Applicable to products in which the content of soluble iron exceeds 2 mg/kg. The preparation of the test solution is carried out according to ISO 2217. Reduction of the iron(III), contained in the aliquot part of the solution, with hydroxylammonium chloride. Formation of the coloured complex between iron(II) and 2,2'-dipyridyl in buffered solution. Photometric measurement of the coloured complex at a wavelength of about 522 nm.