Spectrophotometric determination of trace iron(III) in natural water after its preconcentration with a chelating resin

A method for the determination of Fe(Ill) at trace levels is described. Thus, prior to the spectrophotometric determination, a preconcentration of the trace amounts of iron(III) using a chelate forming resin is proposed. A strong base anion-exchange resin (Dowex 2X4) loaded with Ferron (7-iodo-8-liydroxyquinol4ie-5-sulphonic acid) was used for Fe(III) preconcentration, at pH 2.2. After desorption with 5 % ascorbic acid in 0.5 M HCl, the analyte (converted from Fe(III) to Fe(II) was determined spectrophotometrically at 5 10 nm as Fe(II)-o-phenanthroline complex. The accuracy of the proposed method was verified by comparing the obtained results with those obtained using AAS with the standard addition method. The sensitivity of the spectrophotometric method (after preconcentration) was 0.01 mug Fe(III)/ml. The recovery for iron(III) at the 7 mug/l level was 97 %.