Novel Capillary Electrochromatographic Column Technology And Applications Based On Bio-inspired Functionalization And In-situ Polymerization

Capillary electrochromatography (CEC) has been considered as a novel micro-column separation technique that combines the merits of capillary electrophoresis and high performance liquid chromatography. It possesses advantages such as high efficiency, high selectivity and low sample and solvent consumption, which is promising for application in chromatographic fields. The development of CEC technique was slowed down due to the lack of commercially available CEC columns. Open tubular capillary columns has been paid great attention by separation scientists, as OT column has many merits such as easy preparation, good permeability and wide potential applications in many fields. This work focuses on the development of novel column technology based on bio-inspired polydopamine (PDA) functionalization and in-situ polymerization. The major work of this thesis includes the following three parts:1. Development of novel capillary column with hydroxyapatite (HAP) as stationary phase based on bio-inspired polydopamine functionalization. To immobilize HAP, bio-inspired method was utilized to modify the capillary firstly, generating a PDA layer; and then a layer of HAP would be formed on PDA layer by a biomineralization process, to produce HAP@capillary. The morphology and characterization of nanostructured HAP grown on the surface of capillary wall have been confirmed by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Electrochromatographic behavior of HAP@capillary was systematically evaluated. The chromatography performance by CEC mode and capillary liquid chromatography (CLC) mode was compared. The study results show that the electroosmotic flow (EOF) characteristic of HAP@capillary exhibits a pH-dependent EOF from anode to cathode; phenols, amines and alkylbenzenes were successfully separated in CEC mode. The separation efficiency in CEC mode driven by EOF was much higher than that in CLC mode. HAP@capillary exhibits high column efficiency for methylbenzene, up to151138plates per meter; and good reproducibility with the relative standard deviations lower than5%.2. Development of novel graphene-based capillary column based on a layer-by-layer strategy. To immobilize graphene onto the inner surface of silica capillary, a bio-inspired method was first used to functionalize the capillary surface with a layer of PDA. Graphene oxide (GO) was then introduced and can covalently react with PDA, realizing immobilization of graphene as a result. To enhance the chromatographic performance, a conductive polymer polyaniline (PANI) was introduced to be a sub-layer; PDA was then introduced following with GO, to generate a multilayer GO-PDA-PANI@capillary. The morphology of different layers modified on the capillary column was characterized by SEM. The electroosmotic flow characteristics of capillaries modified with different layers were investigated by varying the pH value of mobile phase and the separation performance of different layers modified capillary was also investigated. It has been demonstrated that GO-PDA-PANI@capillary exhibited a pH-dependent EOF from anode to cathode. Both PANI and PDA layers contribute to separation, however, GO layer played the crucial role in CEC separation. The chromatographic parameters between GO-PDA@capillary and GO-PDA-PANI@capillary were systematically compared. The results indicate that separation selectivity and efficiency on GO-PDA-PANI@capillary were much better than that on GO-PDA@capillary, with column efficiency, up to107084plates per meter for methylbenzene was obtained on the former capillary column. GO-PDA-PANI@capillary exhibits a reversed phase chromatographic retention mechanism. It possesses good stability and reproducibility with the inter-day and intra-day relative standard deviations of migration time lower than3%, relative standard deviations of column-to-column lower than6.17%.3. Development of high performance poly(stearyl methacrylate-co-ethylene glycol dimethacrylate)(SMA-EGDMA) capillary monolithic column. The column has been successfully used for separation and determination polycyclic aromatic hydrocarbons (PAHs) by CEC. The prepared column exhibits good efficiency of20000plates/m for naphthalene. In addition, an on-line concentration technology was employed to the CEC separation, which dramatically improved the detection sensitivity up to50-fold enhancement so as to achieve nanogram level. Six PAHs showed good linearity with linear correlation coefficient R>0.99. Poly(SMA-EGDMA) capillary monolithic column exhibits good reproducibility, with relative standard deviations of migration time and peak area in range of4.71-4.93%and4.88-6.65%, respectively, for the six polycyclic aromatic hydrocarbons. The method has been successfully applied to PAHs detection in East Lake water samples. The recoveries of six PAHs were in range of91.8-108.1%.