Temperature and humidity compensation in the determination of solvent vapors with a microsensor system

Accounting for changes in temperature and ambient humidity is critical to t he development of practical field vapor-monitoring instrumentation employin g microfabricated sensor arrays. In this study, responses to six organic va pors were collected from two prototype field instruments over a range of am bient temperatures and relative humidities (RH). Each instrument contains a n array of three unthermostated polymer-coated surface acoustic wave (SAW) resonators, a thermally desorbed adsorbent preconcentrator bed, a reversibl e pump and a small scrubber cartridge. Negligible changes in the vapor sens itivities with atmospheric RH were observed owing, in large part, to the te mporal separation of co-adsorbed water from the organic vapor analytes upon thermal desorption of preconcentrated air samples. As a result, calibratio ns performed at one RH level could be used to determine vapors at any other RH without corrections using standard pattern recognition methods. Negativ e exponential temperature dependences that agreed reasonably well with thos e predicted from theory were observed for many of the vapor-sensor combinat ions. It was possible to select a subset of sensors with structurally diver se polymer coatings whose sensitivities to all six test vapors and selected binary vapor mixtures had similar temperature dependences. Thus, vapor rec ognition could be rendered independent of temperature and vapor quantificat ion could be corrected for temperature with sufficient accuracy for most ap plications. The results indicate that active temperature control is not nec essary and that temperature and RH compensation is achievable with a relati vely simple microsensor system.