1. The Operating Potential on the Sensitivity of Detection of Hydrogen Peroxide for the Carbon Paste Electrode Modified with Ferrocene Pao-Tsai Kuo ( 郭寶財 ), Ting-Li Lin ( 林庭立 ), Hau Lin ( 林浩 ) Department of Chemical and Materials Engineering, Southern Taiwan University 南台科技大學化學工程與材料工程系 ABSTRACT Due to wide use of hydrogen peroxide in the industry and food preservation, a rapid and convenient sensor for detecting the hydrogen peroxide is an important research subject. A study was conducted to use the ferrocene to modify the carbon paste electrode. Because the ferrocene(Fe(C 5 H 5 ) 2 ) possesses the excellent catalytic characteristic, it can be used with the graphite carbon powders which possess the excellent conductivity to make the carbon paste electrode and to elevate the responding current of hydrogen peroxide. The responding current of hydrogen peroxide is detected in the phosphate buffer solution(PBS) and then the concentration of the hydrogen peroxide can be obtained and consequently, the concentration of the glucose can be determined. At 30 ℃, and in 0.05 M phosphate buffer solution (PBS), the TB (Time Base) graphs for the carbon paste electrode at different operating potentials were plotted to evaluate the effect of the operating potential on the responding current of detection of hydrogen peroxide. At the optimum operating conditions -0.2 V operating potential, 500 rpm stirring rate and in 0.05M PBS buffer solution ( pH = 7.4 ), when the carbon paste electrode was modified with ferrocene [ferrocene : graphite carbon powders= 3 : 7 ( weight ratio )], the detection limit was 0.02 mM H 2 O 2, the linear range was 0.02 ～ 1.2 mM H 2 O 2, R 2 = 0.9998 and the sensitivity was 161.43µA/cm 2 ． mM H 2 O 2. This study can be further applied to the glucose biosensor. INTRODUCTION Because hydrogen peroxide is widely used in the food industry for the purpose of preservation nowadays, a rapid and convenient sensor for detecting the hydrogen peroxide is an important research subject. In recent years, diabetes has become one of the top ten causes of death for the people in our country. Therefore developing a rapid and convenient glucose biosensor also has become an important research subject. The glucose and oxygen can be catalyzed by the glucose oxidase and the glucose is oxidized to gluconic acid and the oxygen is reduced to hydrogen peroxide. The electrode releases the electrons at the reductive potential and converts the mediator to the reductive state. Then the mediator at the reductive state releases the electrons to reduce the hydrogen peroxide to water and consequently the mediator at the reductive state is converted to the oxidizing state. The responding current for detecting the hydrogen peroxide is used to measure the amount of hydrogen peroxide and consequently determine the concentration of the glucose. Therefore, the detecting technique for the hydrogen peroxide is an important research subject. Because the ferrocene(Fe(C 5 H 5 ) 2 ) possesses the excellent catalytic characteristic, it can be used with the graphite carbon powders which possess the excellent conductivity to make the carbon paste electrode and to elevate the responding current of hydrogen peroxide. The responding current of hydrogen peroxide is detected in the phosphate buffer solution(PBS) and then the concentration of the hydrogen peroxide can be obtained and consequently, the concentration of the glucose can be determined. At 30 ℃, and in 0.05 M phosphate buffer solution (PBS), the TB (Time Base) graphs for the carbon paste electrode at different operating potentials were plotted to evaluate the effect of the operating potential on the responding current of detection of hydrogen peroxide. The optimum operating conditions were used to detect the detection limit, linear range and sensitivity of detection of hydrogen peroxide for the carbon paste electrode modified with ferrocene. EXPERIMENTAL 1. Equipment Electrochemical Analyzer (CHI 401A, CH Instruments, Inc) was used to measure the activity of electrode by Cyclic Voltammetry ( CV ) and Time Base ( TB ) mode ; Electric Stirrer(Fargo) ; pH meter (Metrohm 731); Constant Temperature Thermal Bath (Wisdom BC-2DT 10L); Oven (DENG YNG) ; Carbon Paste Electrode was used as the working electrodes, Coiled Platinum Wire was used as the counter electrode and Ag / AgCl was used as the reference electrode. 