Stripping Analyses of Mercury Using Gold Electrodes:  Irreversible Adsorption of Mercury

The electrochemical deposition and stripping of mercury on gold surfaces was investigated to assess whether gold electrodes would return to mercury-free states after stripping analyses. X-ray photoelectron spectroscopy studies demonstrate the presence of mercury on gold foil electrodes that have undergone controlled-potential deposition procedures in Hg2+ solutions (10 nM−0.1 mM) followed by stripping and cleaning in mercury-free electrolyte. Results show that mercury is not completely removed electrochemically from the gold electrodes, even when the oxidizing potential is +2.5 V vs Ag/AgCl. Bulk electrolyses deposition and stripping procedures coupled with cold vapor atomic absorption spectroscopic analyses of solutions after deposition and stripping are also reported. Results suggest that the nature of the gold electrode is fundamentally altered by irreversible adsorption of mercury; that is, mercury is adsorbed during deposition and some of the mercury is retained even after stripping and cleaning. The implications and strategies for using stripping analysis and gold electrodes for the measurement of mercury under the experimental conditions employed in this study are discussed.