Impedance spectroscopy on xerogel layer for chemical sensing

This paper deals with a new approach for toluene detection in water based on conductivity measurement on a xerogel layer deposited on Si/SiO2 electrode. The conductivity changes is evaluated by means of resistance and phase variation of absolute impedance of the TEOS xerogel layer in contact with small amounts of toluene in water. The electrical properties of such xerogel layer can be measured with impedance spectroscopy technique and modelised with electrical model. The molecule structure of such layer has been obtained with Fourier transformed infrared spectroscopy. For toluene detection, impedance spectroscopy shows a decrease of the membrane resistance over time and an increase of the phase. This decrease can be attributed to the conductivity and dielectric constant variation. A detection limit of 100 ppm and a dynamic range 100 ppm-0.7% are obtained in our experimental conditions. (c) 2005 Elsevier B.V. All rights reserved.