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

Removal of carbonates 5.2 Place the sample for analysis in the reaction flask (B). Add 100 ml of sulfuric acid (3.2). The prills dissolve in about 10 minutes at ambient temperature. Assemble the apparatus as indicated in the diagram: connect one end of the absorption tube (A) to the nitrogen source (4.2) via a non-return flow device containing 5 to 6 mm of mercury and the other end to the feed tube which enters the reaction flask. Place the Vigreux fractioning column (C') and the condenser (C) with cooling water supply in position. Adjust the nitrogen to provide a moderate flow through the solution, bring the solution to boiling point and heat for two minutes. At the end of this time there should be no more effervescence. If effervescence is seen, continue heating for 30 minutes. Allow the solution to cool for at least 20 minutes with the nitrogen flowing through it. Complete assembly of the apparatus as indicated in the diagram by connecting the condenser tube to the Drechsel bottle (D) and the bottle to the absorption vessel F₁ and F₂. The nitrogen must continue to pass through the solution during the assembly operation. Rapidly introduce 50 ml of barium hydroxide solution (3.4) into each of the absorption vessels (F₁ and F₂). Bubble a stream of nitrogen through for about 10 minutes. The solution in the absorbers must remain clear. If this does not happen, the carbonate removal process must be repeated with a fresh barium hydroxide solution.

Oxidation and absorption 5.3 After withdrawing the nitrogen feed tube, rapidly introduce 20 grams of chromium trioxide (3.1) and 6 ml of silver nitrate solution (3.3) via the side arm of the reaction flask (B). Connect the apparatus to the suction pump and adjust the nitrogen flow so that a steady stream of gas bubbles passes through the sintered-glass absorbers (F₁) and (F₂). Heat the reaction flask (B) until the liquid boils and keep it boiling for 90 minutes[^f00018]. It may be necessary to adjust the suction-regulating valve (G) to control the nitogen flow since it is possible that the barium carbonate precipitated during the test may block the sintered glass discs. The operation is satisfactory when the barium hydroxide solution in the absorber (F₂) remains clear. Otherwise repeat the test. Stop heating and dismantle the apparatus. Wash each of the distributors both inside and outside to remove barium hydroxide and collect the washings in the corresponding absorber. Place the distributors one after the other in a 600 ml beaker which will subsequently be used for the determination. Rapidly filter under vacuum firstly the contents of absorber F₂ and then absorber F₁ using the sintered glass crucible. Collect the precipitate by rinsing the absorbers with water (3.10) and wash the crucible with 50 ml of the same water. Place the crucible in the 600 ml beaker and add about 100 ml of boiled water (3.10). Introduce 50 ml of boiled water into each of the absorbers and pass nitrogen through the distributors for five minutes. Combine the water with that from the beaker. Repeat the operation once to ensure that the distributors are rinsed thoroughly.

Measurement of the carbonates originating from organic material 5.4 Add five drops of phenolphthalein (3.8) to the contents of the beaker. The solution becomes red in colour. Add hydrochloric acid (3.5) drop by drop until the pink colour just disappears. Stir the solution well in the crucible to check the pink colour does not reappear. Add five drops of bromophenol blue and titrate with hydrochloric acid until the solution turns yellow. Add a further 10 ml of hydrochloric acid. Heat the solution to boiling point and continue boiling for a maximum of one minute. Check carefully that no precipitate remains in the liquid. Allow to cool and titrate with the sodium hydroxide solution (3.6).

BLANK TEST

6

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

EXPRESSION OF RESULTS

7

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

$$C%=0.06×V1—V2E$ where: E = the mass in grams of the test portion: V₁ = the total volume in ml of 0.1 M hydrochloric acid added after the change in colour of the phenolphthalein; V₂ = the volume in ml of the 0.1 M sodium hydroxide solution used in the titration.$

14d. — DETERMINATION OF THE pH VALUE

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedure for measuring the pH value of a solution of a straight ammonium nitrate fertiliser containing more than 28% nitrogen by weight.

PRINCIPLE

2

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

REAGENTS

3

Distilled or demineralised water, free from carbon dioxide.

Buffer solution, pH 6.88 at 20°C 3.1 Dissolve 3.40 ± 0.01 grams of potassium dihydrogen orthophosphate (KH₂PO₄) in approximately 400 ml of water. Then dissolve 3.55 ± 0.01 gram of disodium hydrogen orthophosphate (Na₂HPO₄) in approximately 400 ml of water. Transfer the two solutions without loss into a 1 litre graduated flask, make up to the mark and mix. Keep the solution in an airtight vessel.

Buffer solution, pH 4.00 at 20°C 3.2 Dissolve 10.21 ± 0.01 grams of potassium hydrogen phthalate (KHC₈O₄H₄) in water, transfer without loss into a 1 litre standard flask, make up to the mark and mix.

APPARATUS

4

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

PROCEDURE

5

Calibration of the pH meter 5.1 Calibrate the pH meter (4) at a temperature of 20 (± 1)°C, using the buffer solutions (3.1), (3.2) or (3.3). Pass a slow stream of nitrogen onto the surface of the solution and maintain this throughout the test.

Determination 5.2 Pour 100.0 ml of water onto 10 (± 0.01) grams of the sample in a 250 ml beaker. Remove the insolubles by filtering, decanting or centrifuging the liquid. Measure the pH value of the clear solution at a temperature of 20 (± 1)°C, according to the same procedure as for the calibration of the meter.

EXPRESSION OF RESULTS

6

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

14e. — DETERMINATION OF THE PARTICLE SIZE

SCOPE AND FIELD OF APPLICATION

1

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

PRINCIPLE

2

The test sample is sieved on a nest of three sieves, either by hand or by mechanical means. The mass retained on each sieve is recorded and the percentage of material passing the required sieves is calculated.

APPARATUS

3

• (3.1) 200mm diameter woven-wire test sieves to BS 410 (1986) with apertures of 2.0 mm, 1. 0 mm and 0.5 mm respectively of standard ranges. One lid and one receiver for these sieves.

• (3.2) Balance to weigh to 0.1 gram.

• (3.3) Mechanical sieve shaker (if available) capable of imparting both vertical and horizontal motion to the test sample.

PROCEDURE

4

• (4.1) The sample is divided representatively into portions of approximately 100 grams.

• (4.2) Weigh one of these portions to the nearest 0.1 gram.

• (4.3) Arrange the nest of sieves in ascending order (receiver, 0.5 mm, 1 mm, 2 mm) and place the weighed test portion on the top sieve. Fit the lid to the top of the nest of sieves.

• (4.4) Shake by hand or machine, imparting both a vertical and horizontal motion and, if by hand, tapping occasionally. Continue this process for 10 minutes or until the quantity passing through each sieve in one minute is less than 0.1 gram.

• (4.5) Remove the sieves from the nest in turn and collect the material retained, brush gently from the reverse side with a soft brush, if necessary.

• (4.6) Weigh the material retained on each sieve and that collected in the receiver, to the nearest 0.1 gram.

EVALUATION OF RESULTS

5

• (5.1) Convert the fraction masses to a percentage of the total of the fraction masses (not of the original charge).

• Calculate the percentage in the receiver (ie < 0.5 mm): A%

• Calculate the percentage retained on the 0.5 mm sieve: B%

• Calculate the percentage passing 1.0 mm, ie (A + B)%.

• The sum of the fraction masses should be within 2% of the initial mass taken.

• (5.2) At least two separate analyses should be carried out and the individual results for A should not differ by more than 1.0% absolute and for B by more than 1.5% absolute. Repeat the test if this is not the case.

EXPRESSION OF RESULTS

6

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

14f. — DETERMINATION OF THE CHLORINE CONTENT (AS CHLORIDE ION)

SCOPE AND FIELD OF APPLICATION

1

This method defines the procedure for the determination of the chlorine content (as chloride ion) of straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

PRINCIPLE

2

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

REAGENTS

3

Distilled or demineralised water, free from chloride ions.

• (3.1) Acetone AR.

• (3.2) Concentrated nitric acid (density at 20°C ρ = 1.40 g/ml).

• (3.3) Silver nitrate 0.1 M standard solution. Store this solution in a brown glass bottle.

• (3.4) Silver nitrate 0.004 M standard solution — prepare this solution at the time of use.

