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

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Zinc extract solution 6.1 See Methods 25a and/or 25b and, if appropriate, 25c.

Preparation of the test solution 6.2 See Method 25d (6.2). The test solution must contain 10% by volume of lanthanum salt solution.

PROCEDURE

7

Preparation of the blank solution 7.1 See Method 25d (7.1). The blank solution must contain 10% by volume of the lanthanum salt solution used in 6.2.

Preparation of the calibration solutions 7.2 See Method 25d (7.2). For an optimum interval of 0 to 5 mg/ml of zinc, place 0, 0.5, 1, 2, 3, 4 and 5 ml, respectively, of the working solution (4.4.2) in a series of 100 ml volumetric flasks. Where necessary, adjust the concentration of hydrochloric acid to bring it as close as possible to that of the test solution. Add 10 ml of the lanthanum salt solution used in (6.2) to each volumetric flask. Make up to 100 ml with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain, respectively, 0, 0.5, 1, 2, 3, 4 and 5 mg/ml of zinc.

Determination 7.3 See Method 25d (7.3). Prepare the spectrometer (5) for measurements at a wavelength of 213.8 nm.

EXPRESSION OF RESULTS

8

See Method 25d (8).

26. — TRACE ELEMENTS AT A CONCENTRATION GREATER THAN 10%

26a. — Extraction of Total Trace Elements

SCOPE

1

This method defines the procedure for extracting the following trace elements: total boron, total cobalt, total copper, total iron, total manganese, total molybdenum and total zinc. The aim is to carry out the minimum number of extractions, making use wherever possible of the same extract to determine the total level of each of the trace elements listed above.

FIELD OF APPLICATION

2

This procedure concerns fertilisers containing one or more of the following trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc. It is applicable to each trace element, the declared content of which is more than 10%.

PRINCIPLE

3

Dissolution in boiling diluted hydrochloric acid.

Note: The extraction is empirical and may not be quantitative depending on the product or the other constituents of the fertiliser. In particular, in the case of certain manganese oxides, the quantity extracted may be substantially smaller than the total quantity of manganese which the product contains. It is the responsibility of the fertiliser manufacturers to ensure that the declared content actually corresponds to the quantity extracted under the conditions pertaining to the method.

REAGENTS

4

Diluted hydrochloric acid (HCl) solution, about 6 M 4.1 Mix 1 volume of hydrochloric acid (r = 1.18 g/ml) with one volume of water.

Concentrated ammonia solution (NH₄OH, r = 0.9 g/ml) 4.2

APPARATUS

5

• (5.1) Electric hotplate with variable temperature control.

• (5.2) pH meter

Note: Where the boron content of an extract is to be determined, do not use borosilicate glassware. As the method involves boiling, teflon or silica is preferable. Rinse the glassware thoroughly if it has been washed in detergents containing borates.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 Take a quantity of fertiliser weighing 1 or 2 g depending on the declared content of element in the product. The following table shall be used to obtain a final solution which, after appropriate dilution, will be within the measuring range for each method. Samples should be weighed to within 1 mg. Declared content of trace element in the fertiliser (%)> 10-< 25≥ 25Mass of test sample (g)21Mass of element in the sample (mg)> 200-< 500≥ 250Volume of extract V (ml)500500Concentration of element in extract (mg/l)> 400-<1000≥ 500 Place the sample in a 250 ml beaker.

Preparation of the solution 7.2 If necessary moisten the sample with a little water, add 10 ml of dilute hydrochloric acid (4.1) per gram of fertiliser carefully, in small amounts, then add about 50 ml of water. Cover the beaker with a watchglass and mix. Bring to the boil on the hotplate and boil for 30 minutes. Allow to cool, stirring occasionally. Transfer quantitatively to a 500 ml volumetric flask. Make up to volume with water and mix thoroughly. Filter through a dry filter into a dry container. Discard the first portion. The extract must be perfectly clear. It is recommended that the determinations be carried out without delay on aliquot portions of the clear filtrate, if not the containers should be stoppered. Note: Extracts in which the boron content has to be determined. Adjust the pH to between 4 and 6 with concentrated ammonia solution (4.2).

DETERMINATION

8

The determination of each trace element is to be carried out on the aliquot portions indicated in the method for each individual trace element.

26b. — Extraction of Water-Soluble Trace Elements

SCOPE

1

This method defines the procedure for extracting water-soluble forms of the following trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc. The aim is to carry out the minimum number of extractions, making use wherever possible of the same extract to determine the level of each of the elements listed above.

FIELD OF APPLICATION

2

This procedure concerns fertilisers containing one or more of the following trace elements: boron, cobalt, copper, iron, manganese, molybdenum and zinc. It is applicable to each trace element, the declared content of which is more than 10%.

PRINCIPLE

3

The trace elements are extracted by shaking the fertiliser in water at 20 ± 2°C.

Note: The extraction is empirical and may not be quantitative.

REAGENTS

4

• (4.1) Diluted hydrochloric acid (HCl) solution, about 6 M

• Mix 1 volume of hydrochloric acid (r = 1.18 g/ml) with 1 volume of water.

APPARATUS

5

• (5.1) Rotary shaker set at about 35 to 40 rpm.

Note: Where the boron content of an extract is to be determined, do not use borosilicate glassware. Teflon or silica is preferable for this extraction. Rinse the glassware thoroughly if it has been washed in detergents containing borates.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

• (7.1) Test sample

• Take a quantity of fertiliser weighing 1 or 2 g depending on the declared content of the product. The following table shall be used to obtain a final solution which, after appropriate dilution, will be within the measuring range for each method. The samples should be weighed to within 1 mg. Declared content of trace element in the fertiliser (%)> 10-< 25≥ 25Mass of test sample (g)21Mass of element in the sample (mg)> 200-< 500≥ 250Volume of extract V (ml)500500Concentration of element in extract (mg/l)> 400-<1000≥ 500

DETERMINATION

8

The determination of each trace element is carried out on the aliquot portions indicated in the method for each individual trace element.

26c. — REMOVAL OF ORGANIC COMPOUNDS FROM FERTILISER EXTRACTS

SCOPE

1

This method defines a procedure for removing organic compounds from fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 26a and 26b for which a declaration of total and/or water-soluble element is required.

Note: The presence of small quantities of organic matter usually does not affect determinations by means of atomic absorption spectrometry.

PRINCIPLE

3

The organic compounds in an aliquot portion of the extract are oxidized with hydrogen peroxide.

REAGENTS

4

Diluted hydrochloric acid solution, about 0.5 M 4.1 Mix 1 volume of hydrochloric acid (r = 1.18 g/ml) with 20 volumes of water.

Hydrogen peroxide solution (30% H₂O₂, ρ = 1.11 g/ml), free from trace elements 4.2

APPARATUS

5

Electric hotplate with variable temperature control.

PROCEDURE

6

Take 25 ml of extract solution obtained by Method 26a or 26b and place in a 100 ml beaker. In the case of Method 26b, add 5 ml of the dilute hydrochloric acid solution (4.1). Then add 5 ml of the hydrogen peroxide solution (4.2). Cover with a watchglass. Allow oxidation to occur at room temperature for about one hour, then bring gradually to boiling and boil for half an hour. If necessary, add a further 5 ml of the hydrogen peroxide to the solution once it has cooled. Then boil to remove the excess hydrogen peroxide. Allow to cool and transfer quantitatively to a 50 ml volumetric flask and make up to volume. Filter where necessary.

