Pronounced Selectivity in Matrix-Assisted Laser Desorption−Ionization Mass Spectrometry with 2,4,6-Trihydroxyacetophenone on a Zeolite Surface: Intensity Enhancement of Protonated Peptides and Suppression of Matrix-Related Ions

A useful technique for matrix-assisted laser desorption−ionization (MALDI) mass spectrometry has been developed, and the mechanism of the proton transfer during desorption/ionization is discussed. By using the zeolite-2,4,6-trihydroxyacetophenone (THAP) complex as a new matrix (zeolite matrix), MALDI mass spectrometric measurements were carried out for model peptides (substance P and neurotensin). The peaks of protonated THAP and peptides were observed almost free from interference by fragments and alkali metal ion adducts. In addition, the peak intensities of protonated peptides were markedly increased compared with conventional MALDI. These advantages of the zeolite matrix were understood based on stable cage structure of zeolite and its strong Bronsted acidity. The adsorption structure of THAP on zeolite surface and the possible mechanism of protonation of THAP are discussed based on the Fourier transform infrared spectra and quantum chemical calculations. The solvent-assisted mechanism has been propos...