The principle consists in the evaporation to dryness of a test portion and dissolution of the residue in hydrochloric acid. Reduction of iron(III) by means of hydroxylammonium chloride. Formation of the iron(II)- 2,2'-dipyridyl complex. Photometric measurement of the coloured complex at a wavelength of about 522 nm. Specifies the use of a spectrophotometer or photoelectric absorptionmeter. As an alternative it is permitted to employ a visual method comparing the test solution with a series of reference solutions. Has also been approved by the IUPAC.
ISO 2886:1973Stage: 95.99
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