Spectrophotometric determination of trivalent cerium with feriin in the presence of tetravalent cerium

A method is suggested for the indirect determination of cerium(III) ions in the presence of a high excess of tetravalent cerium. Ce(III) is oxidized to Ce(IV) by tris(1,10-phenanthroline)iron(III) complex (ferriin) in the presence of sodium diphosphate, and the purple-red iron(II) complex (ferroin) formed is determined photometrically at 530 nm. Trivalent cerium can be so determined in quantities of 0-400 μg/50 ml with a relative error of ±3.5%. Cerium(III) was determined in commercial cerium(IV) sulphate and cerium dioxide preparations.