ISO 2997:1974 Preview
Phosphoric acid for industrial use -- Determination of sulphate content -- Method by reduction and titrimetry
This standard was last reviewed and confirmed in 2011. Therefore this version remains current.
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.