Research On New In-line Sample Enrichment Methods For Capillary Electrophoresis

Capillary electrophoresis (CE) is one of the most frequently used analytical techniques with high resolution and efficiency. However, the application of CE for the trace analysis is usually restricted due to the relatively poor sensitivity because of the small sampling volume and short optical path-length of detection. Although there were several types of detectors had been used in CE analysis for improving its sensiticity, it was still a limited approache. Therefore, it mainly relies on sample enrichment methods to solve this problem. In order to improve the detecting sensitivity and accuracy for the target components in various samples, the development of sample enrichment methods has becomes a focus. At the same time, each enrichment technology has a certain applicable scope and the prerequisite. Therefore, because of the complexity of samples been analysed, it usually needs to utilize more than one type of methods for the sample enrichment. The coupling of two enrichment technologies and the coupling between enrichment technology and CE instrument greatly affect the accuracy and reproducibility of analysis results. For CE analysis, on-line and in-line coupling techniques have the advantages of simple operation and better reproducibility. In this thesis, in order to improve the sensitivity of CE and solve the influence on separation efficiency affected by the dead volume of interface between solid-phase microextraction (SPME) and CE, the in-line coupling techniques of in-tube SPME and CE were investigated.In chapter one, a detailed review about the enrichment techniques usually utilized in CE were described. Firstly, the enrichment techniques based on chromatographic and electrophoretic principles were introduced. Secondly, the coupling of different encrichment methods was also described. Lastly, the basic principles for solid-phase microextraction (SPME) and sweeping, which will be used in the following chapters, were intensively discussed.On the basis of in-tube SPME, a novel open tubular capillary microextraction and sweeping coupling method (OT-ME-CE) was established for the analysis of hydrophobic compounds in chapter two. This sample pre-concentration method is based on the in-line coupling of in-tube SPME and electrophoretic sweeping. The sample pre-concentration and electrophoretic separation processes were simply and sequentially carried out with a (35%-Phenyl)-methylpolysiloxane-coated capillary. The developed method was validated and applied to enrich and separate several pharmaceuticals including loratadine, indomethacin, ibuprofen and doxazosin. Several parameters of microextration were investigated such as temperature, pH and eluant. And the concentration of microemulsion that influences separation efficiency and microextraction efficiency were also studied. Central composite design (CCD) was applied for the optimization of sample concentration, sampling flow rate and sampling time, which will interact with each other. The precision, sensitivity and recovery of the method were investigated. Under the optimum conditions, the maximum enrichment factors for loratadine, indomethacin, ibuprofen and doxazosin in aqueous solutions are 1355, 571, 523 and 318, respectively. Finally, the developed method was applied to determine loratadine in real biological sample (rabbit blood sample).In chapter three, the electrostatic adsorption effection between double long-chained surfactants (dioctadecyl dimethyl ammonium chloride, DDAC) and Si-O- on capillary inner surface was ultilized. DDAC adsorb onto fused-silica capillary to form semipermanent bilayer coating. A in-capillary microextraction by selfassembled dynamic bilayer coating on capillary for in-line preconcentration was estabulised for the enrichment of hydrophobic compounds. The developed method was validated and applied to enrich and separate several pharmaceuticals including loratadine, indomethacin, ibuprofen and doxazosin. Several parameters affect on the stability of self-assembled coating were investigated such as DDAC solution concentration, coating time, pH value and capillary interior diameter. And the parameters including sampling time, pH value, eluant affect the enrichment efficiency were also investigated. The precision, sensitivity and recovery of the method were investigated.In chapter four, the established OT-ME-CE method was then used for the determination of pesticide residues in Chinese cabbage. Several pesticides including fenvalerate, chlorpyrifos and avermectin B1b were enriched and separated by the developed method. The parameters such as salt effect, pH and eluant for microextraction were investigated. And the concentration of microemulsion that influences the separation efficiency and microextraction efficiency were also studied. Under the optimum conditions, the avermectin B1b residual in Chinese cabbage was determined, and the precision, sensitivity and recovery of the method were investigated.The established in-capillary microextraction by selfassembled dynamic bilayer coating on capillary for in-line preconcentration method was used to analyse the phenolic compounds in environmental samples. The parameters affect the enrichment efficiency were investigated. Under the optimal conditions, the precision, sensitivity and recovery of the method were investigated for analysis of phenol, o-Dihydroxybenzene, m-Dihydroxybenzene and p-Dihydroxybenzene.In conclusion, the in-line coupling of sample enrichment techniques and CE analysis were studied to improve the sensitivity in this thesis.