Low-level detection of ethanol and H2S with temperature-modulated WO3 nanoparticle gas sensors

Low-level detection of ethanol and H2S was achieved with thermally modulated WO3 nanoparticle gas sensors. Nanoparticle WO3 films, with a mean grain size of ∼5 nm and a thickness of ∼20 μm, were produced by advanced reactive gas evaporation onto alumina substrates. The working temperature of the sensor was periodically modulated between 150 and 250 °C, and the response was analysed by fast Fourier transform (FFT) and discrete wavelet transform (DWT) methods in order to extract characteristic parameters from the sensors' response transients. After calibration of the sensor for low concentrations of ethanol and H2S, it was possible to detect as little as 200 ppb of ethanol and 20 ppb of H2S (both of them dry gases) with good accuracy. Long-term sensor behaviour was assessed. Unsupervised and supervised linear pattern recognition methods, specifically principal component analysis (PCA) and discriminant factor analysis (DFA), were successfully applied to distinguish the investigated gases.