The Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991

PART II

General

1.—(a) When two or more methods are prescribed in this part of this Schedule to determine a component of a fertiliser the choice of the method shall, except where otherwide indicated, be left to the agricultural analyst concerned; the method used must however be indicated in the certificate of analysis.

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

Reagents and Apparatus

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

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

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

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

Methods of Analysis

1. Preparation of the sample for analysis

2. Determination of moisture

3. Determination of total nitrogen — chromium powder reduction method

4. Determination of urea

5.a Extraction of phosphorus — by mineral acids (total phosphorus)

b Extraction of phosphorus — by 2% citric acid

6. Determination of extracted phosphorus — spectrophotometric method

7.a Determination of potassium — gravimetric method

b Determination of potassium — flame photometric method

8. Determination of total magnesium

9.a Determination of boron — titrimetric method

b Determination of boron — spectrophotometric method

10. Determination of cobalt

11. Determination of molybdenum

12. Determination of copper

13. Determination of iron

14. Determination of manganese

15. Determination of the neutralising value in liming materials

16. Determination of fineness of products other than potassic basic slag

17. Determination of fineness of potassic basic stag

1. PREPARATION OF THE SAMPLE FOR ANALYSIS

1.    INTRODUCTION

The preparation of a sample for analysis from the final sample received at the laboratory is a series of operations, usually sieving, grinding and mixing, carried out in such a way that the smallest amount weighed, as prescribed by the method of analysis chosen, is representative of the final sample. The sample should be ground to the fineness required by the method of analysis. (Over-grinding must be avoided in cases where this will affect the solubility in various reagents). With some materials, fine grinding may lead to loss or gain of moisture and allowance for this must be made.

2.    SCOPE AND FIELD OF APPLICATION

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

This method is also applicable to fluid fertilisers.

The determination of the fineness of fertilisers is carried out on the sample as received.

3.    PRINCIPLE

Solid fertilisers: the whole final sample is ground to the required fineness. All the ground sample is thoroughly mixed before each test portion is taken.

Fluid fertilisers: the final sample is thoroughly mixed before each test portion is taken.

4.    APPARATUS

Sample grinder capable of grinding the fertiliser to pass the specified sieve.

Mortar and pestle of suitable material and size.

Sieves having square apertures of 0.18 mm, 0.5 mm and 1 .O mm. Test sieves conforming to British Standard 410 : 1976 are suitable.

Sample containers of non-corrodible materials, with air-tight closures.

5.    PROCEDURE

WARNING

All operations connected with this procedure should be carried out as quickly as possible to minimise absorption or loss of water.-Care should be taken during grinding that the temperature of the fertiliser does not rise above 45°C to avoid loss of volatile constituents. Grinding beyond the fineness required must in all cases be avoided.

Grinding and sieving

5.1  The procedure in 5.1.1 should be followed except when a grinding machine is not available, in which case 5.1.2 is applicable.

5.1.1 Grind the final sample until all the sample has passed through, or for the specified time, depending on the type of grinder (4.1). To check that the grinding has been adequate sieve a small portion of the ground sample through a 0.5 mm sieve (4.3) and discard it. If the whole of this portion does not pass the sieve, return the remainder of the sample to the grinder and repeat the grinding until satisfactory grinding is achieved.

5.1.2 Sieve the whole final sample through a 0.5 mm sieve (4.3). Grind the residue on the sieve, using the pestle and mortar (4.2), until all the material passes through the sieve. Carefully mix the sample.

5.2  Place the prepared sample in a clean container (4.4) and seal it until required for analysis

5.3  Before taking each test portion for analysis, the whole sample must be well mixed. Form the material into a flattened cone and using a spatula take the required test portion at random in small increments.

5.4  If the sample contains foreign matter which cannot be ground this shall be removed, weighed and allowed for in the results of the analysis. This material shall be retained and if possible its nature recorded.

6.    SPECIAL CASES

Samples not to be ground

6.1  For those samples where the amount of phosphorus pentoxide soluble in 2% citric acid and the fineness of grinding are to be determined, the sample should be well mixed (soft lumps may be disintegrated by lightly crushing) and divided into two parts, which are as identical as possible. The above mentioned determinations shall be carried out on the unground sample. All other determinations shall be carried out on the sample prepared in accordance with the directions in paragraph 5.1.

Products which may be difficult to grind mechanically, including products with abnormal moisture or products which become doughy through grinding

6.2  Some products such as superphosphate may become doughy if ground mechanically. In these cases crush the sample in a mortar (4.2) so that all the material passes through a 1 .O mm sieve (4.3). Place the material so crushed in a clean container (4.4) and seal it until required for analysis.

Organic materials

6.3  Some organic materials may be of such a nature that the procedures given above cannot be used (for example fresh guano, leather, wool and animal residues). In these cases the analyst should use the best practicable means to obtain a representative sample.

Fertilisers comprising several different materials

6.4  These fertilisers include materials with marked differences in texture or mechanical properties (hardness, density, etc). They may be difficult to grind entirely (for example mixtures of organic and inorganic materials) or they may segregate during handling (for example “Kalimagnesia”). Special procedures are necessary in these cases:—

6.4.1 For mixtures other than those in 6.4.2, follow the procedure in 5.1.1, replacing the 0.5 mm sieve by one with apertures of 0.18 mm. A grinding machine, capable of grinding the whole of the sample to the required fineness in one pass, is strongly recommended;

6.4.2 In the case of mixtures containing one or more very hard components, or mixtures containing organic materials, it may be difficult to grind and homogenise all the components. To avoid overgrinding some of the softer components proceed as follows:—

Grind the sample as in 5.1.1 or 5.1.2 to pass a 0.5 mm sieve. Re-sieve the sample through a 0.18 mm sieve and reduce the residue to a convenient size by further grinding or other practicable means. Thoroughly remix the sample and place in a clean container (4.4).

7.    FLUID FERTILISERS

Mix thoroughly by shaking, ensuring that any insoluble matter, particularly crystalline material, is thoroughly dispersed, immediately before drawing a portion of the sample for analysis.

2. DETERMINATION OF MOISTURE

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers where a correction for moisture is necessary.

2.    PRINCIPLE

The sample is dried to constant weight in an oven at 100°C. The loss in weight corresponds to the moisture content of the sample.

3.    APPARATUS

Suitable containers with lids ensuring air-tight closure; the dimensions should allow the sample to be spread at about 0.3 g per cm².

Electricially heated oven, suitably ventilated and capable of being maintained at 100 ± 2°C.

4.    PREPARATION OF SAMPLE

See Method 1.

5.    PROCEDURE

Weigh to the nearest 0.001 g, 5 g of the prepared sample and transfer to a previously weighed container (3.1). Place the uncovered container and the lid in the oven (3.2) for 2 to 3 hours. Replace the lid on the container, remove from the oven and allow to cool in a desiccator and weigh. Reheat for another hour, cool and reweigh. If the difference in weight exceeds 0.01 g continue the heating and cooling procedure until a weight constant within 0.01 g is attained.

6.    EXPRESSION OF THE RESULT

Calculate the total loss of weight and express it as a percentage of the original weight.

3. DETERMINATION OF TOTAL NITROGEN — CHROMIUM POWDER REDUCTION METHOD

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to fertilisers in Groups l(b), l(c), 3(b), 4(a) and 4(c) of Section A, Group 5 of Section B and Groups l(c) and I(d) of Section C of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990(2) in respect of which the indication of total nitrogen is required.

2.    PRINCIPLE

The nitrate is reduced to ammonia by chromium powder in an acid medium. Organic and ureic nitrogen is converted into ammonium sulphate by digestion with concentrated sulphuric acid using a catalyst. The ammonia is distilled from an alkaline solution and absorbed in a standard acid. The excess acid is titrated with standard alkali.

3.    REAGENTS

Sodium hydroxide solution: 40 g per 100 ml, ammonia free.

Sulphuric acid, 0.1 N solution.

Sulphuric acid, 0.2 N solution.

Sulphuric acid, 0.5 N solution.

Sodium hydroxide, 0.2 N solution, carbonate free.

Chromium metal powder, 100 mesh, low nitrogen content.

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

Anti-foaming agent, paraffin wax.

Sulphuric acid (d = 1.84 g/ml).

Hydrochloric acid (d = 1.18 g/ml).

Catalyst mixture: 1,000 g potassium sulphate and 50 g copper sulphate pentahydrate. The ingredients must be ground and thoroughly mixed.

Indicator solutions:

Mixed indicator:

3.12.1 mix 50 ml of 2 g/litre ethanolic solution of methyl red with 50 ml of 1g./litre ethanolic solution of methylene blue.

Methyl red indicator:

3.12.2 dissolve 0.1 g methyl red in 50 ml ethanol. This indicator may be used instead of the preceding one.

pH indicator paper, wide range.

4.    APPARATUS

Apparatus for mineral acid digestion and distillation according to Kjeldahl’s method.

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Reduction

6.1  Weigh, to the nearest 0.001 g, between 0.5 and

2.0  g of the prepared sample, containing not more than 0.06 g nitric nitrogen and 0.235 g total nitrogen, and transfer to a Kjeldahl flask. Add sufficient water to make the total volume 35ml. Allow the flask to stand for 10 minutes with occassional gentle swirling to ensure solution of all nitrate salts.

Add 1.2 g chromium powder (3.6) and 7 ml hydrochloric acid (3.10), mix well and allow the flask to stand for at least 5 minutes but not more than 10 minutes at ambient temperature. Heat the flask gently so that the contents just begin to boil in about 7 minutes. Continue boiling gently for 10 minutes, Remove the flask from the heat and allow to cool.

