Flow-injection manifold for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) using 2,2′-dipyridyl-2-pyridylhydrazone and a single-line double injection approach

. A simple and rapid flow-injection (FI) method is reported for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products. The method is based on the reaction of Fe(II) with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a water-soluble reddish complex ( λ max =535 nm). Fe(III) reacts with DPPH under flow conditions only after its on-line reduction by ascorbic acid (AsA). Both analytes were determined in the same run via a double-injection valve, which enabled the simultaneous injection of two sample volumes in the same carrier stream ("single-line double-injection" approach). The two well-defined peaks produced corresponded to total iron [Fe(II)+Fe(III)] and Fe(II). Speciation of the analytes in their mixtures was achieved by multiple regression analysis. The calibration curves obtained were linear over the ranges 0–30 and 0–50 mg L –1 for Fe(II) and Fe(III), respectively, and the precision [ s r =1.0% for Fe(II) and 1.5% for Fe(III)] was satisfactory. The method proved to be selective and adequately sensitive ( c L =0.25 and 0.17 mg L –1 for Fe(III) and Fe(II), respectively, in mixtures). Application of the method to the analysis of pharmaceutical samples resulted in excellent accuracy; the percent mean recoveries were in the range 99.0–102.0% for both Fe(II) and Fe(III) and the mean relative error was e r =1.0%.