The Fertilisers (Sampling and Analysis) Regulations 1996

4.1	Glacial acetic acid.
4.2	Ammonia solution: dilute one volume of ammonia (p=0.88 pg/ml) with 3 volumes of water.p
4.3	Ammoniacal silver solution, according to Tollens, freshly prepared: mix 500 ml silver nitrate solution (10 g per 100 ml) with 500 ml ammonia solution (4.2).
Do not expose unnecessarily to light, heat or air.	Do not expose unnecessarily to light, heat or air.
Safety precaution: when handling ammoniacal silver nitrate solution, safety goggles must be worn.	Safety precaution: when handling ammoniacal silver nitrate solution, safety goggles must be worn.
4.4	Concentrated sulfuric acid (p=1.84 g/ml).
4.5	Potassium sulfate.
4.6	Copper oxide (CuO), 0.3 – 0.4 g for each determination or an equivalent quantity of copper sulfate pentahydrate (0.95 – 1.25 g) for each determination.
4.7	Sodium hydroxide solution, 30 g per 100 ml, ammonia free.
4.8	Sulfuric acid, 0.05 M solution.
4.9	Sodium or potassium hydroxide, 0.1 M solution.
4.10	Indicator solutions:
	4.10.1 Mixed indicator:
	Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.
	Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of solution B.
	This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).
4.10.2 Methyl red indicator:
	Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water. Filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.
4.11	Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.
4.12	Potassium thiocyanate.

APPARATUS

5

5.1

Distillation apparatus. See Method 2.

5.2

500 ml graduated flask (e.g. Stohmann).

5.3

Rotary shaker, 35 – 40 turns per minute.

PREPARATION OF THE SAMPLE

6

See Method 1.

PROCEDURE

7

Preparation of the solution for analysis

7.1

Weigh, to the nearest 0.001 g, 2.5 g of the prepared sample into a small glass mortar. Grind the sample three times with water, pouring off the water after each grinding into the 500 ml graduated flask (5.2). Transfer the sample quantitatively into the flask, washing the mortar, pestle and funnel with water. Make up with water to approximately 400 ml. Add 15 ml acetic acid (4.1). Shake on the rotary shaker (5.3) for two hours.

Determination

7.2

Transfer 50.0 ml of the filtrate to a 250 ml beaker. Add ammonia solution (4.2) until slightly alkaline and add 30 ml warm ammoniacal silver nitrate (4.3) to precipitate the yellow silver complex of cyanamide. Leave overnight, filter and wash the precipitate with cold water until completely free of ammonia.

Blank test

7.3

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

Control test

7.4

Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, with an aliquot portion of a standard solution of potassium thiocyanate (4.12), corresponding to 0.05 g of nitrogen.

EXPRESSION OF RESULT

8

Express the result as the percentage of cyanamide nitrogen contained in the fertiliser as received for analysis.

7. — DETERMINATION OF BIURET IN UREA

SCOPE

1

This method is for the determination of biuret in urea.

FIELD OF APPLICATION

2

The method is applied exclusively to urea.

PRINCIPLE

3

In an alkaline medium, in the presence of potassium sodium tartrate, biuret and bivalent copper form a violet cupric compound, the absorbance of which is measured at 546 nm.

REAGENTS

4

4.1	Methanol.
4.2	Sulfuric acid solution, approximately 0.05 M.
4.3	Sodium hydroxide solution, approximately 0.1 M.
4.4	Alkaline solution of potassium sodium tartrate:
In a 1 litre graduated flask dissolve 40 g of sodium hydroxide in 500 ml of water and leave to cool. Add 50 g of potassium sodium tartrate (KNaC4H4O6.4H2O). Make up to the mark and mix. Leave standing 24 hours before use.	In a 1 litre graduated flask dissolve 40 g of sodium hydroxide in 500 ml of water and leave to cool. Add 50 g of potassium sodium tartrate (KNaC4H4O6.4H2O). Make up to the mark and mix. Leave standing 24 hours before use.
4.5	Copper sulfate solution:
In a 1 litre graduated flask dissolve 15 g of copper sulfate (CuSO4.5H2O) in 500 ml of water. Make up to the mark and mix.	In a 1 litre graduated flask dissolve 15 g of copper sulfate (CuSO4.5H2O) in 500 ml of water. Make up to the mark and mix.
4.6	Biuret standard solution:
In a 250 ml graduated flask, dissolve 0.250 g of pure biuret[^f00008] in water. Make up to the mark and mix. 1 ml of this solution contains 0.001 g of biuret. This solution should be freshly prepared.	In a 250 ml graduated flask, dissolve 0.250 g of pure biuret[^f00008] in water. Make up to the mark and mix. 1 ml of this solution contains 0.001 g of biuret. This solution should be freshly prepared.
4.7	Methyl red indicator solution:
Dissolve 0.1 g methyl red in 50 ml 95% ethanol and make up to 100 ml with water. Filter if necessary.	Dissolve 0.1 g methyl red in 50 ml 95% ethanol and make up to 100 ml with water. Filter if necessary.

