| Sample preparation is one of the most important and crucial steps in the whole analytical process. It is often the bottleneck for rapidly obtaining the desired results, especially for the determination of trace analytes in complex matrix samples. The objective of the sample preparation is not only to isolate the target analytes from the samples, thus reducing or even eliminating the interferences originally present in the sample, but also simultaneously to concentrate the analytes to facilitate their determinations at low levels. Since conventional extraction techniques, such as liquid liquid extraction and solid phase extraction, are laborious, time-consuming and need large volumes of samples and toxic organic solvents, much attention is being paid to the development of miniaturized, more efficient and environment-friendly extraction techniques that could greatly reduce the solvent consuming. For this purpose, the liquid-phase microextraction (LPME) procedure, which is based on the distribution of the analytes between a microvolume of organic solvent and the aqueous solution, has emerged as an attractive alternative for the sample preparation because of its simplicity, effectiveness, low cost, minimum use of organic solvents。In the dissertation, several analytical methods were developed for the sensitive determination of some pesticide residues in environmental samples including water, soil and vegetable samples by liquid-phase microextraction technique coupled with high performance liquid chromatography (HPLC). This dissertation is mainly concerned with the following aspects:(1) Water pollution is becoming a global environmental problem due to the wide use of pesticides in agriculture. Therefore, monitoring pesticides in waters is important for human health protection and environmental control. A rapid and sensitive method was established for the determination of four carbamate pesticides (carbofuran, carbaryl, pirimicarb and diethofencarb) in water samples using dispersive liquid-liquid microextraction (DLLME) coupled with high performance liquid chromatography-diode array detection. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time and salt addition, were investigated and optimized. Under the optimum conditions, the enrichment factors were in the range between 101 ~ 145. The linearity of the method was obtained in the range of 5 ~ 500 ng/mL with the correlation coefficients (r) ranging from 0.9978 to 0.9997. The limits of detection of the method were 0.4-1.0 ng/mL. The relative standard deviations (RSDs) varied from 4.7% to 6.5% (n = 5). The relative recoveries of the four carbamates from water samples at spiking levels of 5.0 ng/mL and 20.0 ng/mL were 76.0% ~ 92.0% and 82.5% ~ 94.0%, respectively. The method has been successfully applied to the analysis of target carbamate residues in river, rain, well and tap water samples with satisfactory results.(2) A rapid and sensitive method for the determination of carbendazim (MBC) and thiabendazole (TBZ) in water and soil samples was developed by using dispersive liquid-liquid microextraction coupled with high performance liquid chromatography with fluorescence detection. In the extraction method, a mixture of extraction solvent (80μL CHCl3) and dispersive solvent (0.75 mL tetrahydron furan) was rapidly injected into the 5.0 mL sample solution (water sample or soil extract) using syringe and the analytes in the sample were extracted into the fine droplets of the CHCl3. The extraction phase was then separated by centrifugation. The resultant sedimented phase was blown to dryness with a mild nitrogen stream. The residue was reconstituted in 15.0μL methanol and 10.0μL was injected into the HPLC system for analysis. Some important experimental parameters, such as the kind and volume of extraction and disperser solvent, extraction time and salt effect were investigated and optimized. Under the optimum conditions, the enrichment factors and extraction recoveries were ranged between 149 ~ 210 and 50.8% ~ 70.9%, respectively. The linearity of the method was obtained in the range of 5 ~ 800 ng/mL for water sample analysis, and 10 ~ 1000 ng/g for soil samples, respectively. The correlation coefficients (r) ranged from 0.9987 to 0.9997. The limits of detection of the method were 0.5 ~ 1.0 ng/mL for water samples, and 1.0 ~ 1.6 ng/g for soil samples. The relative standard deviations varied from 3.5% to 6.8% (n = 5). The recoveries of the method for MBC and TBZ from water samples at spiking levels of 5 ng/mL and 20 ng/mL were 84.0% ~ 94.0% and 86.0% ~ 92.5%, respectively. The recoveries of the method for soil samples at spiking levels of 10 ng/g and 100 ng/g varied between 82.0% and 93.4%. The proposed method has been successfully applied to the analysis of the target fungicide residues in real water and soil samples.(3) A new method for the determination of four sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron, bensulfuron-methyl and chlorimuron-ethyl) in water samples was developed by dispersive liquid-liquid microextraction coupled with high performance liquid chromatography-diode array detector. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction and dispersive solvent, extraction time and salt addition, were investigated and optimized. Under the optimum conditions, the enrichment factors were in the range between 102 and 216. The linearity of the method was obtained in the range of 1.0 ~ 100 ng/mL with the correlation coefficients (r) ranging from 0.9982 to 0.9995. The limits of detection were 0.2 ~ 0.3 ng/mL. The proposed method has been successfully applied to the analysis of target sulfonylurea herbicides in river, stream and well water samples with satisfactory results.