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Platinum Metals Rev., 1997, 41, (1), 11

Iridium Microelectrode Array for Trace Metal Detection

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The accurate detection of pollutants in natural waters is of continuing importance to the authorities who police water quality and to the water user. There are a variety of laboratory-based methods for detecting and measuring the amounts of toxic pollutants, including heavy metals, in water. Now, an improvement to an iridium microelectrode (Platinum Metals Rev ., 1995, 39, (3), 132) is reported, which was developed to detect lead and cadmium in river water.

The earlier microelectrode could detect trace amounts of free cadmium and lead in concentrations as low as 0.5 nM and 0.1 nM, respectively. The group that developed this iridium microelectrode now reports an improved design, with lower detection limits (C. Belmont, M.-L. Tercier and J. Buffle, the Department of Inorganic, Analytical and Applied Chemistry, Sciences II, Geneva, and G. C. Fiaccabrino and M. Koudelka-Hep, Institute of Microtechnology, University of Neuchâtel, Switzerland, Anal. Chim. Acta, 1996, 329, (3), 203–214).

The new amperometric microsensor is constructed by successively evaporating iridium and silicon nitride both to a thickness of 2000 Å onto a silicon wafer, followed by photolithographic patterning. The microdisc iridium electrodes of size 5 μm diameter, separated by 150 μm to avoid overlapping of diffusion layers, in 10 x 10 arrays were then bonded to printed circuit board and encapsulated by epoxy resin. Mercury was electroplated onto the iridium microarray. After assessing the reproducibility and reliability of the array, trace metal analyses were performed by the square wave anodic striping voltammetry technique.

The array had good stability over long periods of time and there was good reproducibility between different arrays. In river water containing lead and cadmium a detection limit of 50 pM was estabilished, which is an improvement upon the earlier, simpler sensor design.

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