New applications of tin oxide gas sensors -: I.: Molecular identification by cyclic variation of the working temperature and numerical analysis of the signals

The molecular identification capabilities of commercial tin oxide semiconductor gas sensor elements (TGS 823, Figaro, Japan) are considerably enhanced by a special operation procedure. Only one gas sensor, operated in a 4-min cycle between 70 degrees C and 300 degrees C is used to determine the type of substance and its concentration. This is achieved by the numerical analysis of conductivity-time profiles recorded periodically and simultaneously during cyclic variation of the working temperature. A concept of a comparatively economic procedure for calibration and analysis was developed and is discussed in the light of the special properties of the sensor elements. Sensor test results employing the sensor element in an immersion probe behind a gas permeable membrane for identification and quantitative determination of volatile organic solvents in water are presented exemplary for the five-component system ethanol, toluene, benzene, acetone and ethylacetate. (C) 1999 Elsevier Science S.A. All rights reserved.