The Study And Application Of The Pre-Anodized Carbon Paste Electrode

Carbon paste as electrode has received increasing attention due to their easy fabrication, low cost,wide potential window. There are some reports about the functional pre-anodized carbon paste electrode（PACPE） which was fabricated by using successive cyclic voltammetry in NaOH （0.2mol/L）. In this thesis,based on carbon paste substrate electrode and electrochemical pretreatment, our studies have been dealt inthe following parts.1. Study on electrochemical oxidation behaviors and the diffusion mechanism of hydroquinone atpre-anodized carbon paste electrode by cyclic voltammetryA functional pre-anodized carbon paste electrode （PACPE） was constructed by using successive cyclicvoltammetry. The electrochemical oxidation behaviors of hydroquinone （HQ） were carefully investigatedby various electrochemical techniques. The driving force for the HQ transport towards anode not onlyrelated to the concentration diffusion but also depended on the transport of H+in the feed phase along aconcentration gradient towards the cathode. The results indicated that the PACPE exhibited excellentelectrocatalytic activity towards the oxidation of HQ. Compared with the bare carbon paste electrode, theoxidation and reduction peak separation （Ep） of HQ at the PACPE has been decreased from578to83mV.Under the optimum conditions, the oxidation peak current was linear with HQ concentrationin the range of4×10^-7-1.0×10^-4mol/L with the linear correlation coefficient of0.9986. The detection limit was1.05×10^-7mol/L. This method can be successfully applied to the determination of HQ in wastewater.2. The diffusion of guanine and adenine at pre-anodized carbon paste electrode and determinationA functional pre-anodized carbon paste electrode （PACPE） was fabricated using simple and fastelectrochemical pretreatment for the simultaneous or individual determination of guanine and adenine. Theresults indicated that PACPE exhibited excellent electrocatalysis for the oxidation of guanine and adenine.Compared with bare carbon paste electrode （CPE）, the oxidation peak currents increased remarkably about10times corresponding to the negative shift of oxidation peak potentials. Under the optimum conditions,the oxidation peak currents for measurement of guanine and adenine were linear to the concentration in arange of5×10^-8-1.5×10^-5mol/L and1×10^-7-1.5×10^-5mol/L. The detection limits were1.7×10^-9mol/L and 2.3×10^-8mol/L, respectively. The proposed method has been applied to simultaneous determination ofguanine and adenine in DNA sample with satisfactory results.3. Study on the acidity influence mechanism of xanthine and hypoxanthine using a pre-anodized carbonpaste electrode and simultaneous determinationA simple electrochemical method was presented based on carbon paste electrode anodized in alkalinemedium （0.2mol/L NaOH） for simultaneous or individual determination of xanthine （Xa） and hypoxanthine（Hxa）. The results indicated that PACPE displayed excellent electrocatalytic activity towards the oxidationof the two analytes. The oxidation peak currents of Xa and Hxa were located at+0.705V and+1.016V onPACPE. The separated extent between the two oxidation peaks of Xa and Hxa was311mV, which wasenough for the simultaneous detection. Moreover, the oxidation peak currents of the two species not onlyrelated to the concentration of the diffusion to the electrode surface, but also depended on the reductiveability of oxidant on cathode reaction. Under the optimal conditions, the calibration curves for Xa and Hxawere obtained over the range of6×10^-8-3×10^-5mol/L and2×10^-7-7×10^-5mol/L, respectively. The detectionlimits for Xa and Hxa were1.2×10^-8mol/L and5.7×10^-8mol/L, respectively. This proposed method hadbeen applied to determine Xa and Hxa in human urine simultaneously with satisfactory results.4. Study the influence of acidity to the simultaneous determination of uric acid and ascorbic acid on thepre-anodized carbon paste electrodeIn this paper, the auxiliary electrode and the working electrode were considered as a whole to studytheir effect on the oxidation peak current by determining simultaneously uric acid （UA） and ascorbic acid（AA） on the pre-anodized carbon paste electrode （PACPE）. The influence of reaction ability of auxiliaryelectrode on the oxidation peak current, especially the influence of acidity has been discussed detailedly.The results indicated that the oxidation peak currents of UA and AA not only related to the concentration ofthe diffusion to the electrode surface, but also depended on the reductive ability of oxidant on cathodereaction （happened on the auxiliary electrode）. Moreover, two distinguishable oxidation peaks of UA andAA with the separated extent of268mV were obtained at PACPE. Under the optimum conditions, twocalibration curves for UA and AA were obtained over the range of5×10^-7-5×10^-5mol/L and3×10^-5-5×10^-3mol/L, respectively. The detection limits for UA and AA were found to be2.05×10^-8mol/Land1.23×10^-6mol/L, respectively. This proposed method had been successfully applied to determine UA and AA in human urine simultaneously with good selectivity and sensitivity.