• (3.5) Potassium chloride 0.1 M standard reference solution. Weigh, to the nearest 0.1 mg, 3.7276 grams of analytical-grade potassium chloride, previously dried for one hour in an oven at 130°C and cooled in a desiccator to ambient temperature. Dissolve in a little water, transfer the solution without loss into a 500 ml standard flask, dilute to the mark and mix.

• (3.6) Potassium chloride 0.004 M standard reference solution — prepare this solution at the time of use.

APPARATUS

4

• (4.1) Potentiometer with silver indicating electrode and calomel reference electrode, sensitivity 2 mV, covering the range −500 to +500 mV, or with silver and mercury (1) sulfate electrodes.

• (4.2) Bridge, containing a saturated potassium nitrate solution, connected to the calomel electrode (4.1), fitted at the ends with porous plugs. This bridge is not necessary if silver and mercury (1) sulfate electrodes are used.

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

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

PROCEDURE

5

Standardisation of the silver nitrate solution 5.1 Take 5.00 ml and 10.00 ml of the standard reference potassium chloride solution (3.6) and place in two low-form beakers of convenient capacity (for example 250 ml). Carry out the following titration of the contents of each beaker. Add 5 ml of the nitric acid solution (3.2), 120 ml of acetone (3.1) and sufficient water to bring the total volume to about 150 ml. Place the rod of the magnetic stirrer (4.3) in the beaker and set the stirrer in motion. Immerse the silver electrode (4.1) and the free end of the bridge (4.2) in the solution. Connect the electrodes to the potentiometer (4.1) and, after verifying the zero of the apparatus, note the value of the starting potential. Titrate, using the microburette (4.4), adding initially 4 or 9 ml respectively of the silver nitrate solution corresponding to the standard reference potassium chloride solution used. Continue the addition in 0.1 ml portions for the 0.004 M solutions and in 0.05 ml portions for the 0.1 M solutions. After each addition, await the stabilisation of the potential. Record the volumes added and the corresponding value of the potential in the first two columns of a table. In a third column of the table, record the successive increments (Δ₁E) of the potential E. In a fourth column, record the differences (Δ₂E) positive or negative, between the potential increments (Δ₁E). The end of the titration corresponds to the addition of the 0.1 or 0.05 ml portion (V₁) of the silver nitrate solution which gives the maximum value of Δ₁E. In order to calculate the exact volume (Veq) of the silver nitrate solution corresponding to the end of the reaction, use the formula: $Veq=Vo+(V1×bB)$ where: Vo is the total volume, in ml, of the silver nitrate solution immediately lower than the volume which gives the maximum increment of Δ₁E; V₁ is the volume, in ml, of the last portion of the silver nitrate solution added (0.1 or 0.05 ml); b is the last positive value of Δ₂E; B is the sum of the absolute values of the last positive values of Δ₂E and the first negative value of Δ₂E (see example in Table 1).

Blank test 5.2 Calculate the blank value using the equation below and take account thereof when calculating the final result. The result V₄ of the blank test on the reagents is given, in ml, by the formula: $V4=2V3—V2$ where: V₂ is the value, in ml, of the exact volume (Veq) of the silver nitrate solution corresponding to the titration of 10 ml of the potassium chloride standard reference solution used; V₃ is the value, in ml, of the exact volume (Veq) of the silver nitrate solution corresponding to the titration of 5 ml of the potassium chloride standard reference solution used.

Check test 5.3 The blank test can at the same time serve as a check that the apparatus is functioning satisfactorily and that the test procedure is being implemented correctly.

Determination 5.4 Take a portion of sample in the range of 10 to 20 grams and weigh to the nearest 0.01 gram. Transfer quantitatively to a 250 ml beaker. Add 20 ml of water, 5 ml of nitric acid solution (3.2), 120 ml of acetone (3.1) and sufficient water to bring the total volume to about 150 ml. Place the rod of the magnetic stirrer (4.3) in the beaker, place the beaker on the stirrer and set the stirrer in motion. Immerse the silver electrode (4.1) and the free end of the bridge (4.2) in the solution, connect the electrodes to the potentiometer (4.1) and, after having verified the zero of the apparatus, note the value of the starting potential. Titrate with the silver nitrate solution, by additions from the microburette (4.4) in increments of 0.1 ml. After each addition, await the stabilisation of the potential. Continue the titration as specified in 5.1, starting from the fourth paragraph: ‘Record the volumes added and the corresponding values of the potential in the first two columns of a table …'

EXPRESSION OF RESULTS

6

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

14g. — DETERMINATION OF COPPER

SCOPE AND FIELD OF APPLICATION

1

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

PRINCIPLE

2

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

REAGENTS

3

• (3.1) Hydrochloric acid (density at 20°C ρ = 1.18 g/ml).

• (3.2) Hydrochloric acid, 6 M solution.

• (3.3) Hydrochloric acid, 0.5 M solution.

• (3.4) Ammonium nitrate.

• (3.5) Hydrogen peroxide, 30%.

• (3.6) Copper solution[^f00019] (stock): weigh, to the nearest 0.001 gram, 1 gram of pure copper, dissolve in 25 ml of 6 M hydrochloric acid solution (3.2), add 5 ml of hydrogen peroxide (3.5) in portions and dilute to 1 litre with water. 1 ml of this solution contains 1,000 μg of copper (Cu).

• (3.6.1) Copper solution (dilute): dilute 10 ml of stock solution (3.6) to 100 ml with water and then dilute 10 ml of the resulting solution to 100 ml with water. 1 ml of the final dilution contains 10 μg of copper (Cu).

APPARATUS

4

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

PROCEDURE

5

Preparation of the solution for analysis 5.1 Weigh 25 grams, to the nearest 0.001 gram, of the sample into a 400 ml beaker, add carefully 20 ml of hydrochloric acid (3.1) (there may be a vigorous reaction due to carbon dioxide formation). Add more hydrochloric acid, if necessary. When effervescence has stopped, evaporate to dryness on a steam bath, stirring occasionally with a glass rod. Add 15 ml 6 M hydrochloric acid solution (3.2) and 120 ml of water. Stir with the glass rod, which should be left in the beaker, and cover the beaker with a watch glass. Boil the solution gently until dissolution is complete and then cool. Transfer the solution quantitatively into a 250 ml graduated flask, by washing the beaker with 5 ml 6 M hydrochloric acid (3.2), and twice with 5 ml of boiling water, cool and make up to the mark with 0.5 M hydrochloric acid (3.3) and mix carefully. Filter through a copper-free filter paper[^f00020], discarding the first 50 ml.

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

Determination 5.3 Preparation of sample and blank test solutions 5.3.1 Dilute the sample solution (5.1) and the blank test solution (5.2) with 0.5 M hydrochloric acid solution (3.3) to a concentration of copper within the optimal measuring range of the spectrometer. Normally no dilution is needed. Preparation of the calibration solutions 5.3.2 By diluting the standard solution (3.6.1) with 0.5 M hydrochloric acid solution (3.3), prepare at least five standard solutions corresponding to the optimal measuring range of the spectrometer (0 to 5.0 μg/1 Cu). Before making up to the mark, add ammonium nitrate (3.4) to every solution to give a final concentration of 100 mg per ml.

Measurement 5.4 Set up the spectrometer (4) at a wavelength of 324.8 nm and use an oxidising air-acetylene flame. Spray, in triplicate, the calibration solutions (5.3.2), the sample solution and the blank solution (5.3.1), washing the instrument through with distilled water between each spraying. Plot the calibration curve using the mean absorbances of every standard used as the ordinates and the corresponding concentrations of copper in μg/ml as the abscissae. Determine the concentration of copper in the final sample and blank solutions by reference to the calibration curve.

EXPRESSION OF RESULTS

6

Calculate the copper content of the sample taking into account the weight of the test sample, the dilutions carried out in the course of the analysis and the value of the blank. Express the result as mg Cu/kg.

15. — EXTRACTION OF TOTAL CALCIUM, TOTAL MAGNESIUM, TOTAL SODIUM AND TOTAL SULFUR IN THE FORM OF SULFATES

SCOPE

1

This method is for the extraction of total calcium, total sodium and total sulfur present in the form of sulfates.

FIELD OF APPLICATION

2

This method applies to all fertilisers, for which a declaration of the total calcium, total magnesium, total sodium and total sulfur in the form of sulfates is required.

PRINCIPLE

3

Dissolution by boiling in dilute hydrochloric acid.