Hydrolysis, when the fertiliser is known not to contain organic matter

6.2  Place the flask (6.1) in a fume cupboard, add a small quantity of anti-bump granules (3.7) and then carefully add 25 ml sulphuric acid (3.9). Mix the contents of the flask and heat gently until boiling. Continue heating until dense white fumes of sulphuric acid are evolved for at least 15 minutes. Allow the mixture to cool and then carefully add 250 ml water. Allow to cool to room temperature and continue as described in 6.4.

Digestion, when the fertiliser is known to contain organic matter

6.3  Add a small quantity of anti-bump granules (3.7), 10 g of the catalyst mixture (3.11) and then carefully add 25 ml sulphuric acid (3.9) (see NOTE). Add 0.5g paraffin wax (3.8) to reduce foaming and mix. Heat the flask moderately at first, shaking from time to time until frothing ceases and the liquid is practically colourless. Continue the digestion for at least a further 60 minutes. Allow the mixture to cool and then carefully add 250 ml water. Allow to cool to room temperature, and continue as described in 6.4.

Note:

If organic matter other than urea exceeds 1 .O g add an additional 1.0 ml sulphuric acid for each 0.1 g organic matter in excess of 1.0 g.

Distillation

6.4  Transfer an appropriate volume of 0.1 N, or 0.2 N, or 0.5 N sulphuric acid (3.2,3.3,3.4) to the collecting flask of the distillation apparatus, according to the presumed level of nitrogen; add a few drops of indicator solution (3.12.1 or 3.12.2). Taking precautions against the loss of ammonia, carefully add to the contents of the Kjeldahl flask (6.2 or 6.3) 100 ml sodium hydroxide solution (3.1). Mix well and connect immediately to the distillation apparatus. Heat the flask so that approximately 150 ml of the liquid are distilled in 30 minutes. At the end of this time, lower the collecting flask so that the tip of the condenser is above the surface of the liquid. Test the subsequent distillate by means of the indicator paper (3.13) to ensure that all the ammonia is completely distilled. Remove the source of heat. Titrate the excess acid with 0.2 N sodium hydroxide solution (3.5) to the end point of the indicator.

Blank test

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

7.    EXPRESSION OF THE RESULTS

Determine the quantity of sulphuric acid consumed.

• 1 ml 0.1 N sulphuric acid = 0.0014 g nitrogen.

• 1 ml 0.2 N sulphuric acid = 0.0028 g nitrogen.

• 1 ml 0.5 N sulphuric acid = 0.0070 g nitrogen.

Express the result as the percentage of nitrogen (N) contained in the fertiliser as received for analysis.

4. DETERMINATION OF UREA

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to fertilisers in Group l(c) of Section A, Group 5 of Section B and Group l(d) of Section C of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990.

2.    PRINCIPLE

The sample is suspended in acid solution with a clarifying agent and filtered. The urea content of the filtrate is determined after the addition of 4-dimethylamino-benzaldehyde (4-DMAB) by measuring the absorbance at 435 nm.

3.    REAGENTS

Activated charcoal.

Carrez solution I:

dissolve 21.9 g zinc acetate dihydrate in water, add 3 ml glacial acetic acid and dilute to 100 ml with water.

Carrez solution II: 10.6 g potassium ferrocyanide per 100 ml.

Hydrochloric acid solution, 0.02 N.

Sodium acetate solution: 136 g sodium acetate trihydrate per litre.

4-dimethylamino-benzaldehyde solution:

dissolve 1.6 g of 4-dimethylamino-benzaldehyde (4-DMAB) in 100 ml 96% ethanol and add 10 ml of hydrochloric acid (d = 1.18 g/ml).

Urea standard solution: 1 .O g per 100 ml (1 ml of this solution = 10 mg urea).

4.    APPARATUS

Spectrophotometer with 10 mm cells.

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

6.1  Weigh to the nearest 0.001 g, 2 g of the prepared sample, or a suitable amount expected to contain between 50 and 500 mg of urea, and transfer it to a 500 ml graduated flask. Add 150 ml 0.02 N hydrochloric acid solution (3.4), shake for 30 minutes then add 10 ml sodium acetate solution (3.5) and mix well. Add 2 g activated charcoal (3.1) to the flask, shake well, and allow to stand for a further 15 minutes. Add 5 ml Carrez solution I (3.2), followed by 5 ml Carrez solution II (3.3), mixing well between additions. Dilute to volume with water and mix well. Filter a portion of the solution through a dry filter paper into a clean dry 2.50 ml beaker.

Determination

6.2  Transfer 10 ml of the filtrate (6.1) to a 50 ml graduated flask, add 10 ml 4-DMAB solution (3.6), dilute to 50 ml with water, mix well and allow to stand for 10 minutes. Measure the absorbance of the solution at 435 nm, in a 10 mm cell against a reference solution prepared by diluting 10 ml 4-DMAB solution (3.6) to 50 ml with water.

Calibration curve

6.3  Transfer amounts of standard urea solution (3.7) corresponding to 50, 100, 150 and 250 mg of urea into a series of 250 ml graduated flasks; add 75 ml 0.02 N hydrochloric acid solution (3.4) and proceed as described above (6.1) commencing at “ ... ... ... ... shake for 30 minutes ... ... ... ...”. Measure the absorbance of the solutions, and construct a calibration graph relating the absorbances to the amounts of urea present.

7.    EXPRESSION OF THE RESULTS

Determine the amount of urea in the sample by reference to the calibration graph. Express the result in terms of percentage ureic nitrogen of the sample:

5a. EXTRACTION OF PHOSPHORUS BY MINERAL ACIDS (TOTAL PHOSPHORUS)

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to fertilisers in Groups 2(b), 2(c), 2(d), 3(b) and 4(c) of Section A and Group 5 of Section B of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990(3) in respect of which the indication of total phosphorus is required.

2.    PRINCIPLE

The phosphorus is extracted from the fertiliser with a mixture of nitric acid and sulphuric acid.

3.    REAGENTS

Sulphuric acid (d = 1.84 g/ml).

Nitric acid (d = 1.42 g/ml).

4.    APPARATUS

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.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

Extraction

6.1  Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and place it in a dry Kjeldahl flask (4.1). Add 15 ml water and stir so as to suspend the substance. Add 20 ml nitric acid (3.2) and carefully add 30 ml sulphuric acid (3.1) (see NOTE). 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. 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

6.2  Determine the phosphorus according to Method 6a or Method 6b on an aliquot part of the clear filtrate.

Note

If the sample contains cellulosic matter, the following procedures 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 sulphuric acid (3.1) and carefully boil until most of the organic matter has been destroyed. Allow to cool, add 15 ml water and 20 ml nitric acid (3.2); bring to the boil and continue boiling for 30 minutes. Continue as described in 6.1 from “Allow to cool and then ... ... ... ...”.

5b. EXTRACTION OF PHOSPHORUS BY 2% CITRIC ACID

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to fertilisers in Groups 2(b), 3(b) and 4(b) of Section A of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990 in respect of which an indication of the phosphorus soluble in 2% citric acid is required.

2.    PRINCIPLE

The phosphorus is extracted from the fertiliser with a 2% citric acid solution (20 g per litre) in given conditions.

3.    REAGENT

2% citric acid solution (20 g per litre), prepared from citric acid monohydrate.

4.    APPARATUS

Rotary shaker: 35 — 40 turns per minute.

5.    PREPARATION OF THE SAMPLE

The analysis is carried out on the product as received after carefully mixing the original sample to ensure it is homogeneous.

See Method 1.

6.    PROCEDURE

Extraction

6.1  Weigh to the nearest 0.001 g, 5 g of the prepared sample, and place it in a dry flask with a sufficiently wide neck, with a capacity of 600 ml, allowing the liquid to be shaken thoroughly. Add 500 ml of the citric acid solution (3.1) at 20 ± 1°C. When adding the first few ml of the reagent, shake vigorously by hand to stop the formation of lumps and to prevent the substance sticking to the sides of the flask. Close the flask with a rubber stopper and shake it in the rotary shaker (4.1) 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 filtering until a sufficient quantity of filtrate is obtained to carry out the phosphorus determination.

Determination

6.2  Determine the phosphorus according to Method 6a or Method 6b on an aliquot part of the clear filtrate.

6. DETERMINATION OF EXTRACTED PHOSPHORUS — SPECTROPHOTOMETRIC METHOD

1.    SCOPE AND FIELD OF APPLICATION

This method is for the determination of the phosphorus extracted in Methods 5a and 5b.

2.    PRINCIPLE

An acidic solution of the extracted phosphorus is treated with molybdo-vanadate reagent and the absorbance of the yellow solution is measured at 430 nm.

3.    REAGENTS

Nitric acid (d =.42 g/ml).

Molybdovanadate reagent: dissolve separately 20 g ammonium molybdate and 0.47 g ammonium vanadate in water, mix, acidify with 140 ml nitric acid (3.1) and dilute to 1 litre with water.

Phosphorus standard solution: dissolve 4.387 g potassium dihydrogen phosphate, previously dried at 105°C for 1 hour, in water and dilute to 1 litre.

1 ml of this solution contains 1 mg phosphorus (P) or 2.29 mg phosphorus pentoxide (P₂O₅).

Sodium hydroxide, approximately 5 N solution.

5.    APPARATUS

Spectrophotometer with 10 mm cells.

