Capillary electrochromatography with novel stationary phases: II. Studies of the retention behavior of nucleosides and bases on capillaries packed with octadecyl-sulfonated-silica microparticles

An octadecyl-sulfonated silica (ODSS) stationary phase specially designed f or performing capillary electrochromatography (CEC) at relatively strong el ectroosmotic flow (EOF) proved useful for the separations of some nucleosid es and bases. The ODSS stationary phase is composed of a hydrophilic, negat ively charged sublayer to which a nonpolar top layer containing octadecyl l igands is covalently attached. The charged sublayer contains sulfonic acid groups which ensure a relatively strong EOF. Due to the presence of permane ntly charged sulfonic acid groups in the sublayer, the hydrophilic nature o f the sublayer and the hydrophobic character of the top octadecyl layer, re tention and selectivity of charged and relatively polar nucleosides and bas es on the ODSS stationary phase are based on electrostatic interaction, hyd rophilic interaction, and reversed-phase mechanisms. This yielded for the O DSS stationary phase a unique selectivity towards the nucleosides and bases , thus allowing their rapid separation. To gain insight into the chromatogr aphic behavior of nucleosides and bases on the ODSS stationary phase, the r esults were compared to those obtained on an octadecyl-silica (ODS) capilla ry under otherwise the same elution conditions. Due to the difference in th e nature of the organic layers on the surface of the ODSS and ODS stationar y phases, the elution order on both stationary phases differed significantl y, and the ODSS capillary proved more suitable for the separation of the nu cleosides and bases than the ODS capillary.