REAGENTS

4

• (4.1) Diluted hydrochloric acid;

• One volume of hydrochloric acid (ρ = 1.18 g/ml) plus one volume of water.

APPARATUS

5

Electric hot plate with adjustable temperature.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 Calcium, magnesium, sodium and sulfur in the form of sulfates are extracted from a test sample of 5 g weighed to within 1 mg. However, when the fertiliser contains more than 15% of sulfur (S) i.e. 37.5% SO₃, and more than 18.8% of calcium (Ca) i.e. 26.3% CaO, the extraction of calcium and sulfur is carried out on a test sample of 1 g, weighed to within 1 mg. Place the test sample in a 600 ml beaker.

Preparation of the solution 7.2 Add approximately 400 ml of water and, taking care when the sample contains a significant quantity of carbonates, 50 ml 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. Transfer quantitatively into a 500 ml 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 clear. Stopper if the filtrate is not used immediately.

16. — EXTRACTION OF TOTAL SULFUR

SCOPE

1

This method is for the extraction of total sulfur contained in fertilisers in elemental form and/or in other chemical combinations.

FIELD OF APPLICATION

2

This method applies to all fertilisers for which a declaration of the total sulfur present in various forms (elemental, thiosulfate, sulfite and sulfate) is required.

PRINCIPLE

3

Elemental sulfur is converted in an alkaline medium into polysulfides and thiosulfate; these, together with any sulfites which may be present, are then oxidised with hydrogen peroxide. The various forms of sulfur are thus converted into sulfate which is determined by precipitation as barium sulfate (method 23).

REAGENTS

4

• (4.1) Diluted hydrochloric acid;

• One volume of hydrochloric acid (ρ = 1.18 g/ml) plus one volume of water.

• (4.2) Sodium hydroxide solution, NaOH, 30% minimum (ρ = 1.33).

• (4.3) Hydrogen peroxide solution, 30% w/w.

• (4.4) Aqueous solution of barium chloride BaCl₂.2H₂O, 122 gram per litre.

APPARATUS

5

Electric hot plate with adjustable temperature.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 Weigh out to within 1 mg a quantity of fertiliser containing between 80 and 350 mg of sulfur (S) or 200 and 875 mg SO₃.

17. — EXTRACTION OF WATER-SOLUBLE CALCIUM, MAGNESIUM, SODIUM AND SULFUR (IN THE FORM OF SULFATES)

SCOPE

1

This method is for the extraction of water-soluble calcium, magnesium, sodium and sulfur (in the form of sulfates), so that the same extract can be used to determine each nutrient required.

2

FIELD OF APPLICATION

PRINCIPLE

3

The nutrients are dissolved in boiling water.

REAGENTS

4

Distilled or demineralised water of equivalent quality.

APPARATUS

5

Electric hot plate with adjustable temperature.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 a Where fertilisers contain no sulfur or where they contain, at the same time, no more than 3% of sulfur (S) i.e. 7.5% SO₃, and no more than 4% of calcium (Ca) i.e. 5.6% CaO, weigh out 5 g of fertiliser to within 1 mg. b Where fertilisers contain more than 3% of sulfur (S) and more than 4% of calcium (Ca), weigh out 1 g of fertiliser to within 1 mg.

18. — EXTRACTION OF WATER-SOLUBLE SULFUR

SCOPE

1

This method is for the extraction of water-soluble sulfur contained in fertilisers, in various forms.

FIELD OF APPLICATION

2

This method applies to all fertilisers for which a declaration of the water-soluble sulfur trioxide is required.

PRINCIPLE

3

Soluble forms of sulfur are dissolved in cold water and converted into sulfate by oxidation with hydrogen peroxide in an alkaline medium.

REAGENTS

4

• (4.1) Diluted hydrochloric acid;

• One volume of hydrochloric acid (ρ = 1.18 g/ml) plus one volume of water.

• (4.2) Sodium hydroxide solution containing at least 30% NaOH (ρ = 1.33 g/ml).

APPARATUS

5

• (5.1) 500 ml graduated Stohmann flask.

• (5.2) Rotary shaker, 30 to 40 turns per minute.

• (5.3) Electric hot plate with adjustable temperature.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 a Where fertilisers contain a maximum of 3% of sulfur (S) i.e. 7.5% SO₃, together with a maximum of 4% of calcium (Ca) i.e. 5.6% CaO, weigh out 5 g of fertiliser to within 1 mg. b Where fertilisers contain more than 3% of sulfur (S) together with more than 4% of calcium (Ca), weigh out 1 g of fertiliser to within 1 mg. Place the test sample in a 500 ml flask (5.1).

Preparation of the solution 7.2 Add approximately 400 ml of water. Stopper. Shake on the rotary shaker (5.2) for 30 minutes. Make up to volume with water and mix. Pass through a dry filter into a dry container. Reject the first portion of the filtrate. Stopper if the solution is not to be used immediately.

Oxidation of the aliquot portion to be analysed 7.3 Take an aliquot of the extraction solution not exceeding 50 ml and, if possible, containing between 20 and 100 mg of sulfur (S). Make up the volume to 50 ml with water, if necessary. Add 3 ml of sodium hydroxide solution (4.2) and 2 ml of hydrogen peroxide solution (4.3). Cover with a watch glass and boil gently for one hour on the hot plate (5.3). Keep adding 1 ml increments of hydrogen peroxide solution for as long as the reaction continues (maximum quantity 5 ml). Then leave to cool. Remove the watch glass and wash the underside into the beaker. Add approximately 20 ml of dilute hydrochloric acid (4.1). Make up to approximately 300 ml with water. Determine the content of sulfates on the whole of the oxidised solution in accordance with method 23.

19. — EXTRACTION AND DETERMINATION OF ELEMENTAL SULFUR

WARNING

This method of analysis involves the use of carbon disulfide (CS₂). Special safety measures must therefore be taken, in particular with regard to:

• the storage of CS₂,

• protective equipment for staff,

• occupational hygiene,

• prevention of fires and explosions,

• disposal of the reagent.

This method requires highly skilled staff and a suitably equipped laboratory.

SCOPE

1

This method is for the extraction and determination of the elemental sulfur content of fertilisers.

FIELD OF APPLICATION

2

This method applies to all fertilisers for which a declaration of the total sulfur in elemental form is required.

PRINCIPLE

3

After the removal of soluble compounds, elemental sulfur is extracted by using carbon disulfide, followed by gravimetric determination of the sulfur extracted.

REAGENTS

4

Carbon disulfide.

APPARATUS

5

• (5.1) 100 ml extraction flask with ground glass stopper.

• (5.2) Soxhlet apparatus.

• (5.3) Vacuum rotary evaporator.

• (5.4) Electric oven, fan assisted, set at 90 ± 2°C.

• (5.5) Petri dishes, five to seven centimetres in diameter, not exceeding five centimetres in height.

• (5.6) Electric hot plate with adjustable temperature.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 Weigh out 5-10 g of the sample to an accuracy of 1 mg and place in the thimble of the Soxhlet apparatus (5.2).

Extraction of the sulfur 7.2 Wash thoroughly the contents of the thimble with hot water to remove all soluble compounds. Dry in the oven at 90°C (5.4) for at least one hour. Place the thimble in the Soxhlet apparatus (5.2). Place a few glass beads in the flask of the apparatus (5.1) and weigh (P₀), then add 50 ml of carbon disulfide (4.1). Connect the apparatus, switch on and leave for six hours. Switch off the heat and, after cooling, disconnect the flask. Connect the flask to the rotary evaporator (5.3) and evaporate until the contents of the flask have solidified in a spongy mass. Dry the flask in the oven at 90°C (5.4) (generally one hour if necessary) until a constant weight is obtained (P₁).

Determination of the purity of the elemental sulfur 7.3 Certain substances may have been extracted by the carbon disulfide at the same time as the elemental sulfur. The purity of the elemental sulfur is determined as follows: homogenize the contents of the flask as thoroughly as possible and remove 2-3 g, weigh to an accuracy of 1 mg (n). Place in the petri dish (5.5). Weigh dish and contents together (P₂). Place on the hot plate (5.6), set at a temperature not exceeding 220°C so as not to cause combustion of the sulfur. Continue sublimation for three to four hours until a constant weight is obtained (P₃).

