SPME coupled to an array of MOS sensors: Reduction of the interferences caused by water and ethanol during the analysis of red wines

A solid phase microextraction (SPME) system has been coupled to an array of metal oxide sensors. The influence of the experimental conditions used in the injection system in the response of the sensors has been analysed. Moreover, with the help of data obtained from gas chromatography, the system has been optimized to reduce the presence of water and ethanol in the sensors chamber while efficiently retaining and concentrating other volatiles present in wine. The best results in terms of elimination of water and ethanol, reproducibility of the signals and discrimination capability are obtained using a polar absorbent fiber such as the polyacrilate fiber. The performance of the sensory system is drastically improved if the thermal desorption is carried out in two steps (a first desorption at low temperature to dry the fiber followed by a thermal desorption at high temperature). Principal component analysis of the signals obtained using the optimized conditions has allowed the discrimination of five red wines elaborated using the same vinification and ageing methods (vintage 2000) being the only variable modified the variety of grape. The results agree with obtained gas chromatography. These facts demonstrate that the experimental conditions of SPME have to be adapted to the particular requirements of the resistive sensors in order to improve the capability of discrimination of the arrays of sensors.