Applicable to products having Fe contents of more than 0.001 % (m/m). Preliminary hydrolysis of polyphophate acids 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.
ISO/R 849:1968Stage: 95.99
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