ISO 1390-6:1977

The principle is based on the dissolution, in hot hydrochloric acid, of the residue from the determination of the ash of a test portion (see ISO 1390/5). Reduction, by hydroxylammonium chloride, of the iron(III) contained in the solution thus obtained, formation of the coloured complex iron(II)-2,2'bipyridyl in a buffered medium. Photometric measurement of the coloured complex at a wavelength of about 510 nm. - ISO 1390, Parts 1 to 6, replace ISO Recommendation R 1390-1970.