Sodium sulphate for industrial use — Determination of iron content — 1,10- Phenanthroline photometric method

Applicable to products the Fe content of which is equal to or more than 0.0003 % (m/m). Dissolution of the test sample in delute hydrochloric acid and bromine water by heating. Preliminary reduction of the iron(III) by hydroxylammonium chloride. Formation of the iron(II)-1,10-phenanthroline complex in a buffered medium. Photometric measurement of the coloured complex at a wavelength of about 510 nm.