Note: For some fertilisers, it may not be necessary to determine how pure the sulfur is. In this case, omit step 7.3.

EXPRESSION OF RESULTS

8

The percentage elemental sulfur (S) content of the fertiliser is as follows:

$Impure S (%) of the fertiliser=P1-P0m×100$

$Purity of sulfur extracted (%)=P2-P3n×100$

$$Pure S (%) of the fertiliser=(P1-P0)(P2-P3)m×n×100$ where: m = the mass of the test sample of fertiliser in grams, P₀ = the mass of the Soxhlet flask in grams, P₁ = the mass of the Soxhlet flask and the impure sulfur after drying, n = the mass of impure sulfur to be purified in grams, P₂ = the mass of the Petri dish and the sample, P₃ = the mass of the Petri dish after sublimation of the sulfur.$

20. — MANGANIMETRIC DETERMINATION OF EXTRACTED CALCIUM FOLLOWING PRECIPITATION IN THE FORM OF OXALATE

SCOPE

1

This method is for the determination of calcium in fertiliser extracts.

FIELD OF APPLICATION

2

This method applies to all fertilisers for which a declaration of the total and/or water-soluble calcium is required.

PRINCIPLE

3

Precipitation of the calcium contained in an aliquot of the extraction solution in the form of an oxalate, which is determined by titration using potassium permanganate.

REAGENTS

4

• (4.1) Diluted hydrochloric acid:

• One volume of hydrochloric acid (ρ = 1.18 g/ml) plus one volume of water.

• (4.2) 1:10 dilute sulfuric acid:

• One volume of sulfuric acid (ρ = 1.84 g/ml) in ten volumes of water.

• (4.3) 1:1 dilute ammonia solution:

• One volume of ammonia (ρ = 0.88 g/ml) and one volume of water.

• (4.4) Saturated solution of ammonium oxalate [(NH₄)₂ C₂O₄ H₂O] at ambient temperature (approximately 40 g per litre).

• (4.5) Citric acid solution, 30% (m/v).

• (4.6) Ammonium chloride solution, 5% (m/v).

• (4.7) Solution of bromothymol blue in 95% ethanol, 0.1% (m/v).

• (4.8) Solution of bromocresol green in 95% ethanol, 0.04% (m/v).

• (4.9) Standard solution of potassium permanganate, 0.02 M.

APPARATUS

5

• (5.1) Filter crucible with 5 to 20μ porosity sintered glass.

• (5.2) Hot water bath.

PREPARATION OF THE ALIQUOT PORTION TO BE ANALYSED

6

Using a pipette, take an aliquot portion of the extraction solution obtained by method 15 or 17, containing between 15 and 50 mg of Ca ( = 21 to 70 mg of CaO). Let the volume of this aliquot be v₂. Pour into a 400 ml beaker. If necessary, neutralise (change of indicator (4.7) from green to blue) with a few drops of the ammonia solution (4.3).

PRECIPITATION OF THE CALCIUM OXALATE

7

Add approximately 100 ml of water. Bring to the boil, add 8 to 10 drops of indicator solution (4.8) and, slowly, 50 ml of the hot ammonium oxalate solution (4.4), stirring constantly. If a precipitate forms, dissolve by adding a few drops of hydrochloric acid (4.1). Neutralise very slowly with ammonia solution (4.3) while stirring continuously to a pH of 4.4 to 4.6 (change of indicator (4.8) from green to blue). Place the beaker in a boiling hot water bath (5.2) for approximately 30 minutes.

TITRATION OF THE OXALATE PRECIPITATE

8

Wash the beaker and crucible until the excess ammonium oxalate has been completely removed (this can be checked by the absence of chloride in the washing water). Place the crucible in the 400 ml beaker and dissolve the precipitate with 50 ml of hot sulfuric acid (4.2). Add water to the beaker in order to obtain a volume of approximately 100 ml. Bring to a temperature of 70° to 80°C and titrate drop by drop with the permanganate solution (4.9) until the pink colour lasts for a minute. Let this volume be n.

EXPRESSION OF RESULTS

9

The calcium (Ca) content of the fertiliser is as follows:

$$Ca(%)=n×0.2004×t0.02×v1v2×m$ where: n = the volume of 0.2 M permanganate used, in millilitres, m = the mass of the test sample in grams, v₂ = the aliquot volume in millilitres, v₁ = the volume of the extraction solution in millilitres, t = the molarity of the permanganate solution in moles per litre. CaO (%) = Ca (%) × 1.400.$

21. — DETERMINATION OF MAGNESIUM BY ATOMIC ABSORPTION SPECTROMETRY

SCOPE

1

This method is for the determination of magnesium in fertiliser extracts.

FIELD OF APPLICATION

2

This method applies to all fertiliser extracts obtained by methods 15 and 17, for which a declaration of the total magnesium and/or water-soluble magnesium is required, with the exception of kieserite, magnesium sulfate, magnesium chloride solution and kieserite with potassium sulfate to which method 22 applies.

PRINCIPLE

3

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

REAGENTS

4

• (4.1) Hydrochloric acid, 1 M solution.

• (4.2) Hydrochloric acid, 0.5 M solution.

• (4.3) Standard solution of magnesium, 1.00 mg per ml.

• (4.3.1) Dissolve 1.013 g of magnesium sulfate (MgSO₄.7H₂O) in 0.5 M in hydrochloric acid solution (4.2).

• or:

• (4.3.2) Weigh out 1.658 g of magnesium oxide (MgO), previously ashed to removed all traces of carbonate. Place in a beaker with 100 ml of water and 120 ml of 1 M hydrochloric acid (4.1). When it has dissolved, transfer quantitatively into a 1 litre graduated flask. Make up to the volume and mix.

• or:

• (4.3.3) Commercial standard solution.

• The laboratory is responsible for testing such solutions.

• (4.4) Strontium chloride solution.

• Dissolve 75 g of strontium chloride (SrCl₂6H₂O) in the hydrochloric acid solution (4.2) and make up to 500 ml with the same acid solution.

APPARATUS

5

• (5.1) Spectrometer fitted for atomic absorption, with a magnesium lamp, set at 285.2 nm.

• (5.2) Air-acetylene flame.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

See Methods 15 and 17.

PROCEDURE

7

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

• (7.2) Using a pipette, take 10 ml of the extraction solution (6) or the solution (7.1). Transfer into a 200 ml graduated flask. Make up to the volume with the 0.5 M hydrochloric acid solution (4.2) and mix. The dilution factor is 200/10.

• (7.3) Dilute this solution (7.2) with the 0.5 M hydrochloric acid solution (4.2) so as to obtain a concentration in the optimum working field of spectrometer (5.1). V₂ is the volume of the sample in 100 ml. The dilution factor is D₂ = 100/V₂.

Preparation of blank solution 7.4 Prepare a blank solution by repeating the whole procedure from the extraction (method 15 or 17), omitting only the test sample of fertiliser.

Preparation of calibration solutions 7.5 By diluting the standard solution (4.3) with 0.5 M hydrochloric acid, prepare at least five calibration solutions in increasing concentrations within the optimum measuring range of the apparatus (5.1). These solutions should contain 10% v/v of the strontium chloride solution (4.4).

Measurement 7.6 Set up the spectrometer (5.1) at a wavelength of 285.2 nm. Spray, successively, the calibration solutions (7.5), the sample solution (7.3) and the blank solution (7.4), 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 calibration solutions (7.5) as the ordinates and the corresponding concentration of magnesium in μg/ml as the abscissae. Determine the concentration of magnesium in the sample (7.3), xs and blank (7.4), xb, by reference to the calibration curve.

EXPRESSION OF RESULTS

8

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.

22. — DETERMINATION OF MAGNESIUM BY COMPLEXOMETRY

SCOPE

1

This method is for the determination of magnesium in fertiliser extracts.

FIELD OF APPLICATION

2

This method applies to the determination of total magnesium and/or water-soluble magnesium in the following fertilisers:

• Straight nitrogenous fertilisers (calcium magnesium nitrate, magnesium sulphonitrate, nitrogenous fertiliser with magnesium) and straight potassic fertilisers (enriched kainite, potassium chloride containing magnesium, potassium sulfate containing magnesium salt), kieserite, magnesium sulfate, magnesium chloride solution, and kieserite with potassium sulfate.

