Thermal stability of ionic matrices for MALDI-MS. A comparative study in solid state with classical matrices

Matrix-Assisted Laser Desorption/Ionization (MALDI) relies on the rapid absorption of laser energy by the matrix initiating a succession of events occurring in a high-vacuum chamber, including energy redistribution, temperature increase, analyte and matrix desorption, and their ionization. This study investigates the thermal behavior of classical acidic MALDI matrices (E-sinapinic acid (ESA), E-ferulic acid (EFE), E-p-coumaric acid (ECUM), and E-α-cyano-4-hydroxycinnamic acid (ECHCA)), their Z-isomers (ZSA, ZFE, ZCUM), and their salts formed with organic amines called ionic matrices (IMs). Using TGA, DSC, and ¹H NMR spectroscopy, we observed that ortho/para-substituted E-cinnamic acids with electron-donating groups thermally decompose via decarboxylation to produce styrene derivatives. IMs exhibited lower melting and decomposition temperatures compared to the crystalline matrix, improving the desorption/ionization process. However, IMs demonstrated lower analyte signal stability under successive laser shots, likely due to increased thermal decomposition.