APPARATUS

5

5.1

Spectrophotometer.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Preparation of the standard curve

7.1

Transfer 2, 5, 10, 20, 25 and 50 ml aliquot portions of biuret standard solution (4.6) into a series of six 100 ml graduated flasks. Make up the volumes to about 50 ml with water, add one drop of indicator solution (4.7) and neutralise, if necessary, with 0.05 M sulfuric acid (4.2). Add the swirling 20.0 ml of the alkaline tartrate solution (4.4) and then 20.0 ml copper sulfate solution (4.5). Make up to the mark with water, mix and allow to stand at 30+ 2 C for fifteen minutes.

Preparation of solution for analysis

7.2

Weigh to the nearest 0.001g, 10 g of the prepared sample; dissolve in about 150 ml of water in a 250 ml graduated flask and make up to the mark and mix. Filter if necessary.

• (Note 1) If the sample for analysis contains more than 0.015 g of ammoniacal nitrogen, dissolve in 50 ml methanol (4.1) in a 250 ml beaker. Reduce by evaporation to a volume of about 25 ml. Transfer quantitatively to a graduated 250 ml flask. Make up to the mark with water. Filter, if necessary, through a dry fluted paper into a dry receiver.

• (Note 2) Elimination of the opalescence: if any colloidal substance is present difficulties may arise during filtration. In that case the solution for analysis is prepared as follows: dissolve the sample in 150 ml of water, add 2 ml 1 M hydrochloric acid, and filter the solution into a 250 ml graduated flask. Wash the filters with water and make up to volume. Continue the process according to the method described in 7.3.

Determination

7.3

According to the presumed biuret content, transfer with a pipette 25 or 50 ml from the solution prepared in 7.2, to a 100 ml graduated flask and neutralise if necessary with 0.05 M sulfuric acid or sodium hydroxide solution (4.2 or 4.3) as required, using methyl red indicator (4.7). Add 20.0 ml of the alkaline solution of potassium sodium tartrate (4.4) and 20.0 ml of the copper solution (4.5). Make up to volume, mix thoroughly and leave standing for 15 minutes at 30 C+2. Measure the absorbance of the solution as described in 7.1.

EXPRESSION OF RESULTS

8

$$%biuret=C×2.5V$ where: C = mass, in mg, of biuret read from the standard curve; V = volume of the aliquot used for the determination.$

8a. — DETERMINATION OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE PRESENCE OF CYANAMIDE NITROGEN

SCOPE

1

This method is for the determination of any one form of nitrogen in the presence of any other form.

FIELD OF APPLICATION

2

Any fertiliser in Group 1(a) of Section A, and Groups 1, 2 and 3 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991 containing nitrogen in various forms.

PRINCIPLE

3

Total soluble and insoluble nitrogen

3.1

• (3.1.1) In the absence of nitrates, the sample is subjected to direct Kjeldahl digestion.

• (3.1.2) In the presence of nitrates, the sample is subjected to Kjeldahl digestion after reduction with the aid of metallic iron and stannous chloride. In both cases, the ammonia is determined according to Method 2.

• (Note) If analysis shows an insoluble nitrogen content of more than 0.5%, it is presumed that the fertiliser contains other forms of insoluble nitrogen not specified for fertilisers covered by the list in paragraph 2.

Forms of soluble nitrogen

3.2

The following are determined from different aliquot parts taken from the same solution of the sample:

• (3.2.1) Total soluble nitrogen

• (3.2.1.1) In the absence of nitrates, by direct Kjeldahl digestion.

• (3.2.1.2) In the presence of nitrates, by Kjeldahl digestion on an aliquot portion taken from the solution after reduction according to Ulsch, the ammonia being determined in both cases as described in Method 2.

• (3.2.2) Total soluble nitrogen with the exception of nitric nitrogen, by Kjeldahl digestion after elimination in an acid medium of nitric nitrogen with ferrous sulfate, the ammonia being determined as described in Method 2.

• (3.2.3) Nitric nitrogen by difference

• (3.2.3.1) In the absence of calcium cyanamide, between (3.2.1.2) and (3.2.2) or between total soluble nitrogen (3.2.1.2) and the sum of ammoniacal nitrogen and ureic nitrogen (3.2.4+3.2.5).

• (3.2.3.2) In the presence of calcium cyanamide, between (3.2.1.2) and (3.2.2) and between (3.2.1.2) and the sum of (3.2.4+3.2.5+3.2.6).

• (3.2.4) Ammoniacal nitrogen

• (3.2.4.1) Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen, by applying Method 2.

• (3.2.4.2) In the presence of ureic nitrogen and/or cyanamide nitrogen, by cold distillation after making slightly alkaline, the ammonia being absorbed in a standard solution of sulfuric acid and determined as described in Method 2.

• (3.2.5) Ureic nitrogen

Either

• (3.2.5.1) By conversion using urease into ammonia which is titrated with a standard solution of hydrochloric acid,

or:

• (3.2.5.2) By gravimetry with xanthydrol, although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.

or:

• (3.2.5.3) By difference, according to the following table:

Case	Nitric Nitrogen	Ammoniacal Nitrogen	Cyanamide Nitrogen	Difference
1	Absent	Present	Present	(3.2.1.1)-(3.2.4.2+3.2.6)
2	Present	Present	Present	(3.2.2)-(3.2.4.2+3.2.6)
3	Absent	Present	Absent	(3.2.1.1)-(3.2.4.2)
4	Present	Present	Absent	(3.2.2)-(3.2.4.2)

• (3.2.6) Cyanamide nitrogen, by precipitation as a silver compound, the nitrogen being estimated in the precipitate by the Kjeldahl method.

