Determination of trace levels of cadmium (II) in tap water samples by anodic stripping voltammetry with boron-doped diamond electrode

Abstract

The specificity to specific cations of a boron-doped diamond (BDD) electrode can be improved by modification via reduction of 4-aminomethyl benzoic acid and was first used as a sensor for the electrochemical stripping analysis of cadmium in tap water. Cyclic voltammetry cycling from +0.20 to -1.20 V versus Ag/AgCl was used for the grafting process leading to the formation of covalent C-C bond on to the film surface. The precursor concentration and number of cycles were optimized correlated to the specificity and sensitivity for cadmium ion detection. The coverage of the electrode was checked by contact angle and cyclic voltammetry measurements of 30.0 mg/l Cd2+ in comparison with bare boron-doped diamond electrode to reveal its effectiveness in Cd2+ determination. It was then applied for electrochemical determination of cadmium in tap water samples by anodic stripping voltammetry with a single well-defined reduction peak at -0.72 V vs Ag/AgCl in acetate buffer solutions at pH 6.0. Optimal conditions were investigated including deposition time, deposition potential, scan rate and pH. Linear standard addition curve (r2=0.9989, n=6 for each concentration) in the range of 2.0 to 50.0 μg/l Cd2+ was obtained and other dissolved metals including Ca, Mg, Zn, Mn, Fe, Cu, Al, Co and Pb had little interference except for Ni. A detection limit of 0.2 μg/l was achieved. High accuracy (0.44 % error compared with natural water SRM 1640) and reproducibility of the results as well as excellent stability of the electrode material prove the capabilities of this system recovery in the range of 101 to 111% further confirmed the usefulness of the proposed method to analyze cadmium in tap water samples. The results with SRM 1640 were in good agreement with those by ICP-OES. The concentration of cadmium in various water samples from eleven regions at Hatyai city was found to be lower than detection limit of the modified electrode, therefore it can be concluded that the concentration are lower than the drinking water contamination standard limited level (<3.0 μg/l) issued by the World Health Organization (WHO).