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

Abstract

We present a novel approach for the increasing reliability of 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 that can be measured using the hydrogen/deuterium (H/D) exchange approach. The number of labile hydrogens (those from −OH and −NH groups) serves as an additional structural descriptor used when performing a database search. For LC-MS experiment, the H/D exchange was performed in the heating capillary of the modified electrospray ionization (ESI) source, while for MALDI imaging, the exchange was performed in the ion funnel at 10 Torr pressure. It was observed that such an approach allowed one to achieve a considerable degree of deuteration, enough to unambiguously distinguish between different classes of lipids. The proposed analytical approach may be successfully used for the identification not only of lipids but also of peptides and metabolites. A special software for the automatic filtration of molecules based on the number of functional groups was also developed.

Analysis of 16O/18O and H/D Exchange Reactions between Carbohydrates and Heavy Water Using High-Resolution Mass Spectrometry

“…The H/D exchange occurredin both the gas phase and—due to the penetration of moisture into the droplets [ 30 ]—in the liquid phase. The details of the ion source design, as well as its applicationsfor investigating various compounds, can be found in our previous publications [ 6 ].…”

“…The primary exchangeable groups are −OH, −COOH, −NH, and −SH. However, it is possible to achieve the exchange in electron-enriched sections of the aromatic ring by using high temperature or acid/base catalysis [ 6 ].…”

“…The stable oxygen isotope 18 O is used to increase the reliability [ 9 , 10 , 11 ] of compound identification and to track some metabolic pathways [ 9 ]. The stable hydrogen isotope D is also used toincreasethe reliability [ 6 ] of compoundidentification, as well as investigate protein structure [ 10 ]. Since heavy water (containing 18 O or D instead of 16 O or H) became generally available, much research has beenconducted in the field of exchange reactions between heavy water and organic compounds [ 11 ].…”

A large-scale genome–lipid association map guides lipid identification

“… 16 , 17 Others have sought to build on this information by adding external complementary data, such as measurement of collisional cross section, 10 or labile hydrogen counting, among others. 18 All of these methods show great promise but share in the common theme that they incorporate lipid chemical properties into their identification inference.…”

Interactive Estimation of Heterogeneity from Mass Spectrometry Imaging

“…Two basic approaches are used for these purposes: (1) the creation of predefined MSI maps − and (2) complex analysis , of MS map data, including, but not limited to, machine learning (ML), clustering, and classification. The results of such analyses are usually compared with histological data for validation and biological interpretation.…”