26d. — Determination of Trace Elements in Fertiliser Extracts by Atomic Absorption Spectrometry (General Procedure)

SCOPE

1

This method defines a general procedure for determining the levels of iron and zinc in fertiliser extracts by atomic absorption spectrometry.

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertiliser extracts obtained by Methods 26a and 26b for which a declaration of total and/or water-soluble iron or zinc is required. Adaptations of this procedure for the various trace elements are detailed in the methods defined specifically for each element.

Note: In most cases the presence of small quantities of organic matter will not affect determinations by means of atomic absorption spectrometry.

PRINCIPLE

3

After the extract has been treated where necessary to reduce or eliminate interfering chemical species, the extract is diluted so that its concentration is in the optimum range of the spectrometer at a wavelength suitable for the trace element to be determined.

REAGENTS

4

Diluted hydrochloric acid solution (HCl), about 6 M 4.1 Mix one volume of hydrochloric acid (ρ = 1.18 g/ml) with 1 volume of water.

Diluted hydrochloric acid solution (HCl), about 0.5 M 4.2 Mix one volume of hydrochloric acid (ρ = 1.18 g/ml) with 20 volumes of water.

Lanthanum salt solutions (10 g of La per litre). 4.3 This reagent is used for determinations of iron and zinc. Lanthanum is added to the extract to eliminate chemical interferences in the air-acetylene flame. It can be prepared either: a with lanthanum oxide dissolved in hydrochloric acid (4.1). Place 11.73 g of lanthanum oxide (La₂O₃) in 150 ml of water in a 1 litre volumetric flask and add 120 ml of 6 M hydrochloric acid (4.1). Allow to dissolve and then make up to 1 litre with water and mix thoroughly. This solution is approximately 0.5 M in hydrochloric acid; or b with solutions of lanthanum chloride, sulfate or nitrate. Place 26.7 g of lanthanum chloride heptahydrate (LaCl₃7H₂O) or 31.2 g of lanthanum nitrate hexahydrate (La(NO₃)₃6H₂O) or 26.2 g of lanthanum sulfate nonahydrate (La₂(SO₄)₃9H₂O) in 150 ml of water in a 1 litre volumetric flask, then add 85 ml of 6 M hydrochloric acid (4.1). Allow to dissolve and then make up to 1 litre with water. Mix thoroughly. This solution is approximately 0.5 M in hydrochloric acid.

Calibration solutions 4.4 For the preparation of these, see the individual methods of determination for each trace element.

APPARATUS

5

Atomic absorption spectrometer fitted with sources emitting radiation characteristic of trace elements to be determined.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Preparation of extract solutions containing the elements to be determined 6.1 See Method 26a and/or 26b and, if appropriate, 26c.

Treatment of the test solution 6.2 Dilute an aliquot portion of the extract obtained by Method 26a, 26b or 26c with water and/or hydrochloric acid (4.1) or (4.2) so as to obtain, in the final solution for measurement, a concentration of the element to be determined that is appropriate to the calibration range used (7.2) and a hydrochloric acid concentration of at least 0.5 M and not more than 2.5 M. This operation may require one or more successive dilutions. The final solution has to be obtained by placing an aliquot portion of the diluted extract in a 100 ml volumetric flask. Let the volume of this aliquot portion be (a) ml. Add 10 ml of the lanthanum salt solution (4.3). Make up to volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. Let D be the dilution factor.

PROCEDURE

7

Preparation of a blank solution 7.1 Prepare a blank solution by repeating the whole procedure from the extraction stage, omitting only the test sample of fertiliser.

Preparation of calibration solutions 7.2 From the working calibration solution prepared using the method given for each individual trace element, prepare in 100 ml volumetric flasks a series of at least five calibration solutions of increasing concentration within the optimum measuring range of the spectrometer. If necessary, adjust the concentration of hydrochloric acid to bring it as close as possible to that of the diluted test solution (6.2). Add 10 ml of the same lanthanum salt solution (4.3) as used in (6.2). Make up to volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.

Determination 7.3 Prepare the spectrometer (5) for the determination and adjust to the wavelength given in the method for the individual trace element concerned. Spray three times in succession the calibration solutions (7.2), the test solution (6.2) and the blank solution (7.1), noting each result and flushing the instrument with distilled water between individual sprayings. Construct the calibration curve by plotting the average spectrometer reading for each calibration solution (7.2) along the ordinate and the corresponding concentration of the element, expressed in mg/ml, along the abscissa. From this curve, determine the concentrations of the relevant trace element in the test solution xs (6.2) and in the blank solution xb (7.1), expressing these concentrations in μg per ml.

EXPRESSION OF RESULTS

8

The percentage of trace element (E) in the fertiliser is given by:

$E(%)=[(xs-xb)×V×D]/(M×104)$

26e. — Determination of BORON in Fertiliser ExtrACTS BY MEANS OF ACIDIMETRIC TITRATION

SCOPE

1

This method defines a procedure for determining the boron content in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Method 26a or Method 26b and for which a declaration of total and/or water-soluble boron content is required.

PRINCIPLE

3

A mannitoboric complex is formed by the following reaction of the borate with mannitol:

$C6H8(OH)6+H3BO3→C6H15O8B+H2O$

REAGENTS

4

Methyl red indicator solution 4.1 Dissolve 0.1 g of methyl red (C₁₅H₁₅N₃O₂) in 50 ml of ethanol (95% in a 100 ml) volumetric flask. Make up the volume to 100 ml with water. Mix thoroughly.

Diluted hydrochloric acid solution, about 0.5 M 4.2 Mix 1 volume of hydrochloric acid HCl (ρ = 1.18 g/ml) with 20 volumes of water.

Sodium hydroxide solution, about 0.5 M 4.3 Must be free of carbon dioxide. Dissolve 20 g of sodium hydroxide (NaOH) in pellet form in a 1 litre volumetric flask containing about 800 ml of boiled water. When the solution has cooled, make up to 1000 ml with boiled water and mix thoroughly.

Standard sodium hydroxide solution, about 0.025 M 4.4 Must be free of carbon dioxide. Dilute the 0.5 M sodium hydroxide solution (4.3) 20 times with boiled water and mix thoroughly. The value of the solution expressed as boron (B) is to be determined (see paragraph 9).

Boron calibration solution (100 mg/ml B) 4.5 Dissolve 0.5719 g of boric acid (H₃BO₃), weighed to the nearest 0.1 mg, in water in a 1 litre volumetric flask. Make up to volume with water and mix thoroughly. Transfer to a plastic bottle for storage in a refrigerator.

• (4.6) D-mannitol (C₆H₁₄O₆) powder.

• (4.7) Sodium chloride (NaCl).

APPARATUS

5

• (5.1) pH meter with glass electrode.

• (5.2) Magnetic stirrer.

• (5.3) 400 ml beaker with teflon rod.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Preparation of the boron solution 6.1 See Methods 26a, 26b and, if appropriate, 26c.

