The Application Of Chemically Modified Miniature Electrodes In Capillary Electrophoresis

Capillary electrophoresis （CE） is a powerful liquid phase separation technique. Theseparation principle is based on the phenomena that ionized molecules of different mass andcharge will travel with different velocities through a fused silica capillary under the influenceof a high-voltage electric field. Capillary electrophoresis with electrochemical detection（CE-ECD） has already been applied to analyse many substances owing to its inherent efficientseparation capabilities, high sensitivity, short analysis time, simplicity of instrumentionneeded. CE-ECD has flourished in wide areas such as analytical chemsitry, environmentalanalysis, biochemieal analysis, pharmaceutical analysis, food analysis and almost all theanalysis field. The interruption of modified electrodes provides a new stage for thedevelopment of CE with electrochemical detection. Compared with traditional electrodes,chemical modified microelectrodes have higher sensitivity and selectlvity, moreover, theresponse rate also can be improved and realized monitor at time. Chemical modifiedmicroelectrodes with CE-ECD are one of the important aspects in morden analyticalchemistry.In this thesis, two kinds of chemical modified microelectrodes were described for thedirect identification of dopamine and hydrogen peroxide by capillary electrophoresis withamperometric detection. The methods with many advantages, such as the high separationspeed, sensitivity effieieney, low volume, short analysis time have been successfully appliedto the analysis of single cells.In the first chapter, the principle of CE, the detection method which were often used withCE, and the microelectrodes used with CE-ECD were introduced. Then, the analysis of singlecell by CE with anperpmetric detection was reviewed. Finally, the application of chemicalmodified microelectrodes used with CE-ECD, were reviewed in detail.In the second chapter, dopamine （DA） is an important sympathetic neurotransmitter thatplays an essential role in the central nervous systems. As a chemical messenger, in particular,DA has relation to the nervous function. Therefore, the regulation of DA plays a crucial rolein our mental and physical health. Thus, the analysis of DA at the low concentration isnecessary and of continuous interest in analytical chemistry. A simple, sensitive, and low costmethod was described for the direct identification of DA by capillary electrophoresis with amperometric detection at a new kind of gold nanoparticles modified carbon fiber microdiskelectrode （AuNPs-CFME） at first time. AuNPs-CFME had high catalytic ability for dopamineand exhibited good stability and reproducibility. The detection conditions were optimizedincluding detection potential, the concentration of phosphate buffer, pH value of phosphatebuffer, and separation voltage etc. Compared with the previously reported method usingcarbon fiber microdisk electrode, more sensitive detection was realized with AuNPs-CFME.It shows that ascorbic acid （AA）, L-cysteine （Cys） and paracetamol （Par） do not interfere withthe determination of H₂O₂. The method has been successfully applied to the determination ofDA in single pheochromocytoma cell.In the third chapter, hydrogen peroxide （H₂O₂） is the most stable species of reactiveoxygen species that is implicated in a number of neurological disease states, cell death, aging,and a variety of pathologies as a byproduct of aerobic metabolism. The levels of H₂O₂areconnected with the degradation and formation of reactive free radials, which play animportant role in normal cell function. Therefore, the analysis of H₂O₂has attracted more andmore attentions in numerous fields owing to its important role in many systems. We haveconstructed sensitive, simple-made electrochemical H₂O₂sensors by immobilizing platinumnanparticles （PtNPs） on platinum microelectrodes （PtE） for the direct identification ofhydrogen peroxide with CE. The Pt nanoparticles could be electrodeposited on the surface ofthe platinum electrode at room temperature without any pretreatment procedure. The platinumnanoparticles modified platinum electrode （PtNPsE） exhibits low background current,excellent electrochemical stability, fast response and high sensitivity due to its high catalyticactivity for the H₂O₂detection. Compared with the previously reported Pt electrode, moresensitive detection is realized with PtNPsE with a detection limit of 0.2μM （S/N = 3）. Themethod has been successfully applied to the determination of H₂O₂in single cell.