Chen-Hsun Hu (胡真熏) , Chih-Ying Wu (巫致穎) , Hau Lin (林浩) The Operating Potential on the Detection of Hydrogen Peroxide for the Electrode Modified with Chromium Hexacyanoferrate Chen-Hsun Hu (胡真熏) , Chih-Ying Wu (巫致穎) , 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 Because the Chromium Hexacyanoferrate possesses the excellent catalytic characteristic, it can be used with the graphite carbon powders and carbon paste to make the carbon paste electrode to elevate the sensitivity of responding current of hydrogen peroxide. The responding current of hydrogen peroxide can be detected in phosphate buffer solution (PBS) and then the concentration of hydrogen peroxide can be determined. 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. Therefore, as the concentration of hydrogen peroxide can be determined the concentration of the glucose can also be determined. A study was conducted to use the Coprecipitation method to prepare the Chromium Hexacyanoferrate . The Chromium Hexacyanoferrate was used to modify the carbon paste electrode [ Chromium Hexacyanoferrate : graphite carbon powders = 3 : 7(weight ratio)] to elevate the sensitivity of responding current of detection of hydrogen peroxide. The CV ( Cyclic Voltammetry ) diagrams were plotted for the carbon paste electrode modified with Chromium Hexacyanoferrate ( Chromium Hexacyanoferrate : graphite carbon powders : carbon paste = 0.3 : 0.7 : 1) and the unmodified carbon paste electrode. The results showed that the responding current for the carbon paste electrode modified with Chromium Hexacyanoferrate was elevated significantly. At 30℃, 700rpm stirring rate and in 0.05 M phosphate buffer solution (pH=7.4), 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 -200mV operating potential, 700 rpm stirring rate and in 0.05M PBS buffer solution ( pH = 7.4 ) , the detection limit was 0.02 mM H2O2 , the linear range was 0.02～2.8 mM H2O2 , R2 = 0.9999 and the sensitivity was 242.57µA/cm2．mM H2O2. INTRODUCTION RESULTS Hydrogen peroxide is widely used in the industry and food preservation, and therefore developing a hydrogen peroxide sensor which can detect the hydrogen peroxide rapidly and conveniently 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. Because the chromium hexacyanoferrate (Ⅱ)possesses the excellent catalytic characteristic it can be used with the carbon paste and graphite carbon powders which possess the excellent conductivity to make the carbon paste electrode and to elevate the responding current of the hydrogen peroxide. The carbon paste electrode is used to detect the responding current of hydrogen peroxide in PBS buffer solution and the concentration of hydrogen peroxide can be determined from the responding current of hydrogen peroxide. The glucose and oxygen can be catalyzed by the glucose oxidase to produce gluconic acid and hydrogen peroxide, and the concentration of the glucose can then be determined. A study was conducted to use the chromium hexacyanoferrate (Ⅱ) [chromium hexacyanoferrate (Ⅱ) : graphite carbon powders = 3 : 7(weight ratio)] to modify the carbon paste electrode to elevate the responding current of detection of the hydrogen peroxide at different operating potentials. The TB (Time Base ) graphs and calibration curves for different operating potentials were plotted to determine the optimum operating conditions in this research. (A) (B) Fig. 1 CV graphs for (A) carbon paste electrode modified with chromium hexacyanoferrate (Ⅱ) ( the range of scanning potential: -0.8～+0.8 V) and (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 H2O2 at different operating potentials (chromium hexacyanoferrate (Ⅱ) : graphite carbon powders = 3 : 7); the operating potentials are [ (A) -50mV (B) –100mV (C) –150mV (D) –200mV (E) –250mV ] EXPERIMENTAL 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 ; pH meter (Metrohm 731); Constant Temperature Thermal Bath (Wisdom BC-2DT 10L); Oven (DENG YNG) ; Electric Stirrer(Fargo); 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: Chromium Chloride, 6-Hydrate (CrCl3．6H2O) ; Potassium Hexacyanoferrate(Ⅱ)( K4[Fe(CN)6] ．3H2O ) ; Hydrochloric Acid (HCl); Sodium Hydroxide (NaOH) ; Hydrogen Peroxide (H2O2); Graphite Carbon Powder ; Carbon Paste ; Cyclohexanone(C6H10O) ; Potassium Dihydrogenphosphate (KH2PO4); 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 chromium hexacyanoferrate (Ⅱ) powders, graphite carbon powders and carbon paste were mixed with the appropriate ratio (chromium hexacyanoferrate (Ⅱ) : 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. Fig. 3 The calibration curves of different operating potentials for the carbon paste electrode modified with chromium hexacyanoferrate (Ⅱ) [ ( A) -50mV (B) –100mV (C) –150mV (D) –200mV (E) –250mV ] Table 1 The sensitivities, responding currents, and R2 values of different operating potentials for the carbon paste electrode modified with chromium hexacyanoferrate (Ⅱ) Fig. 5 The TB graphs of carbon paste electrodes for determining the linear range of H2O2 (chromium hexacyanoferrate (Ⅱ) : graphite carbon powders = 3 : 7); At 30 ℃; the operating potential = –200m V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH= 7.4 ); stirring rate =700 rpm; 10μL of 100mM H2O2 is injected per 100 seconds Fig. 4 The TB graphs of carbon paste electrodes for determining the detection limit of H2O2 (chromium hexacyanoferrate (Ⅱ) : graphite carbon powders = 3 : 7); At 30 ℃; the operating potential = –200m V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH= 7.4 ) 7 cm 0.05 cm 0.5 cm CONCLUSIONS The results showed that the responding current for the carbon paste electrode modified with the chromium hexacyanoferrate (Ⅱ) 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 -250mV, it caused the detection to be unstable, -200mV operating potential was used in this research and 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 –200mV operating potential, 700rpm stirring rate and in 0.05M phosphate buffer solution (pH=7.4), the detection limit was 0.02 mM H2O2, the linear range was 0.02~2.8 mM H2O2, R2=0.9999 and the sensitivity was 242.57 μA/cm2ּmM H2O2. This research can be further applied to the glucose biosensor in the future. chromium hexacyanoferrate Mixing with Carbon Paste REFERENCES 1. W. Oungpipat, P. W. Alexander and P. Southwell-Keely,“ A Reagentless Amperometric Biosensor for Hydrogen Peroxide Determination Based on Asparagus, Tissue and Ferrocene Mediation, ” Analytica Chimica Acta, Vol. 309, 35 (1995). L. Mao and K.Yamamoto,“Glucose and Choline On-Line Biosensors Based on Electropolymerized Meldola’s Blue, ”Talanta, Vol. 51, 187 (2000). 3. Y.-M. Uang and T.-C. Chou , “Criteria for Designing a Polypyrrole Glucose Biosensor by Galvanostatic Electropolymerization, ” Electroanalysis, Vol. 14, 1564 (2002). 4. M. A. Kim and W. Y. Lee, “Amperometric Phenol Biosensor Based on Sol-Gel Silicate/Nafion Composite Film,” Analytica Chimica Acta, Vol. 479, 143 (2003). Carbon Powders DEPARTMENT OF CHEMICAL AND MATERIALS ENGINEERING, SOUTHERN TAIWAN UNIVERSITY