In this study, we develop an alternating current (AC)-induced electro-epoxidation reaction and incorporate it into nanoelectrospray ionization for locating carbon-carbon double-bonds in positively and negatively charged forms of lipids simultaneously. An AC voltage plays multiple roles in this method, including initiation of the electro-epoxidation of carbon-carbon double-bonds in both charged states of lipids and protonation/deprotonation of lipids for detection in both ion modes. Moreover, the rapid switch between native lipids and their electro-epoxidation products can be achieved at different AC voltages. The efficacy of the present method was demonstrated in mixtures of lipid standards and in a biological polar lipid extract. The advantages of simultaneous detection of negatively and positively charged unsaturated lipids, the low sample consumption, and on-demand electro-epoxidation should allow its wide applications in lipid-related research.
Keywords: AC-ESI; carbon−carbon double-bond positions; interfacial reaction; lipidomics.