Voltammetric detection of mercury and copper in seawater using a gold microwire electrode

A procedure is presented by which mercury and copper are determined simultaneously in seawater and dilute acid (0.01 M HCl) by anodic stripping voltammetry using gold microwire electrodes. It was found that anion (halide) adsorption is the cause for a gradual decrease in the height and potential of the mercury peak. The effect is eliminated by including an anion desorption step in the analysis at -0.8 V prior to each scan. This step was found to greatly improve the stability of the scans and enabled the use of background subtraction. Advantages of the microwire electrodes were a low roughness of the surface, without a need for pretreatment, and a very small diffusion layer (2 mu m with stirring). Under the optimized voltammetric conditions, the detection limits were 6 pM mercury and 25 pM copper using 300-s deposition. These values are well below those reported previously for other electrodes including rotating disk electrodes. Measurements of the influence of the major anions I-, Br-, Cl-, SO42-, F-, HCO3-, and B(OH)(4) on the response for mercury showed that bromide and chloride are predominantly responsible for the underpotential deposition mechanism of mercury in seawater. The method was applied to coastal water samples from Liverpool Bay.