PROCEDURE

7

Determination 7.1 Place in a 400 ml beaker (5.3) an aliquot portion (a) of the extract (6.1) containing 2 to 4 mg B. Add 150 ml of water. Add several drops of the methyl red indicator solution (4.1). In the case of extraction with Method 26b, acidify by adding 0.5 M hydrochloric acid (4.2) up to the point of change of the indicator solution, then add a further 0.5 ml of 0.5 M hydrochloric acid (4.2). After adding 3 g of sodium chloride (4.7), bring to boiling to drive off the carbon dioxide. Allow to cool. Place the beaker on the magnetic stirrer (5.2) and insert the precalibrated pH meter electrodes (5.1). Adjust the pH to exactly 6.3, first with the 0.5 M sodium hydroxide solution (4.3), then with the 0.025 M solution (4.4). Add 20 g of D-mannitol (4.6), dissolve completely and mix thoroughly. Titrate with the 0.025 M sodium hydroxide solution (4.4) to pH 6.3 (at least 1 minute stability). Let x₁ be the volume required.

BLANK SOLUTION

8

Prepare a blank solution by repeating the whole procedure from the preparation of solution stage, omitting only the fertiliser. Let x₀ be the volume required.

BORON (B) VALUE OF THE SODIUM HYDROXIDE SOLUTION (4.4)

9

Transfer by pipette 20 ml (2.0 mg B) of the calibration solution (4.5), into a 400 ml beaker and add several drops of methyl red indicator solution (4.1). Add 3 g of sodium chloride (4.7) and the hydrochloric acid solution (4.2) up to the point of change of the indicator solution (4.1).

EXPRESSION OF RESULTS

10

The percentage of boron in fertiliser is given by:

$$B%=(X1-X0)×F×V10×a×M$ where: B% is the percentage of boron in the fertiliser; x₁ is the volume, in ml, of the 0.025 M sodium hydroxide solution (4.4); xo is the volume, in ml, of the 0.025 M sodium hydroxide solution M (4.4); F is the boron (B) value, in mg/ml, of the 0.025 M sodium hydroxide solution (4.4); V is the volume, in ml, of the extract solution obtained in accordance with Method 26a or 26b; a is the volume, in ml, of the aliquot (7.1) taken from the extract solution (6.1); M is the mass, in grams, of the test sample taken in accordance with Method 26a or 26b.$

26f. — Determination of COBALT in Fertiliser Extracts by THE GRAVIMETRIC METHOD WITH 1-NITROSO-2-NAPHTHOL

SCOPE

1

This method defines a procedure for determining cobalt in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Method 26a or Method 26b for which a declaration of cobalt content is required.

PRINCIPLE

3

CobaltIII combines with 1-nitroso-2-naphthol to give a red precipitate Co(C₁₀H₆ONO)₃.2H₂O. After the cobalt present in the extract has been brought to the cobaltIII state, the cobalt is precipitated in an acetic acid medium by a solution of 1-nitroso-2-naphthol. After filtration, the precipitate is washed and dried to constant weight and then weighed as Co(C₁₀H₆ONO)₃.2H₂O.

REAGENTS

4

• (4.1) Hydrogen peroxide solution (H₂O₂ ρ = 1.11 g/ml) 30%.

Sodium hydroxide solution, about 2 M 4.2 Dissolve 8 g of sodium hydroxide in pellet form in 100 ml of water.

Diluted hydrochloric acid solution, about 6 M 4.3 Mix one volume of hydrochloric acid (ρ = 1.18 g/ml) with 1 volume of water.

4.4 Acetic acid (99.7% CH₃COOH) (ρ = 1.05 g/ml)

Acetic acid solution (1:2), about 6 M 4.5 Mix one volume of acetic acid (4.4) with 2 volumes of water.

• (4.6) Solution of 1-nitroso-2-naphthol in 100 ml of acetic acid (4.4). Add 100 ml of lukewarm water. Mix thoroughly. Filter at once. The solution obtained must be used immediately.

APPARATUS

5

• (5.1) Filter crucible P 16/ISO 4793, porosity 4, capacity 30 or 50 ml.

• (5.2) Drying oven at 130 ± 2°C.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Preparation of the cobalt solution 6.1 See Methods 26a or 26b.

Preparation of the solution to be analysed 6.2 Place the aliquot portion of the extract containing not more than 20 mg Co in a 400 ml beaker. If the extract is obtained according to Method 26b, acidify with five drops of hydrochloric acid (4.3). Add about 10 ml of the hydrogen peroxide solution (4.1). Allow the oxidant to react in the cold state for 15 minutes, then make up to about 100 ml with water. Cover the beaker with a watchglass. Bring the solution to boiling point and allow to boil for about 10 minutes. Cool. Make alkaline with the sodium hydroxide solution (4.21) drop by drop until black cobalt hydroxide begins to precipitate.

PROCEDURE

7

Add 10 ml of acetic acid (4.4) and make up the solution with water to about 200 ml. Heat until boiling. Using a burette, add 20 ml of the 1-nitroso-2-naphthol solution (4.6) drop by drop, stirring constantly. Complete by vigorous stirring to make the precipitate coagulate.

EXPRESSION OF RESULTS

8

1 mg of Co (C₁₀H₆ONO)₃.2H₂O precipitate corresponds to 0.096381 mg Co.

26g. — Determination of COPPER in Fertiliser Extracts by THE TITRIMETRIC METHOD

SCOPE

1

This method defines a procedure for determining copper in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Method 26a or Method 26b for which a declaration of copper content is required.

PRINCIPLE

3

The cupric ions are reduced in an acidic medium with potassium iodide:

$2Cu+++4I-→2CuI+I2.$

REAGENTS

4

• (4.1) Nitric acid (HNO₃ ρ = 1.40 g/ml).

• (4.2) Urea [(NH₂)₂ C O].

Ammonium biflouride (NH₄HF₂) solution (10% w/v) 4.3 Keep the solution in a plastic container.

Ammonium hydroxide solution (1 + 1) 4.4 Mix 1 volume of ammonia (NH₄OH, ρ = 0.9 g/ml) with 1 volume of water.

Sodium thiosulfate standard solution 4.5 Dissolve 7.812 g of sodium thiosulfate pentahydrate (Na₂S₂O₃.5H₂O) with water in a litre volumetric flask. This solution must be prepared so that 1 ml = 2 mg Cu. For stabilization, add several drops of chloroform. The solution must be kept in a glass container and protected from direct light.

• (4.6) Potassium iodide (KI).

Potassium thiocyanate (KSCN) solution (25% w/v) 4.7 Keep this solution in a plastic flask.

Starch solution (about 0.5%) 4.8 Place 2.5 g of starch in a 600 ml beaker. Add about 500 ml of water. Boil while stirring. Cool to ambient temperature. The solution has a short preservation period. Its preservation can be extended by adding about 10 mg of mercury iodide.

PREPARATION OF THE SOLUTION TO BE ANALYSED

5

Preparation of the copper solution.

