Reference number
ISO 984:1974
ISO 984:1974
© ISO 2025
ISO 984:1974
Sodium hydroxide for industrial use — Determination of silica content — Reduced silico-molybdic complex photometric method
Edition 1
1974-12
1974-12
Withdrawn
Abstract
The method is applicable to products having silica contents exceeding 10 mg/kg. The principle is based on the formation of yellow oxidized silico-molybdic complex in a strongly acid medium, in the presence of boric acid to suppress interference by fluorides. Selective reduction of this complex with a mixture of aminonaphtholsulphonic acid (4-amino-3-hydroxynaphthalene-1-sulphonic acid), sodium metabisulphite and sodium sulphite, in the presence of oxalic acid and in a strongly acid medium so as to suppress interference by phosphates. Photometric measurement of the blue-coloured complex at a wavelength of about 795 nm.