Preparation and Chromatographic Characterization of Molecularly Imprinted Polymers

• Main Authors: Ching-Chiang Hwang, 黃清江
• Other Authors: Wen-Chien Lee
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/56257278332259701254

博士 === 國立中正大學 === 化學工程研究所 === 90 === Abstract Molecular imprinting techniques can afford the complementary binding site for a template molecule and the molecularly imprinted polymers (MIPs) are used for chromatographic separation of the target molecule. The technology for preparing molecularly imprinted polymer through bulk and suspension polymerizations of a complex forming by template, functional monomer, and a cross-linker was developed in this research. For a chiral resolution, the molecularly imprinted polymer was prepared by non-covalent molecular imprinting with either (-)-phenylpropanolamine or (+)-phenylpropanolamine as the template. Both covalent and non-covalent imprinting methods were employed for the prepared of MIP using cholesterol as the template. By the non-covalent method, methacrylic acid or 4-vinylpyridine and ethylene glycol dimethacrylate were copolymerized in the presence of the template molecule. Those polymers were prepared in the model of bulk polymerization, which was carried out in chloroform with 2,2’-azobisisobutyonitrile as the initiator at 4℃ and under UV radiation. These MIPs were ground and sieved to yield particles with the sizes ranging from 25 to 44μm. After removal of template molecules, these particles were packed into columns for the chromatography of (±)-phenylpropanolamine racemates or cholesterol from other steroids. The separation factor for the enantiomers of phenylpropanolamine ranged between 1.8 and 3.8 when the column was packed with MIP prepared with (+)-phenylpropanolamine as the template. A separation factor ranging from 2.1 to 3.6 could be achieved from the column packed with MIP prepared with (-)-phenylpropanolamine as the template. In order to compare the results from covalent and non-covalent imprinting methods, cholesterol was employed as the template. For the covalent imprinting, a covalently template-bound monomer, cholestery(4-vinyl)phenyl carbonate was prepared and then allowed for polymerization with a cross-linker. The covalently imprinted polymer was found to have the largest adsorption capacity for cholesterol (95μmol/g) and highest chromatographic efficiency for cholesterol separation. The 4-vinylpyridine-based non-covalently imprinted polymer could also have a higher capacity, but resulted in peak broadening and tailing due to the heterogeneity in the distribution of recognition sites for binding affinity to cholesterol. This is because that the complex was just stabilized by weak interactions between template and functional monomer. However, all the prepared cholesterol-imprinted polymers could be well packed into chromatographic columns and employed for separating cholesterol from b-estradiol effectively. Specific recognition sites were successfully created in these imprinted polymers for the adsorption of cholesterol. The bulk polymerization led to synthesize porous molecularly imprinted polymer that needs to be crushed, ground and sieved to produce packing materials. The MIPs obtained are unsuitable as packing materials owing to their random shape and size distribution. We then also prepared uniformly sized MIPs for cholesterol using one—step swelling and polymerization method. The synthesis of cholesterol-MIPs by a seed suspension polymerization in a mixture of 2-propanol and water or chloroform as solvent using polystyrene microbeads as the seeds prepared by dispersion polymerization. Methacrylic acid was employed as the functional monomer to form complexes with template along with ethylene glycol dimethacrylate as the crosslinker. After removal of template molecules, the columns packed with cholesterol-imprinted polymers were effective for the chromatographic separation of cholesterol from other steroids. When the sample of steroids was eluted isocratically from a column (15 cm ×0.46 cm I.D.) packed with this MIP at a flow-rate of 0.5 ml/min, using a mixture of water and acetonitrile (5：95) as the mobile phase, the retention times for estrone, b-estradiol, and cholesterol were respectively 5.3, 12.3, and 17.2min. The average retention times were 5.3, 10.9, and 16.7 min respectively for estrone, progesterone and cholesterol in the sample. A separation factor of 1.6 for cholesterol and b-estradiol, was obtained from the column with MIP particles prepared by either low- or high-temperature method. Compared with particles from bulk polymerization, the column packed with MIP particles from seeded suspension polymerization had advantages of being easy to prepare uniformly sized and monodispersed particles, and suitable as the HPLC packing materials.