Capillary electrochromatography with monolithic-silica columns.II.preparation of amphiphilic silica monoliths having surface-bound cationic octadecyl moieties and their chromatographic characterization and application to the chromatographic charactei

摘要

Three different synthetic routes have been introduced and evaluated for the preparation of amphiphilic silica-based monoliths possessing surface-bound octadecyl ligands and positively charged groups.The amphiphilic silica monoliths (designated as cationic C_18-monliths) have been designed for use in reversed-phase capillary electrochromatography(RP-CEC) withhydro-organic mobie phases.These amphiphilic stationary phases yielded anodic electroosmotic flow(EOF)over a wide range of mobile phases.These amphiphilic statioanry phases yielded anodic electroosmotic flow (EOF) over a wide range of mobile phase pH.The magnitude of EOF remained constnat up to pH 4.0 and then decreased at pH>4.0 due to the ionizationof silanol groups and the subsequent decrease in the net positive surface charge density of the amphiphilic monliths.The cationic C_18-monoliths exhibited reversed-phase chromatography(RPC) behaviro toward non-polar solutes (e.g.,alkyl benzenes),which parallels that observed with octadecyl-silica (ODS) monoliths.On the other hand,the amphiphilic stationary phases exhibited both non-polar and polar interactions toward slightly polar solutes such as anilines and PTH-amino acids.CEC retention factor K~*_e,whichreflects the contribution of the electrophoretic mobility,wer evaluated for charged solutes such as anilines and proteins.