5.    PROCEDURE

Determination

For Total Phosphorus

5.1—5.1.1 Dilute, if necessary, the prepared extract to obtain a phosphorus concentration of about 20 pg/ml. Transfer 10 ml of this solution to a glass stoppered test tube, add 10 ml freshly prepared molybdovanadate reagent (3.2) and mix. Allow to stand for 10 minutes at 20°C and then measure the absorbance of the solution at 430 nm against a freshly prepared reference solution made by adding 10 ml molybdovanadate reagent (3.2) to 10 ml water.

For Water Soluble Phosphorus and Citric Acid Soluble Phosphorus

5.1.2 Dilute, if necessary, the prepared extract to obtain a phosphorus concentration of about 80 μglml. Transfer 25 ml of this solution to a 100 ml conical flask, add 5 ml nitric acid (3.1) and boil gently for 30 minutes. Cool the solution and neutralise with sodium hydroxide solution (3.4). Cool the solution to 20°C, transfer quantitatively to a 100 ml graduated flask and make up to the mark with water. Transfer 10 ml of this solution to a glass stoppered test tube, add 10 ml freshly prepared molybdovanadate reagent (3.2) and mix. Proceed as described in 5.1.1 from “Allow to stand ... ... ... ...”.

Calibration

5.2  From the standard solution (3.3) prepare a series of solutions containing respectively 5, 10, 20, 30 and 40 pg/ml of phosphorus (P).

Transfer 10 ml of each solution into glass-stoppered test tubes, add 10 ml molybdovanadate reagent (3.2), mix and proceed as described in 5.1.1 from “Allow to stand ... ... ... ...”.

Construct a graph relating the absorbance to the amount of phosphorus present. The calibration curve should be prepared at the same time as the determination is carried out.

6.    EXPRESSION OF THE RESULTS

Determine the amount of phosphorus in the sample by reference to the calibration curve. Express the result in terms of percentage phosphorus (P) or percentage phosphorus pentoxide (P205) of the sample:

mg phosphorus (P) × 2.29 = mg phosphorus pentoxide (P₂O₅)

7a. DETERMINATION OF POTASSIUM — GRAVIMETRIC METHOD

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to fertilisers in Groups 3(b), 3(c), 3(d) and 4(c) of Section A and Group 5 of Section B of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990 in respect of which an indication of total potassium is required.

2.    PRINCIPLE

The sample is ashed and dissolved in dilute hydrochloric acid or, if it contains no organic substances, it is dissolved directly in dilute hydrochloric acid. After the removal of interfering substances the potassium is precipitated in a slightly alkaline medium in the form of potassium tetraphenylborate (KTPB).

3.    REAGENTS

Formaldehyde, 25 – 35% solution, filtered if necessary before use.

Potassium chloride.

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

Indicator solution: Dissolve 0.5 g phenolphthalein in 100 ml 90% ethanol.

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

STPB solution: dissolve 32.5 g sodium tetraphenylborate in 480 ml of water, add 2 ml of sodium hydroxide solution (3.3) and 20 ml of a magnesium chloride solution (100 g of MgC1₂.6H₂O per litre). Stir for fifteen minutes and filter through a fine, ashless filter. Store this reagent in a plastic container.

Liquid for washing: dilute 20 ml of the STPB solution (3.6) to 1 litre with water.

Hydrochloric acid (d = 1.18 g/ml).

4.    APPARATUS

Filter crucibles with a porosity of 5 to 20 microns.

Oven regulated at 120°C + 10°C.

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

Fertilisers containing little or no organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and transfer to a 400 ml beaker. Add 50 ml water and 5 ml hydrochloric acid (3.8) and evaporate to dryness on a steam bath. Add 5 ml hydrochloric acid (3.8) and 50 ml water. Bring the contents to the boiling point, breaking down any crystals or lumps with a glass rod. Dilute the solution with water to about 100 ml and boil gently for a few minutes. Allow to cool, transfer to a 250 ml graduated flask, dilute to the mark with water and mix; filter through a dry paper.

Fertilisers containing organic matter

6.1.2 Weigh to the nearest 0.01 g, 10 g of the prepared sample into a suitable crucible and place in a cold muffle furnace. Gradually raise the temperature to about 475°C (not to exceed 500°C). Maintain at this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Grind the residue to eliminate any lumps, add 50 ml water and 10 ml hydrochloric acid (3.8) and evaporate to dryness on a steam bath. Proceed as in 6.1.1, commencing “Add 5 ml hydrochloric acid (3.8) and 50 ml water”.

Determination

6.2—6.2.1 Transfer by pipette an aliquot part of the filtrate (6.1.1 or 6.1.2), containing 25 — 50 mg of potassium (30 — 60 mg K20) into a 250 ml beaker; make up to 50 ml with water.

6.2.2 To remove interferences, add 10 ml of the EDTA solution (3.5)) several drops of the phenolphthalein solution (3.4) and stir in, drop by drop, sodium hydroxide solution (3.3) until it turns red, then finally add a few more drops of sodium hydroxide to ensure an excess (usually 1 ml of sodium hydroxide is sufficient to neutralise the sample and ensure an excess).

6.2.3 To eliminate most of the ammonia boil gently for 15 minutes. Add water to make the volume up to 60 ml. Bring the solution to the boil, remove the beaker from the heat and add 10 ml formaldehyde (3.1). Add several drops of phenolphthalein solution (3.4) and if necessary, more sodium hydroxide solution until a distinct red colour appears. Cover the beaker with a watch glass and place it on a steam bath for fifteen minutes.

Weighing the crucible

6.3  Dry the filter crucible (4.1) to constant weight in the oven at 120°C (4.2) (about 15 minutes).

Allow the crucible to cool in a desiccator and then weigh it.

Precipitation

6.4  Remove the beaker from the steam bath and stir in drop by drop 10 ml of the STPB solution (3.6). This addition should take about 2 minutes; allow to stand for at least 10 minutes before filtering.

Filtering and washing

6.5  Filter under vacuum into the weighed crucible, rinse the beaker with the liquid for washing (3.7), wash the precipitate three times with the liquid for washing (60 ml in all of the liquid for washing) and twice with 5 to 10 ml of water.

Drying and weighing

6.6  Wipe the outside of the crucible with a filter paper and place in the oven (4.2) for one and a half hours at a temperature of 120°C. Allow the crucible to cool in a desiccator to ambient temperature and weigh rapidly.

Blank test

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

Control test

6.8  Carry out the determination on an aliquot part of an aqueous solution of potassium chloride, containing at the most 40 mg of K₂O

7.    EXPRESSION OF THE RESULTS

Calculate the percentage potassium content of the sample as K₂O, taking into account the weight of the test sample, the volume of the aliquot part taken for the determination and the value of the blank determination. (Conversion factor, KTPB to K₂O = 0.1314).

7b. DETERMINATION OF POTASSIUM — FLAME PHOTOMETRIC METHOD

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to fertilisers in Groups 3(b), 3(c), 3(d) and 4(c) of Section A and Group 5 of Section B of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990(4) in respect of which an indication of total potassium is required.

2.    PRINCIPLE

The sample is ashed and dissolved in dilute hydrochloric acid or, if it contains no organic substances, it is dissolved directly in dilute hydrochloric acid. The solution is diluted and the potassium content of the extract is determined by flame photometry.

3.    REAGENTS

Ammonia solution (30% V/V): dilute 30 ml concentrated ammonia solution (d = 0.88 g/ml) to 100 ml.

Ammonium oxalate solution: saturated aqueous solution.

Hydrochloric acid (d = 1.18 g/ml).

Potassium dihydrogen phosphate: dried for one hour at 105°C.

Potassium solution (stock): dissolve 3.4807 g potassium dihydrogen phosphate (3.4) in water and dilute to 1 litre.

Potassium solution (dilute): dilute 50 ml stock solution (3.5) to 1 litre with water. 1 ml contains 50 μg potassium (K).

4.    APPARATUS

Flame photometer.

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

Fertilisers containing little or no organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and transfer to a 400 ml beaker. Add 50 ml water and 5 ml hydrochloric acid (3.3) and evaporate to dryness on a steam bath. Add to the residue 125 ml water and 50 ml ammonium oxalate solution (3.2) and boil for 30 minutes. If necessary, a small quantity of potassium-free antifoaming agent may be added. Cool the mixture, add a slight excess of ammonia solution (3.1) and allow to cool. Transfer to a 250 ml graduated flask, dilute to the mark with water, mix and filter through a dry paper.

Fertilisers containing organic matter

6.1.2 Weigh to the nearest 0.01 g, 10 g of the prepared sample into a suitable crucible and place in a cold muffle furnace. Gradually raise the temperature to about 475°C (not to exceed 500°C). Maintain at this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Grind the residue to eliminate any lumps, add 50 ml water and 10 ml hydrochloric acid (3.3) and evaporate to dryness on a steam bath. Add to the residue 125 ml water and 50 ml ammonium oxalate solution (3.2) and boil for 30 minutes. Cool the mixture, add a slight excess of ammonia solution (3.1) and allow to cool. Transfer to a 500 ml graduated flask, dilute to the mark with water, mix and filter through a dry paper.

Blank solution

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

Determination

Preparation of sample and blank test solutions

6.3—6.3.1 Dilute sample solutions (6.1.1 or 6.1.2) and the blank solution (6.2) to a concentration within the optimal measuring range of the flame photometer.

Preparation of the calibration solutions

6.3.2 By diluting the standard solution (3.6), prepare at least five standard solutions of increasing concentration corresponding to the optimal measuring range of the flame photometer.

