ISO 9061:1993

The method specified is based on alkaline fusion of a test portion with a mixture of sodium carbonate and boric acid, dissolution of the melt in excess hydrochloric acid, reduction of the iron(III) with hydroxylammonium chloride, formation of the iron(II)-1,10-phenanthroline complex in a buffered medium (pH between 3 and 5), spectrometric measurement of the absorbance of the coloured complex at a wavelength of about 510 nm, corresponding to the absorption maximum. Applies to products having iron contents, expressed as Fe2O3, in the range 0,1 % (m/m) to 2,0 % (m/m).