Determination of Trace Mercury (Hg(II)) by Anodic Stripping Voltammetry at a Gold Electrode

ronment, the determination of trace Hg(II) is important. Atomic absorpt ion and inductively coupled plasma spectroscopic methods are currently widely used. Many publications on this subject focus on electrochemical methods (anodic and potentiometric stripping voltammetry) at a variety of electrode materials. Glassy carbon, goldplated glassy carbon, screen-printed carbon, platinum (Pt) and gold (Au) have all been utilized in these investigations. The use of a bare glassy carbon electrode was investigated by Allen and Johnson and they noted that deposition of Hg onto this electrode from very dilute solutions occurs only when a second metal cation which can co-deposit with Hg, such as Cu or Au, is present in the solution (1). Early work on the use of a wax-impregnated graphite electrode was reported by Perone and Kretlow (2). The USEPA method 7472 for Hg(II) determination involves electrochemical deposition of a thin gold film on a glassy carbon electrode. Accumulation of Hg vapor on an Au-plated glassy carbon electrode followed by voltammetric determination has been the subject of a recent publication (3). Simultaneous determination of arsenic (As) and Hg was performed on a gold-plated glassy carbon electrode as recently reported by Viltchinskaia, et al. (4). Disposable screen-printed carbon electrodes with a coating of Au were used by Wang and Tian in potentiometric stripping voltammetry for the determination of trace quantities of inorganic Hg as well as organic mercury compounds such as dimethylmercury (5). The determination of Hg(II) at Pt by anodic stripping voltammetry has been studied by many people (6,7). Different surface species formed between Pt and Hg give rise to multiple peaks that interfere with the analysis. These multiple peaks have been proposed to be due to varying amounts of Hg plating, i.e., more or less than a monolayer. Careful control of deposition time, depending on the sample concentration, is therefore necessary. The use of solid gold electrodes for on-site Hg analysis in soil samples was proposed recently (8). A good correlation between the results from the solid 1 mm Au electrode and the EPA method with the Au-plated glassy carbon electrode has been indicated here. The EPA method requires deposition of Au onto the carbon electrode, which lengthens the analysis time and significantly increases the cost of analysis. The acceptance of a solid Au electrode for this analysis has been slow, probably due to the strong interaction between Hg and Au (6). A remedy to this situation can be electrochemical cleaning of the electrode after a single use as suggested by Hsi, et al. (9). This procedure is very easy to perform and can conveniently be integrated into fully automated systems. Continuous use of a gold electrode with a better cleaning procedure could make the procedure more adaptable Determination of Trace Mercury (Hg(II)) by Anodic Stripping Voltammetry at a Gold Electrode A Look at Different Techniques, Common Background Electrolytes, and Electrode Surface Cleaning Procedures