PROCEDURE

6

Preparation of the solution for titration 6.1 Place an aliquot portion of the solution containing not less than 20 mg Cu in a 500 ml Erlenmeyer flask. Drive off any excess oxygen present by boiling briefly. Make up to volume of about 100 ml water. Add 5 ml of nitric acid (4.1), bring to boiling and allow to boil for about half a minute. Remove the Erlenmeyer flask from the heating apparatus, add about 3 g of urea (4.2) and resume boiling for about half a minute. Remove from the heating apparatus and add 200 ml of cold water. Where necessary, cool the contents of the Erlenmeyer flask to ambient temperature. Gradually add ammonium hydroxide solution (4.4) until the solution becomes blue, then add 1 ml in excess. Add 50 ml of ammonium bifluoride solution (4.3) and mix. Add 10 g of potassium iodide (4.6) and allow it to dissolve.

Titration of the solution 6.2 Place the Erlenmeyer flask on a magnetic stirrer. Insert the rod into the Erlenmeyer flask and adjust the stirrer to the desired speed. Using a burette, add standard sodium thiosulfate solution (4.5) until the brown colour of the iodine released from the solution becomes less intense. Add 10 ml of the starch solution (4.8). Continue to titrate with the sodium thiosulfate solution (4.5) until the purple colour has almost disappeared. Add 20 ml of the potassium thiocyanate solution (4.7) and continue titration until the violet blue colour has completely disappeared. Note the volume of thiosulfate solution employed.

EXPRESSION OF RESULTS

7

1 ml of standard sodium thiosulfate solution (4.5) corresponds to 2 mg Cu.

26h. — Determination of IRON in Fertiliser Extracts by ATOMIC ABSORPTION Spectrometry

SCOPE

1

This method describes a procedure for determining iron in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Methods 26a and 26b for which a declaration of total and/or water-soluble iron is required.

PRINCIPLE

3

After suitable treatment and dilution of the extract, the iron content is determined by atomic absorption spectrometry.

REAGENTS

4

Hydrochloric acid solution, about 6 M 4.1 See Method 26d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 26d (4.2).

• (4.3) Hydrogen peroxide solution (30% H₂O₂ ρ = 1.11 g/ml) free from trace elements.

Lanthanum salt solutions (10 g of La per litre) 4.4 See Method 26d (4.3).

Iron calibration solution 4.5 Iron stock solution (1000 μg/ml) 4.5.1 In a 500 ml beaker, weigh to the nearest 0.1 mg, 1 g of pure iron wire, add 200 ml of 6 M hydrochloric acid (4.1) and 15 ml of hydrogen peroxide solution (4.3). Heat on a hotplate until the iron is completely dissolved. When cool, transfer quantitatively to a 1 litre volumetric flask. Make up to volume with water and mix thoroughly. Iron working solution (100 μg/ml) 4.5.2 Place 20 ml of the stock solution (4.5.1) in a 200 ml volumetric flask. Make up to volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.

APPARATUS

5

Atomic absorption spectrometer: see Method 26d (5). The instrument must be fitted with a source of rays characteristic of iron (248.3 nm).

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Iron extract solution 6.1 See Methods 26a and/or 26b and, if appropriate, 26c.

Preparation of the test solution 6.2 See Method 26d (6.2). The test solution must contain 10% (v/v) of a lanthanum salt solution.

PROCEDURE

7

Preparation of the blank solution 7.1 See Method 26d (7.1). The blank solution must contain 10% (v/v) of the lanthanum salt solution used in 6.2.

Preparation of calibration solutions 7.2 See Method 26d (7.2). For an optimum determination range of 0 to 10 μg/ml of iron, place 0, 2, 4, 6, 8 and 10 ml respectively of working solution (4.5.2) in a series of 100 ml volumetric flasks. If necessary adjust the hydrochloric acid concentration as closely as possible to that of the test solution. Add 10 ml of the lanthanum salt solution used in 6.2. Make up to volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain 0, 2, 4, 6, 8 and 10 μg/ml respectively of iron.

Determination 7.3 See Method 26d (7.3). Prepare the spectrometer (5) for measurement at a wavelength of 248.3 nm.

EXPRESSION OF RESULTS

8

See Method 26d (8).

26i. — Determination of MANGANESE in Fertiliser Extracts by TITRATION

SCOPE

1

This method describes a procedure for determining manganese in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Methods 26a and 26b for which a declaration of manganese is required.

PRINCIPLE

3

If chloride ions are present in the extract, they are driven off by boiling with sulfuric acid. The manganese is oxidized by sodium bismuthate in a nitric acid medium. The permanganate formed is reduced by an excess of ferrous sulfate. This excess is titrated with a potassium permanganate solution.

REAGENTS

4

• (4.1) Concentrated sulfuric acid (H₂SO₄, ρ = 1.84 g/ml).

Sulfuric acid, about 9 M 4.2 Carefully mix 1 volume of concentrated sulfuric acid (4.1) with 1 volume of water.

Nitric acid, 6 M 4.3 Mix 3 volumes of nitric acid (HNO₃, ρ = 1.40 g/ml) with 4 volumes of water.

Nitric acid, 0.3 M 4.4 Mix 1 volume of 6 M nitric acid with 19 volumes of water.

• (4.5) Sodium bismuthate (NaBiO₃) (85%).

• (4.6) Kieselguhr.

• (4.7) Orthophosphoric acid, 15 M (H₃PO₄, ρ = 1.71 g/ml).

Ferrous sulfate solution, 0.15 M 4.8 Dissolve 41.6 g of ferrous sulfate heptahydrate (FeSO₄, 7 H₂O) in a 1 litre volumetric flask. Add 25 ml of concentrated sulfuric acid (4.1) and 25 ml phosphoric acid (4.7). Make up to 1000 ml. Mix.

Potassium permanganate solution, 0.02 M 4.9 Weigh out 3.160 g of potassium permanganate (KMnO₄) to within 0.1 mg. Dissolve and make up 1000 ml with water.

Silver nitrate solution, 0.1 M 4.10 Dissolve 1.7 g of silver nitrate (AgNO₃) in water and make up to 100 ml.

APPARATUS

5

• (5.1) Filter crucible P16/ISO 4793, porosity 4, capacity 50 ml, mounted on a 500 ml filtration flask.

• (5.2) Magnetic stirrer.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Manganese extract solution 6.1 See Methods 26a and 26b. If it is not known whether chloride ions are present, perform a test on the solution with one drop of the silver nitrate solution (4.10).

• (6.2) In the absence of chloride ions, place an aliquot portion of the extract containing 10 to 20 mg of manganese in a tall form 400 ml beaker. Bring to a volume of about 25 ml either by evaporation or by adding water. Add 2 ml of concentrated sulfuric acid (4.1).

If chloride ions are present, it is necessary to remove them as follows: 6.3 Place an aliquot portion of the extract containing 10 to 20 mg of manganese in a tall form 400 ml beaker. Add 5 ml of 9 M sulfuric acid (4.2). Under a fume hood, bring to boiling on a hotplate and allow to boil until copious white fumes are released. Continue until the volume is reduced to about 2 ml (thin film of syrupy liquid at the bottom of the beaker). Allow to cool to ambient temperature. Carefully add 25 ml of water and once again test for the presence of chlorides with one drop of the silver nitrate solution (4.10). If chlorides still remain, repeat the operation after adding 5 ml of 9 M sulfuric acid (4.2).

