A gas chromatographic-like system for the separation and monitoring of benzene, toluene and xylene compounds at the ppb level using solid state metal oxide gas sensors

This paper reports recent advancements in the realization of a system based on solid-sate metal-oxide gas sensors suitable for the detection of benzene, toluene and xylene (BTX) compounds in the ppb range for outdoor applications. The system follows a gas chromatographic-like approach in which a preconcentration trap and a separation column are used together with a SnO2 thin film sensor fabricated on a micro-hotplate which had a very thin Si3N4 membrane as a physical support for the entire sensor stack. Following this approach we were able to detect benzene, toluene and xylene separately at concentrations as low as 3 ppb in a gas mixture containing all three compounds. The feasibility of a very innovative, simple and cheap detection unit based on a metal semiconducting oxide layer as a detector in GC systems is presented here, and the degradation of the output signal experienced when the sensor is operated in a small chamber together with the preconcentration and the separation columns is discussed.