ISO/R 852:1968

Sodium tripolyphosphate and sodium pyrophosphate for industrial use — Determination of iron content — 2,2'- Bipyridyl spectrophotometric method ISO/R 852:1968

Publication date:   Oct 1, 1968

Scope

Applicable to products having Fe contents of more than 0.001 % (m/m). Preliminary hydrolysis of polyphophates by prolonged boiling in the presence of hydrochloric acid. Reduction of iron(III) by means of hydroxylammonium chloride. Formation of the iron(II)-2,2'-dipyridyl complex in the presence of ammonium acetate at pH of 3.1 and a temperature of 75 °C (under the test conditions the phosphate ions do not interfere). Spectrophotometric measurement of the coloured complex at a wavelength of about 522 nm.