ISO 2991:1974

Applicable to products containing more than 0.0001 % (m/m) of ammoniacal nitrogen. The procedure described is siutable for contents between 0.0001 % (m/m) and 0.0005 % (m/m). The principle of the analysis consists in distillation, with entrainment by steam, of the ammonia in the presence of an excess of sodium hydroxide and collection of the distillate in an excess of acid solution. Neutralization of the excess of acid and formation of the coloured complex by treatment with sodium phenate and sodium hypochlorite in the presence of acetone. Spectrophotometric measurement of the indophenol obtained at a wavelength of about 630 nm. Has also been approved by the IUPAC.