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 of nitric nitrogen).

4.3

Potassium thiocyanate.

4.4

Potassium nitrate.

4.5

Ammonium sulfate.

4.6

Urea.

4.7

Sulfuric acid solution: dilute an appropriate volume of sulfuric acid (p=1.84 g/ml) with an equal volume of water.

4.8

Sulfuric acid, 0.1 M solution.

4.9

Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.10

Sodium or potassium hydroxide, 0.2 M solution, free from carbonates.

4.11

Stannous chloride solution:

4.12

Sulfuric acid, concentrated (p=1.84 g/ml).

4.13

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

4.14

Glacial acetic acids.

4.15

Sulfuric acid solution, approximately 30% (W/V) H2SO4.

4.16

Ferrous sulfate, crystalline, FeSO4.7H2O

4.17

Sulfuric acid, 0.05 M solution.

4.18

Octan-1-ol.

4.19

Potassium carbonate, saturated solution.

4.20

Sodium or potassium hydroxide, 0.1 M solution, free from carbonate.

4.21

Barium hydroxide, saturated solution.

4.22

Sodium carbonate solution, 10 g per 100 ml.

4.23

Hydrochloric acid, 2 M solution.

4.24

Hydrochloric acid, 0.1 M solution.

4.25

Urease solution: Suspend 0.5 g of active urease in 100 ml of distilled water. Using 0.1 M hydrochloric acid (4.24), adjust the pH to 5.4, measured by pH meter.

4.26

Xanthydrol solution, 5 g per 100 ml in ethanol or methanol (4.31) (do not use products giving a high proportion of insoluble matter). The solution may be kept for three months in a well-stoppered bottle, away from the light.

4.27

Copper oxide (CuO): 0.3 to 0.4 g per determination or an equivalent quantity of copper sulfate pentahydrate (0.95 to 1.25 g) per determination.

4.28

Anti-bump granules washed in hydrochloric acid and ignited.

4.29

Indicator solutions:

• (4.29.1) Mixed indicator solution: Solution A: dissolve 1 g of methyl red in 37 ml of 0.1 M sodium hydroxide solution and make up to one litre with water. Solution B: dissolve 1 g of methylene blue in water and make up to one litre. Mix one volume of solution A and 2 volumes of solution B. This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.

• (4.29.2) Methyl red indicator solution: Dissolve 0.1 g of methyl red in 50 ml of 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator (4 to 5 drops) can be used instead of the previous one.

4.30

Indicator papers: Litmus, bromothymol blue (or other papers sensitive in the range pH 6 to 8).

4.31

Ethanol or methanol: solution 95%.

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.

5.3

Apparatus for the estimation of urea nitrogen (7.2.6.1).

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 THE SAMPLE

6

See Method 1.

PROCEDURE

7

Total soluble and insoluble nitrogen

7.1

• (7.1.1) In the absence of nitrate

• (7.1.1.1) Digestion

Weigh to the nearest 0.001 g, a quantity of the prepared sample containing not more than 100 mg of nitrogen. Place in the flask of the distillation apparatus (5.1). Add 10 to 15 g of potassium sulfate (4.1), the prescribed quantity of catalyst (4.27), and a few anti-bump granules (4.28). Then add 50 ml of dilute sulfuric acid (4.7), and mix thoroughly. First heat gently, mixing from time to time, until foaming ceases. Then heat so that the liquid boils steadily and keep it boiling for one hour after the solution has become clear, preventing any organic matter from sticking to the sides of the flask. Allow to cool. Carefully add about 350 ml of water, with mixing. Ensure that the dissolution is as complete as possible. Allow to cool and connect the flask to the distillation apparatus (5.1).

• (7.1.1.2) Distillation of ammonia

Transfer with a pipette 50 ml of standard 0.1 M sulfuric acid (4.8) into the receiver of the apparatus. Add the indicator (4.29.1 or 4.29.2). Ensure that the tip of the condenser is at least 1 cm below the level of the solution.

Taking the necessary precautions to avoid any loss of ammonia, carefully add to the distillation flask enough of the concentrated sodium hydroxide solution (4.9) to make the liquid strongly alkaline (120 ml is generally sufficient: check by adding a few drops of phenolphthalein. At the end of the distillation the solution in the flask must still be clearly alkaline). Adjust the heating of the flask so as to distil 150 ml in half an hour. Test with indicator paper (4.30) that the distillation has been completed. If it has not, distil a further 50 ml and repeat the test until the supplementary distillate reacts neutrally to the indicator paper (4.30). Then lower the receiver, distil a few ml more and rinse the tip of the condenser. Titrate the excess acid with a standard solution of potassium or sodium hydroxide 0.2 M (4.10) to the end point of the indicator.

• (7.1.1.3) Blank test

Make a blank test under the same conditions (omitting only the sample) and use this value in the calculation of the final result.

• (7.1.14) Expression of the result

$$%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.$

• (7.1.2) In the presence of nitrate

• (7.1.2.1) Test sample

Weigh to the nearest 0.001g, a quantity of the sample containing not more than 40 mg of nitric nitrogen.