Measurement

6.4  Set the flame photometer to measure the potassium emission according to the manufacturer’s instructions. Spray successively, in triplicate, the standard solutions (6.3.2), the sample solution and the blank solution (6.3.1), washing the instrument through with distilled water between each spraying. Plot the calibration curve using the median emissions as the ordinates and the corresponding concentrations of potassium in μg/ml as the abscissae. Determine the concentration of potassium in the final sample solution by reference to the calibration curve.

The concentration of potassium in the final solution may be confirmed as follows:

prepare two further dilutions of the standard potassium solution to contain respectively 1 mg/litre more and 1 mg/litre less than the estimated potassium content of the diluted solution of the sample. Successively spray the low standard solution, the diluted solution of the sample and the high standard solution. Take the median result of each of the three readings and calculate the potassium content of the sample solution.

7.    EXPRESSION OF THE RESULTS

Calculate the percentage potassium content of the sample as K taking into account the weight of the test sample and the dilutions carried out in the course of the analysis. (Conversion factor K to K₂O = 1.204).

8. DETERMINATION OF TOTAL MAGNESIUM

EXTRACTION OF TOTAL MAGNESIUM

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers.

2.    PRINCIPLE

Solubilisation by boiling in dilute hydrochloric acid.

3.    REAGENTS

Diluted hydrochloric acid:

One volume of hydrochloric acid (d = 1.18) plus one volume of water.

4.    APPARATUS

Electric hot plate with adjustable temperature.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

Test sample

6.1  Magnesium is extracted from a test sample of five grams weighed to within one milligram.

Preparation of the solution

6.2  Add approximately 400 millilitres of water and, taking care when the sample contains a significant quantity of carbonates, 50 millilitres of dilute hydrochloric acid (4.1) a small amount at a time. Bring to the boil and maintain for 30 minutes. Allow to cool, stirring occasionally. Decant quantitatively into a 500 millilitre graduated flask. Make up to volume with water, and mix. Pass through a dry filter into a dry container, discarding the initial portion. The extract must be completely transparent. Stopper if the filtrate is not used immediately.

8.2 DETERMINATION OF MAGNESIUM BY ATOMIC ABSORPTION SPECTROPHOTOMETRY

1.    SCOPE AND FIELD OF APPLICATION

This method applies to all fertiliser extracts obtained by method 8.1

2.    PRINCIPLE

Determination of magnesium by atomic absorption spectrophotometry after appropriate dilution of the extract.

3.    REAGENTS

Hydrochloric acid, 1 M solution.

Hydrochloric acid, 0.5 M solution.

Standard solution of magnesium, 1.00 mg/ml.

3.3.1 Dissolve 1.013 grams of magnesium sulphate (MgS04.7H₂O) in the 0.5 M hydrochloric acid solution (4.2).

3.3.2 Weigh out 1.658 grams of magnesium oxide (MgO), previously calcined to remove all traces of carbonation. Place in a beaker with 100 ml of water and 120 ml of 1 M hydrochloric acid (3.1). When it has dissolved, decant quantitatively into a 1,000 ml graduated flask. Make up the volume by adding and mix.

or

Commercial standard solution

3.3.3 The laboratory is responsible for testing such solutions.

Strontium chloride solution

3.4  Dissolve 75 grams of strontium chloride (SrC1₂.6H₂O) in a hydrochloric acid solution (3.2) and make up to 500 ml with the same acid solution.

4.    APPARATUS

Spectrophotometer fitted for atomic absorption, with a magnesium lamp, set at 285.2 nm.

Air-acetylene flame.

5.    PREPARATION OF THE SAMPLE

See Method 8.1

6.    PROCEDURE

Test sample

6.1  Magnesium is extracted from a test sample of five grams weighed to within one milligram.

Preparation of the solution

6.2  Add approximately 400 millilitres of water and, taking care when the sample contains a significant quantity of carbonates, 50 millilitres of dilute hydrochloric acid (4.1) a small amount at a time. Bring to the boil and maintain for 30 minutes. Allow to cool, stirring occasionally. Decant quantitatively into a 500 millilitre graduated flask. Make up to volume with water, and mix. Pass through a dry filter into a dry container, discarding the initial portion. The extract must be completely transparent. Stopper if the filtrate is not used immediately.

8.2 DETERMINATION OF MAGNESIUM BY ATOMIC ABSORPTION SPECTROPHOTOMETRY

1.    SCOPE AND FIELD OF APPLICATION

This method applies to all fertiliser extracts obtained by method 8.1

2.    PRINCIPLE

Determination of magnesium by atomic absorption spectrophotometry after appropriate dilution of the extract.

3.    REAGENTS

Hydrochloric acid, 1 M solution.

Hydrochloric acid, 0.5 M solution.

Standard solution of magnesium, 1.00 mg/ml.

3.3.1 Dissolve 1.013 grams of magnesium sulphate (MgSO₄.7H₂O) in the 0.5 M hydrochloric acid solution (4.2).

3.3.2 Weigh out 1.658 grams of magnesium oxide (MgO), previously calcined to remove all traces of carbonation. Place in a beaker with 100 ml of water and 120 ml of 1 M hydrochloric acid (3.1). When it has dissolved, decant quantitatively into a 1,000 ml graduated flask. Make up the volume by adding and mix,

or

Commercial standard solution

3.3.3 The laboratory is responsible for testing such solutions.

Strontium chloride solution

3.4  Dissolve 75 grams of strontium chloride (SrC12.6H₂O) in a hydrochloric acid solution (3.2) and make up to 500 ml with the same acid solution.

4.    APPARATUS

Spectrophotometer fitted for atomic absorption, with a magnesium lamp, set at 285.2 nm.

Air-acetylene flame.

5.    PREPARATION OF THE SAMPLE

See Method 8.1

6.    PROCEDURE

If the fertiliser has a declared magnesium (Mg) content of more than 6% (i.e. 10%) as MgO), take 25 ml (VI) of the extraction solution c5). Transfer into a 100 ml graduated flask, and make up to volume with water and mix. The dilution factor is D₁ = 100/V₁.

Using a pipette, take 10 ml of the extraction solution (5) or the solution (6.1). Transfer into a 200 ml graduated flask. Make up to volume with the 0.5 M hydrochloric acid solution (3.2) and mix. The dilution factor is 200/10.

Dilute this solution (6.2) with the 0.5 M hydrochloric acid solution (3.2) so as to obtain a concentration in the optimum working field of the spectrophotometer (4.1). V₂ is the volume of the sample in 100 ml. The dilution factor is D₂ = 100/V₂.

The final solution should contain 10% v/v of the strontium chloride solution (3.4).

Preparation of blank solution

6.4  Prepare a blank solution by repeating the whole procedure from the extraction (method 8.1), omitting only the test sample of fertiliser.

Preparation of calibration solutions

6.5  By diluting the standard solution (3.3) with the 0.5 M hydrochloric acid, prepare at least five calibration solutions of increasing concentration within the optimum measuring range of the apparatus (4.1).

These solutions should contain 10% v/v of the strontium chloride solution (3.4).

Measurement

6.6.  Set up the spectrophotometer (4.1) at a wavelength of 285.2 nm.

Spray, successively, the calibration solutions (6.5). the sample solution (6.3) and the blank solution (6.4), washing the instrument through with the solution to be measured next. Repeat this operation three times. Plot the calibration curve using the mean absorbances of each of the calibrations (6.5) as the ordinates and the corresponding concentration of magnesium in μ/ml as the abscissae. Determine the concentration of magnesium in the sample (6.3), X_s, and blank (6.4). X_b, by reference to the calibration curve.

7.    EXPRESSION OF RESULTS

Calculate the amount of magnesium (Mg) or magnesium oxide (MgO) in the sample by reference to the calibration solutions and taking into consideration the blank.

The percentage of magnesium (Mg) in the fertiliser is equal to:

• X_s = the concentration of the solution to be analysed recorded on the calibration curve, in μg/ml.

• X_b = the concentration of the blank solution as recorded on the calibration curve, in μg/ml

• D₁ = the dilution factor when the solution is diluted (6.1).

• It is equal to four if 25 ml are taken.

• It is equal to one when the solution is not diluted.

• D₂ =he dilution factor in 6.3.

• M = the mass of the test sample at the time of extraction.

9a. DETERMINATION OF BORON — TITRIMETRIC METHOD

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers where the levels of boron are greater than 1,000 mg/kg.

2.    PRINCIPLE

The sample is dissolved in acid, the solution treated with lead nitrate in order to remove phosphate, and the borate in the filtrate is titrated potentiometrically in the presence of mannitol.

3.    REAGENTS

Calcium oxide.

Mannitol.

Sodium carbonate.

Hydrochloric acid solution 50% (V/V): dilute 50 ml concentrated hydrochloric acid (d = 1.18 g/ml) with water to 100 ml.

Hydrochloric acid, 0.5 N solution.

Lead nitrate solution, 10 g per 100 ml.

Sodium hydroxide, 0.5 N solution.

Sodium hydroxide, 0.05 N solution, carbonate free.

Methyl red indicator solution: dissolve 0.1 g of methyl red in SO ml 95% ethanol, make up to 100 ml with water and filter if necessary.

Phenolphthalein indicator solution: dissolve 0.25 g phenolphthalein in 1.50 ml 95% alcohol and dilute with water to 250 ml.

4.    APPARATUS

pH meter.

