ISO 6685:1982

All the iron(III) present in the test solution is reduced to iron(II) with ascorbic acid. At a pH between 2 and 9 1,10-phenanthroline is added. the measurement of the absorbance of the orange-red complex formed is carried out at the wavelength of maximum absorption (510 nm). The method is applicable to test solutions from which an aliquot portion can be taken containing between 10 and 500 g of Fe in a volume of not more than 60 m. Details of certain interferences and means by which they can be overcome are given in an annex.