• (7.1.2.2) Reduction of the nitrate

Mix the sample in a small mortar with 50 ml of water. Transfer with the minimum amount of distilled water into a 500 ml Kjeldahl flask. Add 5 g of reduced iron (4.2) and 50 ml of stannous chloride solution (4.11). Shake and leave to stand for half an hour. During this time shake again after 10 and 20 minutes.

• (7.1.2.3) Kjeldahl digestion

Add 30 ml of sulfuric acid (4.12), 5 g of potassium sulfate (4.1), the prescribed quantity of catalyst (4.27) and some anti-bump granules (4.28). Heat gently with the flask slightly tilted. Increase the heat slowly and swirl the solution frequently to keep the mixture suspended; the liquid darkens and then clears with the formation of a yellow-green anhydrous iron sulfate suspension. After obtaining a clear solution simmer for one hour. Leave to cool. Cautiously take up the contents of the flask in a little water and add little by little 100 ml of water. Mix and transfer the contents of the flask into a 500 ml graduated flask. Rinse the flask several times with distilled water. Make up the volume with water and mix. Filter through a dry paper into a dry receiver. Discard the first portion of the filtrate.

• (7.1.2.4) Distillation of ammonia

Transfer into the flask of the distillation apparatus (5.1), an aliquot part containing not more than 100 mg of nitrogen. Dilute to about 350 ml with distilled water, add a few anti-bump granules (4.28), connect the flask to the distillation apparatus and continue the determination as described in paragraph 7.1.1.2.

• (7.1.2.5) Blank test

See 7.1.1.3.

• (7.1.2.6) Expression of the result

$$%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 a analysis.$

Forms of soluble nitrogen

7.2

• (7.2.1) Preparation of the solution to be analysed

Weigh to the nearest 0.001 g, 10 g of the sample and place it in a 500 ml graduated flask.

• (7.2.1.1) In the case of fertilisers not containing cyanamide nitrogen

Add to the flask 50 ml of water and then 20 ml of dilute hydrochloric acid (4.13). Shake and leave it to stand until the evolution of carbon dioxide ceases. Then add 400 ml of water and shake for half an hour on the rotary shaker (5.4).

Make up to the volume with water, mix and filter through a dry filter into a dry receiver. Discard the first portion of the filtrate.

• (7.2.1.2) In the case of fertilisers containing cyanamide nitrogen

Add to the flask 400 ml of water and a few drops of methyl red (4.29.2). If necessary make the solution acidic by using acetic acid (4.14). Add 15 ml of acetic acid (4.14). Shake on the rotary shaker (5.4) for 2 hours. If necessary, re-acidify the solution during the operation, using acetic acid (4.14). Make up to the volume with water, mix, filter immediately through a dry filter into a dry receiver and immediately determine the cyanamide nitrogen.

In both cases, determine the various soluble forms of nitrogen the same day the solution is made up, starting with cyanamide nitrogen and urea nitrogen, if they are present.

• (7.2.2) Total soluble nitrogen

• (7.2.2.1) In the absence of nitrate

Transfer by pipette into a 300 ml Kjeldahl flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2), containing not more than 100 mg of nitrogen. Add 15 ml of concentrated sulfuric acid (4.12), 0.4 g of copper oxide or 1.25 g of copper sulfate (4.27) and a few anti-bump granules (4.28). First heat gently to begin the digestion and then at a higher temperature until the liquid becomes colourless or slightly greenish and white fumes are clearly apparent. After cooling, quantitatively transfer the solution into the distillation flask, dilute to about 500 ml with water and add a few anti-bump granules (4.28). Connect the flask to the distillation apparatus (5.1) and continue the distillation as described in paragraph 7.1.1.2.

• (7.2.2.2) In the presence of nitrate

Transfer by pipette into a 500 ml Erlenmeyer flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 40 mg of nitric nitrogen. At this stage of the analysis the total quantity of nitrogen is not important. Add 100 ml of 30% sulfuric acid (4.15), 5 g of reduced iron (4.2) and immediately cover the Erlenmeyer flask with a watch glass. Heat gently until the reaction is steady but not vigorous. At this juncture stop the heating and allow the flask to stand for at least three hours at ambient temperature. With water, quantitatively transfer the liquid into a 250 ml graduated flask, leaving behind the undissolved iron and make up to the mark with water. Mix thoroughly, and transfer by pipette into a 300 ml Kjeldahl flask, an aliquot part containing not more than 100 mg of nitrogen. Add 15 ml of concentrated sulfuric acid (4.12), 0.4 g of copper oxide or 1.25 g of copper sulfate (4.27) and some anti-bump granules (4.28). First heat gently to begin the digestion and then at a higher temperature until the liquid becomes colourless or slightly greenish and white fumes are clearly apparent. After cooling transfer the solution quantitatively into the distillation flask, dilute to approximately 500 ml with water and add some anti-bump granules (4.28). Connect the flask to the distillation apparatus (5.1) and continue the determination as described in paragraph 7.1.1.2.

• (7.2.2.3) Blank test

See 7.1.1.3.

