Selection in system and sensor

Since the dawn of chemical sensors, there were high hopes of rapid and widespread utilization of these devices. This predicted success, however, has not yet been achieved, due to several causes: (bio)chemical fouling of the sensor, instability in the sensor signal resulting in drift, and lack of available selector materials, specific for all species to be detected.

In this chapter, a more realistic approach is pursued, i.e., the incorporation of the sensing element in a Total Analysis System (TAS). This system comprises a double-lumen microdialysis probe, providing a coarse first-stage selection of molecules, to be allowed into the system, decreasing the possibility of sensor fouling. Additionally, the system is provided with integrated electrochemically driven pumps to precisely dose nanoliter amounts of calibration liquid, for periodic calibration of the possibly drifting sensing element.

A possible and simple sensing element in these kind of TAS's is a conductivity probe. Electrolyte Conductivity (EC) is not selective for specific ions. It is shown in this chapter, however, that separate ion concentrations can be calculated, when the EC is measured at several temperatures, using the characteristic temperature responses of the ionic conductivities of these ions.