Evaluation of a New Reagent-Ion Source and Focusing Ion-Molecule Reactor for Use in Proton-Transfer-Reaction Mass Spectrometry
| Autor: | Manuel A. Hutterli, Benjamin L. Deming, Carsten Stoermer, Abigail R. Koss, Marc Gonin, Rupert Holzinger, Douglas R. Worsnop, Carsten Warneke, Felipe D. Lopez-Hilfiker, John T. Jayne, Joel R. Kimmel, Joost A. de Gouw, Katrin Fuhrer, Jordan E. Krechmer |
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| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: |
Chemical ionization
010504 meteorology & atmospheric sciences Chemistry Inorganic chemistry 010501 environmental sciences Mass spectrometry 01 natural sciences Ion source Ion Analytical Chemistry Reagent Molecule Proton-transfer-reaction mass spectrometry 0105 earth and related environmental sciences |
| Zdroj: | Analytical Chemistry, 90(20), 12011. American Chemical Society |
| ISSN: | 0003-2700 |
| Popis: | We evaluate the performance of a new chemical ionization source called Vocus, consisting of a discharge reagent-ion source and focusing ion-molecule reactor (FIMR) for use in proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF) measurements of volatile organic compounds (VOCs) in air. The reagent ion source uses a low-pressure discharge. The FIMR consists of a glass tube with a resistive coating, mounted inside a radio frequency (RF) quadrupole. The axial electric field is used to enhance ion collision energies and limit cluster ion formation. The RF field focuses ions to the central axis of the reactor and improves the detection efficiency of product ions. Ion trajectory calculations demonstrate the mass-dependent focusing of ions and enhancement of the ion collision energy by the RF field, in particular for the lighter ions. Product ion signals are increased by a factor of 10 when the RF field is applied (5000-18000 cps ppbv-1), improving measurement precision and detection limits while operating at very similar reaction conditions as traditional PTR instruments. Because of the high water mixing ratio in the FIMR, we observe no dependence of the sensitivity on ambient sample humidity. In this work, the Vocus is interfaced to a TOF mass analyzer with a mass resolving power up to 12000, which allows clear separation of isobaric ions, observed at nearly every nominal mass when measuring ambient air. Measurement response times are determined for a range of ketones with saturation vapor concentrations down to 5 × 104 μg m-3 and compare favorably with previously published results for a PTR-MS instrument. |
| Databáze: | OpenAIRE |
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