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

A study on surface modification of an octadecylsilica (ODS) column with amphoteric surfactants has been carried out for efficient reversed-phase liquid chromatographic separations of hydrophobic analytes only with water eluent. Two amphoteric surfactants each with different terminal groups (betaine-type and sulfobetaine-type surfactants) were employed as the stationary phase 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 adsorption of amphoteric surfactant led to a decrease in the retention of nucleosides and their bases, while an increase in the retention of inorganic anions. These results indicate that the amphoteric surfactant adsorbed on the ODS surface suppresses the hydrophobicity of the reversed-phase surface, but it also generates a specific electrostatic field. In other words, the modified ODS columns exhibit hydrophobic/electrostatic mixed-mode separation properties. The degree of the contribution of each property to the separation of analytes can be varied with the amount of the adsorbed surfactant. Consequently, nucleosides and their bases were effectively separated on the ODS column coated with 0.55 mmol of betaine-type surfactant in water elution.