Features extraction. For VOC analysis, three parameters are extracted from each sensor response: (i) the normalized change of sensor resistance at the middle of the exposure (S1); (ii) the normalized change of sensor resistance at the end of the exposure (S2); and (iii) the area under the response curve (S3). S1 and S2 are calculated with regard to the value of sensor resistance prior to the exposure. For breath analysis, two parameters are extracted from each sensor response (either to the control VOC or to each release of breath sample): (i) the normalized change of sensors resistance soon after the exposure (S4); and (ii) the normalized change of sensors resistance at the middle of the exposure (S5). S4 and S5 are calculated with regard to the value of sensor resistance prior to the exposure. A compensation and calibration process is posteriorly applied to these parameters to retain from sensor responses only that information related to their response to the VOCs from the breath samples. The mean values of the parameters obtained over the two successive exposures to the same sample are then calculated.