ISO 2368:1972

The method is applicable to products having a content greater than 0,020 %. The principle consists in dissolution of a test portion by either alkaline or acid fusion. Reduction of the iron(III) by hydroxylammonium chloride. Formation of the iro(II)-1, 10-phenanthroline complex in a buffered medium (pH value between 3,5 and 4,2) Photometric measurement of the coloured complex at a wavelength of about 510 nm.