MALDI imaging and structural analysis of rat brain lipid negative ions with 9-aminoacridine matrix

Mass spectrometry imaging is of growing interest for chemical mapping of lipids at the surface of tissue sections. Many efforts have been devoted to optimize matrix choice and deposition technique for positive ion mode analyses. The identification of lipid species desorbed from tissue sections in the negative mode can be significantly improved by using 9-aminoacridine together with a robust deposition method, yielding a superior signal-to-noise ratio and thus a better contrast for the ion images in comparison to classical matrices such as α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxybenzoic acid, or 2,4,6-trihydroxyacetophenone. Twenty-eight different lipid species (phosphatidic acids, phosphatidylethanolamines, phosphatidylserines, phosphatidylglycerols, phosphatidylinositols, phosphatidylinositol-phosphates, and sulfatides) were scrutinized on rat brain tissue sections, and systematic MS/MS studies were conducted. It was possible to identify isobaric species differing by their fatty acid chains thanks to the improved sensitivity.