| With the development of science and technology, analytical methods are required for the determination of trace elements in geological, biological and environmental samples. Flame atomic absorption spectrometry (FAAS) has been widely used for the determination of trace metal ions because of the relatively simple and inexpensive equipment required. However, direct determination of metal ions at trace levels by FAAS is limited not only due to insufficient sensitivity, but also to matrix interference. Under these circumstances, in order to determine trace levels of metal ions, a separation and enrichment step prior to their determinations may be beneficial.Ultrasound-assisted dispersive liquid-liquid microextraction (USADLLME) is a novel liquid-phase microextraction technique which is based on the distribution of the analytes between microliters volume of the extraction solvent and the aqueous sample matrix. The advantages of USADLLME method are environmental friendliness, simplicity of operation, rapidity, low-cost, high-recovery and high enrichment factor.In the first part of this thesis, the progress of the analytical methods for metal elements and sample pre-treatment technologies are summarized. A detailed review concerning the procedure and theory of USADLLME is presented.In the second part, a novel method for the extraction and preconcentration of trace zinc from water samples by USADLLME coupled with FAAS was developed. In the proposed approach, 1-(2-pyridylazo)-2-naphthol (PAN) was used as chelating agent and carbon tetrachloride was selected as extraction solvent. Some effective parameters on the microextraction and the complex formation were selected and optimized. These parameters included extraction solvent type, extraction time, extraction temperature, pH and the amount of the chelating agent. Under optimum conditions, an enrichment factor of 12.5 was obtained from only 5.0 mL of water sample. The calibration graph was linear in the range of 10.0～450.0μg/L with a detection limit of 0.95μg/L. The relative standard deviation (RSD) for eleven replicate measurements of 300μg/L of zinc were 3.55%. The method was applied to the analysis of tap, river, and sea water samples and good spiked recoveries over the range of 92.4～101.5% were obtained. In the third part, a novel method for the extraction and preconcentration of trace copper from water samples by USADLLME coupled with FAAS was developed. In the proposed approach, PAN was used as chelating agent and carbon tetrachloride was selected as extraction solvent. Some effective parameters on the microextraction and the complex formation were selected and optimized. These parameters included extraction solvent type, extraction time, extraction temperature, pH and the amount of the chelating agent. Under optimum conditions, an enrichment factor of 14.3 was obtained from only 6.0 mL of water sample. The calibration graph was linear in the range of 10.0～500.0μg/L with a detection limit of 0.85μg/L. The relative standard deviation (RSD) for eleven replicate measurements of 20 and 400μg/L of copper were 3.71 and 3.20%. The method was applied to the analysis of tap, river, and sea water samples and good spiked recoveries over the range of 90.4～100.5% were obtained.In the fourth part, a simple and rapid USADLLME coupled with FAAS was developed for the extraction and analysis of trace cobalt from water samples. In the proposed approach, ammonium pyrrolidine dithiocarbamate (APDC) was used as chelating agent and carbon tetrachloride was selected as extraction solvent. Some effective parameters on the microextraction and the complex formation were selected and optimized. Under optimum conditions, an enrichment factor of 14.2 was obtained from only 5.0 mL of water sample. The calibration graph was linear in the range of 8～500μg/L, with a detection limit of 0.76μg/L. The relative standard deviation (RSD) for eleven replicate measurements of 20 and 500μg/L of cobalt were 3.30 and 2.21%. This proposed method was successfully applied to tap water, river water, and sea water, and accuracy was assessed through the analysis of certified reference water or recovery experiments.In the fifth part, a new method was developed for the determination of trace cadmium from water samples by USADLLME coupled with FAAS. In the proposed approach, sodium diethyldithiocarbamate trihydrate solution (DDTC) was used as chelating agent and carbon tetrachloride was selected as extraction solvent. Some experimental parameters that influence the extraction efficiency were studied and optimized to obtain the best extraction results. Under optimum conditions, an enrichment factor of 15.3 was obtained from only 5.0 mL of water sample. The calibration graph was linear in the range of 10～600μg/L with a detection limit of 0.91μg/L. The relative standard deviation (RSD) for eleven replicate measurements of 50 and 500μg/L of cadmium were 2.56 and 1.62%. This proposed method was successfully applied in the analysis of four real environmental water samples and good spiked recoveries over the range of 96.5～101.7% were obtained.In the sixth part, a simple and rapid USADLLME technique was successfully applied for the extraction and preconcentration of trace lead from water samples, prior to FAAS. In the proposed approach, dithizone was used as chelating agent, carbon tetrachloride was selected as extraction solvent. Some effective parameters on the microextraction and the complex formation were selected and optimized. Under optimum conditions, an enrichment factor of 14.5 was obtained from only 7.0 mL of water sample. The calibration graph was linear in the range of 10～600μg/L with a detection limit of 1.14μg/L. The relative standard deviation (RSD) for eleven replicate measurements of 20 and 600μg/L of lead were 3.23 and 2.56%. This proposed method was successfully applied to tap water, river water and sea water, and accuracy was assessed through the analysis of certified reference water or recovery experiments. Operation simplicity, low cost, high enrichment factor, and low consumption of the extraction solvent are the main advantages of the proposed method.
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