Preparation And Application Of Some Novel Chromatographic Column And Stationary Phase

The discovery of ordered mesoporous materials has opened a new era in the field of material science. During the past decades, progress has been made in the controllable synthesis of mesoporous materials with novel chemical compositions, various mesostructure, high specific surface area and adjustable morphologies, which allowed their use in high performance liquid chromatography (HPLC) and capillary electrokinetic chromatography (CEC).In chapter2, different procedures for the synthesis of mesoporous silica spheres with controlled particle size was developed. It was based on the hydrothermal syntheses by mixing nonionic surfactant and TEOS. The size of spheres was controlled by adjusting the synthesis temperature, the synthesis time and so on. The size of the spheres was analyzed by optical microscopy and further confirmed by scanning electron microscopy (SEM). These mesoporous silica spheres with diameter ab.5μm in size have been used as stationary phase in HPLC. To synthesize a new kind of stationary phase, hexadecyltrimethylammonium chloride (CTAC1) was used as template to prepare mesoporous silica nanoparticles (MSNs), and then the urea-formaldehyde (UF) polymer/SiO2composite microspheres were prepared by polymerization induced colloid aggregation (PICA). The results showed that the5μm average particle size of UF/SiO2can stably obtained in the condition of pH=2,R=1-3, Ve=10%.In chapter3,columns for open tubular capillary electrokinetic chromatography (OTCEC), coated with a mixed-mode (reversed-phase/ion-exchange) stationary phase by use of the sol-gel technique, have been developed and investigated. The surface of this stationary phase contains octyl, amine and residual silanol moieties;the amine and silanol groups determine the net charge and the charge density on the inner surface of the capillary and can produce a switchable electroosmotic flow (anodal/cathodal).The synthesizing procedure was optimized by changing the ratios of tetraethoxysilane, n-octyltriethoxysilane, and3-aminopropyltriethoxysilane in the initial sol.The inner surface properties of these capillaries are probed by measuring the electroosmotic flow (EOF) as a function of pH. The performances of the columns were evaluated by OTCEC using a wide range of compounds (neutral solutes, aromatic acids, and aromatic amines). It is shown that both reversed phase (RP) and weak anion-exchange (WAX) interactions contribute to the retention of these analytes.In chapter4, open-tubular columns (OTCs) coated with n-octyl (C8) functionalized mesoporous silica were prepared, and utilized to OTCEC to separation polycyclic aromatic hydrocarbon (PAH) compounds. The sol-gel solution was prepared by mixing tetraethoxysilane, n-octyltriethoxysilane, surfactant, ethanol, hydrochloric acid and water, and then was coated onto the inner wall of the fused silica capillaries. The SEM photographs show a layer of mesoporous materials with a thickness around100nm covering the inner surface of the capillary. Comparing with a non-mesoporous columns coated by the same procedure except absence of the surfactant, the mesoporous coated column offered much higher separation characters. This can be ascribed to an increasing in the surface area of the stationary phase, which is one of the characteristics of mesoporous materials. The resolution and retention of the OTCs can be adjusted by simply changing the ratio of the two silane precursors added to the initial solution.In chapter5, we have developed a high performance capillary electrophoresis, in which mesoporous silica nanoparticles (MSNs) with50nm particle size were used as pseudostationary phase to improve the separation efficiency of analytes. Firstly, the dispersing ability of MSNs in various buffer solutions was compared. Secondly, the optimal materials were used as a pseudostationary phase in capillary elctrokinetic chromatography to separate the environment pollutions. Mesoporous nanoparticles have not only the properties that the pseudostationary phase should possess, but also the properties of the big surface areas, unified pore size distribution which better than other already in use pseudostationary phase, such as polymer, carbon nanotube etc.