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

In the absence of organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 2g of the prepared sample if the boron content is 0.5% or less, or 1 g if the boron content is from 0.5 – 1.0%, and place in a 400 ml beaker. Add 100 ml water, a few drops of phenolphthalein indicator solution (3.10) and sufficient sodium carbonate (3.3) to make the solution slightly alkaline. Boil gently and keep the boiling solution alkaline, adding more sodium carbonate (3.3) as necessary until all the ammonia which may be present has been evolved. Cool the solution and add 12 ml hydrochloric acid solution (3.4).

In the presence of organic matter

6.1.2 Weigh to the nearest 0.001 g, 2 g of the prepared sample if the boron content is 0.5% or less, or 1 g if the boron content is from 0.5 – 1.0%, and place it in a silica dish. Add 0.2 g calcium oxide (3.1) for each 1 g of sample, moisten with water, mix thoroughly, evaporate the mixture to dryness and transfer the crucible to a cold muffle furnace. Raise the temperature slowly to 4.50 ± 10°C and then ignite for about 3 hours. Remove the crucible from the furnace, cool and moisten the ash with 10 ml of hydrochloric acid solution (3.4). Warm the solution on a steam bath for 15 minutes, covering the dish with a watch glass. Transfer the contents of the dish quantitatively into a 400 ml beaker, add a few drops of phenolphthalein indicator solution (3.10) and dilute to about 120 ml with water.

Determination

6.2  To the prepared solution (6.1.1 or 6.1.2), add 20 ml lead nitrate solution (3.6) for each 12% P₂O₅ in the sample if 2 g of the sample has been used; add 10 ml lead nitrate solution for each 12% P₂O₅ in the sample if 1 g of the sample has been used. Heat to boiling, remove from the source of heat, and make slightly alkaline by addition of sodium carbonate (3.3). Warm the solution on a steam bath for five minutes, cool and transfer the solution quantitatively into a 200 ml graduated flask. Make up to the mark with water, mix and filter through a 24 cm filter paper(5), rejecting the first 10 — 21 ml of the filtrate.

Transfer 100 ml of the filtrate into a 250 ml beaker, add a few drops of methyl red indicator (3.9) and acidify the solution with 0.5 N hydrochloric acid solution (3.5). Heat almost to boiling, stir vigorously to remove carbon dioxide, keeping the solution acidic, by adding if necessary more 0.5 N hydrochloric acid solution (3.5). Neutralise the solution with 0.5 N sodium hydroxide solution (3.7), and then make just acid by addition of 0.5 N hydrochloric acid solution (3.5). Cover the beaker with a watch glass and boil the solution gently for 5 minutes in order to expel any remaining carbon dioxide.

Cool the solution rapidly and using the pH meter (4.1), adjust the pH of the solution to 6.3 by the addition of 0.05 N sodium hydroxide solution (3.8). Add 10 g mannitol(3.2) and titrate the solution with 0.05 N sodium hydroxide solution to a pH of 6.3. Continue to add further 10 g portions of mannitol(3.2) and to re-adjust the pH to 6.3 until after the final addition of mannitol the pH remains constant at 6.3. The total amount of 0.05 N sodium hydroxide solution used after the first addition of mannitol corresponds to the amount of boron present in the sample solution. Allow a standard value of 0.1 ml 0.05 N sodium hydroxide solution as ‘blank’ value.

7.    EXPRESSION OF THE RESULT

The percentage boron content of the sample is given by the formula

where:

• T = ml of 0.05 N sodium hydroxide the mannitol

• M = weight of the sample in grams.

9b. DETERMINATION OF BORON — SPECTROPHOTOMETRIC METHOD

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers for levels of boron up to 1,000 mg/kg .

2.    PRINCIPLE

The sample is ashed in the presence of calcium oxide and the residue is dissolved in hydrochloric acid. The resulting solution is treated with carmine to form a coloured complex with boron, the absorption of which is measured at 625 nm.

3.    REAGENTS

Calcium oxide.

Sulphuric acid (d = 1.84 g/ml).

Carminic acid solution: dissolve 0.025 g carminic acid in sulphuric acid (3.2) and dilute to 100 ml with sulphuric acid (3.2).

Hydrochloric acid solution 20% (V/V): dilute 20 ml hydrochloric acid (d = 1.18 g/ml) with water to 100 ml.

Boron solution (stock):

3.5.1 weigh to the nearest 0.001 g, 1.905 g boric acid, dissolve in water and dilute to 1 litre with water.

1 ml of this solution = 0.333 mg boron.

Boron solution (working standard):

3.5.2 dilute 10 ml of boric acid stock solution (3.5.1) with water to 100 ml.

Transfer 5, 10, 15, 20 and 25 ml respectively into separate 100 ml graduated flasks and dilute to the marks with water. These solutions contain 5, 10, 15, 20 and 25 μg of boron per 3 ml of solution.

Hydrazine hydrate (approximately 60% W/W solution).

WARNING:

Hydrazine hydrate is toxic and corrosive, causing burns; avoid contact with eyes and skin.

4.    APPARATUS

Spectrophotometer with 10 mm cells.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

6.1  Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a silica dish. Add 1 g calcium oxide (3.1)) moisten with water, mix thoroughly, evaporate the mixture to dryness and then transfer the crucible to a cold muffle furnace. Raise the temperature slowly to 450 ± 10°C and ignite for about 3 hours. Remove the crucible from the furnace, cool and add hydrochloric acid solution (3.4) until the resulting mixture is acid, then add 5 ml hydrochloric acid solution (3.4) in excess. Heat the mixture at 70°C for 15 minutes, cool and filter through a filter paper(6) into a suitable graduated flask washing both the dish and the filter with water. Make up to the mark with water and mix. Dilute an aliquot of this solution so that 3 ml contains between 5 and 25 kg of boron.

Blank test

6.2.  Carry out a blank test omitting only the sample.

Determination

6.3.  Transfer 3 ml of the prepared solution (6.1) to a small conical flask, add cautiously 15 ml sulphuric acid (3.2), swirl the flask and add 10 ml carminic acid solution (3.3). Cool the flask rapidly to room temperature, mix well and allow to stand for 2 hours. Measure the absorbance in the spectrophotometer (4.1) at 625 nm with water as reference. Determine the quantity of boron in the solution by reference to the calibration curve (6.4).

Calibration curve

6.4  Transfer 3 ml of each working standard solution (3.5.2) into a series of small conical flasks and proceed as described in 6.3 commencing at “ ... ... ... ... add cautiously 15 ml sulphuric acid (3.2) ... ... ... ...”. Plot a calibration curve of the absorbance of the solutions against the corresponding quantities of boron, in μg.

7.    EXPRESSION OF THE RESULTS

The boron content in mg/kg is given by the formula:

where:

• A = weight of boron in the 3 ml aliquot taken for colour development after allowing for the blank reading (pg)

• V = volume of prepared solution before dilution

• F = factor allowing for dilution under 6.1

• M = weight of the sample in grams.

Note

The colour of the boron-carmine complex is affected by nitrate nitrogen. When this form of nitrogen is known to be present in the sample, the “Determination” procedure (6.3) should be modified by the addition of 0.5 ml hydrazine hydrate (3.6) before the addition of the sulphuric acid which should be carried out under conditions of extreme caution because of the (3.2) violent nature of the reaction. (The use of a burette for the addition of the sulphuric acid is recommended).

The hydrazine hydrate (3.6) has no influence on the absorption of the boron-carmine complex and therefore is not added to the standard solutions in the preparation of the calibration curve. However, in order to equalise the volumes of the solutions of both samples and standards, add 0.5 ml water to the latter.

10. DETERMINATION OF COBALT

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers.

2.    PRINCIPLE

The sample is dissolved in hydrochloric acid (after ashing if necessary) and the solution is treated with citric acid in order to prevent precipitation of iron and phosphate. Cobalt is extracted as its 2-nitroso-1-naphthol complex into toluene. The cobalt content is measured at 367 nm, by reference to a calibration curve.

3.    REAGENTS

Sodium sulphate, anhydrous.

Toluene.

Hydrochloric acid, 2 N solution.

Hydrochloric acid solution, 50% (V/V): dilute 50 ml concentrated hydrochloric acid solution (d = 1.18 g/ml) to 100 ml with water.

Hydrogen peroxide solution, 3% (10 volume).

Nitric acid solution, 30% (V/V): dilute 30 ml nitric acid (d = 1.42 g/ml) with water to 100 ml.

2-nitroso-I-naphthol solution:

dissolve 1 g of 2-nitroso-1-naphthol in 100 ml glacial acetic acid and add 1 g activated carbon. Shake the solution before use and filter off the required amount.

Sodium citrate solution: 40 g per 100 ml.

Sodium hydroxide, 2 N solution.

Cobalt solution (stock):

weigh to the nearest 0.001 g, 0.670 g ammonium cobaltous sulphate, [(NH₄)₂Co(SO₄)₂.6H₂O] dissolve in water and make up to 100 ml with water. 1 ml of this solution contains 1,000 μg cobalt.

Cobalt solution (working standard):

dilute the stock cobalt solution (3.10) as required so that 1 ml contains 1 μg cobalt. Prepare the solution freshly before use.

4.    APPARATUS

Spectrophotometer with 10 mm cells.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

In the absence of organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample, place in a 100 ml beaker, add 10 ml hydrochloric acid solution (3.4) and evaporate to dryness on a steam bath. Extract the soluble salts with three successive 10 ml portions of boiling 2 N hydrochloric acid solution (3.3), decanting the solution each time through the same filter paper(7) into a 50 ml graduated flask. Wash the filter paper with a little water, cool the solution to room temperature and make up to the mark with water.

