COMPARISON OF LOW-ENERGY AND HIGH-ENERGY COLLISION-INDUCED DISSOCIATION TANDEM MASS-SPECTROMETRY IN THE ANALYSIS OF RICINOLEIC AND RICINELAIDIC ACID

Ricinoleic acid and its trans isomer ricinelaidic acid, and their meth yl esters, were analyzed by low- and high-energy collision-induced dis sociation (CID) tandem mass spectrometry. It is shown that a stable ch arge centre is required to observe the rearrangement, which occurs in the beta-hydroxyalkene part and results in the loss of heptaldehyde, a nd that this rearrangement corresponds to a low-energy CID reaction. D ifferences between the CID behaviour of ricinoleic acid and that of it s trans isomer are related to the loss of water, which can also be reg arded as a low-energy rearrangement reaction. Comparison of low- and h igh-energy CID spectra further revealed that high-energy CID gives ris e to loss of a H-. radical and H-2 together with low-energy fragmentat ion. 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 fragmenta tion is most pronounced for the [M + Li](+) ions of the methyl esters. (C) 1997 by John Whey & Sons, Ltd.