Electrochemical sensors.

T he oldest electrochemical sensors date back to the 1950s and were used for oxygen monitoring. More recently, as the Occupational Safety and Health Administration (OSHA) began requiring the monitoring of toxic and combustible gases in confined space applications, new and better electrochemical sensors have been developed. By the mid-1980s, miniaturized electrochemical sensors became available for detection of many different toxic gases in PEL ranges, with the sensors exhibiting good sensitivity and selectivity. Currently, a variety of electrochemical sensors are being used extensively in many stationary and portable applications for personal safety. Figure 1 shows a small collection of such electrochemical sensors. The physical size, geometry, selection of various components, and the construction of an electrochemi-cal sensor usually depends on its intended use. Quite often, the final design results in a compromise between various performance parameters of the electrochemi-cal sensor. The most common misconception about electrochemical sensors is that they are all the same. In fact, the appearance of the electrochemical sensors used to detect various gases may be similar, but their functions are markedly different. Consequently,