Chemical sensing is part of an information acquisition process in which some insight is obtained about the chemical composition of the system in real time. In this process an amplified electric signal results from the presence of some chemical species. Generally, it consists of two distinct steps: recognition and amplification. An example is the ordinary measurement of pH with a glass electrode (Figure 1-1). The interaction of the hydronium ion with the electrode is highly specific, but the power in the primary electric signal is very low. For a 10 MΩ glass electrode and 1 mV error it would be approximately 1 pW. If we try to draw more power from such an electrode, the information would be distorted or destroyed. In other words, the source of the signal (electrode) requires an amplifier (pH meter) in order to obtain the information in a useful, undistorted form. Thus the recognition (selectivity) is provided by some chemical interaction while the amplification can be provided by some physical means. There are exceptions, however, to this statement: for example, enzymatic reactions combine the high selectivity of the enzyme binding for a given substrate with catalytic properties of the enzyme that represent an amplification step in its own right.
KeywordsBinding Constant General Aspect Chemical Sensor Flow Injection Analysis Selectivity Coefficient
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