Improved detection limit of the proton-transfer reaction mass spectrometer: on-line monitoring of volatile organic compounds at mixing ratios of a few pptv

The sensitivity of our proton-transfer reaction mass spectrometer system has been improved by nearly two orders of magnitude, so that now on-line monitoring of volatile organic compounds at levels of a few pptv is possible. This has been demonstrated by means of calibration data down to 200 pptv and data on the diurnal variation of C9-alkylbenzene and its 13C-isotope in ambient air obtained at the western outskirts of Innsbruck. During night time the concentration of C9-alkylbenzene showed minimum values of about 200 pptv and its 13C-isotope, representing concentrations of ca. 20 pptv, closely followed time dependent relative variations of 10%, indicating a detection limit of 2 to 5 pptv.