The Fertilisers (Sampling and Analysis) Regulations 1996

Ammoniacal nitrogen

7.5—7.5.1 In the presence of ureic nitrogen

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-1-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).

7.5.2 Blank test

See 7.2.3.

7.5.3 Expression of result

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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.