Articles | Volume 9, issue 4
https://doi.org/10.5194/amt-9-1473-2016
https://doi.org/10.5194/amt-9-1473-2016
Research article
 | 
05 Apr 2016
Research article |  | 05 Apr 2016

Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds

Michelle J. Kim, Matthew C. Zoerb, Nicole R. Campbell, Kathryn J. Zimmermann, Byron W. Blomquist, Barry J. Huebert, and Timothy H. Bertram

Abstract. Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt−1) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion–molecule reactions likely proceed through a combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The in-field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer, where measurements from the two instruments were highly correlated (R2 > 0.95, 10 s averages) over a wide range of sampling conditions.

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Short summary
Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory and field measurements were used to assess the sensitivity of the ionization scheme under a wide array of operating condition. Underway measurements of DMS in the North Atlantic were validated against an atmospheric pressure ionization mass spectrometer.