Using ambient ozone for assignment of double bond position in unsaturated lipids

Abstract

Unsaturated lipids deposited onto a range of materials are observed to react with the low concentrations of ozone present in normal laboratory air. Parent lipids and ozonolysis cleavage products are both detected directly from surfaces by desorption electrospray ionisation mass spectrometry (DESI-MS) with the resulting mass spectra providing clear evidence of the double bond position within these molecules. This serendipitous process has been coupled with thin-layer chromatography (TLC) to provide a simple but powerful approach for the detailed structural elucidation of lipids present in complex biological extracts. Lipid extracts from human lens were deposited onto normal phase TLC plates and then developed to separate components according to lipid class. Exposure of the developed plates to laboratory air for ca. 1 h prior to DESI-MS analysis gave rise to ozonolysis products allowing for the unambiguous identification of double bond positions in even low abundant, unsaturated lipids. In particular, the co-localization of intact unsaturated lactosylceramides (LacCer) with products from their oxidative cleavage provide the first evidence for the presence of three isomeric LacCer (d18:0/24:1) species in the ocular lens lipidome, i.e., variants with double bonds at the n-9, n-7 and n-5 positions.

Surface analysis of lipids by mass spectrometry: More than just imaging

“…This is likely due to the low volatility of such species making desorption difficult. Furthermore, while using discharge generated ozone is a simple approach for assigning double bond position in fatty acids, it is not as effective for analysis of complex mixtures as the TLC/DESI approach described above, which allows spatially-resolved detection of more complex lipids [184].…”

“…Owing to its ability to readily desorb and ionize lipids from a variety of surfaces including glass, poly(methyl methacrylate) and polytetrafluoroethylene (PTFE) [182], tissue sections [20] and silica TLC plates [183,184], lipid analysis has become one of the most popular applications of DESI. Early studies focused on optimization of solvent composition and surface structure to enhance the sensitivity of lipid detection from standards and extracts [182].…”

“…DESI too has been coupled with TLC analysis for the analysis of porcine brain [183] and human lens lipids extracts [184]. In the latter study, TLC/DESI was performed following separation and oxidation of surface exposed unsaturated lipids by ambient ozone (~20 ppb).…”

Dissociation of proton-bound complexes reveals geometry and arrangement of double bonds in unsaturated lipids

“…Subsequent CID yields diagnostic products that allow the determination of double bond position(s). 5,6 In the same manner, Moe et al…”

Rapid Identification and Quantification of Linear Olefin Isomers by Online Ozonolysis-Single Photon Ionization Time-of-Flight Mass Spectrometry

“…Target ion CH 2 [20][21][22][23][24][25]. Structurally characteristic fragments, including aldehydes and Criegee ions, occurred in the mass spectra recorded in the course of ozone electrospray ionization (OzESI) [21,24] and in ozone-induced dissociation (OzID) [23,25], which allowed assignment of double bond positions._ENREF_27 Both of OzESI and OzID simplified the complicated sample manipulation process needed prior to MS analysis so that the online location of double bond positions could be done more efficiently. Besides, OzID can be applied to the analysis of complex mixtures compared with OzESI, but it requires specialized equipment and instrumental modification.…”