Stationary phase structures enhancing electroosmotic flow in capillary electrochromatography

Several chemically bonded silicas with C18 groups were examined with respect to electroosmotic flow (EOF) velocities under CEC conditions. Stationary phases with low hydrophobic selectivity generally provided high EOFs. The stationary phases prepared by using octadecyltrichlorosilane showed greater EOF than those from octadecyldimethylchlorosilane. Restricted-access reversed-phase (RARP) packing materials having C18 groups inside the pores and silanols on the external surfaces showed higher EOF than monomeric C18 phases with similarly high hydrophobic selectivity. The RARP-type structure having silanols at the external surface seems to be effective for increasing EOF while maintaining the hydrophobic character of the solute binding sites.