ISO 2997:1974 Preview
Phosphoric acid for industrial use -- Determination of sulphate content -- Method by reduction and titrimetry
Applicable to products having sulphate contents equal to or more than 0.0005 % (m/m). Analysis by reduction of the sulphate to sulphide by a mixture of hydriodic acid and hypophosphorus acid. Absorption of the hydrogen sulphide evolved in a mixture of acetone and sodium hydroxide solution. Titration with a standard volumetric solution of mercury(II) acetate in the presence of dithizone as indicator. Has also been approved by the IUPAC.