Structure Elucidation for MALDI Mass Spectrometry Imaging Using Infrared Ion Spectroscopy

Infrared ion spectroscopy (IRIS) is a tandem mass spectrometry (MS) technique that generates structurally diagnostic vibrational spectra for mass-selected ions trapped in a mass spectrometer. Until now, IRIS applications for biological samples have primarily focused on solution-based analyses, such as body fluids (e.g., plasma and urine) and tissue homogenates, using electrospray ionization (ESI) coupled with liquid chromatography-mass spectrometry (LC-MS). In this study, we have combined matrix-assisted laser desorption/ionization (MALDI) with IRIS for the direct analysis of small molecules from biological tissues on a Fourier-transform ion cyclotron resonance mass spectrometer. We applied this technique alongside MALDI mass spectrometry imaging to analyse brain tissue from two knockout mouse models of l-lysine catabolism disorders: pyridoxine-dependent epilepsy (ALDH7A1) and glutaric aciduria type 1 (GCDH). The MALDI-IRIS platform, now available for users at HFML-FELIX, represents a significant advance in the direct structural characterization of metabolites in complex biological tissues and opens new possibilities for structure elucidation in the field of MALDI mass spectrometry imaging.