Study Of Chemically Modified Electrodes And Their Application In Determining Trace Elements

The environment problem has become the focus in the world. In the environment contamination, metal ions now are one of the most serious contaminated substances. Metal ions have been noticed by Ecology because they have a serious effect on metabolism and growth of plants with their increasing in the environment. At the same time, it is very difficult to remove them when they come into the environment. Furthermore, it leads to serious pollution for the soil with the transferring of metal ions in water. There is no biology separation in nature by itself, so with the accumulation of metal ions, the result is so bad that they make much harm to the animals and plants. The society has given its attention to the danger begot by the metal ions so that the determination technologies of them have been developed gradually. Now chemically modified electrodes continue to be a field of exciting research. This idea is to transfer the known chemical or electron transfer reactivity of the attached molecular species to the interface region. In this paper, sensitive voltammetric methods were developed for the determination of metal ions using chemically modified carbon paste electrode. This thesis includes the following researches:A calix[6]arene modified carbon paste electrode (CAL-CPE) is described for the simultaneous measurement of Pb2+ and Cd2+. As the modifier, calix[6]arene can accumulate Pb2+ and Cd2+ from aqueous solution to the electrode surface via forming complexes with them. Advantages of the new procedure are simultaneous determination of Pb2+ and Cd2+, compared with a bare carbon paste electrode, the calix[6]arene modified CPE greatly improves the sensitivity of determining lead and cadmium. The modified carbon paste electrode was successfully applied to determine trace levels of lead and cadmium in water samples. The results obtained were compared with that by atomic absorption spectrometry and the comparison suggests that the calix[6]arene modified CPE has great potential for the practical sample analysis.According to the electron transfer mechanism of Europium(III), amontmorillonite chemically modified carbon paste electrode was used for the determination of Eu(III), and investigated the electrochemical and surface properties of Eu(III) on the modified electrode. This chemically modified electrode exhibits strong and stable electroactivity towards Eu(III) because the interlamellar region within the montmorillonite provides a confined reaction space which is most likely to promote selective chemical reactions. The recommended method has been applied to the quantitation of Eu(III) in stream sediment samples, the results obtained by the SWV approach are in good agreement with reference values.A gold-plated acetylene paste electrode can be used for the determination of As(III). The investigations performed included the choice of supporting electrolyte composition, the optimization of important experimental parameters, and some tests of practical applications of the method, including the interference studies. The analytical performance of the method has been tested in recovery measurements with tea samples.