• (7.2.2.4) Expression of result

$$%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.$

• (7.2.3) Total soluble nitrogen with the exception of nitric nitrogen

Transfer by pipette into a 300 ml Kjeldahl flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 50 mg of nitrogen. Dilute to 100 ml with water, add 5 g of ferrous sulfate (4.16), 20 ml of concentrated sulfuric acid (4.1) and some anti-bump granules (4.28). First heat gently and then increase the heat until white fumes appear. Continue the digestion for 15 minutes. Stop the heating, introduce the copper oxide (4.27) as a catalyst and keep it at a temperature such that white fumes are emitted for a further 10 to 15 minutes. After cooling, quantitatively transfer the contents of the Kjeldahl flask into the distillation flask of the apparatus (5.1). Dilute to approximately 500 ml with water and add a few anti-bump granules (4.28). Connect the flask to the distillation apparatus and continue the determination as described in paragraph 7.1.1.2.

• (7.2.3.1) Blank test

See 7.1.1.3

• (7.2.3.2) Expression of result

$$%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 cyanamide

By the difference between the results obtained in paragraphs 7.2.2.4 and 7.2.3.2 and between the result obtained in paragraph 7.2.2.4 and the sum of the results obtained in paragraphs 7.2.5.5 and 7.2.6.3 or 7.2.6.5 or 7.2.6.6 and 7.2.7.

• (7.2.5) Ammoniacal nitrogen

• (7.2.5.1) Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen

Transfer by pipette into the flask of the distillation apparatus (5.1) an aliquot portion of the filtrate (7.2.1.1) containing not more than 100 mg of ammoniacal nitrogen. Add water to obtain a total volume of about 350 ml and some anti-bump granules (4.28) to facilitate boiling. Connect the flask to the distillation apparatus, add 20 ml of sodium hydroxide solution (4.9) and distil as described in paragraph 7.1.1.2.

• (7.2.5.2) Expression of result

$$%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 nitrogen

Transfer by pipette into the dry flask of the apparatus (5.2), an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 20 mg of ammoniacal nitrogen. Then assemble the apparatus. Transfer by pipette into the 300 ml Erlenmeyer flask 50 ml of the standard sulfuric acid solution 0.1 M (4.17) and enough distilled water for the level of the liquid to be approximately 5 cm above the opening of the delivery tube; add the indicator (4.29.1). Introduce, through the side neck of the reaction flask, distilled water to make up the volume to about 50 ml and mix. To avoid foaming during aeration, add a few drops of octan-1-ol (4.18). Make the solution alkaline by adding 50 ml of saturated potassium carbonate solution (4.19) and immediately begin to expel the ammonia thus liberated from the cold suspension. A strong current of air is necessary (flow of approximately 3 litres per minute) and should be purified beforehand by passing it through washing flasks containing dilute sulfuric acid and dilute sodium hydroxide. Instead of using pressurised air, it is also possible to use a vacuum (water pump) provided that the inflow tube is connected in a sufficiently airtight manner to the receiver used to collect the ammonia. The liberation of the ammonia is generally complete after three hours. It is nevertheless advisable to verify this by changing the receiving flask. When the operation is finished, disconnect the flask from the apparatus, rinse the tip of the tube and the sides of the flask with a little distilled water. Titrate the excess acid with standard sodium hydroxide solution (0.1 M) (4.20) to the end point of the indicator (4.29.1).

• (7.2.5.4) Blank test

See 7.1.1.3.

• (7.2.5.5) Expression of result

$$%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.$

• (7.2.6) Ureic nitrogen

• (7.2.6.1) Urease method

Transfer by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 250 mg of ureic nitrogen. To remove phosphates add saturated barium hydroxide solution (4.21) until no further precipitation occurs. Eliminate the excess of barium ions and any dissolved calcium ions by adding 10% sodium carbonate solution (4.22). Allow the precipitate to settle and check whether total precipitation has occurred. Make up to the mark, mix and filter through a pleated filter. Transfer by pipette 50 ml of the filtrate into the 300 ml Erlenmeyer flask of the apparatus (5.3). Acidify the filtrate with 2 M hydrochloric acid (4.23), until a pH of 3.0 measured by the pH meter (5.5) is obtained. Then raise the pH to 5.4 with 0.1 M sodium hydroxide solution (4.20).

To avoid losses of ammonia during reaction with urease, close the Erlenmeyer flask with a stopper provided with a separating funnel and a small bubble trap containing exactly 2 ml of standard 0.1 M hydrochloric acid (4.24). Introduce through the separating funnel 20 ml of urease solution (4.25), and allow to stand for one hour at 20 – 25 C. Transfer by pipette 25 ml of standard 0.1 M hydrochloric acid (4.24) into the separating funnel, allow it to run through into the solution and then rinse with a little water. In the same way transfer quantitatively the contents of the bubble trap into the solution contained in the Erlenmeyer flask. Titrate the excess acid with the standard solution of sodium hydroxide (0.1 M) (4.20), until a pH of 5.4 is obtained, measured by the pH meter.

• (7.2.6.2) Blank test

See 7.1.1.3.

