Elution, Partial Separation, and Identification of Lipids Directly from Tissue Slices on Planar Chromatography Media by Desorption Electrospray Ionization Mass Spectrometry

A method for the examination of intact tissue sections for gangliosides and other lipids using desorption electrospray ionization (DESI) mass spectrometry (MS) is presented. In the present work, thin tissue slices (16 mu m) taken from the rat brain are thaw mounted onto planar chromatographic media and the lipids are eluted, partially separated, and analyzed directly from the plate by DESI-MS in the negative ion mode. With the lanes scanned parallel to the direction of the chromatographic separation in the full scan mode, the selected ion current associated with ions of separated lipid molecules is plotted in order of increasing Rf values. Distinctly different classes of lipids are detected using this method, including several ganglioside species (i.e., GQ1, GT1, GD1, and GM1) and sulfoglycosphingolipids. For the examination of gangliosides in the full scan negative ion mode from high-performance thin-layer chromatography (HPTLC) plates, the limit of detection (LOD) was determined to be approximately 3 pmol. Tandem mass spectrometry (MS/MS) using the linear ion trap was used to confirm the presence of selected gangliosides and other lipids directly from the HPTLC plate. DESI-MS/MS revealed the presence of both the GD1a and GD1b isomers. The simplicity of this approach where planar separations are relied upon for sample preparation and presentation to the MS should allow for the examination of a variety of complex samples including the rapid examination of foodstuffs, bacteria, whole blood, and needle biopsies for cancer diagnostics.