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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/amt-2020-264
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-264
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  12 Aug 2020

12 Aug 2020

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This preprint is currently under review for the journal AMT.

Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

Chenyang Bi1, Jordan E. Krechmer2, Graham O. Frazier1, Wen Xu2, Andrew T. Lambe2, Megan S. Claflin2, Brian M. Lerner2, John T. Jayne2, Douglas R. Worsnop2, Manjula R. Canagaratna2, and Gabriel Isaacman-VanWertz1 Chenyang Bi et al.
  • 1Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia, 24060, USA
  • 2Aerodyne Research Inc, Billerica, Massachusetts, 01821, USA

Abstract. Atmospheric oxidation products of volatile organic compounds consist of thousands of unique chemicals that have distinctly different physical and chemical properties depending on their detailed structures and functional groups. Measurement techniques that can achieve molecular characterizations with details down to functional groups (i.e., isomer-resolved resolution) are consequently necessary to provide understandings of differences of fate and transport within isomers produced in the oxidation process. We demonstrate a new instrument coupling the thermal desorption aerosol gas chromatograph (TAG), which enables the separation of isomers, with the high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS), which has the capability of classifying unknown compounds by their molecular formulas, and the flame ion detector (FID), which provide a near-universal response to organic compounds. The TAG-CIMS/FID is used to provide isomer-resolved measurements of samples from liquid standard injections and particle-phase organics generated in oxidation flow reactors. By coupling a TAG to a CIMS, the CIMS is enhanced with an additional dimension of information (resolution of individual molecules) at the cost of time resolution (i.e., one sample per hour instead of per minute). We found that isomers are prevalent in sample matrix with an average number of three to five isomers per formula depending on the precursors in the oxidation experiments. Additionally, a multi-reagent ionization mode is investigated in which both zero air and iodide are introduced as reagent ions, to examine the feasibility of extending the use of an individual CIMS to a broader range of analytes with still selective reagent ions. While this approach reduces iodide-adduct ions by a factor of two, [M−H] and [M+O2] ions produced from lower-polarity compounds increase by a factor of five to ten, improving their detection by CIMS. The method expands the range of detected chemical species by using two chemical ionization reagents simultaneously, enabled by the pre-separation of analyte molecules before ionization.

Chenyang Bi et al.

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Chenyang Bi et al.

Chenyang Bi et al.

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Latest update: 27 Nov 2020
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Short summary
Measurement techniques that can achieve molecular characterizations are necessary to understand the differences of fate and transport within isomers produced in the atmospheric oxidation process. In this work, we develop an instrument to conduct isomer-resolved measurements of particle-phase organics. We assess the number of isomers per chemical formula in atmospherically-relevant samples and examine the feasibility of extending the use of an existing instrument to a broader range of analytes.
Measurement techniques that can achieve molecular characterizations are necessary to understand...
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