Voltammetric Determination of Cocaine Using Carbon Screen Printed Electrodes Chemically Modified with Uranyl Schiff Base Films

Chemically modified screen printed electrodes (CM-SPE) using [UO2(4-MeOSalen)(H2O)]center dot H2O films were employed in the voltammetric determination of cocaine. The chemical modification was performed by dip coating electrode surfaces (carbon, gold, and platinum) with methanolic solution containing the Schiff base complex with subsequent drying step at room temperature. The optimized amount of the chemical modifier over the working electrode was found to be 2.39 mu g mm(-2) (geometric area). The voltammetric measurements were carried out in 50 : 50 v/v methanol: water solution containing 0.05 mol L-1 KCl and 0.1 mol L-1 LiCl as a supporting electrolyte without oxygen elimination by inert gas flow. The best results were obtained with carbon electrodes. Cocaine exhibits a well defined irreversible anodic peak current (i(pa)) at a potential (E-pa) of 0.85 V vs Ag/AgCl. The current is directly proportional to the drug concentration. An optimal accumulation potential (E-prec), and time (t(prec)) of -0.80 V (vs Ag/AgCl), and 120 s, respectively, were determined. The linear dependence of i(pa) with square root of scan rate (u) indicates that the mass transport at the electrode surface is controlled by diffusion. An optimized scan rate of 100 mVs(-1) was obtained for analytical purposes. A limit of detection (LOD) and limit of quantification (LOQ) in 110 and 390 mu mol L-1, respectively, with intra and inter-day repeatability of 2.61% and 3.77%, respectively, were obtained. In interference studies the proposed method demonstrated high specificity for cocaine in the presence of morphine and 3,4-methylenedioxymethanphetamine. The above results demonstrate that this method provides a fast and low cost procedure for determination of cocaine in trace levels.