• (7.2.6.3) Expression of result

$$%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 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: —

Case	Nitric Nitrogen	Ammoniacal Nitrogen	Cyanamide Nitrogen	Ureic Nitrogen
1	Absent	Present	Present	(7.2.2.4) – (7.2.5.5+7.2.7)
2	Present	Present	Present	(7.2.3.2) – (7.2.5.5+7.2.7)
3	Absent	Present	Absent	(7.2.2.4) – (7.2.5.5)
4	Present	Present	Absent	(7.2.3.2) – (7.2.5.5)

• (7.2.7) Cyanamide Nitrogen

Take an aliquot part of the filtrate (7.2.1.2), containing 10 to 30 mg of cyanamide nitrogen and place it in a 250 ml beaker. Continue the analysis according to Method 6.

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 of the Fertilisers Regulations 1991 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 (p=1.84 g/ml).

4.10

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

4.11

Glacial acetic acid.

4.12

Sulfuric acid solution, approximately 30% (W/V) H2SO4.

4.13

Ferrous sulfate, crystalline FeSO4.7H2O.

4.14

Sulfuric acid, 0.05 M solution.

4.15

Octan-1-ol.

4.16

Potassium carbonate, saturated solution.

4.17

Sodium or potassium hydroxide, 0.1 M solution.

4.18

Barium hydroxide, saturated solution.

4.19

Sodium carbonate solution, 10 g per 100 ml.

4.20

Hydrochloric acid, 2 M solution.

4.21

Hydrochloric acid, 0.1 M solution.

4.22

Urease solution: suspend 0.5 g active urease in 100 ml distilled water. Using 0.1 M hydrochloric acid (4.21), adjust to pH 5.4, measured with pH meter.

4.23

Xanthydrol solution, 5 g per 100 ml in ethanol or methanol (4.28) (do not use products giving a high proportion of insoluble material). The solution can be kept for 3 months in a carefully stoppered bottle in the dark.

4.24

Catalyst: copper oxide (CuO), 0.3 to 0.4 g per determination, or an equivalent amount of copper sulfate pentahydrate, (0.95 to 1.25 g).

4.25

Anti-bump granules of pumice stone washed with hydrochloric acid and ignited.

4.26

Indicator solutions:

• (4.26.1) Mixed indicator: Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water. Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of solution A and 2 volumes of solution B. This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution; use 0.5 ml (10 drops) of this indicator.

• (4.26.2) Methyl red indicator solution: Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary; 4 – 5 drops of this indicator can be used instead of the previous one.

4.27

Indicator papers: litmus, bromothymol blue (or other papers sensitive in the range pH 6 – 8).

4.28

Ethanol or methanol, 95% (V/V).

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

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

• (7.2.1) In the absence of nitrates

Transfer by pipette into a 300 ml Kjeldahl flask an aliquot portion of the filtrate (7.1) containing a maximum of 100 mg nitrogen. Add 15 ml concentrated sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few glass beads to control boiling. Heat moderately at first in order to initiate the reaction, then more strongly until the liquid becomes colourless or slightly greenish and white fumes appear. After cooling, transfer the solution into the distillation flask, dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1) and carry out the determination as described in Method 8a, 7.1.1.2.

• (7.2.2) In the presence of nitrates

Transfer by pipette into a 500 ml Erlenmeyer flask a aliquot portion of the filtrate (7.1) containing not more than 40 mg nitric nitrogen. At this stage of the analysis, the total quantity of nitrogen is unimportant. Add 10 ml of 30% sulfuric acid (4.12), 5 g reduced iron (4.2) and immediately cover the Erlenmeyer flask with a watch glass. Heat gently until the reaction becomes strong but not violent. Stop heating and allow to stand for at least 3 hours at ambient temperature. Transfer the liquid quantitatively to a 250 ml graduated flask, ignoring undissolved iron. Make up to the mark with water and mix carefully. Transfer by pipette a portion containing a maximum of 100 mg nitrogen into a 300 ml Kjeldahl flask. Add 15 ml concentrated sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few glass beads.

Heat moderately at first in order to initiate the reaction, then more strongly until the liquid becomes colourless or slightly greenish and white fumes appear. After cooling, transfer the solution quantitatively to the distillation flask, dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1) and continue the determination as described in Method 8a, 7.1.1.2.

• (7.2.3) Blank test

Carry out a blank test under the same conditions (omitting only the sample), and use this value in the calculation of the final result.

• (7.2.4) Expression of result

$$%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 (425). Heat moderately at first then more strongly until white fumes appear. Continue the reaction for 15 minutes. Stop heating, introduce 0.4 g copper oxide or 1.25 g copper sulfate (4.24) as catalyst, resume heating and maintain production of white fumes for 10 – 15 minutes. After cooling, transfer the contents of the Kjeldahl flask quantitatively to the distillation flask (5.1). Dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus and continue the determinations as in Method 8a, 7.1.1.2.

• (7.3.2) Blank test

See 7.2.3.

