Green Analytical Methodologies In Liquid-Phase Microcextraction Combined With Capillary Electrophoresis

Capillary electrophoresis (CE) is a powerful separation technique with high separation efficiency, fast separation speed and low sample consumption. For its small injected sample volume and short optical path, the detection sensitivity of ultraviolet-visible (UV-Vis) spectrophotometry is not satisfied. High sensitivity detector and sample preconcentration techniques are often adopted to improve concentration detection limits in CE. The author reviews the developments and applications of liquid-phase microextraction (LPME) and on-column sample stacking in CE analysis. The main research in this thesis include design and production of liquid-phase microextraction unit, study of extraction conditions in headspace liquid-phase microextraction, the integration of headspace liquid phase microextraction with capillary electrophoresis, and the combination of liquid-liquid-liquid microextraction with base stacking as a dual preconcentration method for capillary zone electrophoresis. The details of the contents and results of the thesis are as follows:1. We design and produce two liquid-phase microextraction units and describe the method and the key point in detail. These liquid-phase microextraction units realize the integration of headspace liquid-phase microextraction with capillary electrophoresis, and the combination of liquid-liquid-liquid microextraction with base stacking as a dual preconcentration method for capillary zone electrophoresis, which highly improve the detection limits in CE and simplify the sample pretreatment steps.2. On the basis of headspace liquid-phase microextraction theory, the effect of the sample volume on the enrichment factor of HS-LPME was studied by both theoretical and experimental methods. The experimental results of our work and most of the analytes in reported work was close to our prediction.3. An analytical technique of in-line coupling headspace liquid-phase microextraction (HS-LPME) with capillary electrophoresis (CE) was proposed to determine volatile analytes. To evaluate the proposed method, phenols were used as model analytes. The parameters affecting the extraction efficiency were investigated, including the configuration of acceptor phase, kind and concentration of acceptor solution, extraction temperature and time, salt-out effect, sample volume, etc. Under the selected conditions, the enrichment factors were obtained from 520 to 1270. The proposed method was successfully applied to the quantitative analysis of the phenols in tap water, and proved to be a simple, convenient and reliable sample preconcentration and determination method for volatile analytes in water samples.4. A simple and efficient dual preconcentration method of on-column liquid-liquid-liquid microextraction (LLLME) coupled with base stacking was developed for capillary zone electrophoresis (CZE) in this paper. Four N-methyl carbamates were used as target compounds to evaluate the enrichment means. The parameters affecting the extraction efficiency were investigated, including the selection of organic phase, kind and concentration of acceptor solution, extraction time, sample volume and the injection time in base stacking etc. Under the selected conditions, the enrichment factors of the carbamates were obtained from 1100 to 1410. The analytical results demonstrated that the LLLME coupled with base stacking was a simple, convenient and reliable on-column sample pretreatment method for the analysis of anionic analytes in CZE.5. We developed in-line headspace liquid phase microextraction technique, and realized the direct preconcentration the non-polar compounds in micellar electrokinetic capillary chromatography (MEKC). The method was applied to the analysis of p-hydroxybenzoate preservatives in medicine. The enrichment factors of methyl-, ethyl-and propyl-parabens ranged from 25 to 86. The integrative coupling technique was able to concentrate analytes and eliminate the matrix interference effectively, and be used to determine neutral analytes in complex samples by CE. The running buffer could be adopted as acceptor phase in the analysis of ionized compouds in the intergrative headspace liquid phase microextraction technique. More recently, benzoic acid and sorbic acid preservatives in diluted soy sauce samples were analyzed by the this method, and we have made some important progress.