Investigation of a novel mixed-mode stationary phase for capillary electrochromatography. Part III: Separation of nucleosides and nucleic acid bases on sulfonated naphthalimido-modified silyl silica gel.

Capillary electrochromatography (CEC) with a novel stationary phase, 3-(4-sulfo-1,8-naphthalimido)propyl-modified silyl silica gel (SNAIP), proved useful for the separation of nucleosides and nucleic acid bases. The application scope of SNAIP, which is a relatively polar reversed-phase (RP)-type stationary phase, was successfully expanded to include the CEC separation of polar compounds although the combination of non-polar RP phase with highly aqueous mobile phase is often inadequate. Due to the permanently charged sulfonic acid groups and the naphthalimidopropyl moiety, the retention of charged and relatively polar nucleosides as well as bases on the SNAIP stationary phase was effected by electrostatic and hydrophobic interactions. This yielded a unique selectivity on SNAIP toward nucleosides and bases. The characteristic EOF on SNAIP, which was stronger at higher aqueous content in the mobile phase, proved suitable for the separation of polar compounds in reversed-phase mode with highly aqueous mobile phase. In addition, when a double stepwise gradient was employed to accelerate the latest peak (adenine), the elution time was shortened to less than half its original duration.