Operation, Sensitivity, and Selectivity

EC sensors are relatively sensitive, as they react to chemical vapor concentrations at the low parts-per-million level. However, EC sensors are not as selective as colorimetric detectors (see Chapter 10). They may respond to various chemicals simultaneously without differentiation capability. This is because the oxidation-reduction reaction between the chemicals in the sample and the electrolyte controls the detection. Any chemicals contained in the sample that will react with the electrolyte on the working electrode surface will generate electrical current and are detected together with those from targeted chemicals. Using a chemical filter may reduce or eliminate some of the chemical interference potential. The nse of a second working electrode that responds to different sets of chemicals from the first working electrode within the same sensor may also lead to better selectivity. 

Several factors may affect the performance of EC sensors. Enviromnental conditions are major concerns. During operation in high-hnmidity conditions, the cell electrolyte may absorb water from the air. In contrasL while operating in low-humidity conditions, the cell electrolyte may lose water. This gain and loss of water 

Sensor lifetime can be reasonably long. However, its sensitivity may vary due to loss of electrolyte and contamination of the catalytic surface. 

The first chemical agent detector that was developed by the U.S. mihtary, the M43, is an EC detector that senses the reaction of a nerve agent with an oxime solution. The electrical signal generated is measured through the use of platinum and silver electrodes. 

Another example of chemical agent detection using an EC cell is the Individual Chemical Agent Detector . The ICAD can detect both nerve and mustard agents simultaneously through the use of two sensor cells. 

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