Comparison between Modified and Unmodified Carbon Paste Electrodes for Hexavalent Chromium Determination

This work consists of developing a simple electroanalytical method which allows the speciation of Cr(VI). Gold modified Carbon Paste Electrodes (CPEs) and unmodified CPEs have been tested for the determination of Cr(VI) in presence of an excess of Cr(III) by using differential pulse voltammetry (DPV), without any accumulation or pre-concentration time. Several parameters affecting the analytical performances of the designed electrodes were investigated, including: electrodeposition technique of AuNPs onto the CPE, amount of AuNPs dropped on the electrode surface, supporting electrolyte, presence of Cr(III), presence of chloride ions and concentration of diphenylcarbazide (DPC). Under the optimal conditions, the use of unmodified CPE in an acidic medium containing DPC exhibited a high selectivity and a good detection limit of 19 mu g L-1, which is much lower than the admissible concentration fixed by the World Health Organization (50 mu g.L-1). A linear range from 50 to 260 mu g.L-1 was obtained with a relative standard deviation of 7.75 %. Furthermore, as opposed to the AuNPs-modified CPE, the current response of Cr(VI) obtained at the unmodified CPE was not affected by the presence of chloride ions and trivalent chromium. Finally, the proposed method was successfully applied for the determination of Cr(VI) in real tap water samples with satisfactory results.