ISO/R 1982:1971

Nitric acid for industrial use — Determination of iron content — 2,2′- Bipyridyl photometric method

The method is applicable to the determination of iron contents greater than 0,0001 % (m/m). The principle consists in evaporation of a test portion, taking up by means of hydrochloric acid and reduction of iron(III) by means of hydroxylammonium chloride. Formation of iron(II)-2,2′ -dipyridyl complex in ammonium acetate medium. Photometric measurement of the coloured complex at a wavelength of about 522 nm.