MALDI imaging mass spectrometry of lipids by adding lithium salts to the matrix solution

• Published in: Analytical and bioanalytical chemistry Vol. 401; no. 1; pp. 75 - 87
• Main Authors: Cerruti, Christopher D., Touboul, David, Guérineau, Vincent, Petit, Vanessa W., Laprévote, Olivier, Brunelle, Alain
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.07.2011; Springer; Springer Verlag
• Subjects: Analytical Chemistry; Animals; Biochemistry; Brain; Brain - ultrastructure; Brain Chemistry; Cerebellum - chemistry; Cerebellum - ultrastructure; Characterization and Evaluation of Materials; Chemical Sciences; Chemistry; Chemistry and Materials Science; Diagnostic Imaging - methods; Food Science; Fragments; Galactosylceramides - analysis; Image contrast; Imaging; Laboratory Medicine; Lipids; Lipids - analysis; Lithium; Lithium compounds; Lithium Compounds - chemistry; Mass spectrometry; Monitoring/Environmental Analysis; Organic chemistry; Original Paper; Phosphatidylcholines - analysis; Rats; Salts - chemistry; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Spectrum analysis; Trifluoroacetates; Lithium salt; MALDI; Lipid; Rat brain; Mass spectrometry imaging
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-011-4814-9

Mass spectrometry imaging of lipids using MALDI–TOF/TOF mass spectrometers is of growing interest for chemical mapping of organic compounds at the surface of tissue sections. Many efforts have been devoted to the best matrix choice and deposition technique. Nevertheless, the identification of lipid species desorbed from tissue sections remains problematic. It is now well-known that protonated, sodium- and potassium-cationized lipids are detected from biological samples, thus complicating the data analysis. A new sample preparation method is proposed, involving the use of lithium salts in the matrix solution in order to simplify the mass spectra with only lithium-cationized molecules instead of a mixture of various cationized species. Five different lithium salts were tested. Among them, lithium trifluoroacetate and lithium iodide merged the different lipid adducts into one single lithium-cationized species. An optimized sample preparation protocol demonstrated that the lithium trifluoroacetate salt slightly increased desorption of phosphatidylcholines. Mass spectrometry images acquired on rat brain tissue sections by adding lithium trifluoroacetate showed the best results in terms of image contrast. Moreover, more structurally relevant fragments were generated by tandem mass spectrometry when analyzing lithium-cationized species.