2. Chemicals and Reagents Ferrocene ; Hydrochloric Acid (HCl); Sodium Hydroxide (NaOH) ; Hydrogen Peroxide (H 2 O 2 ); Graphite Carbon Powder( C ); Carbon Paste; Cyclohexanone(C 6 H 10 O); Potassium Dihydrogenphosphate (KH 2 PO 4 ); Potassium Chloride (KCl). 3. Preparation of the Carbon Paste Electrode : Take one section of 7 cm electric wire with 0.05 cm inside diameter. After depriving the coating 0.5 cm length from both ends, the nake-ended wire was washed, dried and ready for use. Then the ferrocene powders, graphite carbon powders and carbon paste were mixed with the appropriate ratio (ferrocene : graphite carbon powders : carbon paste = 0.3 : 0.7 : 1). After the mixing was complete, the mixture was evenly coated on the nake-ended electric wire and dried in the oven and then we obtained the carbon paste electrode. 7 cm 0.5 cm 0.05 cm Ferrocene Graphite carbon powders Mixing with equal amount of carbon paste DEPARTMENT OF CHEMICAL AND MATERIALS ENGINEERING, SOUTHERN TAIWAN UNIVERSITY RESULTS CONCLUSIONS The results showed that the responding current for the carbon paste electrode modified with the ferrocene was elevated significantly. The TB (Time Base ) graphs at different operating potentials were plotted to evaluate the effect of the operating potential on the responding current of detection of hydrogen peroxide and determine the optimum operating conditions. Because when the operating potential was -0.25V, it caused the detection to be unstable, -0.2V operating potential was used in this research. Because the pH of human blood is about 7.4, phosphate buffer solution pH=7.4 was used in this study. The results showed that at the optimum operating conditions –0.2V operating potential, 500rpm stirring rate and in 0.05M phosphate buffer solution(pH=7.4), the detection limit was 0.02 mM H 2 O 2, the linear range was 0.02~1.2 mM H 2 O 2, R 2 =0.9998 and the sensitivity was 161.43 μA/cm 2 ּmM H 2 O 2. This research can be further applied to the glucose biosensor in the future. 1. L. Charpentier and N. El Murr, “Amperometric Determination of Cholesterol in Serum with Use of a Renewable Surface Peroxidase Electrode,” Analytica Chimica Acta, Vol. 318, 83 (1995). 2. R. Nagata, S. A. Clark, K. Yokoyama, E. Tamiya and K. Isao, “Amperometric Glucose Biosensor Manufactured by a Printing Technique” Analytica Chimica Acta, Vol. 304, 157(1995). 3. H. Liu, H. Li, T. Ying, K. Sun, Y. Qin, and D. Qi, “Amperometric Biosensor Snesitive to Glucose and Lactose Based on Co-Immobilization of Ferrocene, Glucose Oxidase, β-Galactosidase and Mutarotase in β-cyclodextrin Polymer,” Analytica Chimica Acta, Vol. 358, 137( 1998) 4. Y.-M. Uang and T.-C. Chou, “Fabrication of Glucose Oxidase/Polypyrrole Biosensor by Galvanostatic Method in Various pH Aqueous Solutions,” Biosensors and Bioelectronics, Vol. 19, 141(2003). REFERENCES (B) (A) Fig 1. CV graphs for (A) carbon paste electrode modified with ferrocene ( the range of scanning potential: -0.8 ～ +0.8 V) (B) unmodified carbon paste electrode( the range of scanning potential: -0.8 ～ +0.8 V ) Fig. 2 The TB graphs of carbon paste electrodes for detection of H 2 O 2 at different operating potentials (ferrocene : graphite carbon powders = 3 : 7); the operating potentials are [ (A) 0V (B) –0.05V (C) –0.1V (D) –0.2V (E) –0.25 V ] Fig. 3 The calibration curves of different operating potentials for the carbon paste electrode modified with ferrocene [ (A) 0V (B) –0.1V (C) –0.15V (D) –0.2V (E) –0.25 V ] Table 1 The sensitivities, responding currents, and R 2 values of different operating potentials for the carbon paste electrode modified with ferrocene Fig. 4 The TB graphs of carbon paste electrodes for determining the detection limit of H 2 O 2 (ferrocene: graphite carbon powders = 3 : 7); At 30 ℃ ; the operating potential = – 0.2 V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH= 7.4 ) Fig. 5 The TB graphs of carbon paste electrodes for determining the linear range of H 2 O 2 (ferrocene : graphite carbon powders = 3 : 7); At 30 ℃ ; the operating potential = –0.2 V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH= 7.4 ); stirring rate =500 rpm; 10μL of 100mM H 2 O 2 is injected per 100 seconds