Superficially ordered porous silica microspheres with smaller mesopore for the separation of structural isomers in...

The separation of structural isomers is always a challenging task for liquid chromatography because of their similar physicochemical property. Research has found that materials with regular microporous structures exhibit excellent isomer separation performance. However, as the most easily available chromatographic material, silica stationary phases with regular and small mesopore structure have not yet been prepared, and it remains to be confirmed whether narrow pores in silica materials have the enhancing effect on shape selectivity in the separation of structural isomers.

SiO₂@SiO₂ core-shell stationary phase with ordered and small mesopore (3.5 nm) was prepared for the separation of structural isomers. The superficially ordered porous silica (SOPS) was synthesized by in-situ growth of radial pore structure on the surface of nonporous silica. To investigate the narrow pore effect on shape selectivity, the SOPS C18 stationary phases with different pore size (3.5 nm and 10.1 nm) were compared in terms of separation performance. Several groups of isomers with different linearity and planarity were chosen as probes to evaluate the shape selectivity of stationary phases. The stationary phase with smaller pore size presented better separation performance in certain circumstances. It was found SOPS C18-3.5 nm column had higher linearity selectivity which may come from its narrow pore channels with stronger limitation ability that imposes steric restrictions on the adsorption of molecules in a non-linear configuration and allows "slender" molecules to penetrate deep.

This work describes the design and preparation of SiO₂@SiO₂ stationary phase possessing regular and small mesopores, showing good separation performance for structural isomers. It reveals the narrow pore effect on enhancing shape selectivity, which may give inspirations for the design of stationary phases with ability of high-resolution separation of isomers.