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Methods and limitations of stable isotope measurements via direct elution of chromatographic peaks using gas chromotography-Orbitrap mass spectrometry

Zeichner, Sarah S. and Wilkes, Elise B. and Hofmann, Amy E. and Chimiak, Laura and Sessions, Alex L. and Makarov, Alexander and Eiler, John M. (2022) Methods and limitations of stable isotope measurements via direct elution of chromatographic peaks using gas chromotography-Orbitrap mass spectrometry. International Journal of Mass Spectrometry, 477 . Art. No. 116848. ISSN 1387-3806. doi:10.1016/j.ijms.2022.116848.

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The Thermo Scientific™ QExactive Orbitrap™ mass spectrometer combined with a Thermo Scientific™ Trace™ 1310 GC enables high-mass-resolution measurements of molecular isotopic structure (e.g., molecular-average, position-specific, and multiple substitution measurements), but thus far has employed non-traditional, slow sample introduction methods and long integrations lasting minutes or tens of minutes to optimize measurement precision. This study examines the performance of the Orbitrap for isotope ratio measurements of analytes eluting directly from the gas chromatograph (GC) as traditional GC peaks — i.e. eluting over a period of seconds and with rapidly varying signal intensities. Such a measurement holds potential for simultaneous compound identification and isotope ratio measurement of numerous analytes separated by GC within a single acquisition. We applied this “direct elution” measurement strategy to molecular and fragment ions of para-xylene, serine, and a mixture of polycyclic aromatic hydrocarbons (PAHs) at natural isotope abundances. We built a mathematical model and used a Monte Carlo simulation to evaluate how variations in data processing decisions and GC peak characteristics (e.g., peak shape and elution timing) affect the accuracy of the resulting absolute isotope ratios and sample-standard comparisons (δ values). These case studies inform our recommendations for applying direct elution measurements. The method is appropriate for systems with large position-specific, molecular, or multiply-substituted isotopic anomalies (e.g., isotopically labelled or extraterrestrial compounds), and for compounds that produce strong molecular ions. Precisions improve when experiments are designed to (1) target ions with relatively high mass spectral intensities, (2) optimize the number of ions and range of masses admitted into the Orbitrap, and (3) minimize the nominal resolution settings while still separating relevant isobars.

Item Type:Article
Related URLs:
URLURL TypeDescription data
Zeichner, Sarah S.0000-0001-8897-7657
Wilkes, Elise B.0000-0002-3379-7832
Hofmann, Amy E.0000-0001-6869-5118
Chimiak, Laura0000-0002-5047-5421
Sessions, Alex L.0000-0001-6120-2763
Makarov, Alexander0000-0002-7046-6709
Eiler, John M.0000-0001-5768-7593
Additional Information:© 2022 Elsevier. Received 22 November 2021, Revised 3 March 2022, Accepted 6 April 2022, Available online 11 April 2022, Version of Record 20 April 2022. We thank Elliott Mueller, Gabriella Weiss, Tim Csernica, and Kate Freeman for helpful feedback and enlightening discussion on topics ranging from methodology to data processing. Additionally, we thank Guannan Dong, Peter Martin, Max Lloyd, Andreas Hilkert, Kostya Ayzikov, and Caj Neubauer for their contributions to the development of Orbitrap data analysis software. Finally, we express our gratitude to Nami Kitchen and Fenfang Wu for their invaluable support on instrumentation and troubleshooting. Author contributions. Sarah S. Zeichner: Methodology, Validation, Formal analysis, Investigation, Data curation, Software, Writing, Visualization, Supervision, Project administration. Elise B. Wilkes: Methodology, Validation, Investigation, Writing, Formal analysis, Software, Funding acquisition. Elle Chimiak: Methodology, Validation, Formal analysis, Investigation, Writing. Amy E. Hofmann: Validation, Investigation, Writing, Funding acquisition. Alexander Makarov: Conceptualization, Investigation, Writing (Review & Editing). Alex Sessions: Conceptualization, Methodology, Formal analysis, Software, Writing (Review & Editing). John Eiler: Conceptualization, Methodology, Writing, Supervision, Resources, Funding acquisition. Funding for SSZ was provided by NSF GRFP and a NASA Emerging Worlds grant to AEH (grant number 18-EW18_2-0084). This work was supported in part by grants from NASA Astrobiology Institute (grant number 80NSSC18M094 to ALS and JME), the Agouron Institute (grant number AI-F-GB54.19.2 to EBW), and Caltech's Center for Environmental Microbial Interactions (CEMI, to EBW, ALS, and JME). A portion of this work was performed at the Jet Propulsion Laboratory, which is operated by the California Institute of Technology under contract with the National Aeronautics and Space Administration (80NM0018D004); AEH was supported by Emerging Worlds grant (grant number 18-EW18_2–0084). Data and materials availability. All RAW data and code is available within online repositories, and cited in the main text or the Supplementary information. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Group:Caltech Center for Environmental Microbial Interactions (CEMI)
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Agouron InstituteAI-F-GB54.19.2
Caltech Center for Environmental Microbial Interactions (CEMI)UNSPECIFIED
Subject Keywords:Orbitrap analyzer; Isotope ratios; Natural abundance; Gas chromatography
Record Number:CaltechAUTHORS:20220513-557936000
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Official Citation:Sarah S. Zeichner, Elise B. Wilkes, Amy E. Hofmann, Laura Chimiak, Alex L. Sessions, Alexander Makarov, John M. Eiler, Methods and limitations of stable isotope measurements via direct elution of chromatographic peaks using gas chromotography-Orbitrap mass spectrometry, International Journal of Mass Spectrometry, Volume 477, 2022, 116848, ISSN 1387-3806,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114743
Deposited By: George Porter
Deposited On:16 May 2022 15:34
Last Modified:16 May 2022 15:34

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