| Electrochemical method has constantly played a important role in the long road towards solving the problems created by pollution, especially the heavy metal pollution in drinking water. Heavy metals are not biodegradable and therefore they remain in ecological systems and in the food-chain indefinitely, exposing top-level predators to very high levels of pollution. Therefore, it is particularly important to develop and design a good performance sensor for the detection of heavy metals. This topic is based on the following two purposes to prepare heavy metal electrochemical sensor:(ⅰ) robust, cheap, accurate, and reliable methods that could also be used by laypeople;(ⅱ) more environmentally-friendly methods, in order to achieve real-time monitoring of heavy metal pollution.This thesis mainly consists of the following two parts:1. A sensitive, rapid and simple sensor for the detection of As(Ⅲ) has been fabricated in alkaline media based on the flower pattern MnOx/Au composite film modified electrode. The gold nanoparticles and MnOx film were co-deposited on the glass carbon electrode by using a cyclic voltammetric method. The resulting electrode surfaces were characterized with scanning electron microscopy (SEM), X-ray photoelectron spectroscopic (XPS) and electrochemical impedance spectroscopy (EIS). Linear sweep anodic stripping voltammetry (LSASV) was performed for the determination of arsenic (Ⅲ) without interference from Cu(Ⅱ) and Hg(Ⅱ). The good detection range of0.5-80μg L-1and a low LOD of0.05μg L-1(S/N=3) were obtained with a preconcentration time of200s under optimal conditions. We use alkaline media in the sensor which is diffident from many other papers. Moreover, the modified electrode exhibited excellent reproducibility and high stability. The developed method was successfully applied to determine arsenic(Ⅲ) in real water samples with satisfactory results.2. A sensitive bismuth-MWNT composite film modified electrode was fabricated by two-step electrodepositing method. A protocol used for trace measurements of total chromium and chromium(VI)(with the aid of anion trapping column) by cathodic adsorptive stripping voltammetric in the presence of N-nitroso-N-phenylhydroxylamine ammonium salt (cupferron) is proposed. The multi-walled carbon nanotubes (MWNT) were electrodeposited instead of drop coating method on the glass carbon electrode firstly; the bismuth film was deposited on the MWNT/GCE, finally, we prepared Bifilm/MWNT/GCE modified electrode. The new protocol is based on accumulation of the Cr-cupferron complex at the preplated bismuth film-MWNT electrode held at-0.35V, followed by a negatively-going square-wave voltammetric waveform. Factors influencing the stripping performance including the film preparation, solution pH, cupferron concentration, deposition potential and deposition time have been optimized. The resulting performance compares well with that observed for analogous measurements at mercury film electrodes. A detection limit of0.05ppb with a preconcentration time of120s and a relative standard deviation at5ppb of5.3%(n=75) were obtained. Applicability to river water samples is demonstrated. The total chromium can be directly determined by standard addition Cr(Ⅲ) or Cr(Ⅵ); the Cr(Ⅵ) can be accumulated and separated with Cr(Ⅲ) by using an anion trapping column and then determined by standard addition Cr(VI). The results were consistent with the detection by ICP-MS. The attractive behavior of the new modified electroed holds great promise for on-site industrial and environmental monitoring of chromium(Ⅵ). |
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