A high resolution and high sensitivity proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS)

Proton-transfer-reaction mass spectrometry (PTR-MS) developed about 10 years ago is used today in a wide range of scientific and technical fields allowing real-time on-line measurements of volatile organic compounds in air with a high sensitivity and a fast response time. Most instruments employed so far use quadrupole filters to analyze product ions generated in the reaction drift tube. Due to the low mass resolution of the quadrupoles used this has the disadvantage that identification of trace gases understudy is not unambiguous. Here we report the development of a new version of PTR-MS instruments using a time-of-flight mass spectrometer, which is capable of measuring VOCs at ultra-low concentrations (as low as a few pptv) under high mass resolution (as high as 6000 m/Delta m in the V-mode) with a mass range of beyond 100 000 amu. This instrument was constructed by interfacing the well characterized and recently improved lonicon hollow cathode ion source and drift tube section with a Tofwerk orthogonal acceleration reflectron time-of-flight mass spectrometer. We will first discuss the set-up of this new PTR-TOF-MS mass spectrometer instrument, its performance (with a sensitivity of several tens of cps/ppbv) and finally give some examples concerning urban air measurements where sensitivity, detection limit and mass resolution is essential to obtain relevant data. (C) 2009 Elsevier B.V. All rights reserved.