Coordination (Ag+) Ion Spray−Mass Spectrometry of Peroxidation Products of Cholesterol Linoleate and Cholesterol Arachidonate: High-Performance Liquid Chromatography−Mass Spectrometry Analysis of Peroxide Products from Polyunsaturated Lipid Autoxidation

Abstract

Lipid peroxidation of polyunsaturated fatty acids and esters leads to a complex mixture of hydroperoxides and cyclic peroxides, some of which possess potent biological activity. These product mixtures contain dozens of diastereomers and regioisomers. The technique of coordination ion spray−mass spectrometry (CIS−MS), recently reported by Bayer and collaborators, proves to be a powerful tool for the analysis of complex peroxide mixtures. Silver ion forms readily detected Ag+ adducts of peroxides and hydroperoxides. These ions, observed at [M+107] and [M+109], undergo fragmentation typical of hydroperoxides, and cyclic peroxides. Thus, Hock fragmentation is observed from many of the silver ion adducts of hydroperoxides and cyclic peroxides undergo fragmentation to give aldehydes and epoxides. Silver ion coordination ion spray−mass spectrometry (Ag+CIS−MS) can be coupled to normal-phase high-performance liquid chromatography (HPLC) by postcolumn addition of AgBF4, allowing the use of powerful techniques such as selected ion monitoring and selected reaction monitoring. This coupling permits, for the first time, the combination of powerful normal-phase separation techniques with detection methods that provide unambiguous structural information of complex peroxide compounds.