Determination of mercury(II) after its preconcentratilon on a carbon paste electrode modified with Cadion A

The use of a carbon paste electrode modified with 4-nitrophenyldiazoaminoazobenzene for the preconcentration and determination of mercury(II) by cyclic voltammetry after its reduction to elementary state was described. First mercury(II) was preconcentrated, from the analyzed sample under open circuit conditions, on the surface of the modified carbon paste electrode. Mercury accumulated from solution (0.2 M sodium acetate, pH 7-7.5) forming with the reagent a stable complex, which was reduced to elementary mercury by electrolysis at -400 mV vs. Ag/AgCl/Cl- (1M) during a period of 60 s. The formed elementary mercury was then determinated by cyclic voltammetry. One anodic peak at +452 mV vs. Ag/AgCl/Cl- (1M) was observed on scanning the potential from -400 mV to +650 mV vs. Ag/AgCl/Cl- (1M) (concentration of nitric acid, 0.12 M; scan rate, 100 mV/s). Optimization of operational parameters such as: the concentration of supporting electrolyte, the preconcentration time, the reduction potential, the reduction time and others were studied in detail. A calibration graph covering the concentration range from 0.1 to 20 mu g mL(-1) was obtained. The precision for six determinations of 2 mu g mL(-1) Hg(II) was 2.68% (relative standard deviation). The interferences of some metal ions on the Hg(II) determination were investigated. The selectivity of mercury determination was very good The method can be used to determine the mercury(II) concentration in contaminated waters.