• (7.3.3) Expression of result

$$%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.$

Nitric nitrogen is obtained: by difference between

7.4

• (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

• (7.5.1) In the presence of ureic nitrogen

Transfer by pipette into the dry flask of the apparatus (5.2) an aliquot portion of the filtrate (7.1) containing a maximum of 20 mg ammoniacal nitrogen. Connect up the apparatus. Place in the 300 ml Erlenmeyer flask 50.0 ml standard 0.05 M sulfuric acid solution (4.14) and an amount of distilled water such that the level of the liquid is about 5 cm above the opening of the intake tube. Introduce through the side neck of the reaction flask distilled water so as to bring the volume to about 50 ml and mix. To avoid foaming during aeration add several drops of octan-1-ol (4.15). Add 50 ml saturated potassium carbonate solution (4.16) and immediately begin to expel the ammonia thus released from the cold suspension. A strong current of air is necessary (flow rate of about 3 litres per minute) and should be purified beforehand by passing it through washing flasks containing dilute sulfuric acid and dilute sodium hydroxide. Instead of using air under pressure, a vacuum may be used (water pump) provided that the connections between the apparatus are air tight. The liberation of ammonia is generally complete after three hours. However, it is desirable to make certain of this by changing the Erlenmeyer flask. When the process is finished, disconnect the Erlenmeyer flask from the apparatus, rinse the end of the intake tube and the walls of the Erlenmeyer flask with a little distilled water and titrate the excess acid against standard 0.1 M sodium hydroxide solution (4.17).

• (7.5.2) Blank test

See 7.2.3.

• (7.5.3) Expression of result

$$%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

• (7.6.1) Urease method

Transfer by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate (7.1) containing not more than 250 mg of ureic nitrogen. To remove phosphates, add a suitable quantity of saturated barium hydroxide solution (4.18) until further addition does not cause the production of more precipitate. Eliminate excess barium ions (and any dissolved calcium ions) with 10% sodium carbonate solution (4.19). Allow to settle and check whether precipitation is complete. Make up to the mark, mix and filter through a fluted filter paper. Transfer by pipette 50 ml of filtrate into the 300 ml Erlenmeyer flask of the apparatus (5.3). Acidify with 2 M hydrochloric acid (4.20) to pH 3.0, measured by means of the pH meter (5.5). Raise the pH to 5.4 by the addition of 0.1 M sodium hydroxide (4.17). To avoid ammonia losses when hydrolysis by urease occurs, close the Erlenmeyer flask by means of a stopper provided with a dropping funnel and a small bubble trap containing exactly 2 ml standard 0.1 M hydrochloric acid solution (4.21). Introduce through the separating funnel, 20 ml urease solution (4.22). Allow to stand for one hour at 20 – 25 C. Place 25.0 ml of the standard 0.1 M hydrochloric acid solution (4.20) in the dropping funnel, allow to run into the solution, then rinse with a little water. Transfer quantitatively the contents of the bubble trap to the solution contained in the Erlenmeyer flask. Titrate the excess acid using standard 0.1 M sodium hydroxide solution (4.17), until a pH of 5.4 is obtained, measured on the pH meter.

• Remarks 1.After precipitation by barium hydroxide and sodium carbonate solutions, make up to the mark, filter and neutralise as quickly as possible.2.The titration may also be carried out using an indicator (4.26), although the change of colour is more difficult to observe.

• (7.6.2) Blank test

See 7.2.3.

• (7.6.3) Expression of result

$$%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.$

• (7.6.4) Gravimetric method using xanthydrol

Transfer by pipette into a 100 ml beaker an aliquot portion of the filtrate (7.1) containing not more than 20 mg urea. Add 40 ml acetic acid (4.11). Stir with a glass rod for one minute. Allow any precipitate to settle for five minutes. Filter, wash with a few ml acetic acid (4.11). Add 10 ml xanthydrol solution (4.23) to the filtrate drop by drop, stirring continuously with a glass rod. Allow to stand until the precipitate appears, then stir again for one or two minutes. Allow to stand for one and a half hours. Filter, using a slight reduction in pressure, through a sintered glass crucible (5.6) which has been previously dried and weighed. Wash three times with 5 ml ethanol (4.28), without trying to remove all the acetic acid. Place in an oven at a temperature of 130°C for one hour (do not exceed 145 C). Allow to cool in a desiccator and weigh.

• (7.6.5) Expression of result

$$%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.

• Note: Although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.

• (7.6.6) Difference method

Ureic N can also be calculated as indicated in the following table:

Case	Nitric N	Ammoniacal N	Ureic N
1	Absent	Present	(7.2.4) – (7.5.3)
2	Present	Present	(7.3.3) – (7.5.3)

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 6(3), applicable only to the phosphatic fertilisers listed in Group 2(a) of Section A and Groups 1, 2 and 4 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991, and to phosphatic fertilisers listed in Groups 1 (a), 1 (b) and 2 of Section C of that table which are not designated as “EEC fertiliser”.

PRINCIPLE

3

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

REAGENTS

4

4.1

Sulfuric acid (p=1.84 g/ml).

4.2

Nitric acid (p=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 THE SAMPLE

6

PROCEDURE

7

Extraction

7.1

Weigh to the nearest 0.001g 2.5 g of the prepared sample and place it in a dry Kjeldahl flask. Add 15 ml water and swirl to suspend the substance. Add 20 ml nitric acid (4.2) and carefully add 30 ml sulfuric acid (4.1). When the initial violent reaction has ceased, slowly bring the contents of the flask to boiling and boil for 30 minutes. Allow to cool and then carefully add with mixing about 150 ml water and boil for 15 minutes.

