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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 6 | Copyright
Atmos. Meas. Tech., 11, 3251-3262, 2018
https://doi.org/10.5194/amt-11-3251-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Jun 2018

Research article | 07 Jun 2018

The sensitivity of benzene cluster cation chemical ionization mass spectrometry to select biogenic terpenes

Avi Lavi1,a, Michael P. Vermeuel1, Gordon A. Novak1, and Timothy H. Bertram1 Avi Lavi et al.
  • 1Department of Chemistry, University of Wisconsin, Madison, WI 53706, USA
  • anow at: Department of Chemistry, University of California-Riverside, Riverside, CA 92521, USA

Abstract. Benzene cluster cations are a sensitive and selective reagent ion for chemical ionization of select biogenic volatile organic compounds. We have previously reported the sensitivity of a field deployable chemical ionization time-of-flight mass spectrometer (CI-ToFMS), using benzene cluster cation ion chemistry, for detection of dimethyl sulfide, isoprene and α-pinene. Here, we present laboratory measurements of the sensitivity of the same instrument to a series of terpenes, including isoprene, α-pinene, β-pinene, D-limonene, ocimene, β-myrcene, farnesene, α-humulene, β-caryophyllene, and isolongifolene at atmospherically relevant mixing ratios (<100pptv). In addition, we determine the dependence of CI-ToFMS sensitivity on the reagent ion neutral delivery concentration and water vapor concentration. We show that isoprene is primarily detected as an adduct (C5H8 ⋅ C6H6+) with a sensitivity ranging between 4 and 10ncpsppt−1, which depends strongly on the reagent ion precursor concentration, de-clustering voltages, and specific humidity (SH). Monoterpenes are detected primarily as the molecular ion (C10H16+) with an average sensitivity, across the five measured compounds, of 14±3ncpsppt−1 for SH between 7 and 14gkg−1, typical of the boreal forest during summer. Sesquiterpenes are detected primarily as the molecular ion (C15H24+) with an average sensitivity, across the four measured compounds, of 9.6±2.3ncpsppt−1, that is also independent of specific humidity. Comparable sensitivities across broad classes of terpenes (e.g., monoterpenes and sesquiterpenes), coupled to the limited dependence on specific humidity, suggest that benzene cluster cation CI-ToFMS is suitable for field studies of biosphere–atmosphere interactions.

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Chemical ionization mass spectrometry has emerged as a versatile tool for the study of reactive gases. Robust calibration is required to assess the sensitivity of these instruments and their dependence on external factors such as specific humidity. Here, we report the sensitivity of benzene cluster cation chemical ionization for an array of terpene compounds. This work permits a more universal understanding of the sensitivity of this technique to a host of isobaric compounds.
Chemical ionization mass spectrometry has emerged as a versatile tool for the study of reactive...
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