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.