| The accurate determination of trace heavy metals in environmental water samples has been a worldwide issue for the elucidation of interaction mechanisms between metal species and human organs. The heavy metal pollutants have attracted extensive attentions attributed to their non-biodegradability, ease of accumulation in human tissues as well as toxicity and irreversibility in environment. The contamination of heavy metals mainly exists in water, therefore, it is highly necessary to provide timely warning of the accurate information about heavy metal accumulation in environmental water samples.However, due to the low concentrations of many heavy metals and the complexity of sample matrix, there is a crucial need for the extraction and preconcentration of trace metals from sample matrix before their analysis. In this respect, an effective separation and preconcentration method is necessary for the determination of trace heavy metals in environmental water samples.Solid phase extraction (SPE) is a widely used effective sample pretreatment technique. As an environmental friendly separation/preconcentration approach, it has received increasing attention owing to several major advantages in applications, e.g., high enrichment factor, favorable selectivity, reusability, low sample and reagent consumption, speedness and ease of automation. It is still highly desirable to develop novel adsorbent materials or modify the existing materials by introducing/immobilizing appropriate functional grupos in order to achieve better performances on the extraction of target species.The present work aims at investigating novel solid phase extraction techniques based on flow injection, by developing new adsorbent materials and sample pretreatment methodologies for trace heavy metal species. In addition to use these methods for the analysis of heavy metals in environmental sample matrixes by hyphenating solid phase extraction protocols with detection by flame atomic adsorption spectrometry (FAAS). The applications of a variety of adsorbents in SPE for separation and preconcentration of trace heavy metals were systematically studied, and the related adsorption mechanisms were explored. These will be discussed separately in the following chapters:Chapter1is an overview of silica gel, modified silica gel and carbon nanotubes as well as their applications in the field of separation and preconcentration.In chapter2, a novel flow injection-solid phase oxide collection-flame atomic adsorption spectrometry was developed for the determination of trace silver in water samples using sodium hydroxide as precipitating reagent and silica beads as adsorbent. Silver was precipitated in the form of oxide and collected on the solid phase surface of a silica beads mini-column as oxide collector. The silanol groups and surface charges contribute to the adsorption of nascent Ag2O. The precipitate was afterwards quantitatively eluted by10%(v/v) nitric acid with detection by FAAS. By loading5.4mL sample solution, an enrichment factor of25.5, a detection limit (3σ) of0.6μg L-1and a sampling frequency of50h-1were achieved, along with a linear range within2-150μg L"1and a precision of2.0%RSD at the40μg L-1level (n=11). The present procedure was applied for the determination of silver by spiking recoveries in a seires of water samples, and the spiking recoveries were93.3%,89.5%,96.6%,108.4%and102.8%, respectively.Chapter3describes the immobilization of dithizone (H2Dz) on silica gel (SG) and its application on solid phase extraction of copper from complex matrix. FT-IR, SEM and EDS showed the binding of dithizone on silica surface. A flow injection solid phase extraction procedure was developed for trace copper separation and preconcentration with detection by flame atomic spectrometry. The sorption efficiency of H2Dz-SG to Cu2+was significantly increased as a result of the introduction of dithizone into silica gel. By loading5.4mL of sample solution, a liner range of0.5-120μg L-1, an enrichment factor of42.6, a detection limit of0.2μg L-1and a precision of1.7%RSD (40μg L-1, n=11) were obtained, along with a sampling frequency of47h-1. The dynamic sorption capacity of H2Dz-SG to Cu2+was0.76mg g-1. The procedure was applied for the extraction of trace copper in a series of water samples, and spiking recoveries within91.0-107.0%are achieved.Chapter4explores the on-line selective sorption of trace silver with oxidized multiwalled carbon nanotubes (MCNTs) as absorbent. A solid phase extraction procedure for silver based on FAAS detection was established. The MCNTs were then loaded onto the surface of silica gel beads, and the CNTs/SG composite was used as adsorbent for the preconcentration of trace silver in a flow injection system by binding the nascent Ag2O. With NaOH as precipitating reagent, the nascent Ag2O was readily retained on the CNTs/SG surface, and afterwards it was recovered by elution with nitric acid (10%, v/v). The quantification is facilitated by FAAS. By loading5.4mL of sample solution, an enrichment factor of34.5, a detection limit of0.35μg L"1was achieved in a linear range of1-120μg L-1. A precision of0.5%RSD (40μg L-1, n=7), a sampling frequency of47h-1were also obtained. The enrichment factor, the detection limit as well as the precision of this procedure are superior to those achieved by using either pure carbon nanotubes or pure silica gel. The procedure was applied for the determination of silver in water samples, and satisfactory spiking recoveries were obtained in the range of96%-108%.In the last chapter, MCNTs were used for the adsorption of chromium and its speciation. At pH3-6, a discrimination of Cr(III) and Cr(VI) is achieved on the MCNTs surface. The adsorbed Cr(III) is quantitatively eluted by10%(v/v) nitric acid with detection by FAAS, while Cr(VI) remains in the solution. By loading6.0mL sample solution, an enrichment factor of22, a detection limit (3σ) of1.2μg L’1and a precision of1.7%RSD (40μg L-1, n=11) were achieved for Cr(III), within a linear range of5-200μg L-1. After Cr(VI) has been reduced to Cr(III) with hydroxylamine hydrochloride, the total amount of chromium is obtained and the content of Cr(VI) is given by substraction. The present procedure was validated by analyzing chromium in a chromium component analysis of analog natural water reference material (GBW(E)080403). It was further applied for the determination of Cr(III) and Cr(VI) by spiking recoveries in a series of water samples, giving rise to spiking recoveries in the range of97.8%-111.5%for Cr(III), and95.7%-108.0%for Cr(VI). |
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