Preparation Of Novel Polymer-based Capillary Monolithic Columns And Application In Electrochromatography

The polymer-based monoliths are highly favorable and widely adoptedattribute to some advantages such as chemical stability over the entire pH range,fast and simple preparation, flexible modification of the supports, and goodreproducibility. The polymerization mixture may also be prepared using a widevariety of monomers, allowing a nearly unlimited choice of both matrix andsurface chemistry. Thus far, the vast majority of CEC separations haveconcentrated mainly on the separation of non-polar and neutral analytes in areversed-phase (RP) mode. The separation of polar solutes and basic compoundsis still a difficult work in RP mode. To achieve highly efficient separation of polarsolutes and basic compounds, several capillary electrochromatography monolithswere prepared in this thesis. The separation mechanisms of these monoliths werealso discussed in detail. Main points of this thesis are listed as following:1. To separate the polar compounds, a hydrophilic interaction-capillaryelectrochromatography (HI-CEC) monolith was firstly prepared. The separationmechanism of the monolithic column was discussed in detail. It was found thatthe separation mechanism of charged solutes could be attributed to a mixedmode of HI and weak electrostatic interaction, as well as the effect ofelectrophoresis, while the separation of neutral solutes was based on thehydrophilic interaction at high ACN content.2. A polar and neutral polymethacrylate-based monolithic column wasprepared by in situ copolymerization of a neutral monomer2-hydroxyethylmethacrylate (HEMA) and a polar cross-linker pentaerythritol triacrylate(PETA). A typical HI-CEC mechanism was observed on the neutral stationary phase. The absence of fixed charges on the surface of the neutral monolithallowed the efficient separation of basic nucleic acid bases and nucleoside, andwith column efficiency greater than140000theoretical plates/m.3. A novel monolithic column with covalently bonded zwitterionicfunctional groups was prepared by in situ copolymerization ofN,N-dimethyl-N-methacryloxyethyl N-(3-sulfopropyl) ammonium betaine(SPE), vinylsulfonic acid (VS) and PETA. The VS enabled the production of anelectroosmotic flow (EOF), thus the monolith can be firstly used as a stationaryphase in CEC mode. The column efficiencies greater than145000theoreticalplates/m for thiourea and132000theoretical plates/m for cytidine wereobtained. The separation mechanism of charged polar solutes was attributed to amixed mode of HI and electrostatic interaction, as well as electrophoresis.4. A capillary electrochromatography monolith with mixed mode of HI andstrong anion-exchange was prepared. While SPE functioned as the polar ligandprovider,(3-acrylamidopropyl)trimethylammonium chloride (APTA) wasemployed to generate EOF. The APTA served at the same time as theanion-exchange sites of the monolith. Diverse series of neutral and ionicsamples, such as phenols, benzoic acid derivatives, basic nucleosides and bases,nucleotides and peptides were well separated on this monolith.5. A novel cationic polystyrene-based monolithic column was prepared by asingle polymerization step. Vinylbenzyl trimethyl ammonium chloride (VBTA),which was firstly used in CEC, provided an EOF under the wide pH range. Theacidic, neutral and basic analytes were successfully separated on the novelmonolithic column. The separation mechanism of charged solutes was attributedto a mixed mode of RP and strong anion-exchange, as well as electrophoresis.