MATRIX-ASSISTED LASER-DESORPTION IONIZATION OF SMALL BIOMOLECULES IMPREGNATED IN SILICA PREPARED BY A SOL-GEL PROCESS

Sol-gel chemistry is emerging as an important tool for immobilizing en zymes and other biomolecules, Investigation of the reactions between e nzymes and substrates in the resulting porous solids has been limited primarily to molecular spectroscopy. Herein, we demonstrate the interr ogation of these solids by matrix-assisted laser desorption/ionization in conjunction with reflectron time-of-flight mass spectrometry. Smal l di-and tri-peptides such as phenylalanylmethionine (PheMet), dipheny lalanine (PhePhe), triphenylalanine (PhePhePhe), and glutathione (gamm a-GluGlyCys) were chosen as the target analytes, The matrix, alpha-cya no-4-hydroxycinnamic acid (CHCA), was incorporated into the sol-gel pr ocess to obtain isotopically resolved peaks in the mass spectra. With the matrix and target analyte 'doped' in the dried gel, a Nd:YAG laser was used to expel the biomolecule from the confines of the silica. Th e presence of the matrix CHCA greatly enhanced peptide ion intensity a nd also, by use of matrix ions as internal calibrants, led to increase d mass accuracy, Using internal calibration, the percent relative erro r for the monoisotopic peak of glutathione in a thin silica film (m/z of 308.04) was approximately 0.02%, while for triphenylalanine in a mo nolith (m/z of 460.22) the error was less than 0.01%. Variations in th e pore size of the silica gel did not affect signal intensity or mass accuracy. (C) 1997 by John Wiley & Sons, Ltd.