In the presence of organic matter

6.1.2 Weigh to the nearest 0.001 g, 5 g of the prepared sample into a silica dish and place a silica cover on top. Transfer the dish to a cold muffle furnace, raise the temperature to about 475°C (do not exceed 500°C). Maintain at this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Add 10 ml hydrochloric acid solution (3.4) and evaporate to dryness on a steam bath. Extract the soluble salts with two successive 10 ml portions of boiling 2 N hydrochloric acid solution (3.3), decanting the solution each time through the same filter paper(7) into a 50 ml graduated flask. Add 5 ml hydrochloric acid solution (3.4) and 5 ml nitric acid solution (3.6) to the residue in the dish and evaporate the mixture to dryness on a hot plate at low heat. Add 10 ml boiling hydrochloric acid solution (3.3) to the residue and filter the solution through the same filter paper into the 50 ml graduated flask. Wash the filter paper with water, cool the solution to room temperature and make up to the mark with water.

Determination

6.2—6.2.1 Transfer a suitable aliquot of the solution prepared in 6.1 (containing 6.2.2 not more than 15 μg cobalt) to a 100 ml-beaker, add 15 ml sodium citrate solution (3.8), dilute to about 50 ml with water and adjust the pH to between 3 and 4 by adding 2 N hydrochloric acid solution (3.3). (A precipitate of ferric hydroxide may form but this can be dissolved by heating the solution). Cool to room temperature, add 10 ml hydrogen peroxide solution (3.5) and, after 5 minutes, 1 ml 2-nitroso-1-naphthol solution (3.7). Heat the solution to about 90°C and then allow to stand for 30 minutes at room temperature. Transfer the solution to a 125 ml separating funnel, add 10 ml toluene (3.2), shake vigorously for 2 minutes, allow the phases to separate and discard the lower aqueous phase.

6.2.2 To the toluene extract add 20 ml 2 N hydrochloric acid solution (3.3), shake for 1 minute and discard the lower aqueous phase. Add 20 ml 2 N sodium hydroxide solution (3.9), shake for 1 minute and again discard the aqueous phase. Repeat the washing with a further 20 ml of 2 N sodium hydroxide solution (3.9). Finally run off the toluene solution through a little anhydrous sodium sulphate (3.1) into a clean dry stoppered tube. Carry out a blank determination repeating the procedure, but omitting the sample. Measure the absorbance of the magenta coloured solutions at a wave length of 367 nm in the spectrophotometer (4.1) with toluene (3.2) as reference. Determine the quantity of cobalt in the solution by reference to the calibration curve (6.3).

Calibration Curve

6.3  Measure amounts of cobalt working standard solution (3.11) corresponding to 3, 6, 9, 12 and 15 μg cobalt into five separate 100 ml beakers and proceed as described in 6.2 commencing at “. ... ... ... ... add 15 ml sodium citrate solution (3.8) ... ... ... ...”. Plot a calibration graph of the absorbance of the solutions against the corresponding amounts of cobalt (μg).

7.    EXPRESSION OF THE RESULTS

The cobalt content in mg/kg is given by the formula:

where:

• A = weight of cobalt taken for colour development as read from the calibration graph after allowing for the blank reading (μg)

• V = volume in millilitres of sample taken for colour development

• M = weight of sample in grams.

11. DETERMINATION OF MOLYBDENUM

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers.

2.    PRINCIPLE

The sample is dissolved in hydrochloric acid (after ashing if necessary) and the molybdenum complexed with thiocyanate in the presence of stannous chloride. The red coloured complex is extracted into an organic solvent mixture and its absorbance measured at 470 nm.

3.    REAGENTS

Hydrochloric acid, 50% (V/V): dilute 50 ml concentrated hydrochloric acid solution (d = 1.18 g/ml) to 100 ml with water.

Hydrochloric acid, 2 N solution.

Hydrochloric acid, N solution.

Nitric acid solution, 30% (V/V): dilute 30 ml nitric acid (d = 1.42 g/ml) with water to 100 ml.

3.5.1 Molybdenum solution (working standard): dissolve 1.84 g ammonium molybdate [(NH₄)₆Mo₇O₂₄.4H₂O] in water and dilute with water to 1 litre.

3.5.2 Molybdenum solution (working standard):

dilute 1.0 ml stock solution (3.5.1) to 1 litre with water.

(1 ml = 1 μg molybdenum).

Prepare this solution immediately prior to use.

Ammonium ferrous sulphate solution, 4 g per 100 ml.

Potassium thiocyanate solution, 40 g per 100 ml.

Sodium sulphate, anhydrous.

Stannous chloride solution: suspend 40 g stannous chloride dihydrate in 20 ml 6.5 N hydrochloric acid, add water to dissolve and dilute to 100 ml. Filter if turbid.

Solvent mixture: mix equal volumes of carbon tetrachloride and 3-methylbutan-1-01.

4.    APPARATUS

Spectrophotometer with 10 mm cells.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

,Preparation of the solution for analysis

In the absence of organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample, place in a 100 ml beaker, add 10 ml hydrochloric acid solution (3.1) and evaporate to dryness on a steam bath. Extract the soluble salts with three successive 10 ml portions of boiling 2 N hydrochloric acid solution (3.2), decanting the solution each time through the same filter paper(8) into a 50 ml graduated flask. Wash the filter paper with a little water, cool the solution to room temperature and make up to the mark with water.

In the presence of organic matter

6.1.2 Weigh to the nearest 0.001 g, 5 g of the prepared sample into a silica dish and place a silica cover on top. Transfer the dish to a cold muffle furnace and gradually raise the temperature to about 475°C (not to exceed 500°C). Maintain at this temperature for at least 16 hours and then open the furnace and allow, the crucible to cool. Add 10 ml hydrochloric acid solution (3.1) and evaporate to dryness on a steam bath. Extract the soluble salts with two successive 10 ml portions of boiling 2 N hydrochloric acid solution (3.2), decanting the solution each time through the same filter paper(8) into a 50 ml graduated flask. Add 5 ml hydrochloric acid solution (3.1) and 5 ml nitric acid solution (3.4) to the residue in the dish and evaporate the mixture to dryness on a hot plate at low heat. Add 10 ml boiling hydrochloric acid solution (3.1) to the residue and filter the solution through the same filter paper into the 50 ml graduated flask. Wash the filter paper with water, cool the solution to room temperature and make up to the mark with water.

Determination

6.2—6.2.1 Transfer a suitable aliquot of the solution, prepared as in 6.1, to a 125 ml separating funnel, add 1 ml ammonium ferrous sulphate solution (3.6) and sufficient N hydrochloric acid (3.3) to bring the volume to 50 ml (see NOTE), then add 1 ml potassium thiocyanate solution (3.7) and mix. Add 1 ml stannous chloride solution (3.9) and mix again. Add exactly 7 ml solvent mixture (3.1), shake vigorously for two minutes and allow to separate for fifteen minutes. Filter the lower layer through a 7 cm paper into a small stoppered tube. (If the lower layer is not clear or if filtration is difficult, filter through a suitable column packed with anhydrous sodium sulphate (3.8), solid stannous chloride and plugged with cotton wool).

6.2.2 Carry out a blank determination repeating the procedure but omitting the sample. Measure the absorbance of the solutions at a wave length of 470 nm, in the spectrophotometer (4.1) with water as reference. Determine the quantity of molybdenum in the solution by reference to the calibration curve (6.3).

Note:

The acidity of the final solution must not exceed 1.5 N with respect to hydrochloric acid; with more strongly acid conditions, fading of the colour will occur.

6.3  Calibration curve

Transfer by pipette, 0,5, 10, 15.20 and 25 ml standard molybdenum solution (3.5.2) into a series of 125 ml separating funnels. To each funnel add 1 ml ammonium ferrous sulphate solution (3.6) and 25 ml of 2 N hydrochloric acid (3.2); dilute to 50 ml with water where necessary and proceed as described at 6.2.1, commencing at “then add 1 ml potassium thiocyanate solution (3.7) and mix ... ... ... ...”. Plot a calibration curve of the absorbance of the solutions against the corresponding amounts of molybdenum (μg).

7.    EXPRESSION OF THE RESULTS

The molybdenum content in me/kg is given by the formula:

where:

• A = weight of molybdenum in the aliquot taken for colour development as read from the calibration curve after allowing for the blank reading (μg)

• V = volume in millilitres of aliquot taken for colour development

• M = weight of sample in grams.

12. DETERMINATION OF COPPER

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers

2.    PRINCIPLE

The sample is ashed and dissolved in dilute hydrochloric acid or, if it contains no organic substances, it is dissolved directly in dilute hydrochloric acid. The solution is diluted and the copper content is determined by atomic absorption spectrophotometry.

3.    REAGENTS

Hydrochloric acid (d = 1.18 g/ml).

Hydrochloric acid, 6 N solution.

Hydrochloric acid, 0.5 N solution.

Hydrogen peroxide, approximately 100 volume, 30% by weight.

Copper solution(9) (stock):

3.5.1 weigh to the nearest 0.001 g, 1 g pure copper, dissolve in 25 ml 6 N hydrochloric acid solution (3.2), add 5 ml hydrogen peroxide (3.4) and dilute to 1 litre with water. 1 ml of this solution = 1,000 μg of copper (Cu).

Copper solution (dilute):

3.5.2 dilute 10 ml of stock solution (3.5.1) to 100 ml with water and then dilute the resulting solution, 10 ml to 100 ml with water. 1 ml of the final dilution = 10 μg of copper (Cu).