PRINCIPLE

3

The magnesium is extracted by methods 15 and/or 17. First titration: with EDTA and Ca and Mg in the presence of Eriochrome black T. Second titration: with EDTA of Ca in the presence of calcein or of calcon carbonic acid. Determination of magnesium by difference.

REAGENTS

4

Standard 0.05 M solution of magnesium: 4.1 4.1.1 Dissolve 1.232 g of magnesium sulfate (MgSO₄7H₂O) in the 0.5 M hydrochloric acid solution (4.11) and make up to 100 ml with the same acid. or: 4.1.2 Weigh out 2.016 g of magnesium oxide, previously calcined to remove all traces of carbonation. Place it in a beaker with 100 ml of water. Stir in approximately 120 ml of approximately 1 M hydrochloric acid (4.12). After dissolution, transfer quantitatively into a graduated 1 litre flask. Make up to volume and mix. 1 ml of these solutions should contain 1.216 mg of Mg ( = 2.016 mg of MgO). The laboratory is responsible for testing the strength of this standard solution.

0.05 M solution of EDTA 4.2 Weigh out 18.61 g of the dihydrated disodium salt of ethylenediaminetetraacetic (C₁₀H₁₄Na₂O₈2H₂O), place it in a 1000 ml beaker and dissolve in 600 to 800 ml of water. Transfer the solution quantitatively into a graduated 1 litre flask. Make up the volume and mix. Check this solution with the standard solution (4.1) by taking a sample of 20 ml of the latter and by titration according to the analytical procedure described at 7.2.

0.05 molar standard solution of calcium 4.3 Weigh out 5.004 g of dry calcium carbonate. Place it in a beaker with 100 ml of water. Progressively stir in 120 ml of approximately 1 M hydrochloric acid (4.12). Bring to the boil in order to drive off the carbon dioxide, cool, transfer quantitatively into a graduated one-litre flask, make up the volume with water and mix. Check this solution against the EDTA solution (4.2) following analytical procedure (8.3). 1 ml of this solution should contain 2.004 mg of Ca ( = 2.804 mg of CaO) and should correspond to 1 ml of the 0.05 M EDTA solution (4.2).

Calcium indicator 4.4 Carefully mix in a mortar one gram of calcein with 100 g of sodium chloride. Use 10 mg of this mixture. This indicator changes colour from green to orange. Titration must be carried out until an orange colour free from green tinges is obtained.

Calcon carbonic acid indicator 4.5 Dissolve 400 mg of calcon carbonic acid in 100 ml of methanol. This solution may only be kept for approximately four weeks. Use three drops of this solution. The indicator changes colour from red to blue. Titration must be carried out until a blue colour free from red tinges is obtained.

Eriochrome black-T indicator 4.6 Dissolve 300 mg of Eriochrome black-T in a mixture of 25 ml of propan-l-ol and 15 ml of triethanolamine. This solution may only be kept for approximately four weeks. Use three drops of this solution. This indicator changes colour from red to blue and titration must be carried out until a blue colour free from red tinges is obtained. It changes colour only when magnesium is present. If necessary add one millilitre of the standard solution (4.1). When both calcium and magnesium are present the EDTA first forms a complex with the calcium and then the magnesium. In that case the two elements are determined concurrently.

Potassium cyanide solution 4.7 Aqueous solution of KCN at 2%. (CAUTION: potassium cyanide is extremely poisonous, take suitable precautions and do not pipette by mouth. See also 10.7).

Solution of potassium hydroxide and potassium cyanide 4.8 Dissolve 280 g of KOH and 66 g of KCN in water, make up the volume to one litre and mix.

Buffer solution, pH 10.5 4.9 In a 500 ml graduated flask, dissolve 33 g of ammonium chloride in 200 ml of water, add 250 ml of ammonia (ρ = 0.91), make up the volume with water and mix. Check the pH of the solution regularly.

Diluted hydrochloric acid 4.10 One volume of hydrochloric acid (ρ = 1.18 g/ml) plus one volume of water.

• (4.11) Hydrochloric acid solution approximately 0.5 M.

• (4.12) Hydrochloric acid solution approximately 1 M.

• (4.13) Sodium hydroxide solution 5 M.

APPARATUS

5

• (5.1) Magnetic or mechanical stirrer.

• (5.2) pH meter.

CONTROL TEST

6

Carry out a determination on aliquot portions of solutions (4.1 and 4.3) such that the Ca/Mg ratio is approximately equal to that of the solutions to be analysed. To this end take (a) of standard solution (4.3) and (b-a) of standard solution (4.1). (a) and (b) are the volumes of EDTA solution in millilitres used in the two titrations performed on the solution to be analysed. This procedure is correct only if the solutions of EDTA, calcium and magnesium are exactly equivalent. If this is not the case, it is necessary to make corrections.

PREPARATION OF THE SOLUTION TO BE ANALYSED

7

See Methods 15 and 17.

DETERMINATION

8

Aliquot portions to be taken 8.1 Take aliquot portions of the extracts which contain between 9 and 18 mg of magnesium ( = 15 to 30 mg of MgO).

Titration in the presence of Eriochrome black-T 8.2 Pipette an aliquot portion (8.1) of the solution to be analysed into a 400 ml beaker. Neutralise the excess acid with the 5 M sodium hydroxide solution (4.12) and check the pH. Dilute with water to approximately 100 ml. Add 5 ml of the buffer solution (4.9). The pH measured by meter must be 10.5 ± 0.1. Add 2 ml of the potassium cyanide solution (4.7) and three drops of the Eriochrome black-T indicator (4.6). Titrate with the EDTA solution (4.2). Stirring gently with the stirrer (5.1) (see 10.2, 10.3 and 10.4). Let ‘b' be the volume in millilitres of 0.05 molar EDTA solution used.

Titration in the presence of calcein or of calcon carbonic acid 8.3 Pipette an aliquot portion of the solution to be analysed equal to that taken for the above titration and place it in a 400 ml beaker. Neutralise the excess acid with the 5 M sodium hydroxide solution (4.13) using the pH meter. Dilute with water to about 100 ml. Add 10 ml of KOH/KCN solution (4.8) and three drops of the indicator (4.4 or 4.5). Stirring gently with the stirrer (5.1) titrate with the EDTA solution (4.2) (see 10.2, 10.3 and 10.4). Let ‘a' be the volume in millilitres of 0.05 M EDTA solution.

EXPRESSION OF RESULTS

9

For the EEC fertilisers to which the method is applicable (5 g of fertiliser in 500 ml of extract), the percentage content of the fertiliser is:

$MgO(%)inthefertiliser=(b-a)×TM$

$$Mg(%)inthefertiliser=——-—-—(b-a)×TlM$ where: a = the volume in millilitres of 0.05 M EDTA solution used for the titration in the presence of calcein or calcon carbonic acid. b = the volume in millilitres of 0.05 M EDTA solution used for the titration in the presence of Eriochrome black-T. M = the mass of the sample present in the aliquot taken (in grams). T = 0.2016× molarity of the EDTA solution/0.05 (see 4.2). Tl = 0.1216× molarity of the EDTA solution/0.05 (see 4.2).$

REMARKS

10

• (10.1) The stoichiometric EDTA-metal ratio in the complexometric analyses is always 1:1 whatever the valency of the metal and in spite of the fact that EDTA is quadrivalent. The EDTA titration solution and the standard solutions will therefore be molar and not normal.

• (10.2) Complexometric indicators are often sensitive to air. The solution may lose colour during titration. In this case, one or two drops of indicator must be added. This is true particularly in the case of Eriochrome black-T and calcon carbonic acid.

• (10.3) The metal-indicator complexes are often relatively stable and it may take some time for the colour to change. The last drops of EDTA must therefore be added slowly and a drop of 0.05 molar solution of magnesium (4.1) or calcium (4.3) added to ensure that the colour change has not already taken place. This is particularly true in the case of the Eriochrome-magnesium complex.

• (10.4) The colour change of the indicator must not be observed vertically, but horizontally across the solution and the beaker must be placed against a white background in a well-lit position. The colour change of the indicator may also be observed easily by placing the beaker on frosted glass lit moderately from below (25 watt lamp).

• (10.5) This analysis requires a certain amount of experience. The task will involve, among other things, observing the colour changes of standard solutions 4.1 and 4.3. It is recommended that the determinations be carried out by the same laboratory chemist.

