High-performance liquid chromatography (HPLC) experiments are an important part of the undergraduate analytical instrumentation laboratory courses and usually use commercial C18 silica-packed reversed-phase columns. In this experiment, a simple method of preparing SiO 2 core−shell packed columns was developed to enable students to master the whole process of HPLC experiment from stationary phase preparation and column packing to separation experiments, just as they do for gas chromatography. Nonporous SiO 2 particles with a particle size of approximately 2.2 μm were prepared by a three-step dilution reaction using the sol−gel method. The product yield was 92.1%. Monodisperse and spherical SiO 2 core−shell particles (SiO 2 @ dSiO 2 ) with a particle size of about 2.4 μm were prepared by a one-step hydrothermal method using the prepared SiO 2 spheres as the core. The product yield was 83.3%. The prepared SiO 2 @dSiO 2 particles were derivatized with n-octadecyldimethylchlorosilane and then packed into a stainless steel chromatography column. A high column efficiency of 83,188 theoretical plates per meter was obtained for fluorene in reversed-phase mode for the separation of a mixture of polycyclic aromatic hydrocarbons. The column efficiency obtained with this method is the same as that of a commercial column packed with fully porous particles of the same particle size. The SiO 2 core−shell stationary phase preparation method developed in this experiment has the advantages of simple process, high yield, and good repeatability. The experiment can be designed to be completed over a period of 1−3 weeks. Inorganic material synthesis is another important aspect of this experiment.
In this work, TiO2 was coated into the pores of the SiO2 core-shell spheres by using tetrabutyl orthotitanate (TBOT) as the titanium source. Then, by simply prolonging the reaction time, a TiO2 layer with a uniform and controllable thickness was obtained on the surface of SiO2 core-shell spheres by Ostwald ripening. The thickness of the TiO2 layer can be tuned from 15 to about 71 nm by either controlling the reaction time or controlling the amount of TBOT. C18-derived core-shell spheres with a TiO2 layer thicknesses of 40 nm (C18-SST-0.5-60) and 70 nm (C18-SST-0.7-30) were used as packings to evaluate the effect of TiO2 layer thickness on the chromatographic separation performance. The separation efficiency of C18-SST-0.5-60 and C18-SST-0.7-30 for fluorene was 115112 plates m− 1 and 83189 plates m− 1, respectively. Both TiO2-coated core-shell packings showed good peak symmetry for basic samples, with peak asymmetry factors below 1.11. The relative standard deviations of the retention time of polycyclic aromatic hydrocarbons and anilines were all lower than 6%. The results demonstrate that the TiO2 based stationary phase possesses great potential for high performance liquid chromatographic separation.
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