Drift tube ion mobility spectrometry (DT-IMS) is a gas-phase technique that separates ions on the basis of their size, shape, and charge. Under the influence of an electric field, these ions undergo collisions with buffer gas molecules such that smaller, more compact ions travel more quickly than larger or more elongated ions. When coupled with mass spectrometry (IM-MS), we are able to rapidly and simultaneously acquire an ion’s collision cross section (CCS) and mass-to-charge (m/z). The added dimension of separation produces more comprehensive analyses, even for complex biological samples.
The structure-based separation mechanism of IMS allows for differentiation of isomers that are otherwise difficult to resolve with conventional liquid chromatography-mass spectrometry (LC-MS) methods. Furthermore, structural differences that dictate biomolecular function (i.e., protein folding) can be studied.
Mass spectrometry (MS)-based analysis in the –omics (lipidomics, metabolomics, proteomics, etc.) is critical for the study of various diseases, their progression, and the identification and quantification of biomarkers. The gold standard methods involve UHPLC-HRMS/MS, however ion mobility (IM) has seen increased use due to improvements in resolution and signal:noise ratio.
Our group is coupling IM-MS with ozone-based methods, ozone-induced dissociation (OzID) and ozone-induced rearrangement (OzIR), for identification of lipids in complex samples and differentiation of structurally similar biomolecules such as steroids and other metabolites. OzIR is a demonstrated method for C=C double bond fragmentation, which allows for precise determination of double bond position within lipid fatty acyl tails. IMS further provides information on structural arrangement in lipids (cis/trans double bonds, sn1 vs. sn2 connectivity, etc.) and so this combination provides unambiguous lipid identification. Our group has also recently introduced OzIR, a novel approach that involves fragmentation of C=C double bonds contained in ring structures. This rearrangement has been shown to improve IM resolution and results in differing MS/MS fragmentation patterns. These reactions can be performed in either the solution- or gas-phase to maximize efficiency, throughput, cost, and simplicity.
Mass spectrometry (MS)-based methods have become a cornerstone of biomolecule structural analysis, with examples ranging from small molecule elucidation to determination of protein complexes. However, the information acquired for isobaric and isomeric species can result in convoluted spectra even when using high resolution (HR) and/or tandem (MS/MS) instruments. IMS provides an additional dimension of separation based on structure that can be used to differentiate structural and conformational differences (such as the Vitamin D metabolites and steroid epimers illustrated below). IM-MS is often paired with computational modeling to produce putative structures and theoretical collision cross section (CCS) values that can be compared with experimentally-derived values. This powerful combination brings together analytical and physical chemists to help solve biological problems such as pharmaceutical drug binding, host-substrate relationships, and protein folding/misfolding.
Check back soon for new info on the instrument development projects in the group!