# Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996, Paragraph 3: PRINCIPLE


The following determinations are made on different portions of a single sample solution.
Total soluble nitrogen
3.1 3.1.1 In the absence of nitrates, by direct Kjeldahl digestion of the solution.
3.1.2 In the presence of nitrates, by Kjeldahl digestion of a portion of the solution after reduction by the Ulsch method; ammonia is determined in both cases as described in Method 2.
3.2 Total soluble nitrogen except nitric nitrogen, by Kjeldahl digestion after elimination of nitric nitrogen in acid medium by means of ferrous sulfate; ammonia is determined as described in Method 2.
3.3 Nitric nitrogen, by difference: between 3.1.2 and 3.2 and/or between total soluble nitrogen (3.1.2) and the sum of ammoniacal and ureic nitrogen (3.4 + 3.5).
3.4 Ammoniacal nitrogen, by cold distillation of a weak alkaline solution; the ammonia is absorbed in a solution of sulfuric acid and determined as described in Method 2.
3.5 Ureic nitrogen, either:
3.5.1 By conversion using urease, into ammonia, which is determined by titration with a standard solution of hydrochloric acid;
or,
3.5.2 By gravimetry using xanthydrol: although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers,
or,
3.5.3 By difference, according to the following table:
Case
Nitric nitrogen
Ammoniacal nitrogen
Difference
1
Absent
Present
(3.1.1)-(3.4)
2
Present
Present
(3.2)-(3.4)

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Source: https://www.legislation.gov.uk/nisr/1996/513/schedule/2/part/I/chapter/8b./paragraph/3 (the official version)
Page: https://openlegislation.uk/fertilisers-sampling-and-analysis-regulations-northern-ireland-1996/schedule-2/part-I/chapter-8b./paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.