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Title: ON THE FORMATION OF CONJUGATED LINOLEIC ACID DIAGNOSTIC IONS WITH ACETONITRILE CHEMICAL IONIZATION TANDEM MASS SPECTROMETRY

Author
item MICHAUD, ANTHONY - CORNELL UNIVERSITY
item LAWRENCE, PETER - CORNELL UNIVERSITY
item Adlof, Richard
item BRENNA, J. THOMAS - CORNELL UNIVERSITY

Submitted to: Journal of American Society for Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2004
Publication Date: 1/29/2005
Citation: Michaud, A.L., Lawrence, P., Adlof, R.O., Brenna, J. 2005. On the formation of conjugated linoleic acid diagnostic ions with acetonitrile chemical ionization tandem mass spectrometry. Journal of American Society for Mass Spectrometry. 19:363-368.

Interpretive Summary: Mass spectrometry (MS) is an important tool for determining the exact structure of fats. Using fats labelled with isotopes, the authors were able to determine the exact pathway of breakdown for the fats during MS analysis. This knowledge will provide a basis allowing future researchers to achieve a better understanding of the data generated during their analyses, and to expand the methodology to the characterization of other unsaturated fats.

Technical Abstract: Acetonitrile chemical ionization tandem mass spectrometry has recently been shown to be a rapid method for the identification of double bond position and geometry in methyl esters of conjugated linoleic acids (CLA), however the structures of intermediate and diagnostic ions and their mechanisms of formation are not known. A mechanism is proposed here in which the m/z 54 ion, (1-methyleneimino)-1-ethenylium (MIE), undergoes nucleophilic attack preferentially by the cis double bond in CLAs with mixed geometry (cis/trans, trans/cis), favoring the observed C-C cleavage vinylic to the trans double bond. The [M+54]+ addition product intermediate contains a heterocyclic six-membered ring resulting from the two-step addition of MIE to the CLA. Experiments with isotopically labeled CLAs and acetonitrile, and from MS/MS/MS experiments, yield data consistent with this proposal. The proposed mechanism is consistent with known ion-molecule chemistry in smaller compounds, and explains most phenomena associated with MIE-CLA ion chemistry.