Differential-pulse polarographic determination of copper and iron in biological and river-water samples as their N-phenylbenzohydroxamic acid complexes by gas-stirred solvent extraction with ethyl acetate

A simple and rapid method for the simultaneous determination of Cu ^II and Fe^III in biological and river-water samples has been developed. The method utilizes the extraction of metal-N- phenylbenzohydroxamic acid complexes into ethyl acetate, followed by direct determination by differential-pulse polarography (DPP) in the organic medium (1.5 ml). Two well defined DPP peaks appear at -0.17 and -0.59 V versus the Ag-AgCl reference electrode for Cu^II and Fe^III, respectively. Both the extraction and oxygen-removal steps in the analytical scheme can be performed by passing nitrogen through the two phases. This feature enhances the time efficiency and simplifies the method of solvent extraction with polarographic detection. Detection limits (signal to noise ratio = 3) are 20 ng ml^-1 for Cu^II and 10 ng ml^-1 for Fe ^III in the original aqueous phase, and both DPP peak heights are directly proportional to metal concentrations in the aqueous phase of up to 10 μg ml^-1. Except for V^V, common metal ions examined do not interfere with the simultaneous determination of the two metal ions.