Effect of stationary phase structure on retention and selectivity in reversed-phase liquid chromatography

Abstract

The effect of the structure of the stationary phase on retention and selectivity in reversed-phase liquid chromatography was studied, using chemically bonded stationary phases on silica gel. Nine stationary phases with various size, rigidity and degree of unsaturation were prepared, including alkyl, aryl, aralkyl and alicyclic structures. In addition to the solvophobic interaction and the solvation of the solutes in the mobile phase, stationary phase effects such as steric recognition and π-π interaction between solutes and the stationary phase, and the effect of solvent molecules bound to the stationary phase, were found to be important in determining retention in reversed-phase liquid chromatography. Planar solutes were preferentially retained by the stationary phases of planar structure and rejected by the non-planar stationary phases. Extended octadecyl groups and large aromatic rings in the stationary phase contributed to the preferential retention of planar solutes. The aromatic stationary phases showed greater retention for aromatic and polar solutes and lesser retention for saturated hydrocarbons than the saturated stationary phases. Retention and selectivity on stationary phases with aryl or aralkyl functionality were found to be more sensitive to solvent changes than on saturated stationary phases. The results suggest the possibility of controlling the magnitude of the stationary phase effects by selecting a stationary phase structure that can enhance the separation capability of reversed-phase liquid chromatography. The versatility of stationary phases with large aromatic groups was shown, and the complementary use of stationary phases of widely different nature was suggested to provide maximum selectivity.