Analytical separations for lipids in complex, non-polar lipidomes using differential mobility spectrometry

Secretions from meibomian glands located within the eyelid (commonly known as meibum) are rich in non-polar lipid classes incorporating very-long (22-30 carbons) and ultra-long (>30 carbon) acyl chains. The complex nature of the meibum lipidome and its preponderance of neutral, non-polar lipid classes presents an analytical challenge; with typically poor chromatographic resolution, even between different lipid classes. To address this challenge, we have deployed differential ion mobility-mass spectrometry (DMS-MS) to interrogate the human meibum lipidome and demonstrate near-baseline resolution of the two major non-polar classes contained therein; namely wax esters and cholesteryl esters. Within these two lipid classes, we describe ion-mobility behaviour that is associated with the length of their acyl chains and location of unsaturation. This mobility behaviour was exploited to profile the molecular speciation within each class and thus extend the meibum lipidome coverage. Intriguingly, structure-mobility trends in unsaturated lipids show similar inflections to those previously reported for lipid phase-transition temperatures. Taken together, these data demonstrate that differential ion mobility provides a powerful orthoganol separation technology for the analysis of neutral lipids in complex matrices such as meibum, and may further provide a means to predict physicochemical properties of lipids that could assist in infering their biological function(s).