Analysis of lipoxygenase-derived fatty acid hydroperoxides by electrospray ionization tandem mass spectrometry.

A rapid method is described for the identification of fatty acid hydroperoxides by electrospray ionization-tandem mass spectrometry coupled to liquid chromatography without any derivatization required prior to analysis. Localization of fatty acid hydroperoxides in complex mixtures was achieved by monitoring the loss of hydrogen peroxide using constant neutral loss scanning. In the presence of 5 mM NH4OAc in methanol-water, adduct ions [M + NH4]+ were formed almost exclusively, directly revealing the molecular mass of the thermolabile hydroperoxides. In addition, low energy collision-induced dissociation of precursor ions [M + NH4]+ led to characteristic product ions from both the 9- and 13-regioisomers. Thus, electrospray ionization-tandem mass spectrometry provides a straightforward approach for the study of the regioselectivity of lipoxygenase catalysis without any derivatization step required prior to analysis.