Study On The New Methods To Improve The Sensitivity Of CE

Capillary electrophoresis (CE) is a liquid phase separation technique with the advantages of high resolution, high effieciency, short analysis time, simplicity, low sample and solvent consumption. The theory and application of CE have proved to be one of the most active research fileds in analytical chemistry. A capillary with smaller inside diameter is preferred for rapid and high-resolution separation by applying higher voltages. However, it is also responsible for the major limitation of the technique. The small detection volume and short optical pathlength typically result in low sensitivity. Development and establishment of novel methods or strategies to overcome the shortcoming are important. In order to improve the sensitivity in CE, the following major innovative researches were carried out in this thesis on the basis of the previous works.1. Combination of MSS with LASEKSI, a method was developed based on methanol assited micelle collapse for the first time, and it was applied to concentrate the berberine and theophylline in urine sample and higher focusing efficiency was obtained.2. NBD-F was selected as in-capillary derivatization reagent to label the hydroxyproline, which is marker of college. A simple, rapid and sensitive method was established based on in-capillary derivatization by MEKC-LIF for fully automated detection of hydroxyproline in dairy products for food safety purpose.3. Guanidine group functionalized Fe3O4nanoparticles were prepared and characterized. The novel nanomaterials were used as solid phase extration material for enrichment of BSA and the sensitivity of CE was improved.4. Graphene oxide-FesO4nanocomposites (GO-Fe3O4) were proved to be a novel solid phase extraction materials for GOx to improve the sensitivity of CE. In addition, the nanocomposites were exploited their peroxidase-like activity and applied for colorimetric detection of H2O2and glucose.This dissertation consists of six chapters.Chapter1:Approaches to improve the sensitivity of CE were briefly described. The recent developments of the methods help address this problem were reviewed.Chapter2:A new on-line method coupling MSS technique with large amount sample electrokinetic stacking injection (LASEKSI) for the analysis of cationic molecules was established. In this MSS-LASEKSI, an equilibrium state was formed and could be maintained for a long time, leading to the continuous stacking of the analytes on the basis of MSS. Extremely large amount of sample was permitted to be injected and then an improved enrichment fold could be achieved, comparing with the each case. Under the optimized conditions,6.4×103-and6.3×102-fold enrichment in peak heights upon normal CZE method and number of plates of2.9×106and6.5×105/m were attained for berberine and theophylline, respectively. The developed method may provide prospect for exploiting a new concentration technique to achieve higher enrichment factor.Chapter3:A rapid, sensitive and automated approach for the determination of hydroxyproline (Hyp) by MEKC-LIF was developed for the first time. The new method employed NBD-F as the fluorescent reagent for in-capillary derivatization and the main parameters were discussed. The CE process could be completed within7min and the detection limit for Hyp was1.6±0.5ng/mL. This approach was applied on the analysis of Hyp in milk powder, liquid milk, milk drink and soymilk powder samples for food safety purpose.Chapter4:Guanidine group functionalized magnetic nanoparticles were prepared and characterized by transmission electron microscopy, X-ray diffraction, fourier transform infrared spectra, vibration sample magnetometer and zeta potential analyzer. The novel multifunctional nanoparticles were served as a solid-phase extraction sorbent for easy isolation and preconcentration of acidic protein from aqueous solution. Fifteen-fold enrichement efficiency was achieved and detection limit was45ng/mL for BSA by CE. Chapter5:Graphene oxide-Fe3O4nanocomposites (GO-Fe3O4) were perepared and characterized. It was found that the GO-Fe3O4nanocomposite can be used as a solid phase sorbent for GOx in CE. The GOx can be enriched for26fold using the nanomaterials and the detection sensitivity of CE was improved. In addition, the nanocomposite was demonstrated to possess intrinsic peroxidase-like activity for the first time, and can be used for colorimetric detection of H2O2and glucose.Chapter6:Conclusion.