A comparative study of in- and post-source decays of peptide and preformed ions in matrix-assisted laser desorption ionization time-of-flight mass spectrometry: Effective temperature and matrix effect

In-source decay (ISD) and post-source decay (PSD) of a peptide ion (Y₆ + H]⁺) and a preformed ion (benzyltriphenylphosphonium, BTPP) generated by matrix-assisted laser desorption ionization (MALDI) were investigated with time-of-flight mass spectrometry. α-Cyano-4-hydroxycinammic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) were used as matrices. For both ions, ISD yield was unaffected by delay time, indicating rapid termination of ISD. This was taken as evidence for rapid expansion cooling of hot “early” plume formed in MALDI. CHCA was hotter than DHB for Y₆ + H]⁺ while the matrix effect was insignificant for BTPP. The “early” plume temperature estimated utilizing previous kinetic results was 800–900 K, versus 400–500 K for “late” plume. The results support our previous finding that the temperature of peptide ions interrogated by tandem mass spectrometry was lower than most rough estimates of MALDI temperature.