# Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996, Paragraph 7: PROCEDURE


Preparation of solution for analysis
7.1 Weigh to the nearest 0.001 g, 10 g of the prepared sample and transfer to a 500 ml graduated flask. Add 50 ml water and then 20 ml dilute hydrochloric acid (4.10) and mix. Allow to stand until the evolution of carbon dioxide ceases. Add 400 ml water; shake for half an hour; make up to volume with water, mix, filter through a dry filter into a dry container.
Total nitrogen
7.2 In the absence of nitrates
7.2.1 Transfer by pipette into a 300 ml Kjeldahl flask an aliquot portion of the filtrate (7.1) containing a maximum of 100 mg nitrogen. Add 15 ml concentrated sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few glass beads to control boiling. Heat moderately at first in order to initiate the reaction, then more strongly until the liquid becomes colourless or slightly greenish and white fumes appear. After cooling, transfer the solution into the distillation flask, dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1) and carry out the determination as described in Method 8a, 7.1.1.2.
In the presence of nitrates
7.2.2 Transfer by pipette into a 500 ml Erlenmeyer flask an aliquot portion of the filtrate (7.1) containing not more than 40 mg nitric nitrogen. At this stage of the analysis, the total quantity of nitrogen is unimportant. Add 10 ml of 30% sulfuric acid (4.12), 5 g reduced iron (4.2) and immediately cover the Erlenmeyer flask with a watch glass. Heat gently until the reaction becomes strong but not violent. Stop heating and allow to stand for at least 3 hours at ambient temperature. Transfer the liquid quantitatively to a 250 ml graduated flask, ignoring undissolved iron. Make up to the mark with water and mix carefully. Transfer by pipette a portion containing a maximum of 100 mg nitrogen into a 300 ml Kjeldahl flask. Add 15 ml concentrated sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few glass beads.
Heat moderately at first in order to initiate the reaction, then more strongly until the liquid becomes colourless or slightly greenish and white fumes appear. After cooling, transfer the solution quantitatively to the distillation flask, dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1) and continue the determination as described in Method 8a, 7.1.1.2.
Blank test
7.2.3 Carry out a blank test under the same conditions (omitting only the sample) and use this value in the calculation of the final result.
Expression of result
7.2.4 %N(total)=(a-A)×0.28M where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank, carried out under the same conditions as the analysis.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for analysis.
Total nitrogen excluding nitric nitrogen
7.3 7.3.1 Transfer by pipette into a 300 ml Kjeldahl flask an aliquot portion of the filtrate (7.1) containing not more than 50 mg of nitrogen. Dilute to 100 ml with water, add 5 g ferrous sulfate (4.13), 20 ml concentrated sulfuric acid (4.9) and a few glass beads to control boiling (4.25). Heat moderately at first then more strongly until white fumes appear. Continue the reaction for 15 minutes. Stop heating, introduce 0.4 g copper oxide or 1.25 g copper sulfate (4.24) as catalyst, resume heating and maintain production of white fumes for 10-15 minutes. After cooling, transfer the contents of the Kjeldahl flask quantitatively to the distillation flask (5.1). Dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus and continue the determinations as in Method 8a, 7.1.1.2.
Blank test
7.3.2 See 7.2.3.
Expression of result
7.3.3 %N(total)=(a-A)×0.28M where:
a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for analysis.
7.4 Nitric nitrogen is obtained: by difference between
(7.2.4)-(7.5.3+7.6.3)or(7.2.4)-(7.5.3+7.6.5)or(7.2.4)-(7.5.3+7.6.6)
Ammoniacal nitrogen
7.5 In the presence of ureic nitrogen
7.5.1 Transfer by pipette into the dry flask of the apparatus (5.2) an aliquot portion of the filtrate (7.1) containing a maximum of 20 mg ammoniacal nitrogen. Connect up the apparatus. Place in the 300 ml Erlenmeyer flask 50.0 ml standard 0.05 M sulfuric acid solution (4.14) and an amount of distilled water such that the level of the liquid is about 5 cm above the opening of the intake tube. Introduce through the side neck of the reaction flask distilled water so as to bring the volume to about 50 ml and mix. To avoid foaming during aeration add several drops of octan-l-ol (4.15). Add 50 ml saturated potassium carbonate solution (4.16) and immediately begin to expel the ammonia thus released from the cold suspension. A strong current of air is necessary (flow rate of about 3 litres per minute) and should be purified beforehand by passing it through washing flasks containing dilute sulfuric acid and dilute sodium hydroxide. Instead of using air under pressure, a vacuum may be used (water pump) provided that the connections between the apparatus are air tight. The liberation of ammonia is generally complete after three hours. However, it is desirable to make certain of this by changing the Erlenmeyer flask. When the process is finished, disconnect the Erlenmeyer flask from the apparatus, rinse the end of the intake tube and the walls of the Erlenmeyer flask with a little distilled water and titrate the excess acid against standard 0.1 M sodium hydroxide solution (4.17).
Blank test
7.5.2 See 7.2.3.
Expression of result
7.5.3 %N(ammoniacal)=(a-A)×0.14M where:
a = ml of standard solution of sodium or potassium hydroxide (0.1 M) (4.17) used for the blank.
A = ml of standard solution of sodium or potassium hydroxide (0.1 M) (4.17) used for the analysis.
M = mass of the sample, in grams, present in the aliquot part taken for analysis.
Ureic nitrogen
7.6 Urease method
7.6.1 Transfer by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate (7.1) containing not more than 250 mg of ureic nitrogen. To remove phosphates, add a suitable quantity of saturated barium hydroxide solution (4.18) until further addition does not cause the production of more precipitate. Eliminate excess barium ions (and any dissolved calcium ions) with 10% sodium carbonate solution (4.19). Allow to settle and check whether precipitation is complete. Make up to the mark, mix and filter through a fluted filter paper. Transfer by pipette 50 ml of filtrate into the 300 ml Erlenmeyer flask of the apparatus (5.3). Acidify with 2 M hydrochloric acid (4.20) to pH 3.0, measured by means of the pH meter (5.5). Raise the pH to 5.4 by the addition of 0.1 M sodium hydroxide (4.17). To avoid ammonia losses when hydrolysis by urease occurs, close the Erlenmeyer flask by means of a stopper provided with a dropping funnel and a small bubble trap containing exactly 2 ml standard 0.1 M hydrochloric acid solution (4.21). Introduce through the separating funnel, 20 ml urease solution (4.22). Allow to stand for one hour at 20-25°C. Place 25.0 ml of the standard 0.1 M hydrochloric acid solution (4.20) in the dropping funnel, allow to run into the solution, then rinse with a little water. Transfer quantitatively the contents of the bubble trap to the solution contained in the Erlenmeyer flask. Titrate the excess acid using standard 0.1 M sodium hydroxide solution (4.17), until a pH of 5.4 is obtained, measured on the pH meter.

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Source: https://www.legislation.gov.uk/nisr/1996/513/schedule/2/part/I/chapter/8b./paragraph/7 (the official version)
Page: https://openlegislation.uk/fertilisers-sampling-and-analysis-regulations-northern-ireland-1996/schedule-2/part-I/chapter-8b./paragraph-7
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.