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Ozone induced dissociation (OzID) is a technique for determining double bond position(s) in lipid (fat) molecules using a mass spectrometer. It employs the ion-molecule reaction between ionised lipid molecules and ozone to determine positions of carbon-carbon double bonds (also called sites of unsaturation). It was first described for analytic purposes in 2008.

Mechanism
OzID is an ion activation technique that exploits the gas-phase oxidation reaction between ozone and ionised lipids to form product ions that are diagnostic of the site(s) of unsaturation. Each site of unsaturation produces two characteristic neutral loss ions, termed the “aldehyde” and “Criegee” ions. The neutral losses are indicative of the position of the site of unsaturation relative to the methyl end of the fatty acyl chain. Because these neutral losses are predictable, a lookup table can be created to determine double bond position. OzID works for any fatty acid or complex lipid containing a mono- or poly-unsaturated fatty acid chain such as triacylgylcerides, glycerophospholipids or fatty acid esters of hydroxy fatty acids.

An example OzID spectrum for the [M+Na]+ adduct of PC 18:1(n-9)/16:0 (i.e. a phosphatidylcholine lipid containing oleic acid (18:1(n-9)) esterified at the sn-1 position and palmitic acid (16:0) at the sn-2 position) is shown in Figure XX. The mass selected precursor ion, m/z 782, is isolated in the presence of ozone for 10 s. Because there is only one double bond present in this lipid standard, only one pair of OzID ions are observed, with neutral losses of 110.1 and 94.2 Da, respectively. These ions indicate that the double bond is at the n-9 position. The presence of ozone in the mass spectrometer has no impact in the quality of the mass spectrum; peak shape, mass accuracy and sensitivity are the same as factory configuration.

Implementations
Ion traps, triple quadrupole instruments , higher pressure regions in ion-mobility enabled quadrupole-time of flight instruments. Relative number densities, and resulting speed-ups. Spectra?