Resolving the Complexity of Spatial Lipidomics with MALDI Trapped Ion Mobility Spectrometry

Lipids are a structurally diverse class of molecules, with important biological functions including cellular signaling and energy storage. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) allows for visualization of molecules directly from tissue, but has difficulty addressing the structural diversity of the lipidome, owing to the presence of many isobaric and isomeric species that overlap in m/z space. Integrating ion mobility separations aids in mass spectral deconvolution and address lipid complexity. Here we demonstrate that a MALDI quadrupole time-of-flight (QTOF) mass spectrometer with trapped ion mobility spectrometry (TIMS) enables a significant increase in the peak capacity (~207%) during lipid IMS experiments. MALDI-TIMS was also used for separation of lipid isomer standards, including sn-backbone isomers, acyl chain isomers, as well as double bond positional and geometric isomers was also demonstrated. Proof of concept, in situ separation and imaging of lipid isomers with distinct spatial distributions was demonstrated using whole-body mouse pup tissue.