| Core-shell composites have attracted widespread attention because of its unique physical and chemical properties in catalysis, biosensors,optical devices, and medical fields. In the field of analytical separation, as a new generation of chromatographic packing materials, core-shell composite has unique characteristics, such as the high specific surface area, low mass transfer resistance. Therefore, they own some advantages.For example, low back pressure, high column efficiency and so on.SiO2@Au is a precious metal composite material with SiO2 as a core, Au as a shell. This kind composite material has been widely used in the fields of optical, thermal, bio-medicine, but rarely used in the field of chromatography.The modification of SiO2 should be done before SiO2@Au core-shell particles are prepared. The reagents that have ? NH2, ? SH groups are widely used.In this thesis, we used SAM-electroless plating method to prepare PEI/SiO2@Au core-shell particles. During the process, some reaction parameters had been optimized. The most important innovation was that the polyethyleneimine(PEI), a kind of polymer with high-density amino groups, was introduced to the surface of Si O2 by Schiff Base reaction.Through this method, the bond density of amino groups on the SiO2 surface was improved. In view of the chemical stability of Au nanoparticles and the easy bonding method on the Au nanoparticles, then-octadecanethiol(C18) and glutathione(GSH) had been chosen to bind on the Au surface. The PEI/SiO2@Au–C18 and PEI/SiO2@Au–GSH packing materials had been successfully prepared. Moreover, this two kinds packing materials were packed into the capillary to prepare two kinds of capillary columns. At last, capillary liquid chromatography(cLC)and pressurized capillary electrochromatography(pCEC) were used to evaluate their basic performance.This thesis is devided into six chapters as follows:The first chapter briefly described the types of liquid chromatography packings and their current status and development, the advantage of core-shell packing materials, the basic principles of capillary electrochromatography(CEC) and pressurized capillary electrochromatography(pCEC), which provided a theoretical basis for this project.The second chapter described an improved two–phase sol–gel method to prepare Si O2 particles. During this process, some reaction parameters were discussed that had much effect on the particle size,monodispersity and uniformity of SiO2. These factors included the volume ratio of water–ethanol–ammonia and the total reaction volume,the added volume of tetraethoxysilane(TEOS),the reacted temperature,the stir speed and so on. Then, scanning electronic microscopy(SEM)was used to verify that the monodispersity and uniformity of SiO2 were good in following experimental condition: ratio of 10:3.1:10(v/v/v) for water–ethanol–ammonia in 67 ml mixed solvent with 46 ml TEOS,reacted at the 27℃ temperature. The particle size of these SiO2 particles was about 1 μm. They were used as the core in the follow-up experiment.Moreover, Au gel was prepared by the reduction of HAuCl4 with Na3 Ct.During this process, the factor of the volume of Na3 Ct was discussed. Atlast optimal conditions were achieved by adding 2 ml 1 wt% Na3 Ct into100 ml 0.01 wt% HAu Cl4. Through Transmission Electron Microscopy,we could see the particle size of Au nanoparticles was about 20 nm, and the dispersibility, homogeneity of them were good. They were used as the shell in the follow-up experiment.The third chapter described the preparation of PEI/SiO2@Au particles using SAM–electroless plating method. The reaction parameters were optimized. It mainly included three parts: The first part was the modification of SiO2. In this study, four modification methods were used.(i) 3-aminopropyltriethoxysilane(APTES) was modified on the suface of SiO2 directly.(ii) 3-mercaptopropyltriethoxysilane(KH-580) was modified on the suface of SiO2 directly.(iii) Polyethylenimine(PEI) was modified on the suface of SiO2 directly.(iv) APTES was modified on the suface of SiO2. Then glutaraldehyde was added to form the Schiff’s base.At last, PEI was added. The modified SiO2 through the last method was signed as PEI/SiO2. Under SEM, Au shell through four modification methods was compared. It had been verified that the best method was introducing PEI, a kind of polymer with high-density amino groups, to the SiO2 surface through Schiff Base reaction. During the process of forming PEI/SiO2@Au seed phase, the concentration of SiO2, the added volume of Au gel and the reaction pH were evaluated. At last, we chose0.04 wt% concentration of SiO2, the added volume of Au gel was 25 ml,and the p H was 8.0. During the growth of PEI/SiO2@Au seed phase, the added volume of formaldehyde was discussed. Through the SEM, it could be certified that when the added volume of formaldehyde was 40 ul, the PEI/SiO2@Au particles with more uniform Au shell were synthesized.The fourth chapter described the bonding of C18 on the surface of Au shell. Then PEI/SiO2@Au–C18 packing materials were packed into the capillary column. Under cLC mode, this kind of column was used toseparate five neutral compounds, namely benzene, toluene, ethylbenzene,propylbenzene, butylbenzene. The shape of chromatographic peaks were symmetric, and for benzene example, the column provided an efficiency of up to 170, 000 plates m-1. Three acidic substance(3,5-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid,2,6-dihydroxybenzoic acid) and three basic substance(2-aminopyridine,theophylline, caffeine) were also used to test the column performance, the shape of chromatographic peaks was not as symmetric as neutral substance, but all were baseline separated. It was also worth mentioning that the pHs of mobile phase were 2.2 and 11.7, respectively. In addition,the pCEC system was used to separate malic acid, citric acid, and fumaric acid. When the applied votage was +8 kV, the mobile phase pH was 1.7,the resolution of the three acid was good. Through this experiment, it could demonstrate that the pCEC system had the advantage when some components could not be separated under cLC system. Finally,methanol–water mobile phase with extreme pH conditions(pH 1.0 and pH 12.0) was used to flush the column for 96 hours respectively. It was found that the retention factor of five neutral components changed only slightly, demonstrating that PEI/SiO2@Au–C18 packing materials could be applied in a very wide pH range.The fifth chapter described the bonding of GSH on the surface of Au shell. Then, PEI/SiO2@Au– GSH packing materials were packed into a capillary column. In cLC mode, the packed column was used to separate three polar substances, such as caffeine, theophylline and thymine. After comparing the retention time and resolution of three substances with methanol–water and with acetonitrile–water mobile phase, the acetonitrile–water mobile phase was chosen. The hydrophilic property of the column was tested by observing the change of the retention time of three polar substances with different acetonitrile volume in the mobilephase. At last, pCEC was used to successfully separate these three substances at an applied voltage of-10 kV. It also demonstrated the superiority of pCEC. |
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