ISO 3198:1975

Sodium hydroxide for industrial use — Determination of sulphur compounds — Method by reduction and titrimetry

Applicable to products the content of which, expressed as sulphate, is equal or more than 5 mg/kg. The principle consists in the reduction of the sulphur compounds to hydrogen sulphide by heating with a mixture of hydriodic acid and hypophosphorous acid. Distillation of the hydrogen sulphide by a current of oxygen-free nitrogen in a mixture of sodium hydroxide and acetone. Titration of the sulphide with standard volumetric mercury(II) nitrate solution in the presence of dithizone as indicator.