PROCEDURE

7

Add 25 ml of 6 M nitric acid (4.3) and 2.5 g of sodium bismuthate (4.5) to the 400 ml beaker containing the test solution. Stir vigorously for three minutes on the magnetic stirrer (5.2).

EXPRESSION OF RESULTS

8

1 ml of 0.02 M potassium permanganate solution corresponds to 1.099 mg of manganese (Mn). The percentage of manganese in the fertiliser is given by:

$$Mn(%)where=(xb-xs)×0.1099×———Va×M$ where: xb is the volume in ml of the permanganate used for the blank; xs is the volume in ml of the permanganate used for the test sample; V is the volume in ml of the extract solution in accordance with Methods 26a and 26b; a is the volume in ml of the aliquot portion taken from the extract (6.2) or (6.3); M is the mass in g of the test sample.$

26j. — Determination of MOLYBDENUM in Fertiliser Extracts by THE GRAVIMETRIC METHOD WITH 8-HYDROXYQUINOLINE

SCOPE

1

This method describes a procedure for determining molybdenum in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Methods 26a and 26b for which a declaration of molybdenum is required.

PRINCIPLE

3

The molybdenum level is determined by precipitation as molybdenyl oxinate under specific conditions.

REAGENTS

4

Sulfuric acid solution, approximately 1M 4.1 Carefully pour 55 ml of sulfuric acid (H₂SO₄, ρ = 1.84 g/ml) into a 1 litre volumetric flask containing 800 ml of water. Mix. After cooling, make up to one litre. Mix again.

Diluted ammonia solution (1:3) 4.2 Mix 1 volume of concentrated ammonia solution (NH₄OH, ρ = 0.9 g/ml) with 3 volumes of water.

Diluted acetic acid solution (1:3) 4.3 Mix 1 volume of concentrated acetic acid (99.7% CH₃COOH, ρ = 1.049 g/ml) with 3 volumes of water.

Solution of disodium salt of ethylene diamine tetraacetic acid (EDTA) 4.4 Dissolve 5 g of Na₂EDTA in water in a 100 ml volumetric flask. Make up to the calibration mark and mix.

Buffer solution 4.5 In a 100 ml volumetric flask, dissolve 15 ml of concentrated acetic acid and 30 g of ammonium acetate in water. Make up to 100 ml.

8-hydroxyquinoline (oxine) solution 4.6 In a 100 ml volumetric flask dissolve 3 g of 8-hydroxyquinoline in 5 ml of concentrated acetic acid. Add 80 ml of water. Add the ammonia solution (4.2) drop by drop until the solution becomes cloudy and then add the acetic acid (4.3) until the solution becomes clear again. Make up to 100 ml with water.

APPARATUS

5

• (5.1) Filter crucible P16/ISO 4793, porosity 4, capacity 30 ml.

• (5.2) pH meter with glass electrode.

• (5.3) Drying oven at 130 to 135°C.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

• (6.1) Preparation of the molybdenum solution. See Methods 26a and 26b.

PROCEDURE

7

Preparation of the test solution 7.1 Place an aliquot portion containing 25 to 100 mg Mo in a 250 ml beaker. Make up the volume to 50 ml with water. Adjust this solution to pH 5 by adding the sulfuric acid solution (4.1) drop by drop. Add 15 ml of EDTA solution (4.4) and then 5 ml of buffer solution (4.5). Make up to about 80 ml with water.

Obtaining and washing the precipitate 7.2 Obtaining the precipitate: Heat the solution slightly. Stirring constantly, add the oxine solution (4.6). Continue the precipitation until formation of a deposit is no longer observed. Add further reagent until the supernatant solution turns slightly yellow. A quantity of 20 ml should normally be sufficient. Continue to heat the precipitate slightly for two to three minutes. Filtration and washing: Filter through a filter crucible (5.1). Rinse several times with 20 ml of hot water. The rinse water should gradually become colourless indicating that oxine is no longer present.

Weighing the precipitate 7.3 Dry the precipitate at 130 to 135°C to constant weight (at least one hour). Allow to cool in a desiccator and then weigh.

EXPRESSION OF RESULTS

8

1 mg of molybdenyl oxinate, MoO₂(C₉H₆ON)₂, corresponds to 0.02305 mg Mo.

26k. — Determination of ZINC in Fertiliser Extracts by ATOMIC ABSORPTION Spectrometry

SCOPE

1

This method describes a procedure for determining zinc in fertiliser extracts.

FIELD OF APPLICATION

2

This procedure is applicable to extracts from samples of fertilisers obtained by Methods 26a and 26b for which a declaration of zinc is required.

PRINCIPLE

3

After suitable treatment and dilution of the extracts, the zinc level is determined by atomic absorption spectrometry.

REAGENTS

4

Hydrochloric acid solution, about 6 M 4.1 See Method 26d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 26d (4.2).

Lanthanum salt solutions (10 g of La per litre) 4.3 See Method 26d (4.3).

Zinc calibration solutions 4.4 Zinc stock solution (1000 mg/ml) 4.4.1 In a 1 litre volumetric flask dissolve 1 g of zinc powder or flakes weighed to within 0.1 mg in 25 ml of 6 M hydrochloric acid (4.1). When completely dissolved, make up to volume with water and mix thoroughly. Zinc working solution (100 mg/ml) 4.4.2 In a 200 ml volumetric flask, dilute 20 ml of the stock solution (4.4.1) in 0.5 M hydrochloric acid solution (4.2). Make up to volume with the 0.5 M hydrochloric acid solution and mix thoroughly.

APPARATUS

5

Atomic absorption spectrometer.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Zinc extract solution 6.1 See Methods 26a and/or 26b.

Preparation of the test solution 6.2 See Method 26d (6.2). The test solution must contain 10% by volume of lanthanum salt solution (4.3).

PROCEDURE

7

Preparation of the blank solution 7.1 See Method 26d (7.1). The blank solution must contain 10% by volume of the lanthanum salt solution used in 6.2.

Preparation of the calibration solutions 7.2 See Method 26d (7.2). For an optimum interval of 0 to 5 mg/ml of zinc, place 0, 0.5, 1, 2, 3, 4 and 5 ml, respectively, of the working solution (4.4.2) in a series of 100 ml volumetric flasks.Where necessary, adjust the concentration of hydrochloric acid to bring it as close as possible to that of the test solution. Add 10 ml of the lanthanum salt solution used in (6.2) to each volumetric flask. Make up to 100 ml with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain, respectively, 0, 0.5, 1, 2, 3, 4 and 5 mg/ml of zinc.

Determination 7.3 See Method 26d (7.3). Prepare the spectrometer (5) for measurements at a wavelength of 213.8 nm.

EXPRESSION OF RESULTS

8

See Method 26d (8).

Part II

General

1

When two or more methods are prescribed in this Part to determine a component of a fertiliser the choice of the method shall, except where otherwise indicated, be left to the agricultural analyst concerned; the method used must however be indicated in the certificate of analysis.

Reagents

2

Except where otherwise specified in the method of analysis, all reagents shall be of analytical quality. Where trace elements are to be determined, the purity of the reagents used shall be checked by means of a blank test.

Water

3

• (a) Except where otherwise specified, a reference in this Part to water shall be a reference to demineralized or distilled water.

