Amphoteric surfactant-modified stationary phase for the reversed-phase high-performance liquid chromatographic separation of nucleosides and their bases by elution with water

A study on surface modification of an octadecylsilica (ODS) column with amp hoteric surfactants has been carried out for efficient reversed-phase liqui d chromatographic separations of hydrophobic analytes only with water eluen t. Two amphoteric surfactants each with different terminal groups (betaine- type and sulfobetaine-type surfactants) were employed as the stationary pha se modifier, and the separation characteristics of the modified ODS columns were evaluated by comparing the elution times of nucleosides, their bases, and inorganic ions. In both surfactant-modified ODS column systems, the ad sorption of amphoteric surfactant led to a decrease in the retention of nuc leosides and their bases, while an increase in the retention of inorganic a nions. These results indicate that the amphoteric surfactant adsorbed on th e ODS surface suppresses the hydrophobicity of the reversed-phase surface, but it also generates a specific electrostatic field. In other words, the m odified ODS columns exhibit hydrophobic/electrostatic mixed-mode separation properties. The degree of the contribution of each property to the separat ion of analytes can be varied with the amount of the adsorbed surfactant. C onsequently, nucleosides and their bases were effectively separated on the ODS column coated with 0.55 mmol of betaine-type surfactant in water elutio n. (C) 2000 Elsevier Science B.V. All rights reserved.