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

Total nitrogen excluding nitric nitrogen

7.3—7.3.1 Transfer by pipette into a 300 ml Kjeldahl flask an aliquot part of filtrate (7.1) containing not more than 50 mg nitrogen to be determined. Dilute to 100 ml with water, add 5 g ferrous sulphate (4.13), 20 ml concentrated sulphuric acid (4.9) and a few glass beads to control boiling (4.29). 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 sulphate (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 (4.2). Connect the flask to the distillation apparatus and continue the determination as in Method 8a, 7.1.1.2.

Blank test

7.3.2 See 7.2.3.

Expression of result

7.3.3 

where:

• a = ml of standard solution of sodium or potassium hydroxide (0.2 N) used for the blank, carried out by placing in the receiver of the apparatus (5.1), 50.0 ml of standard solution of sulphuric acid (0.2 N) (4.6).

• A = ml of standard solution of sodium or potassium hydroxide (0.2 N) used for the analysis.

• M = weight of the sample, in grams, present in the aliquot part taken for analysis.

where:

• a = ml of standard solution of sodium or potassium hydroxide (0.2 N) used for the blank, carried out by placing in the receiver of the apparatus (5.1), 50.0 ml of standard solution of sulphuric acid (0.2 N) (4.6).

• A = ml of standard solution of sodium or potassium hydroxide (0.2 N) used for the analysis.

• M = weight of the sample, in grams, present in the aliquot part taken for analysis.