ISO 3701:1976

Anhydrous hydrogen fluoride for industrial use — Determination of hexafluorosilicic acid content — Reduced molybdosilicate photometric method

Applicable to products having H2 SiF6 contents between 0.01 % (m/m) and 0.2 % (m/m). Gives introductory instructions to the risk in handling with the product. The principle of analysis consists in formation of oxidized molybdosilicate (yellow) in weakly acid medium in the presence of boric acid to suppress interference by fluorine. Selective reduction of this complex after addition of sulphuric acid solution and oxalic acid to eliminate interference from phosphates. Photometric measurement of the blue coloured complex at a wavelength of about 795 nm.