Imaging Mass Spectrometry of Sulfatide Isomers from Rat Brain Tissue Using Gas-Phase Charge Inversion Ion/Ion Reactions

Sulfatides are abundant components of the brain, and dysregulation of these molecules has been linked to several diseases. In sulfatide structures, a sugar is linked to a sphingoid backbone via an α-glycosidic or β-glycosidic linkage. While sulfatides are readily generated in negative ion mode imaging mass spectrometry experiments, resolving sulfatide diastereomers is challenging; therefore, identifications are usually reported as a single sulfatide. Herein, a gas-phase charge inversion ion/ion reaction between sulfatides and a strontium tris-phenanthroline [Sr(Phen)₃]²⁺ reagent is performed to separate the diastereomers, as they form complexes containing different numbers of phenanthroline ligands. The ability to separate these diastereomers using the reaction alone, without the need for any further dissociation, allows for the workflow to be readily implemented in an imaging mass spectrometry experiment. Imaging mass spectrometry was performed on sulfatides generated directly from rat brain tissue, and both the α- and β-linked sulfatide images were obtained.