• (10.6) If an EDTA solution of guaranteed strength is used (Titrisol, Normex, for example) this may simplify the control of the equivalence of standard solutions 4.1, 4.2 and 4.3.

• (10.7) The solutions containing potassium cyanide must not be poured down the sink until the cyanide has been converted into a harmless compound, for example, by oxidation with sodium hypochlorite after having been made alkaline.

23. — DETERMINATION OF SULFATES

SCOPE

1

This method is for the determination of sulfur present in fertiliser extracts in the form of sulfates.

FIELD OF APPLICATION

2

This method applies to the determination of sulfates present in the extractions performed in methods 15, 16, 17 and 18.

PRINCIPLE

3

Gravimetric determination as barium sulfate.

REAGENTS

4

Diluted hydrochloric acid: 4.1 One volume of hydrochloric acid (ρ = 1.18 g/ml) and one volume of water.

• (4.2) Barium chloride solution BaCl₂.2H₂O: 122 grams per litre.

• (4.3) Silver nitrate solution: 5 grams per litre.

APPARATUS

5

• (5.1) Crucibles.

• (5.2) Hot water bath.

• (5.3) Drying oven set at 105°C ± 1°C.

• (5.4) Electric furnace set at 800°C ± 50°C.

PROCEDURE

6

Sampling of the solution 6.1 Pipette an aliquot portion of one of the extraction solutions indicated at (2) containing between 20 and 100 mg of S or 50 and 250 mg of SO₃. Place this aliquot portion in a beaker of suitable capacity. Add 20 ml of dilute hydrochloric acid (4.1). Make up to about 300 ml with water.

Preparation of the precipitate 6.2 Bring the solution to the boil. Add, drop by drop, about 20 ml of the hot barium chloride solution (4.2) while stirring the solution vigorously. Boil for a few minutes. Place the beaker, covered with a watch glass, in a boiling water bath (5.2) for an hour. Then leave standing hot (~60°C) until the supernatant liquor is clear. Decant the clear solution through a slow filtration ash-free filter. Wash the precipitate several times with hot water. Continue to wash the precipitate on the filter until the filtrate is chloride free. This can be checked by using silver nitrate solution (4.3).

Incineration and weighing of the precipitate 6.3 Place the filter paper and precipitate in a crucible (5.1) previously weighed to the nearest 0.1 mg. Dry in the oven (5.3) and ash at approximately 800°C for half an hour (5.4). Allow to cool in a desiccator and weigh to within 0.1 mg.

EXPRESSION OF RESULTS

7

One mg of barium sulfate corresponds to 0.137 mg of S or to 0.343 mg of SO₃.The percentage S content of the fertiliser is obtained as follows:

$S(%)=w×0.0137×v1v2×m$

$$SO3(%)=S(%)×2.5$ where: w = the mass of the barium sulfate precipitate in milligrams, v₁ = the volume of the extraction solution in millilitres, v₂ = the aliquot volume in millilitres, m = the mass of the test sample in grams.$

24. — DETERMINATION OF THE SODIUM EXTRACTED

SCOPE

1

This method is for the determination of sodium in fertiliser extracts.

FIELD OF APPLICATION

2

This method applies to fertilisers for which a declaration of sodium is required.

PRINCIPLE

3

Following suitable dilution of the extract obtained via method 15 and/or 17 the sodium content of the solution is determined by flame-emission spectrometry.

REAGENTS

4

Diluted hydrochloric acid: 4.1 One volume of hydrochloric acid (ρ = 1.18 g/ml) plus one volume of water.

• (4.2) Aluminium nitrate Al(NO₃)₃. 9H₂O.

• (4.3) Caesium chloride, CsCl.

• (4.4) Anhydrous sodium chloride, NaCl.

Caesium chloride and aluminium nitrate solution 4.5 Dissolve in water 50 g of caesium chloride (4.3) and 250 g of aluminium nitrate (4.2) in a 1 litre graduated flask. Make up to volume with water and mix.

Standard sodium solution of 1 mg/ml of Na 4.6 Dissolve in water 2.542 g of sodium chloride (4.4) in a 1 litre graduated flask. Add 10 ml of hydrochloric acid (4.1). Make up to volume with water and mix.

APPARATUS

5

Spectrometer equipped for flame emission, set at 589.3 nm.

CALIBRATION SOLUTIONS

6

• (6.1) Pipette 10 ml of standard solution (4.6) into a 250 ml graduated flask. Make up to volume and mix. Concentration of solution: 40μg/ml of Na.

• (6.2) Using a burette place 0, 5, 10, 15, 20, 25 ml of the intermediate solution (6.1) in 100 ml graduated flasks. Add 10 ml of the solution (4.5). Make up to volume and mix. Concentration of solutions: 0, 2, 4, 6, 8, 10 μg/ml of Na.

PREPARATION OF SOLUTIONS TO BE MEASURED

7

Depending upon the expected sodium content of the extraction solution as in method 15 or 17 (5 g of fertiliser in 500 ml), carry out the dilutions in accordance with the following table:

		Intermediate dilution	Intermediate dilution	Final dilution	Final dilution
Na₂O (%)	Na (%)	Sample (ml) (v₂)	Dilution to ml (v₃)	Sample (ml) (v₄)	Dilution to ml	Degree of dilution
3-5	2.2-3.7	10	50	10	100	50
5-10	3.7-7.4	10	100	10	100	100
10-20	7.4-15	10	100	5	100	200
20-38	15-28	5	100	5	100	400

DETERMINATION

8

Prepare the spectrometer (5) for the measurements at 589.3 nm. Calibrate the instrument by measuring the response of the calibration solutions (6.2). Then adjust the sensitivity of the instrument to use its entire scale when the most concentrated calibration solution is used. Then measure the response of the sample solution to be analysed (7). Repeat this operation twice.

CALCULATION OF RESULTS

9

Draw a calibration curve by plotting the average response for each calibration solution along the ordinate and the corresponding concentrations, expressed in μg per ml on the abscissa. Determine from this the sodium concentration of the test solution. Calculate the quantity of sodium from the standard solutions taking account of the levels of dilution. Express the results as a percentage of the sample.

25. — TRACE ELEMENTS AT A CONCENTRATION LESS THAN 10%

25a. — 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 less than or equal to 10%.

PRINCIPLE

3

Dissolution in boiling dilute 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 manufacturer to ensure that the declared content actually corresponds to the quantity extracted under the conditions pertaining to the method.

REAGENTS

4

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

• (4.2) Concentrated ammonia solution (NH₄OH, ρ = 0.9 g/ml).

APPARATUS

5

Electric hot plate with variable temperature control.

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 between 2 and 10 g depending on the declared content of the 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 (%)< 0.010.01-< 5≥ 5-10 Mass of test sample (g)1052Mass of element in the sample (mg)10.5-250100-200Volume of extract V (ml)250500500Concentration of element in extract (mg/l)41-500200-400

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.

25b. — 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 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 less than or equal to 10%.

PRINCIPLE

3

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

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

REAGENTS

4

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

APPARATUS

5

Rotary shaker set at about 35 to 40 rpm. 5.1

• (5.2) pH-meter.

Note: Where the boron content of the 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 THE SAMPLE

6

See Method 1.

PROCEDURE

7

Test sample 7.1 Take a quantity of fertiliser weighing between 2 and 10 g depending on the declared content of the 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. The samples should be weighed to within 1 mg. Declared content of trace element in the fertiliser (%)< 0.010.01-< 5≥ 5-10 Mass of test sample (g)1052Mass of element in the sample (mg)10.5-250100-200Volume of extract V (ml)250500500Concentration of element in extract (mg/l)41-500200-400 Place the sample in a 250 or 500 ml flask (according to the Table).

Preparation of the solution 7.2 Add about 200 ml of water to the 250 ml flask or 400 ml of water to the 500 ml flask.

DETERMINATION

8

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

25c. — 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 25a and 25b 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 determination by means of atomic absorption spectrometry.

PRINCIPLE

3

The organic compounds in an aliquot proportion of the extract are oxidised with hydrogen peroxide.

REAGENTS

4

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

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

APPARATUS

5

Electric hot plate with variable temperature control.

PROCEDURE

6

Take 25 ml of the extract solution obtained by Method 25a or Method 25b and place in a 100 ml beaker. In the case of Method 25b 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 watch glass. 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.

25d. — 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 certain trace elements in fertiliser extracts by atomic absorption spectrometry.

