| Electrochemical method is one of the most favorable techniques for the determination of heavy metal ions, because of its low cost, high sensitivity, easy operation and the ability of analyzing element speciation. In previous works, the determination of heavy metal ions was mostly carried out at mercury electrodes. Despite good properties of mercury electrodes, future regulations and occupational health consideration may severely restrict the use of mercury because of the toxicity of mercury. In search for alternative electrode materials, chemically modified electrodes (CMEs) offer several advantages for voltammetric measurements of trace metals. To date, many kinds of CMEs have been reported for the determination of metal ions. The design of electrodes with controllable surface properties can be effectively achieved employing self-assembled monolayers which have become one of the most popular techniques for the determination of metal ions. In 2000, Wang et al. introduced a new type of electrode, bismuth film electrodes (BiFEs), and recent researches have indicated that, in many cases, BiFEs have been shown to offer a successful replacement of mercury-film electrodes in anodic stripping voltammetry. In particular, the sensitivity and selectivity of the BiFEs could be further improved by covering with polymeric membrane, which can protect the bismuth surface against abrasion adsorption of surface-active compounds and formation of intermetallic compounds. Moreover, stannum and bismuth are in catercorner position at periodic table of chemical elements, stannum may have analogical character of bismuth. It is reported that stannum can build alloys with both Zn and Cd. In addition, stannum is a more "green" element, with very low toxicity and cost. Stannum film electrode (SnFE) possesses many of the same attributes as BiFE. Therefore, SnFE appears to be a viable sensor for the electroanalytical measurement. To expand the scope of applying BiFEs, some chemically modified electrodes were fabricated. The main researches are as follows:1. Study on the bismuth/poly(p-aminobenzene sulfonic acid) film electrode and its applicationA novel sensor was designed for simultaneous detection of Pb(II), Cd(II) and Zn(II), based on the differential pulse anodic stripping response at a bismuth/poly(p-aminobenzene sulfonic acid) film electrode. This electrode was generated in situ by depositing simultaneously bismuth and the metals by reduction of the metal ions at -1.40 V on the poly(p-aminobenzene sulfonic acid) modified electrode. Compared with bismuth film electrode, this electrode could yield a large stripping signal for Pb(II), Cd(II) and Zn(II). The poly(p-ABSA) film could protect the bismuth surface against abrasion, adsorption of surface-active compounds and enhance the sensitivity of bismuth film for determining heavy metals. In addition, this type of low-cost and environmentally friendly voltammetric sensor had good sensitivity, selectivity and stability. This sensor has been applied to the synchronous determination of Pb(II), Cd(II) and Zn(II) in water samples and the results were satisfied.2. Research of stannum film electrode and its applicationSimultaneous detection of Zn(II) and Cd(II) by differential pulse anodic stripping voltammetry at a stannum film electrode was investigated. This new electrode was prepared in situ by depositing simultaneously stannum and the target metal ions on a bare glassy carbon electrode. Compared with the bismuth film electrode, the stannum film electrode could yield an equally well-defined and sharp stripping signals for Cd(II) and Zn(II). In addition, the stannum film electrode had a highly excellent reproducibility for detection. The favorable performance obtained at stannum-coated electrode coupled with the negligible toxicity of stannum made these stannum film electrode extremely attractive for on-site environmental and industrial measurements of Cd(II) and Zn(II). The stannum film electrode was applied to the determination of Zn(II) in tap water, and the results were quite corresponding to the value obtained by atomic absorption Spectrometry.3. Research of stannum/poly(p-aminobenzene sulfonic acid) film electrode and its applicationA new method for the simultaneous determination of Cd(II) and Zn(II) at low concentration levels in non-deoxygenated soltutions was reported by using a novel stannum/poly(p-aminobenzene sulfonic acid) film electrode by differential pulse anodic stripping voltammetry. The stannum/poly(p-aminobenzene sulfonic acid) film electrode with the aim to lower the adherence of stannum, was generated in situ by depositing simultaneously the stannum and the metal ions by reduction at -1.5 V on the poly(p-aminobenzene sulfonic acid) modified electrode. The parameters for the simultaneous determination of the two metals were investigated. This type of low-cost and non-toxic voltammetric electrode displayed high-quality stripping performance and has been successfully applied to the determination of Zn(II) in tap water, and the result was in satisfactory agreement with the value obtained by atomic absorption Spectrometry.4. Research of 2,5-dimercapto-1,3,4-thiadiazoIe (DMTD) self-assembled monolayer modified electrode and its application in the determination of lead ionDMTD can bind onto the surface of gold electrode through the strong gold-sulfur interaction. The fabrication and electrochemical characteristics of DMTD self-assembled monolayer modified gold electrode was investigated by electrochemical measurements. The influence of various experimental parameters on the voltammetric response of Pb(II) was studied. The DMTD/Au electrode exhibited a significantly increased sensitivity and selectivity for Pb(II). The possible reaction mechanism has also been discussed. A study of interfering substances was also performed, and this method was applied to the determination of Pb(II) in water samples with satisfactory results.
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