Studies On The Stripping Voltammetric Analysis At A Novel Aminoacid Copolymer/Cyano-bridged Heterometallic Coordination Polymers Composite Modified Electrode

In this dissertation,the aminoacid copolymer/cyano-bridged heterometallic coordination polymers composite modified glass carbon electrode(Aminoacid copolymer/CyHMCPs/GCE)was prepared by using the multistep electrochemical polymerization method.Using Pb²⁺and Cd²⁺mixture solution as probe,the experimental conditions for the preparation of the new composite chemically modified electrode were carefully optimized.As the conclusion of the experiments,it was showed that the environmental-friendly mercury-free working electrode was especially suitable for stripping voltammetry,and could greatly improve the sensitivity,stability and reproducibility of the analytical response signal.On this basis,the mutual interference between stripping voltammetric peaks of lead(Pb²⁺)and cadmium(Cd²⁺)had been made a profound study,and a green stripping analysis method for the simultaneous determination of trace lead and cadmium ions was established.Secondly,we found that Bi³⁺also had the special voltammetric response on this working electrode,a stripping voltammetric method for the rapid and direct determination of trace Bi³⁺in the common stomach medicine was proposed.Finally,in consideration of the unique cathodic stripping voltammetric properties of the composite modified electrode for Se(?),we found that the underpotential co-deposition between selenium and bismuth in the testing solution containing Se(?)could be occurred,thus the autocatalytic reduction wave of Se(?)could be generated.As a result,the electrocatalytic reduction mechanism of the cathodic stripping voltammetric behavior of Se(?)could be preliminarily elucidated.This paper consists of four chapters.Chapter one:The literature review of this thesisThis section was consisted by the following five parts:(1)An overview of stripping voltammetry and its working electrodes;(2)Introduction of chemically modified electrode materials;(3)Poly-aminoacid modified electrode;(4)Cyano-bridged coordination polymers modified electrode;(5)The significance and innovation of my studies.Chapter two:Preparation of aminoacid copolymer/cyano-bridged heterometallic coordination polymers(CyHMCPs)composite modified electrode and determination of trace lead and cadmium by a free-mercury anodic stripping voltammetry.In this section,aminoacid copolymer/neodymium-containing cyano-bridged heterometallic coordination polymers composite modified glass carbon electrode(Aminoacid copolymer/Nd(?)-Fe(?)-WO₄^2-CyHMCPs/GCE)was obtained by using the multistep electrochemical polymerization method.The surface morphology of the modified electrode was characterized by scanning electron microscopy(SEM).Using the mixture solution of lead and cadmium as probe,we carefully optimized the experimental conditions for the preparation of the new composite modified electrode.At the same time,the anodic stripping voltammetric behaviors of lead and cadmium ions were studied by differential pulse voltammetry at the modified electrode,and the signal interference due to the coexistence of two heavy metal ions was completely eliminated by using in-situ plating bismuth mode.Under the best optimized experimental conditions,there was a two-segment linear relationship between the stripping peak current of two heavy metal ions and its concentrations in range from0.01-1.00?mol/L and 1.00-100?mol/L.The quantitative detection range was expanded to about four orders of magnitude,and their detection limit(LOD,S/N=3)were 4.4 nmol/L and 3.3 nmol/L,respectively.Chapter three:Rapid determination of trace bismuth in stomach medicine by stripping voltammetry at an aminoacid copolymer/neodymium-containing cyano-bridged heterometallic coordination polymers composite modified electrodeUsing the aminoacid copolymer/Nd(?)-Fe(?)-WO₄^2-CyHMCPs/GCE as a working electrode,we had studied the anodic stripping voltammetric behavior of bismuth ions by differential pulse voltammetry,and found that bismuth ion could produce a high stripping peak current,but there usually was a very low peak current,even no response peak at the conventional working electrode.Therefore,a new stripping voltammetric method for rapid determination of bismuth ions was established.The experimental results showed that bismuth ions had a good linear relationship between the stripping peak current and the concentrations in the range of0.10-60.0?mol/L.The linear regression equation was I_p(?A)=-0.62+0.93C_Bi(?mol/L),(R²=0.9985),and the lower detection limit(LOD,S/N=3)was 58 nmol/L.Furthermore,the method was also applied to the rapid determination of bismuth content in actual stomach medicine samples with the recoveries of 96.5%-110%,and the results were satisfactory.Chapter four:Study on the cathodic stripping electrocatalytic reduction reaction mechanism of hexavalent selenium at an aminoacid copolymer/neodymium-containi-ng cyano-bridged heterometallic coordination polymers composite modified electrode.The cathodic stripping voltammetric behavior of hexavalent selenium(Se(?))was studied by differential pulse voltammetry at a novel aminoacid copolymer/Nd(?)-Pb(II)-WO₄^2-CyHMCPs/GCE working electrode.We found that Se(?)could also produce the underpotential co-deposition with bismuth ion to form Se-Bi alloy,and then the cathodic stripping peak of Se(?)would be generated.Therefore,the subjective conclusion that Se(?)has no electrical activity reported in a few literatures can be completely denied.In addition,we have studied the kinetics of electrocatalytic reduction of Se(?)by cyclic voltammetry(CV),and found for the first time that there was a reverse sweep reduction peak.Moreover,the critical sweep rate newly defined was a good linear correlation with the initial concentration of Se(?).Thus,we could deduce that the voltammetric behavior of Se(?)on the composite modified electrode was an autocatalytic electroreduction reaction.Under the optimized conditions of differential pulse voltammetry,the cathodic stripping peak current of Se(?)has a good linear relationship with its concentrations in the range of0.05-20.0 mmol/L,and the linear regression equation was I_p(?A)=-0.99+18.2C_Se(?)(mmol/L),(R²=0.9994);But unfortunately,when the concentration of Se(?)was lower than 0.02 mmol/L,the cathodic stripping peak of Se(?)might tend to disappear rapidly.Therefore,based on these experimental results,we proposed a new mechanism to elucidate the main cause of producing the cathodic stripping electrocatalytic reduction waves of Se(?).