| The pollutions caused by toxic heavy metals in the environment and biological matrices are the most pressing problems endangering human health. Most of the previous studies have been limited only to the determination of the total concentration of heavy metals. But toxicological studies have shown that speciation of heavy metals is necessary for risk assessment purposes since their potential toxicity, bioavailability and transformations depends not only the quantity involved, but more importantly, also on the chemical forms of the heavy metals. Against this background, the development of techniques for the speciation of heavy metals and for predicting toxicity of these pollutants in environmental and biological samples is of more important significance.However the common availability of the instrumentation and the advantages of rapid still make flame atomic absorption spectrometry(FAAS) method an attractive alternative. But its sensitivity is not usually sufficient for the speciation of metal ions at trace level in samples. As a result, preliminary species separation and preconcentration is required prior to their determination by FAAS. Cloud point extraction (CPE) is a kind of new environmentally benign liquid-liquid extraction method. It is widely used in the separation and speciation of trace metal ions due to the predominance of high extraction efficiency and preconcentration factors, conveniention, safety, lower toxicity to the environment.The aim of this dissertation is to develop a new method for the separation/preconcentration and speciation of Cr, Cu by flame atomic absorption spectrometry after cloud point extraction and its application to environmental water and soil samples. The major contents are described as follows:1 Study on speciation of chromium in environmental water samples by cloud point extraction-flame atomic absorption spectrometryA new method has been proposed for speciation of chromium in environmental water samples by flame atomic absorption spectrometry after cloud point extraction with l-(2-pyridylazo)-2-naphthol(PAN) as the chelating agent and OP as the cloud point extractant. In this method, Cr(Ⅲ) reacts with PAN yielding a hydrophobic complex at pH=7.7, which then is entrapped in the surfactant-rich phase, whereas Cr(Ⅵ) remained in aqueous phase. Thus, separation of Cr(Ⅲ) and Cr(Ⅵ) could be realized. The effects of experimental conditions were discussed. Under the optimum conditions, the detection limit for Cr(Ⅲ) was 5.74 ng·mL-1 with an enrichment factor of 20, and the relative standard deviation (RSD) was 2.9%. The proposed method has been applied to the determination of Cr(Ⅲ) and Cr(Ⅵ) in environmental water samples of Zhengzhou with satisfactory results. The recoveries of the procedure ranged from 90.3% to 108.7%. The advantages of the analytical method were simple, sensitive, highly efficient, reproducible and low toxicity to the environment.2 Speciation of trace Cr(Ⅵ) in soil samples by cloud point extraction-flame atomic absorption spectrometry after alkaline extractionReference to the alkaline extraction method of US EPA 3060A, it was experimentally proven that the extraction efficiency of 0.1 mol·L-1 Na2CO3 is effective in leaching of all forms of hexavalent chromium (Cr(Ⅵ)) in soil samples by comparing with several other alkaline extractants. Due to the typically low concentration levels of Cr(Ⅵ) in soils and the complexity of soil matrix components, a novel method has been developed for thepreconcentration and speciation of Cr(Ⅵ) in soil samples by flame atomic absorption spectrometry (FAAS) after cloud point extraction(CPE), with ammonium pyrrolidine dithiocarbamate (APDC) as the chelating agent and OP as the cloud point extractant. The conditions of CPE were studied. Under the optimized conditions, the preconcentration system permitted an enrichment factor of 25, detection limit of 5.31 ng·mL-1 and the relative standard deviation (RSD) of 2.3%. The procedure affords recoveries of 88%-93%. The proposed procedure has been applied to the preconcentration and speciation of Cr(Ⅵ) in soil samples of Zhengzhou suburbs with satisfactory results. And the results of this study clearly show that the concentration of Cr(Ⅵ) in soil samples of Zhengzhou suburbs is low.3 Determination of available copper in soil samples by flame atomic absorption spectrometry after cloud point extraction The available heavy meatals in soils are more dangerous to human than the other forms. A novel method has been developed for the determination of available copper in soil samples by flame atomic absorption spectrometry (FAAS) after cloud point extraction (CPE), with ammonium pyrrolidine dithiocarbamate (APDC) as the chelating agent and OP as the cloud point extractant. The conditions of CPE were studied. Under the optimum conditions, the detection limit was 4.17 ng·mL-1 with an enrichment factor of 20, and the relative standard deviation (RSD) was 1.0%. The proposed method has been applied to the determination of available copper in soil samples of Zhengzhou with satisfactory results, and the procedure affords recoveries of 89.3%-96.2%. Also it has provided a theoretical basis to regulate the classification method of the chemical forms of heavy metals in soils and explore their standard analytical methods. |
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