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Sol-gel chemistry is emerging as an important tool for immobilizing enzymes and other biomolecules. Investigation of the reactions between enzymes and substrates in the resulting porous solids has been limited primarily to molecular spectroscopy. Herein, we demonstrate the interrogation of these solids by matrix-assisted laser desorption/ionization in conjunction with reflectron time-of-flight mass spectrometry. Small di-and tri-peptides such as phenylalanylmethionine (PheMet), diphenylalanine (PhePhe), triphenylalanine (PhePhePhe), and glutathione (γ-GluGlyCys) were chosen as the target analytes. The matrix, α-cyano-4-hydroxycinnamic acid (CHCA), was incorporated into the sol-gel process 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. The presence of the matrix CHCA greatly enhanced peptide ion intensity and also, by use of matrix ions as internal calibrants, led to increased mass accuracy. Using internal calibration, the percent relative error 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 monolith (m/z of 460.22) the error was less than 0.01%. Variations in the pore size of the silica gel did not affect signal intensity or mass accuracy.

This study provides electrochemical and LCEC determination for three of the most abundant and most important isoflavones, Biochanin A, formononetin, and genistein. Cyclic voltammetry and pH-potential diagrams show that the isoflavones undergo pH-dependent irreversible oxidations. The LCEC determination of the isoflavones has been optimized for mobile phase composition and detection potential. Sub-nanogram detection limits have been achieved.

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