Fatty acids charge-remote fragmentation

An important issue in fatty acid analysis is the stractural characterization, especially in terms of positions of double-bond, hydroxy, and other groups. Although results with low-energy negative-ion ESI-MS-MS was described [13], the MS-MS analysis of lithiated lithium salts [M-H+2Li] is the method of choice. Determination of the double-bond position relies on charge-remote fragmentation [2, 14]. 

Deterding, L. J. and Gross, M. L. Tandem mass spectrometry for identifying fatty acid derivatives that undergo charge-remote fragmentations. Org. Mass Spectrom. 23 169-177, 1988. 

Figure 12 The mass spectrum of the fatty acid methyl ester (FAME) of linolenic acid (C18 2A9-12) contains no readily discernable structural information beyond the molecular ion (a). However, the dimethyloxazoline (DMOX) derivative, in which the charge is retained by the heterocyclic ring, can undergo charge remote fragmentation yielding a mass spectrum from which the location of the double bonds, but not their geometry (c/ s versus trans), can be readily determined (b). The latter stereochemistry can usually be distinguished by the GC retention time on an appropriate column.

Scheme 12.1. Charge-remote fragmentation of fatty acids via a 1,4-hydrogen elimination.

Y.-S. Chang and J. T. Watson, Charge-remote fragmentation during FAB-CAD-B/E linked-scan mass spectrometry of (aminoethyl)triphenylphosphonium derivatives of fatty acids, J. Am. Soc. Mass Spectrom. 3, 769-775 (1992). 

Trimpin, S. Clemmer, D. E. McEwen, C. N. Charge-remote fragmentation of lithi-ated fatty acids on a TOE-TOE instmment nsing matrix-ionization. J. Am. Soc. Mass Spectrom. 2007,18, 1967-1972. 

Griffiths, W. J. Yang, Y Lindgren, J. A. Sjoevall, J. Charge remote fragmentation of fatty acid anions in 400 eV collisions with xenon atoms. Rapid Commun. Mass Spec. 1996, 10, 21-28. 

Claeys, M. Nizigiyimana, L. Van den Heuvel, H. Derrick, P. J. Mechanistic aspects of charge-remote fragmentation in saturated and mono-unsaturated fatty acid derivatives. Evidence for homolytic cleavage. Rapid Commun. Mass Spec. 1996, 10, 770-774. 

M. Claeys, L. Nizigiyimana, H. Van den Heuvel, I. Vedernikova, and A. Haemers, Charge-remote and charge-proximate fragmentation processes in alkali-cationized fatty acid esters upon high-energy collision activation, J. Mass Spectrom. 33, 631-641 (1998). 

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