Preparation And Applications Of Novel Mixed-mode Monolithic Capillary Columns

Packed columns are widely applied in commercially available liquidchromatography system. Although higher column efficiency has been achived by usingsmaller particles, pressure drop is associated with the use of small particles. As analternative, monolithic column can simultaneously provide higher column efficiencyand lower pressure drop than packed column. Many papers have reported thepreparation and applications of monolithic column. However, further investigation isin need to diversify the surface chemistry of monolithic stationary phases and facilitatethe preparation of monolithic columns.The main work of this thesis is summarized as follows:1. One-pot synthesis of porous polymer monolith decorated withN-methylimidazolium in a capillary was described. The polymer matrix wassynthesized by in situ copolymerization and quaterisation of3-chloro-2-hydroxylpropyl methacrylate (CHPMA), ethylene dimethacrylate (EDMA) andN-methylimidazole (N-MIz). The influencing factors including amount of cross-linkers,composition of porogenic solvents and polymerization temperature on the formation ofthe monolithic column were investigated. The monolithic column exhibited highcolumn efficiency for thiourea, up to135000plates/m and phenylmethanol, up to102000plates/m. Different types of compounds including alkylbenzenes, phenols andinorganic anions were successfully baseline separated by capillaryelectrochromatography (CEC). The separation of theses analytes on the columnindicated typical reversed-phase and anion-exchange chromatographic retentionmechanism.2. A new organic-inorganic hybrid silica monolithic column possessingoctadecyl/amino has been developed for capillary electrochromatography.1-Octadecanethiol was incorporated into a vinyl/amino modified silica monolithiccolumn which was fabricated by sol-gel chemistry using tetraethoxysilane(TEOS),vinyltriethoxysilane (VTES) and3-aminopropyltriethoxysilane (APTES) as theprecursors combined with supramolecular template-directed synthesis to form aoctadecyl/amino-functionalized silica monolithic column via thiol-ene click chemistry.The influences of the key factors including VTES/APTES ratio, amount ofsupramolecular template, polycondensation temperature and amount of solvent on the vinyl/amino monolith formation were discussed in detail. The column efficiency wasevaluated using thiourea and phenylmethanol with efficiency up to82700plates/m and39200plates/m. Acceptable separations of alkylbenzenes and phenols were obtained.The monolithic stationary phase presents typical reversed-phase chromatographicretention mechanism toward neutral analytes.3. A new mixed-mode organic-silica hybrid monolithic column was prepared byhydrolysis and polycondensation of tetramethoxysilane (TMOS) and3-mercapto-propyltrimethoxysilane (MPTMS) followed by subsequent “click” reaction betweenmercapto and2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as well as freeradical polymerization of AMPS. The monolith was prepared inside a75-μm-id and250-μm-id capillary for CEC and capillary liquid chromatography (CLC), respectively.Anilines and neutral analytes were rapidly separated on the poly(AMPS) grafted silicamonolithic column by both CEC and CLC. The column showed high separationefficiency for anlines (N=104000-26200plates/m) in CEC separation. The separationof theses analytes on the column demonstrated typical reversed-phase andcation-exchange retention mechanism.