| Scope and method of study. The purpose of this study was to examine the use of sol-gel silica monoliths as supports for the separation of various biological species in capillary electrochromatography. A detailed investigation of the various parameters that influence the development of the sol-gel derived monoliths was performed including the effects of pore tailoring and bonded phase reaction time on retention and separation efficiency. Hydrophobic octadecyl ligands, amphiphilic phases possessing cationic octadecyl moieties, and hydrophilic cyano-bonded phases were prepared to impart differing selectivity on the separations. Several different reaction pathways for each bonded phase were thoroughly evaluated using model compounds, and subsequently applied to the separation of both neutral and charged species.; Findings and conclusions. In optimizing the sol-gel backbone, pore tailoring performed with 0.01 M NH4OH for 270 min at 120°C while gels were in the "wet state" provided the best results in terms of both retention and separation efficiency. The presence of 2,6-lutidine in the silanization reaction between the silica monolith and dimethyloctadecylchlorosilane enhanced surface coverage of the octadecyl phase. A mobility moduli expression was introduced to describe chromatographic retention of charged species in situations where the magnitude of electrophoretic mobility exceeded that of electroosmosis. Stationary phases bearing octadecylated quaternary and secondary amine functions yielded a strong anodal flow over a wide range of mobile phase pH using a negative applied potential. The hydrophobic and amphiphilic bonded phases proved to be useful in the separation of anilines, phenylthiohydantoin amino acids, 2,4-dinitrophenyl amino acids and proteins, with each exhibiting different selectivity. The cyano-phases generated allowed successful separations of phenols, nucleic acid bases, nucleosides, mono- and oligosaccharides. Cyano-phases derived from the reaction of an epoxide moiety with 3-hydroxypropionitrile provided enhanced retention resulting from interactions with the polar, hydroxy sublayer in addition to the hydrophobic, cyano top layer. |
