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Using Orbitrap mass spectrometry to assess the isotopic compositions of individual compounds in mixtures

Hofmann, Amy E. and Chimiak, Laura and Dallas, Brooke and Griep-Raming, Jens and Juchelka, Dieter and Makarov, Alexander and Schwieters, Johannes and Eiler, John M. (2020) Using Orbitrap mass spectrometry to assess the isotopic compositions of individual compounds in mixtures. International Journal of Mass Spectrometry, 457 . Art. No. 116410. ISSN 1387-3806. doi:10.1016/j.ijms.2020.116410.

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The isotopic compositions of individual chemical species are routinely used by the geochemical, environmental, forensic, anthropological, chemical, and biomedical communities to elucidate the conditions, sources, and reaction pathways of the molecules in question. Mass spectrometric methods of measuring isotopic compositions of individual compounds generally require that analytes be pure to yield precise, accurate results, yet most applications examine materials that are mixtures of multiple components. Various methods of chemical purification, e.g., chromatography, are used to isolate analytes from mixtures prior to mass spectrometric analysis. However, these techniques take time and specialized instrumentation, both of which could potentially be obviated via the use of ultra-high-resolution mass spectrometry. Here we report on the use of Orbitrap™-based Fourier-transform mass spectrometry to perform isotope ratio measurements of single species within mixtures delivered to the mass spectrometer (MS) without prior chromatographic separation. We demonstrate that instrument biases (attributed here to space charge effects) within the Orbitrap mass analyzer can cause the measured ¹³C/¹²C ratio of a molecular ion in the presence of non-analyte-derived ‘contaminating’ species to spuriously decrease relative to the ¹³C/¹²C ratio measured for the same ion in a pure analyte. We observe that the decrease in ¹³C/¹²C is proportional to the relative concentrations of the additional ‘contaminating’ components. We then recommend several strategies by which this effect can be mediated such that accurate isotope ratios can be obtained.

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Dallas, Brooke0000-0002-1313-3270
Additional Information:© 2020 Published by Elsevier B.V. Received 15 May 2020, Revised 5 August 2020, Accepted 6 August 2020, Available online 15 August 2020. This work was carried out at in the Laboratories for Stable Isotope Geochemistry at the California Institute of Technology and was supported by the Thermo Fisher Scientific-Caltech collaboration, the United States Department of Energy, and an internal award at the Jet Propulsion Laboratory, which is operated by the California Institute of Technology under contract with the National Aeronautics and Space Administration (80NM0018D0004). The authors thank Rob Hodyss and Morgan Cable (JPL) for productive discussions, Annie Moradian (Proteome Exploration Laboratory at Caltech) and Nami Kitchen (Laboratory for Stable Isotope Geochemistry at Caltech) for assistance with the Q Exactive HF and Q Exactive GC, respectively, and two anonymous reviewers for their constructive comments. CRediT authorship contribution statement: Amy E. Hofmann: Methodology, Validation, Formal analysis, Writing - original draft, Writing - review & editing, Visualization. Laura Chimiak: Methodology, Investigation, Validation. Brooke Dallas: Methodology, Investigation, Validation. Jens Griep-Raming: Conceptualization, Project administration, Writing - review & editing, Resources. Dieter Juchelka: Methodology, Investigation, Validation. Alexander Makarov: Conceptualization, Writing - original draft, Writing - review & editing. Johannes Schwieters: Conceptualization, Project administration. John M. Eiler: Conceptualization, Methodology, Investigation, Validation, Writing - original draft, Writing - review & editing, Supervision, Project administration, Funding acquisition. Declaration of competing interest: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The author list includes employees of Thermo Fisher, which manufactures Orbitrap-based mass spectrometers.
Funding AgencyGrant Number
Thermo Fisher ScientificUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Subject Keywords:Orbitrap analyzer; Isotope ratios; Natural abundance; Complex mixtures
Record Number:CaltechAUTHORS:20200819-130447888
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Official Citation:Amy E. Hofmann, Laura Chimiak, Brooke Dallas, Jens Griep-Raming, Dieter Juchelka, Alexander Makarov, Johannes Schwieters, John M. Eiler, Using Orbitrap mass spectrometry to assess the isotopic compositions of individual compounds in mixtures, International Journal of Mass Spectrometry, Volume 457, 2020, 116410, ISSN 1387-3806, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105033
Deposited By: Tony Diaz
Deposited On:19 Aug 2020 20:47
Last Modified:16 Nov 2021 18:39

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