| 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. Sweeping, an on-line sample concentration technique, is defined as a phenomenon where analytes are picked up and concentrated by the pseudostationary phase that penetrates the sample zone containing no pseudostationary phase in micellar electrokinetic chromatography (MEKC). In sweeping, both charged and neutral analytes can be preconcentrated, making it a versatile enrichment technique. Conventional sample preparation methods, such as liquid-liquid extarction and solid phase exrtaction, are time- and solvent- consuming and often involve several complicated procedures. In 2006, Assadi and co-workers developed a novel liquid-phase microextraction technique, named dispersive liquid-liquid microextraction (DLLME). The method is based on the use of a ternary component solvent system. The advantages of DLLME method are environmental friendliness, simplicity of operation, rapidity, low-cost, and high-recovery and high enrichment factor.In this work, on the basis of dispersive liquid–liquid microextraction (DLLME) and dispersive solid-phase extraction (DSPE) technique in combination with on-line sweeping concentration technique in micellar electrokinetic chromatography (sweeping-MEKC), several analytical methods were developed for the determination of some pesticide residues in water, soil and agricultural samples. This thesis is mainly concerned with the following aspects:1. The application of an on-line sweeping concentration technique in micellar electrokinetic chromatography was investigated for the determination of atrazine, simazine and prometryn in water samples. Various parameters affecting sample enrichment and separation efficiency were systematically studied. Compared with the conventional MEKC method, up to 60~200 fold improvement in concentration sensivity was achieved in terms of peak height by using this sweeping injection technique. The compound strychnine was used as the internal standard for the improvement of the experimental reproducibility, a good linear relationship existed in the range of 0.005~5.0, 0.05~5.0 and 0.05~5.0μg/mL of each herbcides in water samples with the correlation coefficients (r) of 0.998, 0.997 and 0.997, and the detection limits (S/N= 3:1) for atrazine, simazine and prometryn were 9, 9 and 0.5 ng/mL, respectively. This method has been successfully applied to the analysis of atrazine, simazine and prometryn in lake, steam and ground water.2. A novel method was developed by using dispersive liquid–liquid microextraction (DLLME) coupled with sweeping-MEKC for the multiresidue analysis of six commonly used carbamate pesticides (methiocarb, fenobcarb, diethofencarb, carbaryl, isoprocarb and tsumacide) in apples. 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 469~1772. The linearity of the method was obtained in the range of the limits of quantification (LOQs, S/N=10)-500 ng/g, with the correlation coefficients (r) ranging from 0.995 to 0.999. The limits of detection (LODs, S/N= 3: 1) were 2.0~3.0 ng/g and LOQs 6.0~9.0 ng/g. The intraday relative standard deviations (RSDs) varied from 3.0% to 5.6% (n=5) and interday from 5.4% to 8.3% (n =10). The recoveries of the six carbamates in apples at spiking levels of 20 ng/g and 100 ng/g were ranging from 85.4% to 113.3% with the RSDs lower than 7.4%. The proposed method has been successfully applied to the analysis of target carbamate residues in apple samples with satisfactory results.3. A rapid and sensitive method for the multiresidue analysis of sulfonylurea herbicides (chlorimuron ethyl, bensulfuron methyl, tribenuron methyl, chlorsulfuron, and metsulfuron methyl) in environment waters was developed using DLLME coupled with sweeping-MEKC. 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, and the pH and concentration of the separation buffer were investigated and optimized. Under the optimum conditions, the enrichment factors were achieved in the range of 3296~5086 (Peak Area). The linearity of the method was obtained in the range of LOQs~100.0μg/mL with the correlation coefficients (r) ranging from 0.997 to 0.999. The limits of detection were 0.2~0.5 ng/mL. The intraday relative standard deviations (RSDs) varied from 1.2 % to 5.3 % (n=5) and interday from 2.6% to 6.1% (n =15). The recoveries of the five herbicides in water samples at spiking levels of 5.0 ng/mL and 20.0 ng/mL were ranging from 78.0% to 108.0% with the RSDs below 7.2%. The proposed method has been successfully applied to the analysis of target herbicide residues in water samples.4. A novel approach, dispersive solid-phase extraction followed by dispersive liquid-liquid microextraction (DLLME), was established for extraction of five commonly used sulfonylurea herbicides in soils prior to determination by sweeping-MEKC. Parameters that affect the extraction and sweeping efficiency were investigated and optimized. The linearity of the method for chlorimuron ethyl, bensulfuron methyl was in the range of 3.3~200 ng/g, and tribenuron methyl, chlorsulfuron, and metsulfuron methyl in the range of 1.7~200 ng/g, with the correlation coefficients (r) ranging from 0.997 to 0.998. The limits of detection (LODs) ranged from 0.2 to 0.5 ng/g. The intraday relative standard deviations (RSDs, n= 5) were below 5.3 % and interday RSDs (n= 15) within 6.8%. The recoveries of the method for the five sulfonylureas from soil samples at spiking levels of 5.0, 20.0 and 100.0 ng/g were 75.2%~93.5%, respectively. The proposed method has been successfully applied to the analysis of the target sulfonylurea herbicide residues in soil samples.
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