Optimization of the surface modification process of cross-linked polythiol-coated chiral stationary phases synthesized by a two-step thiol-ene click reaction

A new platform technology for the preparation of stable chiral stationary phases was successfully optimized. The chiral selector tert-butylcarbamoylquinine was firstly covalently connected to the polymer poly(3-mercaptopropyl)methylsiloxane by thiol-ene click reaction. Secondly, the quinine carbamate functionalized polysiloxane conjugate was coated onto the surface of vinyl modified silica particles and cross-linked via thiol-ene click reaction. The amount of polysiloxane, chiral selector, radical initiator, reaction solvent (chloroform and methanol), reaction time, and pore size of the supporting silica particles were varied and systematically optimized in terms of achievable plate numbers while maintaining simultaneously enantioselectivity. The optimization was based on elemental analysis data, chromatographic results, and H/u-curves (Van Deemter) of the resultant chiral stationary phases. The results suggest that better chromatographic efficiency (higher plate numbers) at equal enantioselectivity can be achieved with methanol (a poor solvent for the polysiloxane that is dispersed rather than dissolved) and a lower film thickness of quinine carbamate functionalized polysiloxane. In this study, chiral stationary phases based on 100 Å silica slightly outperformed 200 Å silica particles (each 5 μm). The optimized two step material exhibited significantly reduced mass transfer resistance compared to the one step material and equal performance as a brush-type chiral stationary phase.