Applicable to the determination in the presence of ammoniacal salts less than 15 mg in the aliquot amount taken for the determination. In the presence of quantities exceeding 15 mg the ammoniacal nitrogen shall be removed by a cation exchange resin because these salts interfere with the determination. The principle of the reaction consists in formation of a violet-red complex between allophanic acid amide (H2 N.CO.NH.CO.NH2 ) and copper sulphate in the presence of an alkaline solution of potassium sodium tartrate. Photometric measurement at a wavelength of about 550 nm. Has also been approved by the IUPAC.