Bismuth-Coated Carbon Electrodes For Anodic Stripping Voltammetry

With the extensive development of industrialization, plenty of heavy metals enter into various waters. Heavy metal ions have great hazard to human even in trace quantities. Therefore, the quantitative analysis of trace heavy metals is extremely important in medical, food, clinical and environmental monitoring fields. Electrochemical analysis has been widely concerned because of its high sensitivity and maneuverable apparatus. Mercury-coated electrodes have been traditionally employed for achieving high reproducibility and sensitivity of the stripping technique. However, because of the toxicity of mercury, alternative electrode materials are highly desired. In recent years, Joseph Wang et al first introduced the bismuth film electrodes for anodic stripping voltammetry. These bismuth film electrodes can offer high sensitivity, renewable surface and reproducible, and bismuth is 'environmentally-friendly', with a widespread pharmaceutical use. This thesis is aimed at developing bismuth-coated electrodes instead of mercury-coated electrodes for anodic stripping voltammetric measurements of heavy metals.The main research works are as follows:1) To enhance electrochemical performances at screen-printed (thick film) carbon electrodes (SPCEs), a method for the pretreatment by two successive steps was proposed. In step one, fresh SPCEs were soaked into NaOH with high concentration for tens of minutes, and the resulted electrodes were called as SPCE-I. In step two, SPCE-I were pre-anodized in low concentration of NaOH.2) Investigations were carried out on the characterization, evaluation and optimization of several key operational parameters for a reliable and effective use of a bismuth coated electrode as an replacement of the mercury coated electrode in anodic stripping voltammetric measurements of heavy metals. Employ lead and cadmium as model analyte ions and apply in situ preparation of the bismuth coated electrodes. Key parameters include preconcentration time, preconcentration potential, concentration of bismuth ions and so on. 3) Recently, chemically modified electrodes (CMEs) have been given highly investigations in the fields of electrochemistry. The Nafion polymer is chemically inert and insoluble in water and thus possesses almost ideal properties for preparation of modified electrodes. Nafion modified thick film carbon electrodes (NMGCE) are fabricated by spreading Nafion on the surface of the carbon electrodes. The advantages and disadvantages of NMGCEs and naked carbon electrodes were given intensive studies.Experimental results indicate that stripping voltametric measurements of lead and cadmium in nondeaerated solutions yielded well defined peaks along with a low background following short preconcentration time. Such an attractive use of "mercury-free", environmentally friendly electrodes offer a new method to centralized and decentralized testing of heavy metals. This method could be used in many fields.