A Study of the Effect of Operating Potential on Detection of Hydrogen Peroxide for the Electrode Modified with Ruthenium Hexacyanoferrate Kuo-Hsiang Liao ( 廖國翔 ), Chung-Min Lien ( 連崇閔 ), 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 Nowadays, sometimes the preservatives are used in the food industry for the purpose of food preservation. Therefore, a hydrogen peroxide sensor has become an important research subject. A study was conducted to use Ruthenium Hexacyanoferrate to modify the carbon paste electrode. Because Ruthenium Hexacyanoferrate possesses the excellent catalytic characteristic, it can be used with the carbon paste and the carbon powders which possess the excellent conductivity to make the carbon paste electrode [Ruthenium Hexacyanoferrate : carbon powders : carbon paste = 0.3 : 0.7 : 1 (weight ratio) ] and 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 determined. At 30 ℃, 600rpm stirring rate, 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 potentials on the sensitivity of detection of hydrogen peroxide. At operating potentials -50mV, -100mV, -200mV and -300mV, the sensitivities were 471.2µA/cm 2 ． mM H 2 O 2, 541.0µA/cm 2 ． mM H 2 O 2, 561.1µA/cm 2 ． mM H 2 O 2 and 688.1µA/cm 2 ． mM H 2 O 2 respectively. In order to reduce the interference of oxygen and avoid the inteferring substances ( Ascorbic acid, Uric acid, and Acetaminophen etc.) in human body, the operating potential at –200mV was used in this research. The results showed that at the optimum operating conditions -200mV operating potential, 600rpm 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 0.02~2.7 mM H 2 O 2, R 2 = and the sensitivity was 661.8μA/cm 2 ּmM H 2 O 2. INTRODUCTION ： Because hydrogen peroxide plays an important role in industry, developing a hydrogen peroxide sensor which can detect the hydrogen peroxide rapidly and conveniently has become an important research subject. A study was conducted to use the ruthenium hexacyanoferrate( Ⅱ ) to modify the carbon paste electrode which was used as the working electrodes to detect the responding current of reduction of hydrogen peroxide in the phosphate solution and then the concentration of hydrogen peroxide could be determined. In this research, the CV (Cyclic Voltammetry) graphs were plotted for the carbon paste electrode modified with ruthenium hexacyanoferrate( Ⅱ ) [ruthenium hexacyanoferrate( Ⅱ ) ： carbon powders =3 ： 7 ( weight ratio)] and the unmodified carbon paste electrode. At 30 ℃, 600rpm stirring rate, 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 potentials on the sensitivity of detection of hydrogen peroxide. EXPERIMENTAL SECTION ： ABSTRACT ： CONCLUSIONS ： The CV ( Cyclic Voltammetry ) graphs were plotted for the carbon paste electrode modified with Ruthenium Hexacyanoferrate and the unmodified carbon paste electrode. The results showed that the responding current for the carbon paste electrode modified with Ruthenium Hexacyanoferrate was elevated significantly. At 30 ℃, 600rpm stirring rate, 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 potentials on the sensitivity of detection of hydrogen peroxide. At operating potentials -50mV, -100mV, -200mV and -300mV, the sensitivities were 471.2µA/cm 2 ． mM H 2 O 2, 541.0µA/cm 2 ． mM H 2 O 2, 561.1µA/cm 2 ． mM H 2 O 2 and 688.1µA/cm 2 ． mM H 2 O 2 respectively. In order to reduce the interference of oxygen and avoid the inteferring substances ( Ascorbic acid, Uric acid, and Acetaminophen etc.) in human body, the operating potential at –200mV was used in this research. The results showed that at the optimum operating conditions -200mV operating potential, 600rpm 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 0.02~2.7 mM H 2 O 2, R 2 = and the sensitivity was 661.8μA/cm 2 ּmM H 2 O 2. Preparation of Working Electrode ： 1. 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. 7 cm 0.5 cm 0.05 cm 2. Then the ruthenium hexacyanoferrate( Ⅱ ) powders, carbon powders and carbon paste were mixed with the appropriate ratio. 3. 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. Fig 1. CV graphs for (A) carbon paste electrode modified with ruthenium hexacyanoferrate( the range of scanning potential: -0.8 ～ +0.8 V) (B) unmodified carbon paste electrode( the range of scanning potential: -0.6 ～ +0.6 V) 1. Pandey, P. C. ; Upadhyay, S., Sensors and Actuators B, 2001, 76, Kim, M. A. ; Lee, W.-Y., Analytica Chimica Acta, 2003, 479, Singh, S. ; Chaubey, A. ; Malhotra, B. D., Analytica Chimica Acta, 2004, 502, Xu, Y. ; Hu, C. ; Hu, S., Sensors and Actuators B, 2008, 130, Qiu, J.-D. ; Zhou, W.-M. ; Guo, J. ; Wang, R. ; Liang, R.-P., Analytical Biochemistry, 2009, 385, REFERENCES ： Ruthenium Hexacyanoferrate Powders Preparation of Ruthenium Hexacyanoferrate ： 30 mM Potassium Hexacyanoferrate 5 mL 3 mM Ruthenium Chloride Hydrate 50 mL Centrifuging Repeat Centrifuging Three Times Drying ruthenium hexacyanoferrate carbon powder ( appropriate ratio ) A powder appropriate A powder adding carbon paste Fig. 2 The TB graphs of carbon paste electrodes for detection of H 2 O 2 at different operating potentials (ruthenium hexacyanoferrate : carbon powders = 3 : 7); the operating potentials are [ (A) -50mV (B) – 100mV (C) –200mV (D) –300mV ] Fig 4 The responding currents of carbon paste electrode for detection of H 2 O 2 at different operating potentials (ruthenium hexacyanoferrate : carbon powders = 3 : 7) Table 1 The sensitivities and R 2 values of different operating potentials for the carbon paste electrode modified with ruthenium hexacyanoferrate Fig. 3 The calibration curves of different operating potentials for the carbon paste electrode modified with ruthenium hexacyanoferrate [ ( A) -50mV (B) – 100mV (C) –200mV (D) –300mV ] Fig. 5 The TB graph of carbon paste electrode for detection of the linear range of H 2 O 2 (A) stirring rate 600 rpm (B) stirring rate 500 rpm (C) unmodified carbon paste electrode; stirring rate 600 rpm