As an alternative to standard commercial reference electrodes, a solid state reference electrode is fabricated for in situ voltammetric analysis in solutions containing little or no added supporting electrolyte. In the fabrication process, a Ag/AgCl wire is coated with an electrolyte immobilized and protected with Nafion or polyurethane. The electrode potential is measured as a function of time, ionic strength, and pH. A stable potential is obtained for Nafion and polyurethane within 30-35 min in water. Both the polyurethane and Nafion solid state reference electrodes are stable for at least 90 days, but the Nafion electrode fluctuates more than the polyurethane electrode. The electrode is demonstrated using square wave anodic stripping voltammetry at a large electrode (3 mm), an ultramicroelectrode (10 µm), and an array of ultramicroelectrodes.

The voltammetric determination of selenium(IV) using a microfabricated array of gold ultramicroelectrodes (Au UMEs) is presented. The array of Au UMEs in conjunction with square wave anodic stripping voltammetry shows a rapid, sensitive and reproducible response for selenium. Using an array of UMEs overcomes the inherent disadvantage of measuring the very low current signals present when using a single UME. The experimental parameters that affect the response of selenium: deposition potential, selection of the electrolyte solution, SW frequency, and deposition time were investigated. The Se redox reaction appears to be kinetically faster and more reversible at the Au UME array than at Au macroelectrode or single Au UME. Calibration plots are given for solutions containing 0-100 ppb and 100-500 ppb. The limit of detection is calculated to be 0.42 ppb. The relative standard deviation at 50 ppb is 4.5 % for 10 runs.

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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