Preparation and retention mechanism of a mixed-mode reversedphase/strong-cationic-exchange chromatographic packing

Abstract

A simple and efficient method has been proposed for the preparation of octyl-sulfonic co-bonded silica (OSS) packing by the method of "mixed ligand". The resulting OSS packing was characterized by elemental analysis and ion-exchange capacity to prove the successful immobilization of octyl and sulfonic groups on the surface of silica gel. Then the retention mechanism of several basic analytes on the developed OSS phases was evaluated under the conditions of reversed-phase liquid chromatography (RPLC) mobile phase. The results indicated that the OSS stationary phases demonstrated a mixed-mode reversed-phase/strong-cationic-exchange (RP/SCX) retention mechanism and ion-exchange interaction maybe dominate the retention of the basic analytes. By changing the salt concentration of mobile phase, the one-site and two-site mixed-mode retention models of the several basic analytes on the OSS phases were obtained by investigating the logarithm and reciprocal relationships of retention factor and salt concentration. On the basis of the linear fitting of the two mathematical equations of the retention models, the experimental results demonstrated that the two-site model was more suitable for the description of the retention mechanism of the basic analytes on the OSS phases. Furthermore, the individual RP or SCX contribution to total retention was obtained according to the mathematical equations of the two-site retention mechanism, which can provide some valuable guidance for the separation of complex samples.