5

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

• (5.2) 500 ml graduated flask with a wide neck (Stohmann).

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 Weigh to the nearest 0.0005 g, 1 g of the prepared sample and place in a small glass or porcelain mortar. Add about 10 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.

Determination 7.2 Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

NOTE

8

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/P₂O₅ > 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

SCOPE

1

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

FIELD OF APPLICATION

2

Applicable to all fertilisers where water-soluble phosphorus is to be determined.

PRINCIPLE

3

Extraction in water by shaking under specified conditions.

APPARATUS

4

• (4.1) 500 ml graduated flask with a wide neck (eg Stohmann).

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

PREPARATION OF 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 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.

Determination 6.2 Determine the phosphorus using Method 10, on an aliquot portion of the clear filtrate.

10. — DETERMINATION OF EXTRACTED PHOSPHORUS

SCOPE

1

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

FIELD OF APPLICATION

2

This method is applicable to all extracts of fertilisers[^f00015], for the determination of the different forms of phosphorus.

PRINCIPLE

3

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.

REAGENTS

4

• (4.1) Concentrated nitric acid (ρ = 1.40 g/ml).

• (4.2) Molybdate reagent:

Preparation of the reagent based on sodium molybdate 4.2.1 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).

Preparation of the reagent based on ammonium molybdate 4.2.2 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 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[^f00015] (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)[^f00016] 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.

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 (5.2) for approximately 15 minutes. Cool in a desiccator and weigh rapidly, repeat this process until a constant mass is attained.

Blank test 6.7 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.

Control test 6.8 Carry out the determination using an aliquot portion of a potassium dihydrogen phosphate solution containing 0.01 g of P₂O₅.

EXPRESSION OF RESULTS

7

If the samples for analysis and dilutions shown in the Table are used the following formulae apply:

$%P2O5inthefertiliser=(A-a)×f$

$$%Pinthefertiliser=(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:

$%P2O5inthefertiliser=(A-a)×f×D×100M$

$$%Pinthefertiliser=(A-a)×f'×D×100M$ 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.$

% P₂O₅in the fertiliser	% P in the fertiliser	Sample for analysis ml	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 (f') 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

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 to the Fertilisers Regulations (Northern Ireland) 1992.

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, 25-35% 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% enthanol.

• (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.

APPARATUS

5

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

• (5.2) Oven regulated at 120 ± 10°C.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Extraction 7.1 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 K₂O 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.

Determination 7.2 Transfer by pipette an aliquot portion of the filtrate containing 25-50 mg of potassium (see Table on page 70) 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.

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 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.

• (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.

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 a temperature of 120°C. Allow the crucible to cool in a desiccator to ambient temperature and weigh rapidly.

Blank test 7.7 Carry out 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 on an aliquot portion 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: $%K2Ointhefertiliser=(A-a)×f$ or $%Kinthefertiliser=(A-a)×f'$ where: A = mass in grams of the precipitate from the sample a = mass in grams of the precipitate from the blank f and f' = factors — see Table. With samples and dilutions which differ from those of the Table use the following formulae: $%K2O=(A-a)×F×D×100M$ or $%K=(A-a)×F'×D×100M$ where: F = conversion factor, KTPB into K₂O = 0.1314 F' = conversion factor, KTPB into K = 0.109 D = dilution factor M = mass in grams of the sample for analysis. TABLE FOR METHOD 11 % of K₂O in the fertiliser% of K in the fertiliserSample for analysis (g)Aliquot portion to be taken as a sample for precipitation (ml)Conversion factor f % K₂O g KTPBConversion factor f' % K g KTPB 1-50.8-4.2205013.1410.915-104.2-8.3105026.2821.8110-208.3-16.6102552.5643.6220-5016.6-41.51010131.40109.10more than 50more than 41.5510262.80218.10

12. — 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 sulfate (Volhard’s method).

REAGENTS

4

• (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 9 g, 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 2.103 g of potassium chloride, previously dried at 130°C, for one hour, in water and make up to 500 ml.

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. 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.

Determination 7.2 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.

Blank test 7.3 Carry out a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test 7.4 Carry out the determination using 50 ml (equivalent to 0.100 g of chloride) of the potassium chloride solution (4.6).

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.

13a. — 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 to the Fertilisers Regulations (Northern Ireland) 1992[^f00017] 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 is 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 separately.

EXPRESSION OF RESULTS

6

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

$$Percentage of material passing sieve of 0.160 mm apertures=[50-(M1+M2)]×2$ where: M₁ = 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 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

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

$$Percentage of material passing sieve of 0.063 mm apertures=[50-(M1+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.$

REMARK

8

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

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

SCOPE

1

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.

FIELD OF APPLICATION

2

This procedure is for thermal cycling prior to determining the oil retention value of the fertiliser.

PRINCIPLE AND DEFINITION

3

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 water bath at 20°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.

APPARATUS

4

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.

PROCEDURE

5

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.

14b. — DETERMINATION OF THE OIL RETENTION VALUE

SCOPE AND FIELD OF APPLICATION

1

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.

DEFINITION

2

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.

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

APPARATUS

5

• (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).

PROCEDURE

6

• (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 × 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 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 unto 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.

Repeating the rolling procedure and reweighing 6.5 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.

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: $Oil retention=m2-m1m1×100$ where: m₁ 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

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 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.

REAGENTS

3

• (3.1) Analytical-grade chromium VI oxide; CrVIO₃

• (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 ρ = 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.

APPARATUS

4

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 15μm);

• (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.

PROCEDURE

5

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