4.    APPARATUS

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

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

In the absence of organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample, place it in a 400 ml beaker, add carefully 5 ml hydrochloric acid (3.1) (there may be a vigorous reaction due to carbon dioxide formation). Add more hydrochloric acid, if necessary. When effervescence has stopped, evaporate to dryness on a steam bath, stirring occasionally with a glass rod. Add 15 ml 6 N hydrochloric acid solution (3.2) and 120 ml water. Stir with the glass rod, which should be left in the beaker, and cover the beaker with a watch glass. Boil the solution gently until dissolution appears complete and then filter through a filter paper(10) into a 250 ml graduated flask. Wash the beaker and filter with 5 ml hot 6 N hydrochloric acid solution (3.2) and twice with boiling water. Cool and make up to the mark with water (the hydrochloric acid concentration of this solution should be about 0.5 N).

6.1.2 In the presence of organic matter Weigh to the nearest 0.001 g, 5 g of the prepared sample into a silica or platinum crucible and place the crucible into a cold muffle furnace. Close the furnace and gradually raise the temperature to 450 – 475°C over about 90 minutes. Maintain this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Moisten the ash with water and transfer it into a 250 ml beaker. Wash the crucible with about 5 ml hydrochloric acid (3.1) and add the latter slowly and carefully to the beaker (there may be a vigorous reaction due to carbon dioxide formation). If necessary, add more hydrochloric acid (3.1) with stirring, until all effervescence has stopped. Evaporate the solution to dryness, occassionally stirring with a glass rod. Add 15 ml 6 N hydrochloric acid solution (3.2) and 120 ml water. Stir with the glass rod, which should be left in the beaker, and cover with a watch glass. Boil the solution gently until dissolution appears complete and filter through a filter paper(10) into a 250 ml graduated flask. Wash the beaker and filter with 5 ml of hot 6 N hydrochloric acid solution (3.2) and twice with boiling water. Cool and make up to the mark with water. (The hydrochloric acid concentration of this solution should be about 0.5 N).

Blank Solution

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

Determination

Preparation of sample and blank test solutions

6.3—6.3.1 Dilute the sample solutions (6.1.1 or 6.1.2) and the blank test solution (6.2) with 0.5 N hydrochloric acid solution (3.3) to a concentration within the optimal measuring range of the spectrophotometer.

Preparation of the calibration solution

6.3.2 By diluting the standard solution (3.5.2) with 0.5 N hydrochloric acid solution (3.3) prepare at least 5 standard solutions corresponding to the optimal measuring range of the spectrophotometer.

Measurement

6.4  Set up the spectrophotometer (4.1) at a wavelength of 324.8 nm using an oxidising air-acetylene flame. Spray successively, in triplicate, the standard solution (6.3.2), the sample solution and the blank test solution (6.3.1), washing the instrument through with distilled water between each spraying. Plot the calibration curve using the mean absorbances as the ordinates and the corresponding concentrations of copper in μg/ml as the abscissae.

Determine the concentration of copper in the final sample and blank solution by reference to the calibration curve.

7.    EXPRESSION OF THE RESULTS

Calculate the copper content of the sample taking into account the weight of the test sample and the dilutions carried out in the course of the analysis. Express the result either as a percentage or as mg/kg.

13. DETERMINATION OF IRON

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers.

2.    PRINCIPLE

The sample is ashed and dissolved in dilute hydrochloric acid or, if it contains no organic substances, it is dissolved directly in dilute hydrochloric acid. The solution is diluted and the iron content of the extract is determined by atomic absorption spectrophotometry.

3.    REAGENTS

Hydrochloric acid (d = 1.18 g/ml).

Hydrochloric acid, 6 N solution.

Hydrochloric acid, 0.5 N solution.

Hydrogen peroxide, approximately 100 volume, 30% by weight.

3.5.1 Iron solution(11) (stock):

weigh to the nearest 0.001 g, 1 g pure iron, dissolve in 200 ml 6 N hydrochloric acid solution (3.2), add 16 ml hydrogen peroxide solution (3.4) and dilute to 1 litre with water.

1 ml of this solution = 1,000 μg of iron (Fe).

3.5.2 Iron solution (dilute):

dilute 10 ml of stock solution (3.5.1) to 100 ml with water.

1 ml of this solution =00 μg of iron (Fe).

Lanthanum chloride solution: dissolve 12 g lanthanum oxide in 150 ml water, add 100 ml 6 N hydrochloric acid solution (3.2) and dilute to 1 litre with water.

4.    APPARATUS

Atomic absorption spectrophotometer with an iron lamp (248.3 nm).

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

6.1—6.1.1 In the absence of organic matter

Weigh to the nearest 0.001 g, 5 g of the prepared sample, place it in a 400 ml beaker, add carefully 5 ml hydrochloric acid (3.1) (there may be a vigorous reaction due to carbon dioxide formation). Add more hydrochloric acid, if necessary. When effervescence has stopped, evaporate to dryness on a steam bath, stirring occasionally with a glass rod. Add 15 ml 6 N hydrochloric acid solution (3.2) and 120 ml water. Stir with the glass rod, which should be left in the beaker, and cover the beaker with a watch glass. Boil the solution gently until dissolution appears complete and then filter through a filter paper(12) into a 250 ml graduated flask. Wash the beaker and filter with 5 ml of hot 6 N hydrochloric acid solution (3.2) and twice with boiling water. Cool and make up to the mark with water. (The hydrochloric acid concentration of this solution should be about 0.5 N).

In the presence of organic matter

6.1.2 Weigh to the nearest 0.001 g, 5 g of the prepared sample into a silica or platinum crucible and place the crucible in a cold muffle furnace. Close the furnace and gradually raise the temperature to 450 – 475°C over about 90 minutes. Maintain this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Moisten the ash with water and transfer it into a 250 ml beaker. Wash the crucible with about 5 ml hydrochloric acid (3.1) and add the latter slowly and carefully to the beaker (there may be a vigorous reaction due to carbon dioxide formation). If necessary, add more hydrochloric acid (3.1) with stirring, until all effervescence has stopped.

Evaporate the solution to dryness, occasionally stirring with a glass rod. Add 15 ml 6 N hydrochloric acid solution (3.2) and 120 ml water. Stir with the glass rod, which should be left in the beaker, and cover with a watch glass. Boil the solution gently until dissolution appears complete and filter through a filter paper(13) into a 250 ml graduated flask. Wash the beaker and filter with 5 ml of hot 6 N hydrochloric acid solution (3.2) and twice with boiling water. Cool and make up to the mark with water. (The hydrochloric acid concentration of this solution should be about 0.5N)

Blank solution

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

Determination

Preparation of sample and blank test solutions

6.3—6.3.1 Dilute the sample solutions (6.1.1 or 6.1.2) and the blank test solution (6.2) with 0.5 N hydrochloric acid solution (3.3) to a concentration within the optimal measuring range of the spectrophotometer. The final solution must contain 10% (V/V) of the lanthanum chloride solution (3.6).

Preparation of the calibration solutions

6.3.2 By diluting the standard solution (3.5.2) with 0.5 N hydrochloric acid solution (3.3) prepare at least 5 standard solutions of increasing concentration corresponding to the optimal measuring range of the spectrophotometer. The final solutions must contain 10% (V/V) of the lanthanum chloride solution (3.6).

Measurement

6.4  Set up the spectrophotometer (4.1), at a wave length of 248.3 nm using an oxidising air-acetylene flame. Spray successively, in triplicate, the standard solutions (6.3.2), the sample solution, and the blank test solution (6.3.1), washing the instrument through with distilled water between each spraying, Plot the calibration curve using the mean absorbances as the ordinates and the corresponding concentrations of iron in Fg/ml as the abscissae. Determine the concentration of iron in the final sample and blank solutions by reference to the calibration curve.

7.    EXPRESSION OF THE RESULTS

Calculate the iron content of the sample taking into account the weight of the test sample and the dilutions carried out in the course of the analysis. Express the result either as a percentage or as mg/kg.

14. DETERMINATION OF MANGANESE

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to all fertilisers.

2.    PRINCIPLE

The sample is ashed and dissolved in dilute hydrochloric acid or, if it contains no organic substances, it is dissolved directly in dilute hydrochloric acid. The solution is diluted and the manganese content of the extract is determined by atomic absorption spectrophotometry.

3.    REAGENTS

Hydrochloric acid (d = 1.18 g/ml).

Hydrochloric acid, 6 N solution.

Hydrochloric acid, 0.5 N solution.

Manganese solution(14) (stock):

3.4.1 weigh to the nearest 0.001 g, 1 g pure manganese, dissolve in 25 ml 6 N hydrochloric acid solution (3.2) and dilute to 1 litre with water. 1 ml of this solution = 1,000 μg of manganese (Mn).

Manganese solution (dilute):

3.4.2 dilute 10 ml of stock solution (3.4.1) to 1 litre with water. 1 ml of this solution = 10 μg of manganese.

Lanthanum chloride solution: dissolve 12 g lanthanum oxide in 150 ml water, add 100 ml 6 N hydrochloric acid solution (3.2) and dilute to 1 litre with water.

4.    APPARATUS

Atomic absorption spectrophotometer with a manganese lamp (279.5 nm).

5.    PREPARATION OF SAMPLE

See Method 1.

