| Capillary electrophoresis (CE) has been recognized as a highly attractive separation technique due to its high separation efficiency, short analysis time, small sample requirements and low operation cost. However, the main drawback of CE is the poor concentration sensitivity due to the small injection volumes and a short optical path length in the most commonly used UV detection. One solution to the problem is to apply off-line and/ or on-line sample concentration methods. The on-line concentration techniques have advantages of simplicity and economy because of no requirements of modification in CE instrumentation. Some on-line concentration techniques such as sweeping, anion or cation selective exhaustive injection-sweeping, large volume sample stacking, field-enhanced sample stacking, acid or base pH-mediated stacking dynamic pH junction-sweeping, micelle to solvent stacking and analyte focusing by micelle collapse have enjoyed much success to the analysis of many types of samples. This thesis is mainly concerned with the following aspects:1. A rapid, sensitive method for the multiresidue analysis of five commonly used triazine herbicides in environment waters was developed using dispersive liquid–liquid microextraction (DLLME) coupled with on-line sweeping in micellar electrokinetic chromatography (MEKC). Parameters that affect the extraction and sweeping efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time, salt addition, the pH in water sample, the pH and concentration of separation buffer were investigated and optimized. Under the optimum conditions, the enrichment factors were achieved in the range of 17540 to 28800. The linearity of the method was obtained in the range of 0.15~20 ng/mL with the correlation coefficients (r2) ranging from 0.9994 to 0.9997. The limits of detection were 0.05~0.1 ng/mL. The intraday relative standard deviations (RSDs) varied from 1.5 % to 5.1 % (n=5) and interday from 2.9% to 5.6% (n =15). The relative recoveries of the five herbicides in water samples at spiking levels of 0.5 ng/mL and 15 ng/mL were 94.9%~112.0% and 80.7%~100.6%. The proposed method has been successfully applied to the analysis of target herbicide residues in water samples with satisfactory results.2. A novel method was developed by using dispersive liquid–liquid microextraction (DLLME) coupled with sweeping-MEKC for the multiresidue analysis of chloronicotinyl insecticide thiacloprid (TCL),acetamiprid (ACT), imidaclothiz(ICZ) and imidacloprid (ICL) in cucumbers. Parameters that affect the extraction and sweeping efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time and salt addition, sample matrix and organic modifiers concentration in separation buffer were investigated and optimized. Under the optimum conditions, the enrichment factors were achieved in the range of 4320~9957 (EFA). The linearity of the method for thiacloprid, acetamiprid, and imidacloprid was in the range of 4.0- 200 ng/g in cucumber samples, and for imidaclothiz ranged from 5.0 to 200 ng/g, with the correlation coefficients (r) ranging from 0.9961 to 0.9984, respectively. The limits of detection (LODs, S/N=3) ranged from 0.7 to 1.2 ng/g. The intraday relative standard deviations (RSDs) varied from 3.8% to 4.4% (n=5) and interday from 6.5% to 8.5% (n =15). The recoveries in cucumbers at spiking levels of 10 ng/g and 100 ng/g were ranging from 83.0 to 98.6% with the RSDs lower than 6.3%. The proposed method has been successfully applied to the analysis of target chloronicotinyl insecticide residues in cucumber samples with satisfactory results.3. The determination of strychnine and brucine in traditional Chinese medicine preparation was established by micelle to solvent stacking in capillary zone electrophoresis. The optimal condition of the running buffer solution was 30 mmol/L phosphates containing 20% acetonitrile at pH 4.00. The sample matrix was 8 mmol/L phosphate and 5 mmol/L SDS pH 3.00. The samples were injected with pressure at 0.5 psi for 150 s. The applied voltage was 20 kV and the wavelength of the detection was 205 nm.The method had good linearity and reproducibility in the range of strychnine and brucine, the correlation coefficients (r) were 0.9984~0.9976. The relative recoveries of strychnine and brucine in Traditional Chinese medicine were 94.1%~114.4%. In this condition, strychnine and brucine can be well separated from the other components. The method is convenient, rapid, accurate and reliable, and can be used to control the quality of effective components in Traditional Chinese medicine.4. A novel method for the determination of oxymatrin and matrin in Sophora flavescens Ait. and Chinese medicine preparation by analyte focusing by micelle collapse in micellar electrokinetic chromatography. The optimal condition of the running buffer solution was 20 mmol/L sodium borate, 30 mmol /L SDS and 25% methanol at pH 9.50. The sample matrix was 30 mmol/L sodium borate and 6 mmol/L SDS. The samples were injected with pressure at 0.5 psi for 120s. The applied voltage was 20 kV and the wavelength of the detection was 205 nm.The calibration curve was linear over a range of 0.5~10μg/mL for oxymatrin and matrin, with correlation coefficients of 0.992and 0.993, respectively. The detection limits (S/N = 3:1)for oxymatrin and matrin were 0.10 and 0.20μg/ml, respectively. The relative recoveries of oxymatrin and matrin in Traditional Chinese medicine and Sophora flavescens Ait. were 94.1%~114.4%. |
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