# Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996, Paragraph 4: REAGENTS


Petermann’s solution
4.1
Characteristics:
Citric acid monohydrate, 173 g per litre.
Ammonia, 42 g per litre ammoniacal nitrogen.
pH, between 9.4 and 9.7.
Preparation from diammonium citrate:
Dissolve 941 g diammonium citrate in about 3,500 ml water in a 5 litre graduated flask. Stand the flask in a bath of running water, mix and cool. Add, in small amounts, 430 ml of ammonia solution (ρ = 0.880 g/ml), from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if ρ = 0.906 g/ml then 502 ml are required). Adjust the temperature to 20°C, make up to volume with water and mix.
Preparation from citric acid and ammonia:
Dissolve 865 g citric acid monohydrate in about 2,500 ml distilled water in a container of about 5 litres capacity. Place the container in an ice bath and add in small amounts, shaking continually, 966 ml of ammonia solution (ρ = 0.880 g/ml), from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if ρ = 0.906 g/ml, then, 1,114 ml are required). Adjust the temperature to 20°C, transfer to a 5 litre graduated flask, make up to the mark with distilled water and mix.
Check the ammoniacal nitrogen content as follows:
Transfer 25 ml of the solution into a 250 ml graduated flask, make up to volume with distilled water and mix. Determine the ammoniacal nitrogen content on 25 ml of this solution using Method 2. If the solution is correct, 15 ml 0.25 M H2SO4 are required — Calculate the concentration of ammoniacal nitrogen in the reagent solution (1 ml 0.25 M H2SO4 = 0.007 g nitrogen).
If the concentration of ammoniacal nitrogen is greater than 42 g/litre, ammonia can be expelled by a stream of inert gas or by moderate heating to bring back the pH to 9.7. Carry out a second determination.
If the concentration of ammoniacal nitrogen is less than 42 g/litre, calculate the volume of ammonia solution required to achieve this level (1 ml ammonia solution, ρ = 0.880 g/ml contains approximately 0.22 g ammoniacal nitrogen). For each ml of ammonia solution required add 0.173 g of citric acid.
Whenever corrections are made to this reagent solution, it is imperative that the final concentration of both the citric acid and ammoniacal nitrogen are as specified.

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Source: https://www.legislation.gov.uk/nisr/1996/513/schedule/2/part/I/chapter/9e./paragraph/4 (the official version)
Page: https://openlegislation.uk/fertilisers-sampling-and-analysis-regulations-northern-ireland-1996/schedule-2/part-I/chapter-9e./paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.