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble element is required.

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 wave-length suitable for the trace element to be determined.

REAGENTS

4

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

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

• (4.3) Lanthanum salt solutions (10 g of La per litre).

This reagent is used for determinations of cobalt, iron, manganese 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 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 (LaCl₃.7H₂O) or 31.2 g of lanthanum nitrate hexahydrate [La(NO₃)₃.6H₂O] or 26.2 g of lanthanum sulfate nonahydrate [La₂(SO₄)₃.9H₂O] 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 method of determination for each trace element.

APPARATUS

5

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

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Preparation of extract solutions of the trace elements to be determined 6.1 See Method 25a and/or 25b and, if appropriate, 25c

Treatment of the test solution 6.2 Dilute an aliquot portion of the extract obtained by Method 25a, 25b or 25c 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. Take an aliquot portion of the final solution obtained by dilution of the extract, let (a) be its volume in ml, and pour into a 100 ml volumetric flask. When determining the cobalt, iron, manganese or zinc content, add 10 ml of the lanthanum salt solution (4.3). Make up to volume with the 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. This is the final solution for measurement. 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). For determining cobalt, iron, manganese or zinc 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), and 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 μg per ml, along the abscissa. From this curve, determine the concentrations of 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 equal to:

$E(%)=[(xs-xb)×V×D]/(M×104).$

25e. — DETERMINATION OF BORON IN FERTILISER EXTRACTS BY MEANS OF SPECTROMETRY WITH AZOMETHINE-H

SCOPE

1

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

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble boron is required.

PRINCIPLE

3

In an azomethine-H solution, borate ions form a yellow complex the concentration of which is determined by molecular absorption spectrometry at 410 nm. Interfering ions are masked with EDTA.

REAGENTS

4

EDTA buffer solution 4.1 Place in a 500 ml volumetric flask containing 300 ml of water: — 75 g of ammonium acetate (NH₄OOCCH₃); — 10 g of disodium salt of ethylene diamine tetraacetic acid (Na₂EDTA); — 40 ml of acetic acid (CH₃COOH, ρ = 1.05 g/ml). Make up to volume with water and mix thoroughly. The pH of the solution, checked by means of a glass electrode, must be 4.8 ± 0.1.

Azomethine-H solution 4.2 Place in a 200 ml volumetric flask — 10 ml of the buffer solution (4.1); — 400 mg of azomethine-H (C₁₇H₁₂NNaO₈S₂); — 2 g of ascorbic acid (C₆H₈O₆). Make up to volume and mix thoroughly. Do not prepare large quantities of this reagent as it is stable for only a few days.

Boron calibration solutions 4.3 Boron stock solution (100 μg/ml) 4.3.1 Dissolve 0.5719 g of boric acid (H₃BO₃) in water in a 1000 ml volumnetric flask. Make up to volume with water and mix thoroughly. Transfer to a plastic bottle for storage in a refrigerator. Boron working solution (10 μg/ml) 4.3.2 Place 50 ml of stock solution (4.3.1) in a 500 ml volumetric flask. Make up to volume with water and mix thoroughly.

APPARATUS

5

Spectrometer fitted for molecular absorption with cells having a 10 mm optical path and set to a wavelength of 410 nm.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Preparation of the boron solution 6.1 See Methods 25a and/or 25b and, if appropriate, 25c.

Preparation of the test solution 6.2 Dilute an aliquot portion of extract (6.1) to obtain a boron concentration as specified in 7.2. Two successive dilutions may be necessary. Let D be the dilution factor.

Preparation of the correction solution 6.3 If the test solution (6.2) is coloured, prepare a corresponding correction solution by placing in a plastic flask 5 ml of test solution (6.2), 5 ml of EDTA buffer solution (4.1) and 5 ml of water and mix thoroughly.

PROCEDURE

7

Preparation of the 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 the calibration solutions 7.2 Transfer 0, 5, 10, 15, 20 and 25 ml of the working calibration solution (4.3.2) to a series of 100 ml volumetric flasks. Make up to 100 ml with water and mix thoroughly. These solutions contain between 0 and 2.5 μg/ml of boron.

Colour development 7.3 Transfer 5 ml of the calibration solutions (7.2), test solutions (6.2) and blank (7.1) to a series of plastic flasks. Add 5 ml of the EDTA buffer solution (4.1). Add 5 ml of the azomethine-H solution (4.2). Mix thoroughly and allow the colour to develop in the dark for 2½ to 3 hours.

Determination 7.4 Measure the absorbance of the solutions obtained at 7.3 and if appropriate the correction solution (6.3) against water at a wavelength of 410 nm. Rinse the cells with water before each new reading.

EXPRESSION OF RESULTS

8

Plot a calibration curve of the concentration of the calibration solutions (7.2) along the abscissa and the absorbance given by the spectrophotometer (7.4) along the ordinate.

25f. — DETERMINATION OF COBALT IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY

SCOPE

1

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

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble cobalt is required.

PRINCIPLE

3

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

REAGENTS

4

Hydrochloric acid solution, about 6M 4.1 See Method 25d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 25d (4.2).

Lanthanum salt solutions (10 g of La per litre) 4.3 See Method 25d (4.3).

Cobalt calibration solutions 4.4 Cobalt stock solution (1000 μg/ml) 4.4.1 In a 250 ml beaker, weigh to the nearest 0.1 mg, 1 g of cobalt, add 25 ml of 6 M hydrochloric acid (4.1) and heat on a hot plate until the cobalt is completely dissolved. When cool, transfer quantitatively to a 1000 ml volumetric flask. Make up to volume with water and mix thoroughly. Cobalt working solution (100 μg/ml) 4.4.2 Place 10 ml of the stock solution (4.4.1) in a 100 ml volumetric flask. Make up to volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.

APPARATUS

5

Atomic absorption spectrometer: see Method 25d (5). The instrument must be equipped with a source of rays characteristic of cobalt (240.7 nm). The spectrometer must allow background correction to be made.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

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

Preparation of the test solution 6.2 See Methods 25d (6.2). The test solution must contain 10% (v/v) of a lanthanum salt solution (4.3).

PROCEDURE

7

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

Preparation of the calibration solutions 7.2 See Method 25d (7.2). For an optimum determination range of 0 to 5 μg/ml of cobalt, place 0, 0.5, 1, 2, 3, 4 and 5 ml respectively of working solution (4.4.2) 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 to each flask 10 ml of the lanthanum salt solution used in 6.2. Make up to 100 ml with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain 0, 0.5, 1, 2, 3, 4 and 5 μg/ml respectively of cobalt.

Determination 7.3 See Method 25d (7.3). Prepare the spectrometer (5) for measurement at a wavelength of 240.7 nm.

EXPRESSION OF RESULTS

8

See Method 25d (8).

25g. — DETERMINATION OF COPPER IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY

SCOPE

1

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

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble copper is required.

PRINCIPLE

3

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

REAGENTS

4

Hydrochloric acid solution, about 6 M 4.1 See Method 25d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 25d (4.2).

• (4.3) Hydrogen peroxide solution (30% H₂O, ρ = 1.11 g/ml), free from trace elements.

Copper calibration solutions 4.4 Copper stock solution (1000 μg/ml) 4.4.1 In a 250 ml beaker, weigh to the nearest 0.1 mg, 1 g of copper, add 25 ml of 6 M hydrochloric acid (4.1), add 5 ml hydrogen peroxide solution (4.3) and heat on a hot plate until the copper is completely dissolved. Transfer quantitatively to a 1 litre volumetric flask. Make up to volume with water and mix thoroughly. Copper working solution (100 μg/ml) 4.4.2 Place 20 ml of the stock solution (4.4.1) in a 200 ml volumetric flask. Make up to volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.

APPARATUS

5

Spectrometer equipped for atomic absorption: see Method 25d (5). The instrument must be fitted with a source of rays characteristic of copper (324.8 nm).

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Copper 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).

PROCEDURE

7

Preparation of blank solution 7.1 See Method 25d (7.1).

Preparation of calibration solutions 7.2 See Method 25d (7.2). For an optimum determination range of 0 to 5 μg/ml of copper, place 0, 0.5, 1, 2, 3, 4 and 5 ml respectively of working solution (4.4.2) 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 (6.2). Make up to 100 ml with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain 0, 0.5, 1, 2, 3, 4 and 5 μg/ml respectively of copper.

