Rapid on-site analysis of arsenic in groundwater was achieved with a small battery-powered unit in conjunction with a microfabricated gold ultramicroelectrode array (Au-UMEA). The sensor, consisting of 564 UME disks with a unique gold surface created by electron beam evaporation, was demonstrated to be highly sensitive to low-ppb As3+ using square wave anodic stripping voltammetry. The influence of the square wave frequency, pulse amplitude, and deposition potential on the arsenic peak stripping current was investigated. Varying those theoretical parameters yielded results surprisingly similar to those for the thin Hg film case. The performance of the Au-UMEA was evaluated for reproducibility and reliability. Three stability tests showed an average relative standard deviation of 2.5% for 15 consecutive runs. Limits of detection were investigated, and 0.05 ppb As3+ could be measured while maintaining a S/N of 3:1. Interference studies were performed in the presence of 50-500 ppb of Cu2+, Hg2+, and Pb2+. On-site analysis of groundwater containing arsenic was performed with a small battery-powered potentiostat. Quantification was done through standard additions, and these results were compared to the standard EPA methodology.

The wider availability of microlithographic techniques for the fabrication of electrochemical devices has led to a significant increase in the development of microfabricated arrays of microelectrodes and their use in a wide variety of analytical problems. The major microfabrication steps and the capabilities and limitations of this microsensor technology are reviewed in this article. Several examples are summarized to illustrate the breadth of work with silicon‐based microelectrode arrays, with special emphasis on their use for environmental analysis in a range of diverse settings including remote electroanalysis on Mars.

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The analytical performance of several mercury-coated iridium ultramicroelectrode arrays (IrUMEAs) was studied using square wave anodic stripping voltammetry (SWASV) for determination of cadmium in a pH 4.5 acetate buffer. The microlithographically fabricated IrUMEAs consisted of either 20 or 25 individual disk shaped UMEs, each 10 mm in diameter. The insulating layer utilized in the fabrication process was either silicon dioxide (5000 Å ) or silicon nitride (1500 Å or 2500 Å ). Calibration plots demonstrated good linearity for cadmium from 0-100 ppb. Standard deviations, detection limits, and correlation coefficients were calculated to determine the stability and reproducibility of the IrUMEAs. Repetitive cycles of depositing and stripping Hg at the IrUMEA surface resulted in increased distortion and loss of the SWASV signal. Atomic force microscopy revealed a subtle transformation in the IrUMEA surfaces.

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