Electrochemical determination of Cd2+ in some Al-Madinah water samples and human plasma by cathodic stripping voltammetry in the presence of oxine as a chelating agent

A fast, simple, sensitive cathodic adsorptive stripping voltammetric procedure for quantitative analysis of Cd–oxine complex in al-Madinah city water samples and human plasma is described. The technique involves adsorptive accumulation of the complex on the working electrode, followed by square wave voltammetric determination of the preconcentrated analyte. In basic media, a cathodic electrochemical process involving the elimination of two protons occurs, and a mechanism for the reduction process is suggested. The optimal experimental parameters for assay of this complex are: carbonate supporting electrolyte pH 8, accumulation time 30 s, accumulation potential −0.1 V, scan rate 200 mV s−1, pulse amplitude 80 mV, frequency 40 Hz, surface area of working electrode 0.6 mm2 and convection rate 1000 rpm. The calibration graph for determination of Cd–oxine was linear over the concentration range 5 × 10−8 to 4 × 10−7 mol l−1 (r = 0.998), with a detection limit of 3.5 × 10−9 mol l−1. The precision of the proposed procedure was estimated by 10 successive voltammetric measurements of 2 × 10−6 mol l−1 Cd with 4 × 10−6 mol l−1 oxine, and the calculated relative standard deviation was 0.39%. The percentage recovery, indicating the accuracy of the analytical method, was 94 ± 1.0%. Possible interference by several substances, including metals and ligands, was also evaluated. The electroanalytical method was successfully applied to assaying cadmium in water samples and biological fluids such as plasma.