Preparation Of Novel Chemically Modified Electrodes And Study On Their Application In The Determination Of Heavy Metals In Food

Heavy metals are one class of contaminants that can lead to undesirable effects (such as mercury,cadmium,lead,arsenic,copper,etc.) because of their nonbiodegradable nature and ability to persist for long periods.All forms of ecological systems are affected to various extents by heavy metals.Toxic heavy metal elements in food,some are enriched from the crop and some will come from the food production,storage and transport.Through the food chain,heavy metals may deposit into the human body,cause serious health problems,specifically cancer.Therefore,it is necessary to study rapid,accurate,sensitive and convenient new method for detecting heavy metals.Recently,the chemically modified electrodes(CMEs) has been widespread concerned.The distinguishing feature of a CME is to endow the electrode with new, specific features,which has unique advantage to improve electrochemical selectivity and sensitivity and greatly expanded the scope of electroanalytical chemisty.The application of chemical modified electrode in the heave metals analysis in recent years has been made great progress.Because of the limited of the electrode materials, therefore,it has always been difficult to achieve a new level despite the improve of sensitivity.So,it is necessary to add some complementary methods to improve its sensitivity if we want to make better development of detection of heavy metals by chemically modified electrodes.In this dissertation,some novel chemically modified electrodes were prepared and characterized.Introducing ultrasonic and microwave technology into electrochemistry,some simplicity,reliability and high sensitivity methods for detection of heavy metals were described,which provides a new concept and ideas for detection of heavy metals.There are five chapters in this paper.Chapter 1 OverviewIn chaperl,a detail outline and reviews mainly on the hazards of heavy metal contamination,development of the heavy metal determination,the preparation and application of the chemically modified electrodes,the principal mechanism and the application of both ultrasound and microwave.Chapter 2 A Nafion-coated bismuth film electrode for the determination of heavy metals in vegetable using differential pulse anodic stripping voltammetry:An alternative to mercury-based electrodes.This chapter reported the simultaneous determination of Pb(â…¡),Cd(â…¡) and Zn(â…¡) by differential pulse anodic stripping voltammetry(DPASV) on a Nafion-coated bismuth film electrode(NCBFE) plated in situ;The parameters for the simultaneous determination of three metals were investigated.The results indicated that lead, cadmium and zinc gave well-defined ASV peaks with no interference,The behavior of bismuth film electrodes was shown to compare favourably to that of mercury electrodes.The linear domain range was 4～36μg/L for three metals,with correlation coefficient of 0.9975 for Pb,0.9985 for Cd and 0.9964 for Zn,respectively.And the limits of determination were 0.17μg/L for Cd and for Pb and 0.30μg/L for Zn at a preconcentration time of 3 min.Finally,NCBFE were successfully applied to the determination of Pb and Cd in vegetables,and the results were in satisfactory agreement with graphite furnace atomic absorption spectrometry(GFAAS) determination.Chapter3 Microwave-irradiated synthesized platinum nanoparticles/carbon nanotubes for oxidative determination of trace arsenic(â…¢)Platinum nanoparticles/carbon nanotubes(Pt_nano/CNTs) were rapidly synthesized by microwave radiation,and applied for the oxidative determination of arsenic(â…¢). The transmission electron microscopy(TEM) revealed the size and morphology of synthesized Pt nanoparticles.Pt_nano/CNTs modified glassy carbon electrode (Pt_nano/CNTs/GCE) exhibited better performance for arsenic(â…¢) analysis than that of Pt nanoparticles modified GCE(Pt_nano/GCE) by electrochemical deposition or Pt foil electrode.The method is accurately and rapidly.it is suitable to detect trace arsenic(â…¢).Chapter4 Sono-voltammetry for Determination of Trace Lead(â…¡) and Copper(â…¡) in Drinking WaterThe simultaneous determination of trace Pb(â…¡) and Cu(â…¡) in drinking water by sono-differential pulse anodic stripping voltammetry on a gold nanoparticle-modified glassy carbon electrode was reported.The morphology and size of gold nanoparticles were characterized by atomic force microscopy(AFM).The principal mechanism of the sonochemical reactions that can improves the voltammetry signal was disscussed. Various experimental parameters,such as pH,ultrasonic power,deposition time and deposition potential,were thoroughly optimized.The results indicated that the sensitivity was improved by the sono-voltammetry.The limits of determination were 0.3μg.L^-1 for Pb and 0.1μg.L^-1 for Cu.Finally,this proposed method was successfully applied to the determination of Pb and Cu in drinking water.Chapter5 Microwave-enhanced vlotammetric detection of copper(â…¡) at gold nanoparticles-modified platinum microelectrodesIn this chapter,in situ microwave activation of electrochemical detection of copper(â…¡) at a gold nanoparticles-modified Pt microelectrode(Au-NPs/Pt). Self-focusing of the microwave radiation creates an extreme localized heating at te electrode/solution(electrolyte) interface within the diffusion layer of the electrode with an inverted thermal gradient and convective flow.The temperature at the electrode/solution interface is calibrated with reversible one electron redox system Fe(CN)₆^3-/4- in aqueous K₂SO₄ solution(pH 3).Significantly increased currents were observed both at Au-NPs/Pt electrode and bare Pt electrode in the lower microwave intensity.A standard addition procedure was developed for sensitive detection of Cu(â…¡) concentration under microwave radiation,and the limit of detection by cyclic voltammetry was found to be 0.1μM and 1.0μM with microwave radiation and without microwave radiation.Microwave activation was also shown to have a considerable effect in enhancing the sensitivity of Cu(â…¡) detection in the presence of surfactant.