Comparison of Low- and High-energy Collision-induced Dissociation Tandem Mass Spectrometry in the Analysis of Ricinoleic and Ricinelaidic Acid

Abstract

Ricinoleic acid and its trans isomer ricinelaidic acid, and their methyl esters, were analyzed by low- and high-energy collision-induced dissociation (CID) tandem mass spectrometry. It is shown that a stable charge centre is required to observe the rearrangement, which occurs in the β-hydroxyalkene part and results in the loss of heptaldehyde, and that this rearrangement corresponds to a low-energy CID reaction. Differences between the CID behaviour of ricinoleic acid and that of its trans isomer are related to the loss of water, which can also be regarded as a low-energy rearrangement reaction. Comparison of low- and high-energy CID spectra further revealed that high-energy CID gives rise to loss of a H• radical and H2 together with low-energy fragmentation. Examination of different molecule ions, including [M-H]-, [M+Li]+ and [M-H+2Li]+ ions of free fatty acids and [M+Li]+ ions of the methyl esters shows that charge-remote homolytic fragmentation is most pronounced for the [M+Li]+ ions of the methyl esters. © 1997 by John Wiley & Sons, Ltd.