ISO 6192:1981 PDF

Covers a method applicable to products having ammonia contents greater than 0,25 mg/kg. Consists in absorbing the ammonia from a gaseous sample in sulphiric acid medium with the formation of ammonium sulphate and passing a current of nitrogen into the absorption liquid to remove hydrogen sulphide which would interfere. This is followed by formation in an alkaline medium of the indophenol complex by reaction of the ammonium ions with phenol and hypochlorite ions in the presence of sodium pentacyanonitrosoferrate(III) as catalyst, and photomeric measurement of the blue coloration obtained at a wavelength of about 625 nm.