Molecular ion fragmentation and its effects on mass isotopomer abundances of fatty acid methyl esters ionized by electron impact View Full Text


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Article Info

DATE

1999-05-01

AUTHORS

Clifton K. Fagerquist, Richard A. Neese, Marc K. Hellerstein

ABSTRACT

We have analyzed the isotopomer abundance ratios of an equimolar mixture of nine fatty acid methyl esters (decanoate, undecanoate, laurate, tridecanoate, myristate, pentadecanoate, palmitate, heptadecanoate, and stearate) by selected-ion monitoring gas chromatography/electron impact/mass spectrometry (GC/EI/MS). The abundance of the second lowest m/z isotopomer (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${I_{{M_1}}}$$ \end{document}) increased disproportionately compared with the abundance of the lowest m/z isotopomer (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${I_{{M_0}}}$$ \end{document}) as a function of: (1) increasing sample size; (2) decreasing repeller voltage; and (3) decreasing alkyl chain length. We also compared the abundance of the third lowest m/z isotopomer (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${I_{{M_2}}}$$ \end{document}) and the abundance of the second lowest m/z isotopomer (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${I_{{M_1}}}$$ \end{document}) of methyl palmitate and [4,4-2H2]methyl palmitate. We observed that the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${I_{{M_2}}}/{I_{{M_1}}}$$ \end{document} for methyl palmitate was significantly lower than \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${I_{{M_2}}}/{I_{{M_1}}}$$ \end{document} for [4,4-2H2]methyl palmitate. From these results, as well as a consideration of basic principles of ion chemistry and ion physics, we conclude that gas-phase chemistry, specifically proton (or deuteron) transfer from fragment ions to molecules, is a major contributor to the sample size dependence observed in mass isotopomer abundance measurements of fatty acid methyl esters ionized by EI. Our results and analysis do not support hydrogen abstraction as the reaction mechanism. In addition, we calculate that rearranged molecular ions are unlikely to contribute significantly to intermolecular proton transfer because of their relatively brief lifetime. We also discuss alternative analytical techniques which might improve the precision and accuracy of isotopomer measurements by reducing molecular ion fragmentation. More... »

PAGES

430-439

References to SciGraph publications

  • 1995-09-01. Relative collision cross sections of organic ions in JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
  • 1995-02-01. Electron impact mass spectrometry of alkanes in supersonic molecular beams in JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
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  • Identifiers

    URI

    http://scigraph.springernature.com/pub.10.1016/s1044-0305(99)00003-3

    DOI

    http://dx.doi.org/10.1016/s1044-0305(99)00003-3

    DIMENSIONS

    https://app.dimensions.ai/details/publication/pub.1020130566

    PUBMED

    https://www.ncbi.nlm.nih.gov/pubmed/10222596


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