Reseacrh And Application Of Online Enrichment Techniques In Capillary Electrophoresis

Capillary electrophoresis (CE) was an important technique for the separation of analytesdeveloped in the last decade. As a well-established separation technique, CE had theadvantages such as high resolving power, low solvent consumption, rapidity, simple samplepretreatment, many operating modes and small amount of samples and reagents required. Butthe application of CE was limited by the low sensitivity due to the small inner dimension ofthe capillary. Typically, a capillary of CE with50or75m diameter and50cm length hadobvious disadvantages such as low capillary volume and short optical path. In order to solvethe problem of low sensitivity and make CE more meet the need for the analysis of trace analytes in complex samples, on-line enhancement techniques were carried out. Up to now, most ofresearches were focused on the optimizing experimental conditions to improve sensitivity, theenhancement techniques aiming to different charged compounds were not studiedsystematically. The mechanism about ionic liquid (IL) and cyclodextrin（CD） improvingsensitivity and selectivity of microemulsion electrokinetic chromatography (MEEKC) was notstudied thoroughly. In view of this, the enhancement techniques about different chargedcompounds were studied systematically. The mechanism of the microemulsion taking IL andCD as additives increasing the selectivity and sensitivity was discussed in detail. The maininnovative work in this dissertation was described as follows:1. On-line enrichment techniques were utilized for different charged analytes. Melamine,glycyrrhiza flavonoid and polycyclic aromatic hydrocarbons (PAHs) were chosen as targetobjects. Three on-line preconcentration techniques, including base plug-field amplifiedsample injection (FESI) with Capillary zone electrophoresis (CZE)(BP-FESI-CZE), FESIand sweeping micellar electrokinetic chromatographic technique (FESI-sweep MEKC), cationselective exhaustive injection (CSEI) and sweeping technology with MEKC (CSEI-sweepMEKC), were used to analyze melamine in various samples. Under the optimal conditions,melamine could be determined within13min and the sensitivity of melamine was increasedby1000,1200and3000times respectively in comparison with that of the CZE method.Namely, the sensitivities were all improved about three orders of magnitude by using theon-line preconcentration techniques. The results showed that BP-FASI-CZE was awell-developed method to analyze cation compound with the advantages of sensitivity,rapidity, stability, and shorter analysis time comparing with CSEI-sweep MEKC and FESI-sweep MEKC.An on-line preconcentration technique coupled anion selective exhaustiveinjection (ASEI), sweeping technology with MEKC was used to analyze three glycyrrhizaflavonoids (isoliquiritigenin, liquiritigenin and liquiritin) in medicine. Under the optimalexperiment conditions such as matrix, injection time of water and injection time of sample,the sensitivity was improved by110,120and300times for isoliquiritigenin, liquiritigenin andliquiritin, respectively. Hydrophobic PAHs were difficult to be separated under conventionalconditions. A reversed MEEKC method was developed for the separation of six PAHsanalytes. Three stacking techniques include large volume sample stacking (LVSS), dynamicpH junction and sweeping (LVSS-DypH-sweep) were combined to preconcentrate and analyze harmful carcinogens PAHs within27min with good enrichment effect. Theenrichment factors were ranged from25to80.2. Positive and reverse MEEKC method were used respectively to separate and concentratesenven corticosteroids with similar structure. The results showed that reverse MEEKCmethod was a well-developed method with the advantages of better separation efficiency andshorter analysis time. The addition of1-butyl-3-methylimizolium tetrafluoborate (BMIM-BF4)ionic liquid (IL) and beta-cyclodextrin (β-CD) in reverse micro-emulsion could improveseparation efficiency and sensitivity. A reversed MEEKC with IL and β-CD as additives wasused to detect seven corticosteroids (fluticasone propionate, triamcinolone acetonide,cortisoneacetate, hydrocortisoneacetate, dexamethasone, hydrocortisone, prednisone). Theinfluence of IL and β-CD on the microstructure of microemulsion was explored in detail.When-CD was used as an additive, the inner polarity of microemulsion decreases, while thesurface change density and the diameter of microemulsion increases instead. However, the useof IL would increase the inner polarity of microemulsion and decrease the surface changedensity and the diameter of microemulsion. So, the synergistic effect of the two additivesenhances the sensitivity and selectivity of reverse MEEKC method, making it more suitablefor applications in separation and concentration.3. An on-line precocentration technique coupled anion selective exhaustive (ASEI) andsweep technology with MEEKC was used to detect seven corticosteroids in cosmetics. Simplesample pretreatment, the short analysis time and high sensitivity were obtained. Theenrichment factors were increased by30-140. Besides, LVSS-DypH-sweep technique wasused to analyze three sensitization fragrances with different charges. The simultaneousdetection was realized for the complicated samples with the enhanced sensitivity. Theenrichment factors were inreased by34-70.