Application Research Of The Chemically Modified Electrode Coated With Poly-(Glutamic Acid)/3d-4f Hybrid-metallic Cyano-bridged Coordination Polymer Composite Film In The Food Analysis

In this dissertation,in order to develop a new type of composite modified electrode,we have prepared a poly-（glutamic acid）/3d-4f hybrid metallic cyano-bridged coordination polymer（Ho-Fe-WO42-Cy MCP）film on glassy carbon substrate by multistep electrodeposition method.With the composite modified electrode as the working electrode,we find that the composite modified electrode is especially suitable for voltammetric analysis due to its good stability,selectivity and repeatability for the signal response.Therefore,we have investigated the electrochemical oxidation behavior of ascorbic acid（AA）,nitrite（NO2-）and oxalic acid（C2O42-）at the modified electrode in detail.Based on these evidences,an electroanalytical method is established to determine the contents of AA,NO2-and C2O42-in real food samples.In addition,a new electrochemical method for indirect determination of sucrose has been established by using the electrogenerated trivalent manganese ions as an electro-catalytic mediator at this composite modified electrode.This paper consists of four chapters.Chapter 1: Review.This chapter mainly contains the following four parts:（1）The conception and its developments about the chemically modified electrodes;（2）Electroanalytical applications of conductive polymer film modified electrodes;（3）Research progress on the application of electroanalytical methods in the food analysis;（4）The significance and innovation of my studies.Chapter 2: Rapid determination of ascorbic acid and nitrite in the food samples by using differential pulse voltammetryIn this study,the composite modified material that was made up of poly-（glutamic acid）and 3d-4f hybrid-metallic cyano-bridged coordination polymer（Ho-Fe-WO42-Cy MCP）film was successfully prepared on a glassy carbon substrate by using the multistep electrochemical polymerization method.The surface morphology of the chemically modified electrode was characterized by scanning electron microscopy（SEM）.All voltammetric results have demonstrated that there were the excellent synergistic catalytic performance and anti-fouling capability for the direct electro-oxidation reaction of ascorbic acid（AA）and nitrite（NO2-）.Additionally,using differential pulse voltammetry（DPV）,AA and NO2-were simultaneously determinated with the good voltammetric peak profile and less mutual interference.Specially,there were the good double logarithm linear relationship between their oxidation peak current and their concentrations in range from 20 to 10000 μmol·L^-1,and their linear regression equations were lg Ip（μA）=-1.425+0.8393 lg CAA(μmol·L^-1),R2=0.9998 and lg Ip（μA）=-1.475+0.9282 lg CNitrite(μmol·L^-1),R2=0.9992,respectively.The lower detection limits of AA and NO2-were 5.8 and 3.9 μmol·L^-1（S/N=3）,respectively.Therefore,the total content of AA and NO2-in real food samples which merely underwent a simple pretreatment operation could be selectively and rapidly determined with a recovery of 88.1% 128.9%.The reproducibility,selectivity and stability of the new proposed method for the quantitative analysis of AA and NO2-were very satisfactory.Chapter 3: Rapid determination of oxalic acid content in the vegetables samples by using differential pulse voltammetry.In this work,the direct electrocatalytic oxidation behavior of oxalate ion（C2O42-）was studied at the poly-（glutamic acid）/Ho-Fe-WO42-/GCE working electrode.Herein,we had established the new method for rapid determination of C2O42-content in vegetables by differential pulse voltammetry（DPV）.All voltammetric results have demonstrated that there was the excellent catalytic performance and anti-fouling capability for the direct electro-oxidation reaction of C2O42-.In addition,C2O42-was detected by DPV with the good voltammetric peak profile and less matrix interference.Specially,there was the good linear relationship between the oxidation peak current and its concentrations in range from 0.5 to 40.0 mmol·L^-1,and the linear regression equation was Ip（μA）=-0.4726+5.116C(mmol·L^-1),R2=0.9991.The lower detection limit of C2O42-was 0.02 mmol·L^-1（S/N=3）.Therefore,the total content of C2O42-in real vegetables samples could be determined with a recovery of 90.4% 113.0%.The reproducibility,selectivity and stability of the new established method for the quantitative analysis of C2O42-were very satisfactory.Chapter 4: Investigation of the electrocatalytic oxidation behavior of sucrose using the electrogenerated trivalent manganese ions as an electro-catalytic mediator at this composite modified electrode.In this work,with the experimental condition adding Mn2+ into the supporting electrolyte solution,the electrocatalytic oxidation behavior of sucrose due to the electrogenerated Mn3+ as a mediator of transferred electron was studied at poly-（glutamic acid）/Ho-Fe-WO42-/GCE.Moreover,the preliminary experiments were performated to explain its electrocatalysis mechanism by a UV-vis spectroscopic method.The experimental results showed that sucrose could produce a distinct electocatalytic oxidation peak at the positive potential region about 1.05 V（vs.Ag/Ag Cl）at the composite modified electrode.Under the optimum conditions,there was the good linear relationship between the oxidation peak current of sucrose and its concentrations in range from 2.0 to 200.0 mmol·L^-1,and the linear regression equation was Ip（μA）= 23.28+0.086C(mmol·L^-1),R2=0.9989.The lower detection limit of sucrose was 0.66 mmol·L^-1（S/N=3）.Therfore,a new method for indirect determination of sucrose content was developed by differential pulse voltammetry,which can hold a good selectivity for the quantitative determination of sucrose.