Sol-gel open tubular ODS columns with reversed eleotroosmotic flow for capillary electrochromatography

Sol-gel chemistry was successfully used for the fabrication of open tubular columns with surface-bonded octadecylsilane (ODS) stationary-phase coating for capillary electrochromatography (OT-CEC). Following column preparation s, a series of experiments were performed to investigate the performance of the sol-gel coated ODS columns in OT-CEC. The incorporation of N-octadecyl dimethyl[3-(trimethoxysilyl)propyl]ammonium chloride as one of the sol-gel precursors played an important role in the electrochromatographic performan ce of the prepared columns. This chemical reagent possesses a chromatograph ically favorable, bonded ODS moiety, in conjunction with three methoxy grou ps allowing for sol-gel reactivity. In addition, a positively charged nitro gen atom is present in the molecular structure of this reagent and provides a positively charged capillary surface responsible for the reversed electr oosmotic now (EOF) in the columns during CEC operation. Comparative studies involving the EOF within such sol-gel ODS coated and uncoated capillaries were performed using acetonitrile and methanol as the organic modifiers hi the mobile phase. The use of a deactivating reagent, phenyldimethylsilane, in the sol-gel solution was evaluated. Efficiency values of over 400 000 th eoretical plates per meter were achieved in CEC on a 63 cm x 25 mum i.d, so l-gel ODS open tubular column. Test mixtures of polycyclic aromatic hydroca rbons, benzene derivatives, and aromatic aldehydes and ketones were used to evaluate the CEC performances of both nondeactivated and deactivated open tubular sol-gel columns. The effects of mobile-phase organic modifier conte nts and pH on EOF in such columns were evaluated. The prepared sol-gel ODS columns are characterized by switchable electroosmotic now. A pH value of s imilar to8.5 was found correspond to the isoelectric point for the prepared sol-gel ODS coatings.