Study And Application Of Capillary Electrophoresis And Electrochemical Detection In Environmental Analysis

Capillary electrophoresis (CE) is a combination of classical electrophoresis technology and modern microcolumn technology. The separation principle is based on the phenomena that ionized molecules of different mass or/and charge will travel with different velocities through a fused silica capillary under the force of a high-voltage electric field. Recently, CE has been widely used in different fields, such as life science, agriculture, food, clinical medicine, environmental analysis and chemistry, because of its powerful capability for the analysis of complex samples due to its high separation speed and efficiency, low volume sample, the relatively simple instrument and low running costs. Environmental issues have more and more serious influence on our daily life, and this requires more effective environmental pollutants analysis and detection methods to privide a scientific basis for the corresponding solutions.Capillary Electrophoresis-Electrochemical Detection (CE-ED) has the advantage of high sensitivity and good selectivity. It can meet all kinds of environmental pollutants traces of detection, and has very good application prospects in environmental analysis.As the devolpment of stcacking online and chemically modified electrodes, the CE will have more great potential in the application of environmental analysis.The characteristic of high sensitivity and convenience in electrochemical detection (ED) makes it very popular in analysts for a long time. Recently, the chemically modified electrodes have been widely concerned, which broadened the ED application prospect in food, environmental monitoring and military fields.This dissertation is based on the capillary electrophoresis and electrochemical detection for determination of estrogens, phenol pesticides and melamine by coupled with stacking online and chemically modified electeodes.The dissertation includes four chapters:Chapter1. IntroductionIn this chapter, the harm and the analysis technologies of environmental pollutants were outline. The applictions of capillary electrophoresis and electrochemical detection in nvironmental analysis were highlighted.Chapter2. Stacking and simultaneous separation of estrogens in water samples by capillary electrophoresis with electrochemical detectionA rapid and sensitive method based on acetonitrile-salt stacking in capillary electrophoresis with eletrochemical detection at copper disk electrode was developed for the simultaneous separation and determination of three estrogens:estrone,17β-estradiol and estriol. The effects of several important factors that influence the separation and detection were investigated. Under the optimum conditions, the estrogens could be separated in0.06mol/L sodium hydroxide solution within14min. With acetonitrile-salt stacking by5%acetonitrile and0.5%NaCl, a good linear response was obtained for three estrogens from0.2to10μmol/L, with correlation coefficients higher than0.9993. And the detection limits of them were8.9×10-8,6.7×10-8and1.1×10-7mol/L (S/N=3) for estriol,17β-estradiol and estrone, respectively. This method was successfully employed to analyze different water samples from waterworks, tap water fishpond, and river samples with recoveries in the range of90.8-108.9%, and RSDs less than4.69%. The satisfied results demonstrated that this method was of convenient preparation, high sensitivity and good repeatability, which could be applied to the rapid determination of environmental water samples.Chapter3. Determination of four phenol pesticides with MWCNTs-COOH@Pdop hybrid nanocomposite by capillary electrophoresis with electrochemical detectionIn this article, the MWCNTs-COOH@Pdop hybrid nanocomposite was synthesized. The carbon disk electrode modified with MWCNTs-COOH@Pdop was used in CE with electrochemical detection system for the simultaneous determination of four types of phenol pesticides, including2,3,5-trimethylphenol (TMP),2-chloro-4,5-dimethylphenol (CDMP), dichlorophene (DCP) and hexachlorophene (HCP). Compared with the bare carbon electrode, the MWCNTs-COOH@Pdop modified electrode greatly improved the sensitivity at a relatively positive detection potential due to its excellent electrocatalytic activities, high conductivity, and large effective surface area. The effects of several important factors were investigated. Under the optimum condition, TMP, CDMP, DCP and HCP could be separated in10mmol/L Na2CO3-NaHCO3buffer (pH9.7) within480s. The detection limits of them were4.6μg/L、2.7μg/L、9.2μg/L and69.2μg/L (S/N=3), respectively. And this method was applied directly for the determination of TMP, CDMP, DCP and HCP in fruits and vegetables samples with satisfactory results.Chapter4. Electrochemical determination of melamine based on FDU-15-Pt/PDDA/GCE in MilkA novel and simple electrochemical method for determination of melamine was developed based on the composite films of FDU-15-Pt/PDD A modified glassy carbon electrode (GCE). Results of cyclic voltammetries (CV), differential pulse voltammetries (DPV), electrochemical impedance spectrometry (EIS) and transmission electron microscopy (TEM) proved that melamine might interact with FDU-15-Pt mainly through electrostatic and hydrogen-bonding interactions. The electrochemical probe of [Fe(CN)6]3-/4-was used to investigate the interactions between FDU-15-Pt and melamine. The reduction of redox peak currents of [Fe(CN)6]3-4-were linear with the concentration of melamine in the range of5.0×10-9-1.4×10-7mol/L with a linear coefficiency of0.991. The detection limit was1.7×10-9mol/L. This proposed procedure has been successfully used for the determination of melamine in milk products.