IDENTIFICATION OF MONOHYDROXY FATTY-ACIDS BY ELECTROSPRAY MASS-SPECTROMETRY AND TANDEM MASS-SPECTROMETRY

Negative-ion electrospray mass spectrometry (ESI-MS) and tandem mass s pectrometry (ESI-MS/MS) were used to characterize saturated and unsatu rated monohydroxy fatty acids and fatty acid metabolites formed follow ing incubation with soybean lipoxygenase. Ions corresponding to [M-H]( -) of eicosanoids were readily observed using ESI-MS, but double bond migration precluded the use of MS to localize double bonds or the posi tion of hydroxyl moieties; however, by following MS analysis with nega tive-ion ESI-MSI RIS of precursor ions, the position of oxygenation co uld be determined for picogram quantities of underivatized monohydroxy fatty acids. Loss of 46 mass units from the precursor ion of saturate d monohydroxy compounds was explained in some cases by resonance stabi lization of enolate ions, but this product ion was found in spectra of compounds where resonance was not possible. Spectra of deuterated ana logs supported charge-driven vinylic processes as the most common mech anism of fragmentation. The utility of low-collision-energy ESI-MS/MS to examine biological samples was shown by examining the products form ed by the metabolism of linoleic (18:2 omega 8) and arachidonic (20:4 omega 6) acids by soybean lipoxygenase using aerobic and anaerobic inc ubation conditions that generated increasingly complex mixes of metabo lites. (C) 1996 Academic Press, Inc.