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

• (c) Except where the method of analysis specifies a particular solvent or diluent, all dissolution, dilution, rinsing and washing operations mentioned in the methods of analysis shall be carried out using water.

Apparatus

4

• (a) Only special instruments and apparatus and specifically required apparatus and equipment are mentioned in the methods of analysis.

• (b) Apparatus and equipment shall be clean.

• (c) The accuracy of graduated glassware shall be assured by reference to the appropriate standards.

Methods of Analysis

5

• (1) Preparation of the sample for analysis

• (2) Determination of moisture

• (3) Determination of total nitrogen — chromium powder reduction method

• (4) Determination of urea

• (5) Determination of potassium — gravimetric method

• (6) Determination of the neutralising value in liming materials

• (7) Determination of fineness of products other than potassic basic slag

• (8) Determination of fineness of potassic basic slag

• (9) Determination of fineness of certain lime products by wet sieving.

1. — PREPARATION OF THE SAMPLE FOR ANALYSIS

INTRODUCTION

1

The preparation of a sample for analysis from the final sample received at the laboratory is a series of operations, usually sieving, grinding and mixing, carried out in such a way that the smallest amount weighed, as prescribed by the method of analysis chosen, is representative of the final sample. The sample should be ground to the fineness required by the method of analysis. (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.

SCOPE AND FIELD OF APPLICATION

2

This method is applicable to fertilisers in Groups 1(b), 1(c), 2(b), 2(c), 2(d), 3(b), 3(c), 4(a), 4(b), 4(c) and 5(b) of Section A and Group 5 and 6 of Section B of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992[^f00021].

PRINCIPLE

3

Solid fertilisers: 3.1 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: 3.2 the final sample is thoroughly mixed before each test portion is taken.

APPARATUS

4

• (4.1) Sample grinder capable of grinding the fertiliser to pass the specified sieve.

• (4.2) Mortar and pestle of suitable material and size.

• (4.3) Sieves having square apertures of 0.18 mm, 0.5 mm and 1.0 mm. Test sieves conforming to British Standard 410: 1986 are suitable.

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

PROCEDURE

5

WARNING

ALL OPERATIONS CONNECTED WITH THIS PROCEDURE SHOULD BE CARRIED OUT AS QUICKLY AS POSSIBLE TO MINIMISE 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 the 0.5 mm sieve (4.3). Grind the residue on the sieve, using the pestle and mortar (4.2), until all the material passes through the sieve. Carefully mix the sample.

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

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

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

SPECIAL CASES

6

Samples not to be ground 6.1 For those samples where the fineness of grinding is to be determined it shall be carried out on an unground sample. The sample should be well mixed (soft lumps may be disintegrated by lightly crushing) and divided into two parts, which are as identical as possible. All other determinations shall be carried out on the sample prepared in accordance with the directions in paragraph 5.1.

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 superphosphates may become doughy if ground mechanically. In these cases crush the sample in a mortar (4.2) so that all the material passes through a 1.0 mm sieve (4.3). Place the material so crushed in a clean container (4.4) and seal it until required for analysis.

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 practical means. Thoroughly remix the sample and place in a clean container (4.4).

FLUID FERTILISERS

7

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

SCOPE AND FIELD OF APPLICATION

1

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

PRINCIPLE

2

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.

APPARATUS

3

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

• (3.2) Electrically heated oven, suitably ventilated and capable of being maintained at 100 ± 2°C.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

5

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.

EXPRESSION OF RESULT

6

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

SCOPE AND FIELD OF APPLICATION

1

This method is applicable to fertilisers in Groups 1(b), 1(c), 3(b), 4(a) and 4(c) of Section A, Group 5 and 6 of Section B and Groups 1(c) and 1(d) of Section C of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992 in respect of which a declaration of total nitrogen is required.

PRINCIPLE

2

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

REAGENTS

3

• (3.1) Sodium hydroxide solution: 40 g per 100 ml, ammonia free.

• (3.2) Sulfuric acid, 0.05 M solution.

• (3.3) Sulfuric acid, 0.1 M solution.

• (3.4) Sulfuric acid, 0.25 M solution.

• (3.5) Sodium hydroxide, 0.2 M solution, carbonate free.

• (3.6) Chromium metal powder, 100 mesh, low nitrogen content.

• (3.7) Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

• (3.8) Anti-foaming agent, paraffin wax.

• (3.9) sulfuric acid (ρ = 1.84 g/ml).

• (3.10) Hydrochloric acid (ρ = 1.18 g/ml).

• (3.11) Catalyst mixture: 1000 g potassium sulfate and 50 g copper sulfate pentahydrate. The ingredients must be ground and thoroughly mixed.

Indicator solutions 3.12 Mixed indicator: 3.12.1 Mix 50 ml of 2 g/litre ethanolic solution of methyl red with 50 ml of 1 g/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.

• (3.13) pH indicator paper, wide range.

APPARATUS

4

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

PREPARATION OF SAMPLE

5

See Method 1.

PROCEDURE

6

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

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 sulfuric acid (3.9). Mix the contents of the flask and heat gently until boiling. Continue heating until dense white fumes of sulfuric acid are evolved for at least 15 minutes. Allow the mixture to cool and then carefully add 250 ml water. Allow to cool to room temperature and continue as described in 6.4.

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 sulfuric acid (3.9) (see Note). Add 0.5 g paraffin wax (3.8) to reduce foaming and mix. Heat the flask moderately at first, shaking from time to time until frothing ceases and the liquid is practically colourless. Continue the digestion for at least a further 60 minutes. Allow the mixture to cool and then carefully add 250 ml water. Allow to cool to room temperature, and continue as described in 6.4. Note: If organic matter other than urea exceeds 1.0 g add an additional 1.0 ml sulfuric acid for each 0.1 g organic matter in excess of 1.0 g.

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

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.

EXPRESSION OF RESULTS

7

Determine the quantity of sulfuric acid consumed.

• 1 ml 0.05 M sulfuric acid = 0.0014 g nitrogen.

• 1 ml 0.1 M sulfuric acid = 0.0028 g nitrogen.

• 1 ml 0.25 M sulfuric acid = 0.0070 g nitrogen.

4. — DETERMINATION OF UREA

SCOPE AND FIELD OF APPLICATION

1

This method is applicable to fertilisers in Group 1(c), of Section A, Group 5 and 6 of Section B and Group 1(d) of Section C of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992.

PRINCIPLE

2

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

REAGENTS

3

• (3.1) Activated charcoal.

Carrez solution I: 3.2 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: 3.3 10.6 g potassium ferrocyanide per 100 ml.

• (3.4) Hydrochloric acid solution, 0.02 M.

• (3.5) Sodium acetate solution, 136 g sodium acetate trihydrate per litre.

4-dimethylaminobenzaldehyde solution: 3.6 dissolve 1.6 g of 4-dimethylaminobenzaldehyde (4-DMAB) in 100 ml 96% ethanol and add 10 ml of hydrochloric acid (ρ = 1.18 g/ml).

• (3.7) Urea standard solution: 1.0 g per 100 ml (1 ml of this solution = 10 mg urea).

APPARATUS

4

• (4.1) Mechanical shaker.

• (4.2) Spectrometer with 10 mm cells.

PREPARATION OF SAMPLE

5

See Method 1.

