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

Capillary electrophoresis (CE) is a combination of classical electrophoresis technology and modern microcolumn technology. Recently, CE has been widely used in different fields, such as life science, agriculture, food, clinical medicine and chemistry. It has exhibited 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. CE can couple with various detectors (UV, MS, ED, LIF, etc). The high sensitivity and selectivity of its detector allow CE to meet the analysis of pollutants, especially for the trace level detection or complex environmental matrix. Therefore, CE has great potential in the application of environmental analysis.At present, environmental problems are one of the world's hot spots, the problems including atmospheric pollution, ozone depletion, global warming, land degradation and desertification, loss of forests and loss of biodiversity, toxic chemicals and hazardous rubbish, which are directly or indirectly related with the chemical substances. Environmental pollution has many potential hazards for human health. To evaluate the environmental pollution fast and accurately, it is important to find or establish effective methods for the qualitative and quantitative analysis of environmental pollutants. In this dissertation, we laid our emphasis on the research of analysis methods of environmental pollutants and established methods to determine aromatic amines, carbamate pesticides and thyroid hormone by using CZE-AD. Moreover, the chemically modified electrode technique was utilized in CZE-AD to improve the sensitivity of detection.The dissertation includes four chapters:Chapter 1. IntroductionIn this chapter, the principle, development and applications of capillary electrophoresis were outlined. The environmental pollution and the analysis technologies for pollutants were introduced, and the applications of capillary electrophoresis in environmental analysis were highlighted.. Chapter 2. Determination of aromatic amines in water samples by capillary electrophoresis with amperometric detectionAromatic amines such as aniline and its derivatives are an important class of environmental pollutants. A method based on capillary zone electrophoresis with amperometic detection (CZE-AD) at carbon disk electrode was developed for the determination of aromatic amines in water samples. The effects of working potential, pH and concentration of running buffer, separation voltage and injection time were investigated. Under the optimum condition,2,3-diaminoaphthalene, aniline, o-phenylenediamine and p-chloroaniline could be well separated in 0.16 mol/L Na2HPO4-citric acid buffer (pH 4.6) within 23 min. The detection limits of them were 1.0×10-7 mol/L,3.3×10-8 mol/L,5.0×10-8 mol/L and 1.3×10-7 mol/L (S/N=3), respectively. The method can be applied directly for the determination of aromatic amines in real water samples with satisfactory results.Chapter 3. Simutaneous determination of carbamate pesticides in agricultural products using capillary electrophoresis-amperometric detection on a platinum nanoparticles modified electrodeIn this paper, a platinum nanoparticles modified carbon disk electrode was firstly used in capillary zone electrophoresis with amperometric detection (CZE-AD) for the determination of three carbamate pesticides:2,3,5-Trimethacarb, (3, 4-dimethylphenyl) N-methylcarbamate (Xylycarb) and (3,5-Dimethylphenyl) N-methylcarbamate (XMC) in agricultural products. The method was based on alkaline hydrolysis of the three carbamate pesticides, and the hydrolysis products (phenols) could be detected by amperometry after capillary electrophoretic separation. Parameters that affect the separation efficiency and the sensitivity of the method were studied and optimized. The analytical performances and possible applications were also investigated. The three pesticides could be well separated and determined within 5 min, and the detection limits were in the range of 2.2×10-8,2.8×10-8 and 2.2×10-8 mol/L, respectively. Relative standard deviations for the studied compounds varied from 2.22% to 3.37%(n=7). The proposed method was successfully applied to the analysis of target carbamate pesticides residues in agricultural products with satisfactory results.Chapter 4. Development of a capillary electrophoresis-amperometric detection method for the determination of thyroxine and triiodothyronine and its applicationA simple, reliable and repeatable method, based on capillary electrophoresis (CE) with amperometric detection (AD) has been developed for the simultaneous separation and determination of thyroxine (T4) and 3,3',5-triiodothyronine (T3). A carbon disk electrode was used as working electrode in this system and exhibited a good response at 1.05 V (vs. Hg/Hg2Cl2,3 mol/L KCl) for two analytes. The CE separations were investigated in detail. At 21 kV of applied voltage, the two compounds were separated within 11 min in 0.05 mol/L Na2B4O7-NaOH buffer (pH 11.3). And the detection limits were as low as 1.0×10-7 mol/L for T4 and 8.5×10-8 mol/L for T3 (S/N=3), respectively. The proposed method has been applied to analyze T4 and T3 in pharmaceutical formulations, and the results were satisfactory.