10.1021/acs.analchem.6b05110.s001 Martin Breitenlechner Martin Breitenlechner Lukas Fischer Lukas Fischer Markus Hainer Markus Hainer Martin Heinritzi Martin Heinritzi Joachim Curtius Joachim Curtius Armin Hansel Armin Hansel PTR3: An Instrument for Studying the Lifecycle of Reactive Organic Carbon in the Atmosphere American Chemical Society 2017 reaction chamber mass resolution gas inlet sample gas proton transfer reaction-time-of-flight mass spectrometer PTR-TOF-MS volatility compounds reaction time SVOC wall losses water molecules Reactive Organic Carbon First calibration tests show sensitivities sample gas flow H 3 O VOC ppbv range 18000 counts reaction chamber design product ions volume rf voltages PTR 3 instrument PTR-TOF HOM 2017-04-24 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/PTR3_An_Instrument_for_Studying_the_Lifecycle_of_Reactive_Organic_Carbon_in_the_Atmosphere/4996703 We have developed and characterized the novel PTR3, a proton transfer reaction-time-of-flight mass spectrometer (PTR-TOF) using a new gas inlet and an innovative reaction chamber design. The reaction chamber consists of a tripole operated with rf voltages generating an electric field only in the radial direction. An elevated electrical field is necessary to reduce clustering of primary hydronium (H<sub>3</sub>O<sup>+</sup>) and product ions with water molecules present in the sample gas. The axial movement of the ions is achieved by the sample gas flow only. Therefore, the new design allows a 30-fold longer reaction time and a 40-fold increase in pressure compared to standard PTR-TOF-MS. First calibration tests show sensitivities of up to 18000 counts per second/parts per billion and volume (cps/ppbv) at a mass resolution of >8000 <i>m</i>/Δ<i>m</i> (fwhm). The new inlet using center-sampling through a critical orifice reduces wall losses of low volatility compounds. Therefore, the new PTR3 instrument is sensitive to VOC typically present in the ppbv range as well as to semivolatile organic compounds (SVOC) and even highly oxidized organic molecules (HOMs) present in the parts per quadrillion per volume (ppqv) range in the atmosphere.