Imaging mass spectrometry is a powerful technology that enables the visualization of biochemical processes directly in tissues by combining the molecular specificity of mass spectrometry with the spatial fidelity of microscopic imaging. Modern imaging mass spectrometry studies are already stressing the limits of current analytical technologies and improvements in molecular specificity and sensitivity are crucial in order to answer increasingly complicated biological and clinical questions. Especially when studying lipids and metabolites, there are many isobaric and isomeric ions that complicate spectral analysis, with each isoform having a potentially unique cellular function. While traditional tandem mass spectrometry (MS/MS) approaches can distinguish amongst these compounds in select instances, this is often not the case. Additionally, the ion type most readily generated from tissue is rarely the type that affords the most chemical structural information upon MS/MS. Our group is developing gas-phase reactions that afford the ability to transform the ion type without manipulating the sample. While traditional analytical analyses oftentimes simply use the mass spectrometer as a detector of molecular mass, we instead use the mass spectrometer as a reaction vessel to perform unique gas-phase transformations to provide unparalleled levels of chemical resolution. These gas-phase transformations are fast, efficient, and specific, making them ideally suited for implementation into imaging mass spectrometry workflows.<br/><br/>We have enabled gas-phase charge inversion ion/ion reactions on a hybrid QhFT-ICR mass spectrometer. Phosphatidylcholine cations generated from tissue using matrix-assisted laser desorption/ionization (MALDI) and doubly deprotonated 1,4-phenylenedipropionic acid reagent anions generated via electrospray ionization are sequentially injected into a hexapole reaction cell. Following a mutual storage reaction period (~750 ms), the product ions are are subjected to MS/MS and then mass analyzed. This technology has enabled the identification of multiple sn-positional isomers directly from mouse brain tissue, the relative contributions of which vary significantly between regions of the brain. This technology has also been used to separate isobaric PC lipids as well as concentrate ion signal from +H, +Na, and +K ion types. Finally, our group is exploring other gas-phase chemistries to enable lipid double bond localization and lipid class differentiation.

High chemical resolution imaging mass spectrometry using gas-phase ion/ion reactions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.