(4) Dispersive solid-phase extraction (DSPE) combined with dispersive liquid-liquid microextraction was developed as a new approach for the extraction of sulfonylurea herbicides in soil prior to high performance liquid chromatography diode array detection. In the DSPE-DLLME, sulfonylurea herbicides were first extracted from soil sample into acetone-0.15 mol/L NaHCO3 (2:8, v/v). The clean-up of the extract by DSPE was carried out by directly adding C18 sorbent into the extract solution, followed by shaking and filtration. After the pH of the filtrate was adjusted to 2.0 with 2 mol/L HCl, 60.0μL chlorobenzene (as extraction solvent) was added into 5.0 mL of it for DLLME procedure (the acetone contained in the solution also acted as dispersive solvent). Under the optimum conditions, the enrichment factors for the compounds were in the range between 102 and 216. The linearity of the method was in the range from 5.0 to 200 ng/g with the correlation coefficients (r) ranging from 0.9967 to 0.9987. The limits of detection were 0.5 ~ 1.2 ng/g. The relative standard deviations varied from 5.2% to 7.2% (n = 5). The relative recoveries of the four sulfonylurea herbicides from soil samples at spiking levels of 6.0, 20.0 and 60.0 ng/g were in the range between 76.3% and 92.5%. The proposed method has been successfully applied to the analysis of target sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron, bensulfuron-methyl and chlorimuron-ethyl) in soil samples, and a satisfactory result was obtained.(5) Dispersive solid-phase extraction clean-up combined with dispersive liquid-liquid microextraction was developed as a new approach for the extraction of neonicotinoid insecticides in vegetable samples prior to high performance liquid chromatography with diode array detection. In the DSPE-DLLME method, neonicotinoid insecticides were first extracted with acetonitrile from vegetable samples, followed by clean-up by a dispersive solid-phase extraction with primary secondary amine (PSA) and multi-walled carbonnanotubes (MWCNTs) as sorbents. A 2.5 mL aliquot of the resulting extract was then added into a centrifuge tube containing 10 mL water, 0.8 g NaCl and 200μL chloroform (as the extraction solvent) for DLLME procedure. Under the optimum conditions, the enrichment factors for the compounds were in the range between 110 and 243. The linearity of the method was in the range from 5.0 to 300 ng/g with the correlation coefficients (r) ranging from 0.9989 to 0.9998. The limits of detection of the method were 0.5 ~ 1.0 ng/g. The repeatability of the method expressed as the relative standard deviations by five parallel experiments at the concentration levels of 10 ng/g and 50 ng/g each of the neonicotinoid insecticides in tomato or cucumber samples varied from 3.6% to 5.8%. The developed method has been successfully applied for the analysis of target neonicotinoid insecticides (acetamiprid, imidacloprid, thiacloprid and thiamethoxam) in tomato and cucumber samples. The recoveries of the method for the target neonicotinoid insecticides from the vegetable samples at spiking levels of 10.0 and 50.0 ng/g were in the range between 84.6% and 97.5% (n = 5).(6) A simple and low-cost sample preparation method, ultrasound-assisted emulsification microextraction (USAEME), was applied to soil samples for the determination of five triazine herbicides by high performance liquid chromatography with diode-array detection. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, ultrasound emulsification time and salt addition, were investigated and optimized for the method. Under the optimum conditions, the enrichment factors were in the range between 148 and 225. The limits of detection of the method were 0.1 ~ 0.5 ng/g. The linearity of the method was obtained in the range of 5.0 ~ 200.0 ng/g for simazine, 1.0 ~ 200.0 ng/g for atrazine, prometon, ametryn and prometryn, with the correlation coefficients (r) ranging from 0.9991 to 0.9998. The relative standard deviations varied from 2.8% to 3.6% (n = 5). The recoveries of the method for the five triazines from soil samples at spiking levels of 5.0 and 50.0 ng/g were ranged from 82.6% to 92.0%. The proposed USAEME technique has demonstrated to be simple, practical, rapid and environmentally friendly for the determination of triazines residues in soil samples.(7) A novel ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) coupled with high performance liquid chromatography-diode array detection was developed for the extraction and determination of six carbamate pesticides (metolcarb, carbofuran, carbaryl, pirimicarb, isoprocarb and diethofencarb) in water samples. In the UASEME technique, Tween 20 was used as emulsifier, and chlorobenzene and chloroform were used as dual extraction solvent without using any organic dispersive solvent that is normally required in the previously described common dispersive liquid-liquid microextraction method. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, ultrasound emulsification time and salt addition, were investigated and optimized for the method. Under the optimum conditions, the enrichment factors were in the range between 170 and 246. The limits of detection of the method were 0.1 ~ 0.3 ng/mL and the limits of quantification were between 0.3 and 0.9 ng/mL, depending on the compounds. The linearity of the method was obtained in the range of 0.3 ~ 200 ng/mL for metolcarb, carbaryl, pirimicarb, and diethofencarb, 0.6 ~ 200 ng/mL for carbofuran, and 0.9 ~ 200 ng/mL for isoprocarb, with the correlation coefficients (r) ranging from 0.9982 to 0.9998. The relative standard deviations varied from 3.2% to 4.8% (n = 5). The recoveries of the method for the six carbamates from water samples at spiking levels of 1.0, 10.0, 50.0 and 100.0 ng/mL were ranged from 81.0% to 97.5%. The proposed UASEME technique has demonstrated to be simple, practical and environmentally friendly for the determination of carbamates residues in river, reservoir and well water samples.(8) A simple, rapid and environmentally friendly method was developed for the determination of four triazole fungicides (myclobutanil, tebuconazole, triadimenol, hexaconazole) in water samples by dispersion-solidification liquid-liquid microextraction coupled with high performance liquid chromatography-diode array detection. Several variables that affect the extraction efficiencies, including the type and volume of the extraction solvent and disperser solvent, extraction time, effect of pH 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, with the correlation coefficients (r) varying from 0.9992 to 0.9998. High enrichment factors were achieved ranging from 190 to 450. The recoveries of the target analytes from water samples at spiking levels of 1.0, 5.0 and 50.0 ng/mL were between 84.8% and 110.2%. The limits of detection (LODs) for the analytes were ranged in 0.06 ~ 0.1 ng/mL, and the relative standard deviations varied from 3.9% to 5.7%. The proposed method has been successfully applied for the determination of the triazole fungicides in real water samples.
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