Applicability of core-shell SiO₂ microspheres with a high TiO₂ loading as stationary phase for HPLC

Due to its high chemical stability, sufficient rigidity and zwitterionic ion exchange properties, TiO₂ can be considered as an alternative stationary phase material to SiO₂ for high performance liquid chromatography. TiO₂ stationary phase is usually prepared by coating TiO₂ onto SiO₂ support by sol-gel method. However, in the traditional coating method, in order to overcome the rapid hydrolysis rate of tetrabutyl orthotitanate, only a very low concentration of tetrabutyl orthotitanate can be used, resulting in a low loading of TiO₂ on the support.

TiO₂ core-shell spheres with a good monodispersity were prepared using 0.25 mol L^-1 tetrabutyl orthotitanate. The specific surface area, pore volume, pore diameter and TiO₂ loading of the TiO₂ core-shell spheres were 66 m² g^-1, 0.15 cm³ g^-1, 9.8 nm and 57%, respectively. The core-shell spheres were derivatized with n-octadecyltrichlorosilane and then packed into a stainless steel column to test the separation performance for neutral, basic and acidic samples in liquid chromatography. A baseline separation of polyaromatic hydrocarbons was achieved, showing a column efficiency for fluorene of 118075 plates m^-1. The prepared stationary phase was also used to separate acidic and basic mixtures, and column efficiencies of 54500 and 25836 plates m^-1 were obtained for N,N-dinitroaniline and p-chlorophenol, respectively. The relative standard deviations of the retention times of polyaromatic hydrocarbons for run-to-run, day-to-day and column-to-column repeatability were all below 5.1%.

This work demonstrated that TiO₂ can be coated in the pores of the shell of SiO₂ core-shell spheres with high TiO₂ loading using a high concentration of tetrabutyl orthotitanate as the titania source. The experimental results show that the TiO₂ coated core-shell spheres can be a good alternative stationary phase for liquid chromatography.