ISO 1981:1977

Two cases are considered: content of nitrous compounds, expressed as HNO2, equal to or greater than 0,01 % (m/m) and content of nitrous compounds, expressed as HNO2, less than 0,01 % (m/m). The principle consists in oxidatiuon of the compounds present in a test portion by an excess of standard volumetric potassium permanganate solution. Addition of an excess of a standard volumetric iron(II) sulphate solution, and titration of this excess with a standard volumetric potassium permanganate solution. Replaces ISO Recommendation R 1981-1971.