Integrating the potential of ion mobility spectrometry-mass spectrometry in the separation and structural characterisation of lipid isomers

Abstract

It is increasingly evident that a more detailed molecular structure analysis of isomeric lipids is critical to better understand their roles in biological processes. The occurrence of isomeric interference complicates conventional tandem mass spectrometry (MS/MS)-based determination, necessitating the development of more specialised methodologies to separate lipid isomers. The present review examines and discusses recent lipidomic studies based on ion mobility spectrometry combined with mass spectrometry (IMS-MS). Selected examples of the separation and elucidation of structural and stereoisomers of lipids are described based on their ion mobility behaviour. These include fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, and sterol lipids. Recent approaches for specific applications to improve isomeric lipid structural information using direct infusion, coupling imaging, or liquid chromatographic separation workflows prior to IMS-MS are also discussed, including: 1) strategies to improve ion mobility shifts; 2) advanced tandem MS methods based on activation of lipid ions with electrons or photons, or gas-phase ion-molecule reactions; and 3) the use of chemical derivatisation techniques for lipid characterisation.

ReTimeML: A retention time predictor that supports the LC-MS/MS analysis of sphingolipids.

“…Although a significant improvement in the resolution of SL variants, it is important to discuss that ReTimeML will not address isomers of SLs (e.g., galactosyl vs glucosylceramide having been referred to as HexCer), given the chromatography conditions ReTimeML was trained on were incapable of their separation. Updated versions of ReTimeML would require training on additional setups, including normal-phase LC-MS/MS [25] and next-generation ion mobility MS employing RT with collision cross-section [55], capable of achieving this level of structure interpretation.…”

Aza-Prilezhaev Aziridination-Enabled Multidimensional Analysis of Isomeric Lipids via High-Resolution U-Shaped Mobility Analyzer–Mass Spectrometry

“…Ion mobility–mass spectrometry (IM-MS) can provide an additional dimension of information that supplements the LC-MS/MS workflow. It has shown promising results in the separation of lipid isomers and improvement on type II chemical interference. − In 2019, Fernandez-Lima and co-workers realized the separation of CC positional, geometric, and sn -positional isomers of glycerophosphocholine (PC) and diacylglycerol at the IM dimension with specified IM parameters . In 2023, Xia and co-worker integrated PB reaction and IM-MS for deep structural annotation of phospholipidome.…”

Development of a Rapid, Targeted LC-IM-MS Method for Anabolic Steroids

“…Ion mobility-mass spectrometry (IM-MS) has emerged over the past decade as a promising technique for the analysis of steroidal compounds in a variety of applications . Early examples included primarily targeted analysis focused on one or a few compounds, including work involving testosterone and epitestosterone glucuronides, separation of derivatized endogenous isomer pairs, development of a targeted clinical assay for five endogenous compounds with differential mobility (DMS), and differentiation of anabolic steroid isomers via dimerization. , As technology has improved, the ability to simultaneously monitor dozens of compounds has enabled more significant biomedical research. , The basis for these measurements is the rotationally averaged ion-neutral collision cross section (CCS), a characteristic property of an ion measured under given experimental parameters. Several groups have endeavored to create broad CCS libraries, , and even some more focused databases focused on steroid compounds. ,− These values can provide tremendous value in identification and structural characterization.…”