MALDI mass spectrometry imaging of lipids and primary metabolites on rat brain sections

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) enables the localization and the structural identification of a large set of molecules on a surface with 10-20 μm resolution. MALDI is often coupled to time-of-flight (TOF) tandem analyzers which remain a versatile instrument for the detection and the structural analysis of molecular ions. This technique can be used to locate either large biomolecules, such as peptides/proteins, or small endogenous or exogenous ones. Among them, lipids and primary metabolites are of high interest because they can reflect the cell state. This chapter is thus dedicated to the analysis, on rat brain tissue sections, of lipids in positive and negative ion modes, and primary metabolites in the negative ion mode. A particular attention is paid to the structural characterization of lipids using lithium cationization in the positive ion mode.