| Sample preparation prior to the chromatographic analysis is one of the most important and crucial steps in the whole analytical procedure to obtain accurate and sensitive results. The primary objective of the sample preparation is to clean up and concentrate the analytes of interest, thus reducing or even eliminating the interferences originally present in the samples to determine the target analytes at low levels. Recently, much attention is being paid to the development of miniaturized, more efficient, and environmentally friendly extraction techniques which could greatly reduce the organic solvent consumptions. For this purpose, several different types of liquid-phase microextraction (LPME) techniques have emerged for sample preparations. LPMEs have advantages of simplicity, rapidity, effectiveness, low cost, and minimum use of solvents.In the work, on the basis of ultrasound-assisted emulsification microextraction (USAEME), ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) and dispersive liquid-liquid microextraction based on solidification of ?oating organic droplet (DLLME-SFO) in combination with high performance liquid chromatography (HPLC), several analytical methods were developed for the determination of some pesticides in environmental water, milk and agricultural samples. This thesis is mainly concerned with the following aspects:1. An ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) was developed as a new approach for the extraction of seven organophosphorus pesticides (Ops) in water samples prior to high performance liquid chromatography with diode array detection (HPLC-DAD). The use of a surfactant as an emulsifier in the UASEME method could enhance the dispersion of water-immiscible extraction solvent into aqueous phase and is favorable for the mass-transfer of the analytes from aqueous phase to the organic phase. Several variables that affect the extraction efficiency, including the kind and volume of the extraction solvent, the type and concentration of the surfactant, salt addition, ultrasound emulsification time and temperature, were investigated and optimized. Under the optimum experimental conditions, the calibration curve was linear in the concentration range from 1 to 200 ng/mL for the seven Ops (isocarbophos, phosmet, parathion, parathion-methyl, fenitrothion, fonofos and phoxim), with the correlation coefficients (r) varying from 0.9973 to 0.9998. High enrichment factors were achieved ranging from 210 to 242. The established UASEME-HPLC-DAD method has been successfully applied for the determination of the Ops in real water samples. The limits of detection were in the range between 0.1 and 0.3 ng/mL. The recoveries of the target analytes over the three spiked concentration levels of the compounds (10, 50, and 100 ng/mL, respectively) in rain, reservoir and well water samples were between 83% and 106% with the relative standard deviations varying from 3.3% to 5.6%. The method was shown to be simple, efficient and sensitive, and was suitable for the determination of these compounds in water samples.2. A novel, simple, rapid, efficient, and environmentally friendly method for the determination of five triazine herbicides in water samples was developed by ultrasound-assisted emulsification microextraction (USAEME) coupled with high performance liquid chromatography-diode array detection (HPLC-DAD). Parameters that affect the extraction efficiencies, such as the kind and volume of the extraction solvent, ultrasound emulsification time and salt addition, were investigated and optimized. Under the optimum conditions, the proposed method is sensitive and shows a good linearity within a range of 0.5~200 ng/mL for simazine, atrazine, prometon, ametryn and prometryn, with the correlation coefficients (r) varying from 0.9993 to 0.9998. High enrichment factors were obtained ranging from 148 to 225. The limits of detection (LODs) were in the range between 0.06 and 0.1 ng/mL. The recoveries of the target analytes from water samples at spiking levels of 5.0 and 50.0 ng/mL were ranged from 82.4% to 107.0%. The relative standard deviations (RSD) varied from 3.0% to 4.6%. The results demonstrated that USAEME-HPLC-DAD was an efficient pretreatment and enrichment procedure for the determination of triazine pesticides in real water samples.3. A novel simple, rapid, efficient and environmentally friendly method, dispersive liquid–liquid microextraction based on solidification of ?oating organic droplet (DLLME-SFO) coupled with high performance liquid chromatography-diode array detection (HPLC-DAD), was developed for the determination of five organophosphorus pesticides (Ops) in water samples. In this method, the extraction solvent is of low density, low toxicity and proper melting point around room temperature, and the extractant droplet can be readily solidified in the lower temperature and carried out from the aqueous sample. A series of parameters that affect the extraction efficiencies were investigated and optimized. Under the optimum conditions for the method, the calibration curve was linear in the concentration range from 1 to 200 ng/mL for the five Ops, with the correlation coefficients (r) varying from 0.9991 to 0.9998. High enrichment factors were achieved ranging from 215 to 557. The limits of detection (LODs) were in the range between 0.1 and 0.3 ng/mL. The recoveries of the target analytes from water samples were 82.2%~104.0%. The relative standard deviations (RSD) varied from 4.4% to 6.3%. The proposed method has been successfully applied for the determination of organophosphorus pesticides in real water samples.4. A dispersive liquid–liquid microextraction based on solidification of ?oating organic droplet (DLLME-SFO) has been developed as a new approach for the extraction of trace copper in water and beverage samples followed by the determination with flame atomic absorption spectrometry. In the DLLME-SFO, 8-hydroxy quinoline, 1-dodecanol, and methanol were used as chelating agent, extraction solvent and dispersive solvent, respectively. The experimental parameters related to the DLLME-SFO such as the type and volume of the extraction and dispersive solvent, extraction time, sample volume, the concentration of chelating agent and salt addition were investigated and optimized. Under the optimum conditions, the enrichment factor for copper was 122. The method was linear in the range from 0.5 to 300 ng/mL of copper in the samples with a correlation coefficient (r) of 0.9996 and a limit of detection of 0.1 ng/mL. The method was applied to the determination of copper in water and beverage samples. The recoveries for the spiked water and beverage samples at the copper concentration levels of 5.0 and 10.0 ng/mL were in the range between 92.0% and 108.0%. The relative standard deviations (RSD) varied from 3.0% to 5.6%.
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