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 PHOSPHORUS BY 2% FORMIC ACID

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% p = 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 THE SAMPLE

6

PROCEDURE

7

7.1

Extraction

7.2

Determination

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

SCOPE

1

FIELD OF APPLICATION

2

PRINCIPLE

3

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 0.1M 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 THE 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.

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

FIELD OF APPLICATION

2

PRINCIPLE

3

REAGENTS

4

4.1

Neutral ammonium citrate solution (pH=7.0).

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 THE SAMPLE

6

PROCEDURE

7

Extraction

7.1

Transfer 1[^f00009] or 3[^f00010] 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.[^f00011] The level of suspension in the flask must stay constantly below that of the water in the bath. After exactly one hour remove the Erlenmeyer flask from the water-bath. Cool immediately under running water to ambient temperature and transfer the contents quantitatively from the Erlenmeyer flask into a graduated 500 ml flask with a jet of water. Make up the volume with water. Mix thoroughly and filter through a dry fluted filter (medium speed) into a dry container, discarding the first part of the filtrate (about 50 ml).

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

FIELD OF APPLICATION

2

PRINCIPLE

3

REAGENTS

4

Petermann’s solution

4.1

Characteristics:

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

PROCEDURE

7

7.1

Extraction

7.2

Determination

9f. — EXTRACTION OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (PETERMANN'S) METHOD AT AMBIENT TEMPERATURE

SCOPE

1

FIELD OF APPLICATION

2

PRINCIPLE

3

REAGENT

4

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 THE SAMPLE

6

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.

Determination

7.2

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

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

SCOPE

1

FIELD OF APPLICATION

2

PRINCIPLE

3

REAGENTS

4

4.1

Joulie’s alkaline solution of ammonium citrate:

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 THE SAMPLE

6

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 ten drops of ammonium citrate solution (4.1) to moisten it and then break it up very carefully with a pestle. Add 20 ml ammonium citrate solution (4.1), mix to a paste and leave to settle for about 1 minute.

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/P205>0.03). If this is the case, add 3 g of oxine to the moistened sample for analysis. The use of oxine in the absence of magnesium is not, moreover, likely to interfere subsequently with the determination. In the known absence of magnesium, oxine may be omitted.

9h. — EXTRACTION OF PHOSPHORUS BY WATER

SCOPE

1

FIELD OF APPLICATION

2

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 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 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 (Gravimetric method using quinoline phosphomolybdate)

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[^f00012] 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 (p = 1.40 g/ml).

4.2

Molybdate reagent:

• (4.2.1) Preparation of the reagent based on sodium molybdate:

Solution A: dissolve 70 g sodium molybdate dihydrate in 100 ml water

Solution B: dissolve 60 g citric acid monohydrate in 100 ml water and 85 ml concentrated nitric acid (4.1).

Solution C: stir solution A into solution B to obtain solution C.

Solution D: to 50 ml water add 25 ml concentrated nitric acid (4.1), add 5 ml freshly distilled quinoline. Add this solution to solution C, mix thoroughly and leave standing overnight in the dark. Make up to 500 ml with water, mix again and filter through a sintered glass funnel (5.3).

• (4.2.2) Preparation of the reagent based on ammonium molybdate:

Solution A: dissolve 100 g ammonium molybdate in 300 ml water, heating gently and stirring from time to time.

Solution B: dissolve 120 g citric acid monohydrate in 200 ml water and add 170 ml of concentrated nitric acid (4.1).

Solution C: add 10 ml freshly distilled quinoline to 70 ml of concentrated nitric acid (4.1).

Solution D: slowly pour, stirring well, solution A into solution B. After thoroughly mixing, add solution C to this mixture and make up to 1 litre with water. Leave standing for two days in a dark place and filter through a sintered glass funnel (5.3).

The reagents 4.2.1 and 4.2.2 can be used in the same way; both must be kept in the dark in stoppered polyethylene bottles.

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[^f00013] (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)[^f00014] 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:

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 1991.

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% ethanol.

4.5

EDTA solution: 4 g of the dihydrated disodium salt of ethylenediaminetetra-acetic acid (EDTA) per 100 ml. Store this reagent in a plastic container.

4.6

STPB solution: dissolve 32.5 g sodium tetraphenylborate in 480 ml of water, add 2 ml sodium hydroxide solution (4.3) and 20 ml of a magnesium chloride solution (100 g of MgCl2.6H2O per litre). Stir for fifteen minutes and filter through a fine, ashless filter paper. Store this reagent in a plastic container.

4.7

Wash liquid: dilute 20 ml of the STPB solution (4.6) to 1 litre with water.

4.8

Bromine water: saturated bromine solution in water.

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

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 K20 and place in a 100 ml beaker, add bromine water and bring to the boil to eliminate any surplus bromine. After cooling transfer quantitatively to a 100 ml graduated flask, make up to the volume, filter and determine the potassium in an aliquot portion of the filtrate.

Determination

7.2

Transfer by pipette an aliquot portion of the filtrate containing 25-50 mg of potassium (see Table on page 50) into a 250 ml beaker; make up to 50 ml with water.

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 a least 10 minutes before filtering.

Filtering and washing

7.5

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 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:

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.

4.6

Potassium Chloride solution: Dissolve 2.103g of potassium chloride, previously dried at 130°C for one hour, in water and make up to 500ml.

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.