Simultaneous determination of copper and iron in biological samples by differential pulse polarography following gas-stirred solvent extraction

Abstract

A differential pulse polarographic method was developed for the simultaneous determination of Cu(II) and Fe(III) after extraction of their N-benzoyl-N-phenylhydroxylamine complexes (BPA) into 1:3 ethyl acetate-acetonitrile. Into a polarographic cell, an aqueous sample solution is taken with 2.0 cm³ of 3 mol dm^-3 sodium acetate solution, 0.5 cm³ of 20% (w/v) trichloroacetic acid solution and then water to make up a total volume of 4.0 cm³ in a polarographic cell. As the organic solvent, 2.0 cm³ of 1:3 ethyl acetate-acetonitrile solution containing 0.05 mol dm^-3 BPA and 0.1 mol dm^-3 tetrabutylammonium perchlorate is added to the aqueous solution. The extraction is performed by passing nitrogen through the two phases at a flow rate of ca. 60 cm³ min^-1 for 7 min. The differential pulse polarogram is measured in the organic phase under the following conditions: 10 mV s^-1 scan rate; 1 s drop time; 50 mV modulation amplitude; 20 ± 0.1°C temperature. The three electrode systems comprise a dropping mercury working electrode, a silver/silver chloride (Ag/AgCl, 3 M KCl) reference electrode and a platinum counter electrode. Two well-defined differential pulse polarographic peaks appear at -0.25 V for Cu(II) and at -0.48 V vs. Ag/AgCl for Fe(III), respectively. The peak heights are directly proportional to the metal concentration in the range of 0.052.0 μg cm ^-3. The lower limit of detection is 0.02 μg cm^-3 Cu(II) and Fe(III) in the original aqueous phase. The method can be applied to the determination of the two metals in biological materials (Bovine Liver, Citrus Leaves and Human Serum).