Ozone induced dissociation: elucidation of double bond position within mass-selected lipid ions

Authors

Michael C. Thomas, University of WollongongFollow
Todd W. Mitchell, University of WollongongFollow
David G. Harman, University of WollongongFollow
Jane M. Deeley, University of WollongongFollow
Jessica R. Nealon, University of WollongongFollow
Stephen J. Blanksby, University of WollongongFollow

RIS ID

21957

Publication Details

Thomas, M., Mitchell, T. W., Harman, D. G., Deeley, J. M., Nealon, J. & Blanksby, S. J. (2008). Ozone induced dissociation: elucidation of double bond position within mass-selected lipid ions. Analytical Chemistry, 80 (1), 303-311.

Abstract

Ions formed from lipids during electrospray ionization of crude lipid extracts have been mass-selected within a quadrupole linear ion trap mass spectrometer and allowed to react with ozone vapor. Gas-phase ion−molecule reactions between unsaturated lipid ions and ozone are found to yield two primary product ions for each carbon−carbon double bond within the molecule. The mass-to-charge ratios of these chemically induced fragments are diagnostic of the position of unsaturation within the precursor ion. This novel analytical technique, dubbed ozone-induced dissociation (OzID), can be applied both in series and in parallel with conventional collision-induced dissociation (CID) to provide near-complete structural assignment of unknown lipids within complex mixtures without prior fractionation or derivatization. In this study, OzID is applied to a suite of complex lipid extracts from sources including human lens, bovine kidney, and commercial olive oil, thus demonstrating the technique to be applicable to a broad range of lipid classes including both neutral and acidic glycerophospholipids, sphingomyelins, and triacylglycerols. Gas-phase ozonolysis reactions are also observed with different types of precursor ions including [M + H]⁺, [M + Li]⁺, [M + Na]⁺, and [M − H]^-: in each case yielding fragmentation data that allow double bond position to be unambiguously assigned. Within the human lens lipid extract, three sphingomyelin regioisomers, namely SM(d18:0/15Z-24:1), SM(d18:0/17Z-24:1), and SM(d18:0/19Z-24:1), and a novel phosphatidylethanolamine alkyl ether, GPEtn(11Z-18:1e/9Z-18:1), are identified using a combination of CID and OzID. These discoveries demonstrate that lipid identification based on CID alone belies the natural structural diversity in lipid biochemistry and illustrate the potential of OzID as a complementary approach within automated, high-throughput lipid analysis protocols.