The principle consists in evaporation of the test portion, taking up by means of hydrochloric acid and reduction of iron(III) by means of hydroxylammonium chloride. Formation of an iron(II)-2.2'-bipyridyl complex in a buffered medium at a pH value between 4.5 and 6. Photometric measurement of the coloured complex at a wavelength of about 522 nm.
ISO/R 909:1968Stage: 95.99
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