6.    PROCEDURE

Preparation of the solution for analysis

In the absence of organic matter

6.1—6.1.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample, place it in a 400 ml beaker, add carefully 5 ml hydrochloric acid (3.1) (there may be a vigorous reaction due to carbon dioxide formation). Add more hydrochloric acid, if necessary. When effervescence has stopped, evaporate to dryness on a steam bath, stirring occasionally with a glass rod. Add 15 ml 6 N hydrochloric acid solution (3.2) and 120 ml water. Stir with the glass rod, which should be left in the beaker, and cover the beaker with a watch glass. Boil the solution gently until dissolution appears complete and then filter through a filter paper(15) into a 250 ml graduated flask. Wash the beaker and filter with 5 ml of hot 6 N hydrochloric acid solution (3.2) and twice with boiling water. Cool and make up to the mark with water. (The hydrochloric acid concentration of this solution should be about 0.5 N).

In the presence of organic matter

6.1.2 Weigh to the nearest 0.001 g, 5 g of the prepared sample into a silica or platinum crucible and place the crucible into a cold muffle furnace. Close the furnace and gradually raise the temperature to 450 – 475°C over about 90 minutes. Maintain this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Moisten the ash with water and transfer it into a 250 ml beaker. Wash the crucible with about 5 ml hydrochloric acid (3.1) and add the latter slowly and carefully to the beaker (there may be a vigorous reaction due to carbon dioxide formation). If necessary, add more hydrochloric acid (3.1) with stirring, until all effervescence has stopped. Evaporate the solution to dryness, occasionally stirring with a glass rod. Add 15 ml 6 N hydrochloric acid solution (3.2) and 120 ml water. Stir with the glass rod, which should be left in the beaker, and cover with a watch glass. Boil the solution gently until dissolution appears complete and filter through a filter paper(16) into a 250 ml graduated flask. Wash the beaker and filter with 5 ml of hot 6 N hydrochloric acid solution (3.2) and twice with boiling water. Cool and make up to the mark with water. (The hydrochloric acid concentration of this solution should be about 0.5 N).

Blank solution

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

Determination

Preparation of sample and blank test solutions

6.3—6.3.1 Dilute the sample solutions (6.1.1 or 6.1.2) and the blank test solution (6.2), with 0.5 N hydrochloric acid solution (3.3) to a concentration within the optimal measuring range of the spectrophotometer. The final solution must contain 10% (V/V) of the lanthanum chloride solution (3.5).

Preparation of the calibration solutions

6.3.2 By diluting the standard solution (3.4.2) with 0.5 N hydrochloric acid solution (3.3) prepare at least 5 standard solutions of increasing concentration corresponding to the optimal measuring range of the spectrophotometer. The final solutions must contain 10% (V/V) of the lanthanum chloride solution (3.5).

Measurement

6.4  Set up the spectrophotometer (4.1), at a wave length of 279.5 nm using an oxidising air-acetylene flame. Spray successively, in triplicate, the standard solutions (6.3.2), the sample solution and the blank test solution (6.3.1), washing the instrument through with distilled water between each spraying. Plot the calibration curve using the mean absorbances as the ordinates and the corresponding concentrations of manganese in μg/ml as the abscissae. Determine the concentration of manganese in the final sample and blank solutions by reference to the calibration curve.

7.    EXPRESSION OF THE RESULTS

Calculate the manganese content of the sample taking into account the weight of the test sample and the dilutions carried out in the course of the analysis. Express the result either as a percentage or as mg/kg.

15. DETERMINATION OF THE NEUTRALISING VALUE IN LIMING MATERIALS

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to products in Groups 5(a) and 5(b) of Section A of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990(17).

2.    PRINCIPLE

The sample is dissolved in a measured quantity of standard hydrochloric acid, the excess of which is titrated with a standard solution of sodium hydroxide.

3.    REAGENTS

Hydrochloric acid, 0.5 N solution.

Sodium hydroxide, 0.5 N solution of carbonate free).

Phenolphthalein indicator solution: dissolve 0.25 g phenolphthalein in 150 ml 95% ethanol and dilute with water to 250 ml.

4.    PREPARATION OF SAMPLE

Rapidly grind 50 g of the representative lime sample to pass through a 1 mm sieve.

5.    PROCEDURE

Determination

5.1  Weigh to the nearest 0.001 g, 0.5 g of the prepared sample and transfer to a 300 ml conical flask. Add 50 ml of 0.5 N hydrochloric acid (3.1), cover the flask with a watch glass and boil the contents gently for five minutes. Cool the mixture to room temperature, add two or three drops of the phenolphthalein indicator (3.3) and titrate with 0.5 N sodium hydroxide solution (3.2) to the end point of the indicator.

6.    EXPRESSION OF THE RESULTS

Determine the amount of hydrochloric acid consumed by the sample. 1 ml 0.5 N hydrochloric acid = 0.01402 g calcium oxide (CaO).

The neutralising value is expressed as a percentage by weight of calcium oxide (CaO), and refers to undried sample as received.

16. DETERMINATION OF FINENESS OF PRODUCTS OTHER THAN POTASSIC BASIC SLAG

1.    SCOPE AND FIELD OF APPLICATION

This method is applicable to “Rock phosphate” in Group 2(b) and to products in Groups 4(c), 5(a) and 5(b) of Section A of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990.

2.    PRINCIPLE

By hand sieve shaking, the proportion of material passing through the prescribed sieve is determined.

3.    APPARATUS

Sieves having square apertures of 45 mm, 6.7 mm, 6.3 mm, 5 mm, 3.35 mm, 1.0 mm and 150 microns: lower receiver to fit sieve. Test sieve conforming to British Standard 410 : 1986 are suitable.

4.    PROCEDURE

For sieving through 3.55 mm, 1.0 mm and 150 micron sieves

4.1  Thoroughly mix the sample and quarter down until a portion of about 100 g is obtained. Heat this portion at 100°C until dry and thoroughly mix. Weigh to the nearest 0.01 g, 20 g and transfer to the sieve with the lower receiver attached. Proceed as described in 4.4.

For sieving through 6.7 mm, 6.3 mm and 5 mm sieves

4.2  Oven dry the sample at 100°C for 24 hours and thoroughly mix. Weigh to the nearest 0.1 g, 200 g and transfer to the sieve with the lower receiver attached. Proceed as described in 4.4.

For sieving through a 45 mm sieve

4.3  If the sample appears moist or damp, oven dry at 100°C for 24 hours, but if the sample appears dry, heating is not necessary. Thoroughly mix the sample and weigh to the nearest 0.1 g, 500 g and transfer to the sieve with the lower receiver attached. Proceed as in 4.4.

Sieving

4.4  Shake the sieve for 5 minutes, frequently tapping the side. Disintegrate soft lumps such as can be caused to crumble by the application of the fibres of a soft brush, taking care that the hard part of the brush does not make contact with the sieve, and that the brush is not used to brush particles through the sieve. Brush out the powder in the lower receiver and weigh. Replace the receiver and repeat the shaking and tapping procedure for 2 minutes. Add the powder in the receiver to the first portion and weigh. Repeat the process until not more than 0.04 g passes through the sieve during 2 minutes.

5.    EXPRESSION OF THE RESULTS

Calculate the fineness by expressing the weight of the material passing through the sieve as a percentage of the weight of the portion of the dried (or as the case may be undried) sample taken for sieving.

17. DETERMINATION OF FINENESS OF POTASSIC BASIC SLAG

1.    SCOPE AND FIELD OF APPLICATION

Exclusively to “Potassic basic slag” in Group 3(b) of Section A of the Table in Schedule 1 of the Fertilisers Regulations (Northern Ireland) 1990.

2.    PRINCIPLE

By hand sieve shaking and dissolution of the soluble salts, the proportion of slag passing through the prescribed sieve is determined.

APPARATUS

3.  Sieve having square apertures of 0.5 mm (500 microns); lower receiver to fit sieve. Test sieves conforming to British Standard 410 : 1986 are suitable.

4.    PROCEDURE

Preparation of the sample

4.1  Thoroughly mix the sample and quarter down until a portion of about 100 g is obtained. Heat this portion at 100°C until dry, and throughly mix.

Sieving

4.2  Weigh to the nearest 0.1 g, 20 g of the dry sample and transfer to the sieve with the lower receiver attached. Shake the sieve for five minutes, frequently tapping the sides. Disintegrate soft lumps that can be caused to crumble by the application of a soft brush, taking care that the hard part of the brush does not make contact with the sieve and that the brush is not used to brush particles through the sieve.

Transfer the finer portion from the container into a 500 ml beaker and add 200 ml of previously boiled water. Stir and then filter through a weighed glass sintered crucible. Thoroughly wash the residue with water, dry and re-weigh the crucible. Calculate the weight of slag in the mixture with a particle size of less than 0.5 mm (A).

Weigh to the nearest 0.01 g about 20 g of the dry sample and transfer to a 500 ml conical flask. Add 200 ml previously boiled water and shake for 30 minutes. Filter through a weighed, sintered glass crucible, wash the residue thoroughly with water, dry and re-weigh the crucible. Calculate the total weight of slag in the mixture (B).

5.    EXPRESSION OF THE RESULTS

Express the fineness of the slag as

(1)

S.R. 1990 No. 286

(2)

S.R. 1990 No. 286

(3)

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(4)

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(5)

Whatman 42 or equivalent.

(6)

Whatman 42 or equivalent.

(7)

Whatman 541 or equivalent.

(8)

Whatman 541 or equivalent.

(9)

Commercially available standard copper solution may be used.

(10)

Whatman 541 or equivalent.

(11)

Commercially available standard iron solution may be used.

(12)

Whatman 541 or equivalent.

(13)

Whatman 541 or equivalent

(14)

Commercially available standard manganese solution may be used.

(15)

Whatman 541 or equivalent

(16)

Whatman 541 or equivalent

(17)

S.R. 1990 No. 286