Negative atmospheric pressure chemical ionisation of NO2 by O-2-CO2(H2O) studied by ion mobility spectrometry

In this study, negative polarity atmospheric pressure chemical ionisation-ion mobility spectrometry (APCI-IMS) was applied to study ionisation of NO2 by O-2(-)center dot CO2 center dot (H2O)(n) reactant ions (RI) generated in the corona discharge ionisation source. The electron transfer reaction between RI and NO2 resulted in the formation of NO2- (center dot)(H2O)(n) ions (drift gas temperature of 373 K). These ions were detected using IMS (reduced ion mobility of 2.46 cm(2)V(-1) s(-1)) and IMS combined with time-of-flight mass spectrometer (IMS-MS) technique (m/z 46, 64, 82). The kinetics of the electron transfer reaction between O-2(-)center dot CO2 center dot (H2O)(0,1) and NO2 was studied using IMS technique and rate coefficient of 0.88(+/- 0.20) x 10(-10) cm(3)s(-1) was determined. The limit of detection (LOD) for NO2 by IMS achieved value of 200 ppb(v) and the linear response range was in the range 0.05-7 ppm(v). The sensitivity of the method was comparable with the electrochemical sensors; however, the present method has better selectivity and faster response time and it has the potential for further improvements.