Hydrogen/Deuterium Exchange Aiding Compound Identification for LC-MS and MALDI Imaging Lipidomics

We present the novel approach for the increasing reliability of the compound identification for LC-MS and MALDI imaging lipidomics. Our approach is based on the characterization of compounds not only by the elution time, accurate mass and fragmentation spectra, but also by the number of labile hydrogens which can be measured using Hydrogen/Deuterium exchange approach. Number of labile hydrogens (those from -OH, -NH groups) serves as an additional structural descriptor used when performing database search. For LC-MS experiment the H/D exchange was performed in the heating capillary of the modified ESI source, while for MALDI- imaging the exchange was performed in the ion funnel at the 10 torr pressure. It was observed that such approach allowed achieving a considerable degree of deuteration enough to unambiguously distinguish between different classes of lipids. The proposed analytical approach may be successfully used not only for identification of lipids but also for peptides and metabolites. A special software for automatic filtration of molecules based on the number of functional groups was also developed.