Ozone-induced dissociation: elucidation of double bond position within mass-selected lipid ions.
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.
Thomas
Michael C
MC
Department of Chemistry and School of Health Sciences, University of Wollongong, Wollongong NSW, 2522, Australia.
Mitchell
Todd W
TW
Harman
David G
DG
Deeley
Jane M
JM
Nealon
Jessica R
JR
Blanksby
Stephen J
SJ
D000818:Animals; D000838:Anions / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D002417:Cattle; D020404:Glycerophospholipids / Q000032:analysis / Q000737:chemistry; D006801:Humans; D007668:Kidney / Q000737:chemistry; D007700:Kinetics; D007908:Lens, Crystalline / Q000737:chemistry; D008055:Lipids / Q000032:analysis / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000032:analysis / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D014280:Triglycerides / Q000032:analysis; D014835:Volatilization
D000838:Anions; D002412:Cations; D020404:Glycerophospholipids; D008055:Lipids; D010713:Phosphatidylcholines; D014280:Triglycerides; D010126:Ozone