Determination 7.3 See Method 25d (7.3). Prepare the spectrometer (5) for measurement at a wavelength of 324.8 nm.

EXPRESSION OF RESULTS

8

See Method 25d (8).

25h. — 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 analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble iron is required.

PRINCIPLE

3

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

REAGENTS

4

Hydrochloric acid solution, about 6 M 4.1 See Method 25d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 25d (4.2).

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

Lanthanum salt solutions (10 g of La per litre) 4.4 See Method 25d (4.3).

Iron calibration solutions 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 25d (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 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% (v/v) of a lanthanum salt solution.

PROCEDURE

7

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

Preparation of calibration solutions 7.2 See Method 25d (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 25d (7.3). Prepare the spectrometer (5) for measurement at a wavelength of 248.3 nm.

EXPRESSION OF RESULTS

8

See Method 25d (8).

25i. — DETERMINATION OF MANGANESE IN FERTILISER EXTRACTS BY ATOMIC ABSORPTION SPECTROMETRY

SCOPE

1

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

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble manganese is required.

PRINCIPLE

3

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

REAGENTS

4

Hydrochloric acid solution, about 6 M 4.1 See Method 25d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 25d (4.2).

Lanthanum salt solutions (10 g of La per litre) 4.3 See Method 25d (4.3).

Manganese calibration solutions 4.4 Manganese stock solution (1000 μg/ml) 4.4.1 In a 250 ml beaker, weigh to the nearest 0.1 mg, 1 g of manganese, add 25 ml of 6 M hydrochloric acid solution (4.1). Heat on a hot plate until the manganese is completely dissolved. When cool, transfer quantitatively to a 1000 ml volumetric flask. Make up to volume with water and mix thoroughly. Manganese working solution (100 μg/ml) 4.4.2 Place 20 ml of the stock solution (4.4.1) 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 25d (5). The apparatus must be fitted with a source of rays characteristic of manganese (279.6 nm).

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

Manganese 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 (4.3).

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 μg/ml of manganese, 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 hydrochloric acid concentration to bring it as close as possible to that of the test solution. To each flask add 10 ml of the lanthanum salt solution used in 6.2. Make up to 100 ml with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly. These solutions contain 0, 0.5, 1, 2, 3, 4 and 5 μg/ml manganese respectively.

Determination 7.3 See Method 25d (7.3). Prepare the spectrometer (5) for measurements at a wavelength of 279.6 nm.

EXPRESSION OF RESULTS

8

See Method 25d (8).

25j. — DETERMINATION OF MOLYBDENUM IN FERTILISER EXTRACTS BY SPECTROMETRY OF A COMPLEX WITH AMMONIUM THIOCYANATE

SCOPE

1

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

FIELD OF APPLICATION

2

This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble molybdenum is required.

PRINCIPLE

3

Molybdenum(v); forms a complex [MoO(SCN)5]– – in an acid medium with SCN– ions. The complex is extracted with n-butyl acetate. Interfering ions such as those of iron remain in the aqueous phase. The yellow-orange colour is determined by molecular absorption spectrometry at 470 nm.

REAGENTS

4

Dilute hydrochloric acid solution (HCl), about 6 M 4.1 See Method 25d (4.1).

Copper solution (70 mg/l) in 1.5 M hydrochloric acid 4.2 Dissolve 275 mg of copper sulfate (CuSO₄ 5H₂O) weighed to within 0.1 mg in 250 ml of the 6 M hydrochloric acid solution (4.1) in a 1000 ml volumetric flask. Make up to volume with water and mix thoroughly.

Ascorbic acid solution (50 g/l) 4.3 Dissolve 50 g of ascorbic acid (C₆H₈O₆) in water in a 1000 ml volumetric flask. Make up to volume with water, mix thoroughly and keep in a refrigerator.

n-butyl acetate 4.4

Ammonium thiocyanate solution, 0.2 M 4.5 Dissolve 15.224 g of NH₄SCN in water in a 1000 ml volumetric flask. Make up to volume with water; mix thoroughly and store in a dark-coloured bottle.

Stannous chloride solution (50 g/l) in 2 M hydrochloric acid 4.6 This solution must be perfectly clear and prepared immediately before use. Very pure stannous chloride must be used otherwise the solution will not be clear. To prepare 100 ml of solution, dissolve 5 g of SnCl₂.2H₂O in 35 ml of 6 M HCl solution (4.1). Add 10 ml of the copper solution (4.2). Make up to volume with water and mix thoroughly.

Molybdenum calibration solutions 4.7 Molybdenum stock solution (500 mg/ml) 4.7.1 Dissolve 0.920 g of ammonium molybdate [(NH₄)₆Mo₇O₂₄.4H₂O]; weighed to within 0.1 mg in the 6 M hydrochloric acid (4.1) in a 1 litre volumetric flask. Make up to volume with that solution and mix thoroughly. molybdenum intermediate solution (25 mg/ml) 4.7.2 Place 25 ml of the stock solution (4.7.1) in a 500 ml volumetric flask. Make up to volume with 6M hydrochloric acid (4.1) and mix thoroughly. Molybdenum working solution (2.5 mg/ml) 4.7.3 Place 10 ml of the intermediate solution (4.7.2) in a 100 ml volumetric flask. Make up to volume with 6 M hydrochloric acid (4.1) and mix thoroughly.

APPARATUS

5

• (5.1) Spectrometer fitted for molecular absorption with cells having a 20 mm optical path and set to a wavelength of 470 nm.

• (5.2) 200 or 250 ml separating funnels.

PREPARATION OF THE SOLUTION TO BE ANALYSED

6

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

Preparation of the test solution 6.2 Dilute an aliquot portion of the extract (6.1) with 6 M hydrochloric acid solution (4.1) so as to obtain an appropriate molybdenum concentration. Let D be the dilution factor. Take an aliquot portion (a) from the extract solution containing 1 to 12 mg molybdenum and place it in the separating funnel (5.2). Make up to 50 ml with the 6 M hydrochloric acid solution (4.1).

PROCEDURE

7

Preparation of the 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 the series of calibration solutions 7.2 Prepare a series of at least six calibration solutions of increasing concentration corresponding to the optimum response range of the spectrometer. For the interval 0-12.5 μg molybdenum, place 0, 1, 2, 3, 4 and 5 ml, respectively, of the working solution (4.7.3) in the separating funnels (5.2). Make up to 50 ml with 6 M hydrochloric acid (4.1). The funnels contain, respectively, 0, 2.5, 5, 7.5, 10 and 12.5 mg molybdenum.

Development and separation of the complex 7.3 To each separating funnel (6.2, 7.1 and 7.2), add in the following order: — 10 ml of the copper solution (4.2); — 20 ml of the ascorbic acid solution (4.3); mix thoroughly and wait for two or three minutes. Then add: — 10 ml of n-butyl acetate (4.4), using a precision pipette; — 20 ml of the thiocyanate solution (4.5). Shake for one minute to extract the complex into the organic phase; allow to separate; after the separation of the two phases, draw off the entire aqueous phase and discard it; then wash the organic phase with: — 10 ml of the stannous chloride solution (4.6). Shake for one minute. Allow to separate and draw off the entire aqueous phase. Remove the organic phase in a test tube; this will make it possible to collect the drops of water in suspension.

Determination 7.4 Measure the absorbencies of the solutions obtained at 7.3 at a wavelength of 470 nm using the 0 mg/ml molybdenum calibration solution (7.2) as a reference.

EXPRESSION OF RESULTS

8

Construct the calibration curve by plotting the corresponding masses of molybdenum in the calibration solutions (7.2) expressed in mg along the abscissa and the corresponding values of the absorbencies (7.4) given by the spectrometer reading along the ordinate.

25k. — 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 analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble 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 25d (4.1).

Hydrochloric acid solution, about 0.5 M 4.2 See Method 25d (4.2).

Lanthanum salt solutions (10 g of La per litre) 4.3 See Method 25d (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 Place 20 ml of the stock solution (4.4.1) in a 200 ml volumetric flask. Make up to volume with 0.5 M hydrochloric acid solution (4.2) and mix thoroughly.

APPARATUS

5

Atomic absorption spectrometer: see Method 25d (5). The apparatus must be fitted with a source of rays characteristic of zinc (213.8 nm). The spectrometer must allow background correction to be made.