Speciation of iron in river and tap waters by catalytic spectrophotometry using oxidation of o-phenylenediamine with hydrogen peroxide

A new sensitive catalytic method for the determination of labile iron has b een developed using iron-catalyzed oxidation of o-phenylenediamine (OPDA) w ith hydrogen peroxide at pH 4.5 and 40 degrees C. Absorbance (A) of the oxi dized OPDA was monitored at 450 nm for a reaction time (t) of 10 min. The c alibration graph was constructed by using Delta A/Delta t. The same calibra tion graph with a linear range of 0-20 mu g l(-1) was obtained for Fe(II) a nd Fe(III). The detection limit was 0.06 mu g l(-1). Labile form of iron wa s characterized by the kinetic and complexation studies for the speciation of iron. The results suggested that Fe(II) was oxidized to Fe(III) at the i nitial reaction step and Fe3+ and (FeLi)-L-III, where i = 1 or 2 for a unid endate and i = 1 for a bidentate ligand (L), were determined as the labile iron. Non-labile Fe(In) hydroxide changed to a labile form by the complexat ion with humic acid. By the combined use of acid decomposition, the propose d method was successfully applied to the determination of soluble labile an d non-labile iron in river and tap water samples. (C) 1999 Elsevier Science B.V. All rights reserved.