Characterization of a mixed-mode reversed-phase/cation-exchange stationary phase prepared by thermal immobilization of poly(dimethylsiloxane) onto the surface of silica

Abstract

A novel stationary phase prepared by the thermal immobilization of poly(dimethylsiloxane) onto the surface of silica (PDMS-SiO(2)) has been described, evaluated and compared with 229 commercially available RP-LC stationary phases using the Tanaka column classification protocol. The phase exhibited many unique chromatographic properties and, based on the phases in the database, was most similar to the fluoroalkylated phases (aside from the obvious lack of fluoro selectivity imposed by the C-F dipole). The phase exhibited classic reversed-phase behaviour in acid mobile phase conditions and mixed-mode reversed-phase/cation-exchange retention behaviour in neutral mobile phase conditions. The phase exhibited acceptable stability at both low and intermediate pH, conditions which should impart optimum chromatographic selectivity to the phase. Retention of basic analytes was shown to occur by a "three site model" as proposed by Neue. This new PDMS-SiO(2) stationary phase is extremely interesting in that the dominancy of its hydrophobic and ion-exchange interactions can be controlled by the influence of mobile phase pH, buffer type and concentration. The PDMS-SiO(2) stationary phase may provide a complementary tool to reversed-phase and HILIC stationary phases. The present results highlight the fact that the type of buffer, its concentration and pH can not only affect peak shape but also retention, selectivity and hence chromatographic resolution. Therefore, in method development and optimization strategies it is suggested that more emphasis should be given to the evaluation of these mobile phase operating parameters especially when basic solutes are involved.

Recent Developments in High-Performance Liquid Chromatography Stationary Phases

“…232 Borges et al synthesized and characterized a thermally immobilized poly(dimethylsiloxane) phase bound to silica particles. 233 The stationary phase provided a reversed-phase mechanism with acidic mobile phases and mixed-mode reversedphase/cation-exchange with neutral mobile phase. Abood et al made a hexylacrylate-based mixed-mode monolith.…”

Multimodal liquid chromatography of small molecules

“…Different multiinteraction stationary phases have been synthesized and characterized to separate compounds from different chemical classes such as neutral, organic and inorganic anions, [43][44][45] polycyclic aromatic hydrocarbons 46 and benzdiazepines. 47 Stationary phases with multiple interaction sites were designed based on the structure of the analyte. Fig.…”