Journal of Lipid Research, Vol. 12, 628-634, September 1971
Copyright © 1971 by Lipid Research, Inc.

Mass spectrometry of the phosphatidylcholines: fragmentation processes for dioleoyl and stearoyl-oleoyl glycerylphosphorylcholine

R. A. Klein

Institute of Animal Physiology, Agricultural Research Council, Babraham, Cambridge, England

Mass spectra for the various phosphatidylcholines, together with accurate mass measurements on the more abundant fragment ions, have been described in a previous paper (Ref. 5). No detailed fragmentation sequence was proposed on the evidence available. In the case of dioleoyl glycerylphosphorylcholine, some question arose as to whether certain ions were produced by electron impact or by pyrolysis.

In this paper, results are reported which enable a more detailed fragmentation sequence to be proposed. By observing metastable transitions in the first field free region of a double-focusing mass spectrometer, it can be shown that the major ions in the spectrum are produced by electron impact processes, and not by pyrolysis; moreover, many of these ions are directly related to one another by metastable processes.

In particular, it has been demonstrated that the ions at m/e 603 for dioleoyl glycerylphosphorylcholine and at m/e 604 for stearoyl-oleoyl glycerylphosphorylcholine are derived from the appropriate molecular ions by an electron impact-induced process.

From measurements of the metastable ion intensities, as well as from the appearance potentials and ionization efficiency curves, conclusions may be drawn about many of the fragmentation mechanisms, allowing a distinction to be made between rearrangement and cleavage reactions.

Supplementary key words first field free region • metastable intensities • appearance potentials • cleavage • rearrangement • electron impact

Submitted on December 29, 1970
Accepted on June 3, 1971

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