The effect of solvation processes on amino acid- and peptide-silica stationary phases

The surface excess adsorption isotherms of water, acetonitrile, and methanol from binary hydro-organic mobile phases were investigated on nine home-made stationary phases with chemically bonded amino acids, dipeptides, and tripeptides using the dynamic minor disturbance method. The stationary phases were modified by the following amino acids: glycine, alanine, phenylalanine, leucine, and aspartic acid. We investigated the influence of the type of immobilized amino acids, in particular their different side chains, on the solvent adsorption. The interpretation of solvation phenomena shows significant accumulation of investigated solvents on the adsorbent surface according to their hydrophilic or hydrophobic properties. Moreover, the accumulated amount was dependent on the length and type of amino acid sequences bonded to the silica surface. Stationary phases with bonded amino acids and peptides show stronger water and acetonitrile adsorption in contrast to the stationary phase modified with aminopropyl groups-a support for the synthesis. The comparison of water and acetonitrile adsorption as well as a data obtained with the two-site adsorption model reveal and confirm the heterogeneity of chemically bonded phases. As a consequence of performed investigations, the classification of tested stationary phases for the potential usage in particular high-performance liquid chromatography mode was also accomplished.