Studies On The Adsorptive Stripping Voltammetry Of Copper (Ⅱ) And Lead (Ⅱ) At Chemically Modified Carbon Paste Electrodes Cotaining Morin Or Quercetin

In this paper, two new chemically modified electrodes for the sensitive and selective determination of copper(Ⅱ) and lead(Ⅱ) by anodic linear scan adsorptive stripping voltammetry were reported for the first time. The electrodes were prepared by incorporating morin and quercetin, respectively, into carbon paste mixture.The paper consists of four chaptersIn chapter 1, the voltammetric behavior of copper(Ⅱ) at a modified carbon paste electrode containing morin was studied in detail. An electoactive complex of copper(Ⅱ) with morin was formed and accumulated on the surface of the electrode in a stirred formate buffer solution at 0.20 V(vs.SCE), after it was reduced at -0.45 V for 30 s without stirring, the voltammogram was then recorded by applying a anodizing scan from -0.45 V to 0.55 V at 250 mV.s-1 rate, and the second derivative peak was obtained at -0.05 V. Under optimized conditions, two linear ranges were obtained in the concentration ranges 2.0×10-8～9.0×10-7 mol/L Cu(Ⅱ) with 2 min pre-concentration and 1.0×10-9～6.0×10-8 mol/L Cu(Ⅱ) with 4 min accumulation. The detection limit was found to be 4.0×10-10 mol/L with 4 min accumulation. The precision obtained for 10 successive determination of 6.0×10-8 mol/L Cu(Ⅱ) was 4.32 %(RSD). The composition of Cu(Ⅱ)–morin complex was found to be 1:1 and the electrode processes mechanism were studied. The developed method was applied to copper(Ⅱ) determination in human hair samples, with good results. In chapter 2, a new system for determination of lead(Ⅱ) with morin modified carbon paste electrode was proposed. The optimum conditions of the determination of lead(Ⅱ) were founded. Under optimum conditions, the second-order derivative stripping peak potential appears at about -0.43 V. Two linear relationship was obtained between the peak current and the lead(Ⅱ) concentration in the range of 2.0×10-8～1.0×10-6 mol/L with 180 s accumulation time and 5.0×10-9～1.0×10-7 mol/L with 360 s accumulation time. The detection limit was found to be 1.0×10-9 mol/L with 360 s accumulation time. The ratio of Pb(Ⅱ) to morin in the complex was found to be 1:1 by the continuous variations method at pure carbon paste electrode. The mechanism of electrode reaction was also studied. The proposed method has successfully applied to the determination of lead(Ⅱ) in human urine samples.In chapter 3, the application of quercetin -modified carbon paste electrode to the adsorptive stripping voltammetric determination of copper(Ⅱ) was reported. The quercetin -modified carbon paste electrode was immersed in a stirred formate buffer (pH 4.7) and accumulation of copper (Ⅱ) was allowed to proceed for a give time at 0.20 V(vs.SCE). The ensuing measurement was carried out by anodic linear scan stripping voltammetry after reducing the copper(Ⅱ) at -0.40 V for 30 s. The second derivative stripping peak was obtained at -0.03 V. Under optimized conditions, two linear ranges were obtained in the concentration ranges 1.5×10-8～9.0×10-7 mol/L Cu(Ⅱ) with 2 min accumulation time and 1.5×10-9～8.0×10-8 mol/L Cu(Ⅱ) with 4 min accumulation time, respectively. The detection limit was found to be 8.0×10-10 mol/L Cu(Ⅱ) with 4 min accumulation. For 10 successively determination of 8.0×10-8 mol/L Cu(Ⅱ), the RSD was 3.85 %. The properties of the Cu(Ⅱ)–quercetin complex and the electrode processes mechanism have been investigated. Applied the procedure to the determination of copper(Ⅱ) in human serum samples, with good results.In chapter 4, the adsorptive stripping voltammetric detection of lead(Ⅱ) using a carbon paste electrode modified with quercetin was described. The optimum experimental conditions include 1.0 % quercetin loading, 0.06 mol/L formate buffer (pH 4.3), the accumulation potential Ea = -0.10 V, the accumulation time Ta = 150 s (for high concentration) or Ta = 300 s (for low concentration), the reduction potential Er = -0.70 V and reduction time Tr = 40 s. A well-defined anodic stripping peak was obtained at about -0.42 V. Under optimum conditions,...