Catalytic flow-injection determination of reactive iron in non-acidified water samples

A flow-injection determination method was proposed for the speciation of reactive species of iron in non-acidified water samples. Iron was determined by the spectrophotometric monitoring of the iron-catalyzed oxidation of o-phenylenediamine with hydrogen peroxide. The reactive iron was characterized as Fe3+ and (FeLi3-n)-L-III, where i = 1 or 2 for a unidentate ligand and i = 1 for a bidentate ligand (Ln-) from the chemical equilibria of hydroxo, oxalato and fluoro Fe(III) complexes. A useful parameter was also proposed to check the reliability of the determination when suffering the adsorption of iron on the inner wall of a PTFE tube of a flow-injection system. Under the optimized FIA condition and by measuring the peak height, a linear calibration curve of iron was obtained up to 0.1 mg L-1 with a detection limit of 0.1 mug L-1. The proposed method was successfully applied to the speciation of reactive and unreactive iron in tap- and river-water samples.