PROCEDURE

6

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 M hydrochloric acid solution (3.4), shake for 30 minutes using a mechanical shaker (4.1) then add 10 ml sodium acetate solution (3.5) and mix well. Add 2 g activated charcoal (3.1) to the flask, shake well and allow to stand for a further 15 minutes. Add 5 ml Carrez solution I (3.2), followed by 5 ml Carrez solution II (3.3), mixing well between additions. Dilute to volume with water and mix well. Filter a portion of the solution through a dry filter paper into a clean dry 250 ml beaker.

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 flask; add 75 ml 0.02 M hydrochloric acid solution (3.4) and proceed as described above (6.1) commencing at “. . . shake for 30 minutes . . .”. Measure the absorbance of the solutions and construct a calibration graph relating the absorbances to the amounts of urea present.

EXPRESSION OF RESULTS

7

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:

5. — DETERMINATION OF POTASSIUM-GRAVIMETRIC METHOD

SCOPE AND FIELD OF APPLICATION

1

This method is applicable to fertilisers in Groups 3(b), 3(c), 3(d) and 4(c) of Section A and Group 5 and 6 of Section B of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992 in respect of which an indication of total potassium is required.

PRINCIPLE

2

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).

REAGENTS

3

• (3.1) Formaldehyde, 25-35% solution, filtered if necessary before use.

• (3.2) Potassium chloride.

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

• (3.4) Indicator solution: dissolve 0.5 g phenolphthalein in 100 ml 90% ethanol.

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

• (3.6) STPB solution: dissolve 32.5 g sodium tetraphenylborate in 480 ml of water, add 2 ml of sodium hydroxide solution (3.3) and 20 ml of a magnesium chloride solution (100 g of MgCl₂.6H₂O per litre). Stir for fifteen minutes and filter through a fine, ashless filter. Store this reagent in a plastic container.

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

• (3.8) Hydrochloric acid (ρ = 1.18 g/ml).

APPARATUS

4

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

• (4.2) Oven regulated to 120°C ± 10°C.

PREPARATION OF SAMPLE

5

See Method 1.

PROCEDURE

6

Preparation of the solution for analysis 6.1 Fertilisers containing little or no organic matter 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 (do not exceed 500°C). Maintain at this temperature for at least 16 hours and then open the furnace and allow the crucible to cool. Grind the residue to eliminate any lumps, add 50 ml water and 10 ml hydrochloric acid (3.8) and evaporate to dryness on a steam bath. Proceed as in 6.1.1, commencing “Add 5 ml hydrochloric acid (3.8) and 50 ml water.”.

Determination 6.2 6.2.1 Transfer by pipette an aliquot portion of the filtrate (6.1.1 or 6.1.2), containing 25-50 mg of potassium (30-60 mg K₂O) into a 250 ml beaker; make up to 50 ml with water. 6.2.2 To remove interferences, add 10 ml of the EDTA solution (3.5), several drops of the phenolphthalein solution (3.4) and stir in sodium hydroxide solution (3.3), drop by drop, until the solution turns red, then finally add a few more drops of sodium hydroxide to ensure an excess (usually 1 ml of sodium hydroxide is sufficient to neutralise the sample and ensure an excess). 6.2.3 To eliminate most of the ammonia boil gently for 15 minutes. Add water to make the volume up to 60 ml. Bring the solution to the boil, remove the beaker from the heat and add 10 ml formaldehyde (3.1). Add several drops of phenolphthalein solution (3.4) and, if necessary, more sodium hydroxide solution until a distinct red colour appears. Cover the beaker with a watch glass and place it on a steam bath for fifteen minutes.

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 weigh.

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) 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 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 on an aliquot portion of an aqueous solution of potassium chloride, containing at the most 40 mg of K₂O.

EXPRESSION OF RESULTS

7

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

6. — DETERMINATION OF THE NEUTRALISING VALUE IN LIMING MATERIALS

SCOPE AND FIELD OF APPLICATION

1

This method is applicable to products in Groups 5(a) and 5(b) of Section A of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992.

PRINCIPLE

2

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

REAGENTS

3

• (3.1) Hydrochloric acid, 0.5 M solution.

• (3.2) Sodium hydroxide, 0.5 M solution (carbonate free).

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

PREPARATION OF SAMPLE

4

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

PROCEDURE

5

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 M hydrochloric acid (3.1), cover the flask with a watch glass and boil the contents gently for five minutes. Cool the mixture to room temperature, add two or three drops of the phenolphthalein indicator (3.3) and titrate with 0.5 M sodium hydroxide solution (3.2) to the end point of the indicator.

EXPRESSION OF RESULTS

6

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

7. — DETERMINATION OF FINENESS OF PRODUCTS OTHER THAN POTASSIC BASIC SLAG

SCOPE AND FIELD OF APPLICATION

1

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 to the Fertilisers Regulations (Northern Ireland) 1992.

PRINCIPLE

2

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

APPARATUS

3

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 sieves conforming to British Standard 410: 1986 are suitable.

PROCEDURE

4

For sieving through 3.5 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 of 100°C for 24 hours and thoroughly mix. Weigh to the nearest 0.1 g, 200 g and transfer to the sieve with the lower receiver attached. Proceed as described in 4.4.

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.

EXPRESSION OF RESULTS

5

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

8. — DETERMINATION OF FINENESS OF POTASSIC BASIC SLAG

SCOPE AND FIELD OF APPLICATION

1

Exclusively to “Potassic basic slag” in Group 3(b) of Section A of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992.

PRINCIPLE

2

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.

PROCEDURE

4

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 thoroughly 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).

EXPRESSION OF RESULTS

5

Express the fineness of the slag as

$AB×100.$

9. — DETERMINATION OF FINENESS OF CERTAIN LIME PRODUCTS BY WET SIEVING

SCOPE

1

This method is applicable to products in Groups 5(b) of Section A of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992[^f00022] which are susceptible to clogging, caking, electrostatic changes or agglomeration on pre-drying. The method is not applicable to burnt and hydrated lime products.

PRINCIPLE

2

The liming material is suspended in water. The suspension is sieved under continuous water spraying or using a mechanical wet-sieving machine. The fractions retained on the sieves are collected and dried.

APPARATUS

3

Usual laboratory apparatus and in particular:

• (3.1) Balance, capable of weighing to the nearest 0.01 g.

• (3.2) Stainless steel woven wire test sieves 100 mm diameter, complying with ISO 3310-1, with nominal apertures of 5.00 mm, 3.35 mm and 150 microns.

• (3.3) Stainless steel woven wire test sieving complying with ISO 3310-1, with nominal apertures of 10.00 mm.

• (3.4) Oven capable of being controlled at 105°C ± 2.

• (3.5) Rotating end over end shaker: 35-40 turns per minute.

SAMPLING

4

Procedure for samples with dry matter content ≥ 60% 4.1 Pass the laboratory sample through a sieve with nominal apertures of 10.00 mm (3.3). If necessary, lightly crush any lumps by means of a soft brush. Remove any lumps which cannot be crushed in this way and record the weight of the residue and the weight of the lumps. Take account of these lumps when recording the final results. Thoroughly mix the sieved sample and quarter down until a representative sample portion of about 50 g is obtained.

