Preparation Of Core-shell Silica Microspheres And Its Application In Fast Separation And Analysis By Liquid Chromatography

Chromatographic matrix plays an important role in the development of chromatography technology. Silica microspheres, as the most popular matrix, have been used for fast separation and analysis in HPLC based on its high specific surface area, mechanical strength, easy surface modification and other advantages. However, the wide distribution of particle size is the bottleneck of the development of the porous silica microspheres. In the meantime, core-shell silica microspheres with high column efficiency, superior performance, high resolution and low back pressure have attracted more and more attention, being two main problems, the agglomeration and the wide particle size distribution, however. To solve these problems, the author carried out the following aspects of the study.1. In order to solve the shortcomings of Stober method in the preparation of the micro-sized silica microspheres, we added electrolyte in the Stober system to increase the particle size and the monodisperse non-porous silica microspheres with diameter in the range of 3-10 ?m were obtained. More importantly, a novel strategy to synthesize the monodisperse superficially porous core-shell silica microspheres (CSSMs) with enlarged mesopore channels perpendicular to the particles surface using a dual-templating approach was presented for the first time. With hexadecyl trimethyl ammonium bromide (CTAB) and trioctylmethylammonium bromide (TOMAB) as the dual-templat to enlarge the size of CTAB micelles, the pore size can be enlarged from 2.6 nm to 10.6 nm and the mesopore channels perpendicular to the surface of CSSMs can be obtained. The CSSMs obtained were modified with ODS to separate the alkyl benzene homologues. The higher efficient separation with fast flow rate and relatively low back pressure of the synthesized column demonstrate that the CSSMs have a great potential application for fast separation and analysis of small solutes with HPLC.2. It is difficult to avoid aggregation in the preparation of core-shell silica microspheres by sol-gel method. In this paper we have successfully resolved the problem of aggregation by template dissolution induced redeposition method. The non-porous particles were transformed into core-shell silica microspheres in the presence of CTAB and TOMAB under basic conditions at ambient. We can control the shell thickness of core-shell microspheres and the pore size of mesoporous shell by adjusting the time of etching and changing the molar ratio of template, respectively. The acid reaming method was used to further increase the pore size of mesoporous shell. The CSSMs obtained were modified with ODS to separate proteins and the baseline separation of 5 kinds of proteins was achieved in 1 minute. Simultaneously, the column delivered a better performance when separating BSA digests comparing with the commercial one currently available.3. For the wide distribution of the micro-sized porous silica microspheres, a new method was developed to synthesize micro-sized monodisperse large-porous silica microspheres with polymer microspheres as templates. First, the monodisperse porous PGMA-EDMA microspheres were synthesized by a single-step swelling and polymerization method. Then the PGMA-EDMA microspheres were functionalized with tetraethylenepentamine to generate amino groups which act as a catalyst in hydrolysis of tetraethylorthosilane to form Si-containing low molecular weight species. Next, the low molecular weight species diffused into the functionalized PGMA-EDMA microspheres by induction force of the amino groups to form polymer/silica hybrid microspheres. Finally, the organic polymer templates were removed by calcination and the large-porous silica microspheres were obtained. The porous structure of the silica spheres can be controlled by adjusting the porous size and structure of the template polymers. The resulting large-porous silica microspheres were modified with octadecyltrichlorosilane (ODS) and the chromatographic evaluation was performed by separating the proteins and the digest of BSA. The baseline separation of seven kinds of protein standards was achieved and the column delivered a better performance when separating BSA digests comparing with the commercial one currently available. The high column efficiency and good reproducibility present that the large-porous silica microspheres obtained can be used as a matrix for peptide and protein separation.4. A new method was developed to synthesize monodisperse silica@porous silica microspheres with controllable shell thickness and aperture size due to the combination of the preparation of porous silica microspheres by template and the preparation of silica@ porous PGMA-EDMA core-shell microspheres by suspension polymerization. First, the monodisperse silica@porous PGMA-EDMA microspheres were successfully prepared by suspension polymerization, and then silica@PGMA-EDMA/silica microspheres were prepared with silica@porous PGMA-EDMA microspheresas template using sol-gel process. Upon calcination of the silica@PGMA-EDMA/silica hybrid microspheres, the silica@porous silica microspheres were obtained. Finally, the prepared core-shell microspheres were derivatized with octadecyltrichlorosilane and packed into a chromatographic cake. The baseline separation of 5 kinds of proteins was achieved in 2 minutes using HPLC, which indicate that the prepared core-shell microspheres could be used as a matrix for rapid separation of proteins, and it has great value for the development of efficient and rapid separation of complex samples.