Ozone-induced dissociation on a modified tandem linear ion-trap: observations of different reactivity for isomeric lipids.
Ozone-induced dissociation (OzID) exploits the gas-phase reaction between mass-selected lipid ions and ozone vapor to determine the position(s) of unsaturation. In this contribution, we describe the modification of a tandem linear ion-trap mass spectrometer specifically for OzID analyses wherein ozone vapor is supplied to the collision cell. This instrumental configuration provides spatial separation between mass-selection, the ozonolysis reaction, and mass-analysis steps in the OzID process and thus delivers significant enhancements in speed and sensitivity (ca. 30-fold). These improvements allow spectra revealing the double-bond position(s) within unsaturated lipids to be acquired within 1 s: significantly enhancing the utility of OzID in high-throughput lipidomic protocols. The stable ozone concentration afforded by this modified instrument also allows direct comparison of relative reactivity of isomeric lipids and reveals reactivity trends related to (1) double-bond position, (2) substitution position on the glycerol backbone, and (3) stereochemistry. For cis- and trans-isomers, differences were also observed in the branching ratio of product ions arising from the gas-phase ozonolysis reaction, suggesting that relative ion abundances could be exploited as markers for double-bond geometry. Additional activation energy applied to mass-selected lipid ions during injection into the collision cell (with ozone present) was found to yield spectra containing both OzID and classical-CID fragment ions. This combination CID-OzID acquisition on an ostensibly simple monounsaturated phosphatidylcholine within a cow brain lipid extract provided evidence for up to four structurally distinct phospholipids differing in both double-bond position and sn-substitution.
Poad
Berwyck L J
BL
School of Chemistry, University of Wollongong, Gwynneville, Australia.
Pham
Huong T
HT
Thomas
Michael C
MC
Nealon
Jessica R
JR
Campbell
J Larry
JL
Mitchell
Todd W
TW
Blanksby
Stephen J
SJ
D000818:Animals; D001923:Brain Chemistry; D002417:Cattle; D005990:Glycerol / Q000737:chemistry; D007536:Isomerism; D010126:Ozone / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
D010713:Phosphatidylcholines; D010126:Ozone; D005990:Glycerol