Procedure for samples with dry matter content < 60% which cannot be treated as per 4.1 due to the nature of the material 4.2 Empty the whole of the sample onto a clean dry surface and flatten to form a regular shape about 25 mm thick. Divide into four approximately equal portions and reject two opposite quarters. Take small portions from random places on all the exposed surfaces to give a sample portion of about 50 g.

PROCEDURE

5

Weigh the sample portion (4.1 or 4.2) to the nearest 0.01 g and transfer to a 500 ml flask. Add approximately 300 ml of de-mineralized water, stopper and shake vigorously by hand for 30 seconds. Remove the stopper for an instant to relieve the pressure and replace the stopper. Place the flask in the rotating end over end shaker (3.5) and shake for 60 minutes to ensure the complete suspension of the sample.

DRY MATTER CONTENT

6

Determine the dry matter content of a portion of the original sample using the method given in Method 2.

EXPRESSION OF RESULTS

7

Original dry mass 7.1 Calculate the original dry mass (Md) of material, using the following formula. $Md=M×DM$ where: M is the mass of the test portion taken for the sieving test. DM is the percentage dry matter obtained in 6.

Sieve fraction 7.2 Calculate the percentage of material retained on each sieve, using the following formula: $Xn=Mn/Md×100$ where: Xₙ is the percentage by mass retained on sieve n. Mₙ is the dry mass retained on sieve n. Md is the dry mass of the test portion. Report the percentages of material (100 − Xn) which will pass through each sieve. Carry out two single tests on separate test portions prepared from the same original sample. Record the mean of the two individual results for each sieve as the result (corrected if necessary for the presence of lumps (4.1)).

SCHEDULE 3

FORM OF CERTIFICATE OF ANALYSIS

Signed

Sealed with the Official Seal of the Department of Agriculture for Northern Ireland on

L. G. McKibben — Assistant Secretary — 31st October 1996.

Explanatory note

(This note is not part of the Regulations.)

1 These Regulations revoke and replace the Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1992, the Fertilisers (Sampling and Analysis) (Amendment) Regulations (Northern Ireland) 1992 and the Fertilisers (Sampling and Analysis) (Amendment) Regulations (Northern Ireland) 1994. They implement as respects Northern Ireland the Directives listed in paragraph 2.

2 The Directives implemented are: Commission Directive 77/535/EEC (O.J. No. L213, 22.8.77) on the approximation of the laws of the Member States relating to methods of sampling and analysis for fertilisers; Commission Directive 79/138/EEC (O.J. No. L39, 14.2.79, p. 3) amending Directive 77/535/EEC in respect of methods of analysis for magnesium; Commission Directive 87/94/EEC (O.J. No. L38, 7.2.87) on the approximation of the laws of Member States relating to procedures for the control of characteristics of, limits for and, resistance to detonation of straight ammonium nitrate fertilisers of high nitrogen content; Commission Directive 87/566/EEC (O.J. No. L342, 4.12.87, p. 32) amending Directive 77/535/EEC in respect of methods of sampling for fluid fertilisers; Commission Directive 88/126/EEC (O.J. No. L63, 9.3.88, p. 12) amending Directive 87/94/EEC, in respect only of its date for implementation by the Member States; Commission Directive 89/519/EEC (O.J. No. L265, 12.9.89, p. 30) supplementing and amending Directive 77/535/EEC (O.J. No. L213, 22.8.77, p. 1) on the approximation of the laws of the Member States relating to methods of sampling and analysis of fertilisers; Commission Directive 93/1/EEC (O.J. No. L113, 7.5.93, p. 17) which amends Commission Directive 77/535/EEC (O.J. No. L213, 22.8.77, p. 1) on the approximation of the laws of the Member States relating to methods of sampling and analysis of fertilisers; Commission Directive 95/8/EC (O.J. No. L86, 20.4.95, p. 41) amending Directive 77/535/EEC (O.J. No. L213, 22.8.77, p. 1) on the approximation of the laws of Member States relating to methods of sampling and analysis of fertilisers.

3 The Regulations provide for a number of matters concerning the sampling and analysis of fertilisers including: a the amounts of fertilisers from which samples are to be taken (regulation 2); b the manner of taking, marking, sealing and fastening up of samples (regulation 3 and Schedule 1); c the methods of sending part of a sample (regulation 4); d the methods by which analyses are to be carried out (regulation 5 and Schedule 2) and the form of certificate of analysis (regulation 6 and Schedule 3).

4 The principal changes are the introduction of sampling procedures for trace elements in fertilisers at a concentration greater than 10%, (Method 26 in Part 1 of Schedule 2) and of a method for the determination of fineness by wet sieving of certain lime products (Method 9 in Part 2 of Schedule 2) and the deletion of certain otiose methods (5a and b, 6, 7b, 8, 9a and b, and 10-14 in Part 2 of Schedule 2).

5 The Regulations come into operation on 16th December 1996.

Footnotes

[^f00001]: 1970 c. 40; section 74A was inserted by s. 4(1) of, and paragraph 6 of Schedule 4 to the European Communities Act 1972 (c. 68) and there are other amendments not relevant to these Regulations

[^f00002]: 1954 c. 33 (N.I.)

[^f00003]: S.R. 1992 No. 187

[^f00004]: S.R. 1991 No. 540

[^f00005]: S.R. 1992 No. 235

[^f00006]: S.R. 1994 No. 166

[^f00007]: Biuret can be purified beforehand by washing with 10% ammonia solution, then with acetone and drying under vacuum at room temperature.

[^f00008]: S.R. 1992 No. 187

[^f00009]: S.R. 1992 No. 187

[^f00010]: S.R. 1992 No. 187

[^f00011]: Where the fertiliser is normal superphosphate or concentrated superphosphate in Group 2(a) of Section A, or NPK fertiliser in Group 1, NP fertiliser in Group 2, or PK fertiliser in Group 4 of Section B or NPK fertiliser suspension, NP fertiliser suspension or PK fertiliser suspension in Section C of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992

[^f00012]: Where the fertiliser is triple superphosphate in Group 2(a) of Section A, or NPK fertiliser containing soft ground rock phosphate or partially solubilised rock phosphate in Group 1, or NP fertiliser containing soft ground rock phosphate or partially solubilised rock phosphate in Group 2, or PK fertiliser containing soft ground rock phosphate or partially solubilised rock phosphate in Group 4 of Section B of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992

[^f00013]: If no mechanical shaker is available, the flask may be shaken by hand every 5 minutes

[^f00015]: 21 ml when the solution to be precipitated contains more than 15 ml of citrate solution (neutral citrate, Petermann or Joulie alkaline citrate).

[^f00016]: To precipitate phosphate solutions containing more than 15 ml citrate solution (neutral, Petermann or Joulie) which have been acidified with 21 ml concentrated nitric acid (see footnote to paragraph 6.1) use 80 ml of the precipitating reagent.

[^f00017]: S.R. 1992 No. 187

[^f00018]: A reaction time of 90 minutes is sufficient in the case of most of the organic substances in the presence of silver nitrate catalyst.

[^f00019]: Commercially available standard copper solution may be used.

[^f00020]: Whatman 541 or equivalent

[^f00021]: S.R. 1992 No. 187

[^f00022]: S.R. 1992 No. 187