Anodic Stripping Semidifferential Electroanalysis of Mercury(II) at Gold Disk Electrode and Its Application to Environmental Analysis

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Abstract
Anodic stripping semidifferential electroanalysis using a gold disk working electrode was proposed for the trace determination of mercury(II) ion, theoretical predictions being verified. A gold electrode was steeped in aqua regia, activated electrochemically before use, and rotated during the course of pre-electrolysis. A hydroxylamine hydrochloride medium was selected as supporting electrolyte. The detection limit was found to be ca. 0.5 nM under the pre-electrolysis conditions of 10 min at 0 V vs. Ag/AgCl. The relative standard deviation was ca. ±4% for the measurement at 2 nM level. Removal of the oxygen dissolved in sample solutions was not necessary. Experiments were carried out to examine the feasibility of the technique to environmental analysis. The method consists of only the following procedure: sample acidification, standard mercury(II) ion addition, UV irradiation pretreatment, and medium exchange for stripping. It was successfully applied to river water and sea water to separately evaluate ionic mercury, mercury occluded in organic matter, and total mercury (excluding mercury occluded in inorganic matter).