1. The pH on the Detection of Hydrogen Peroxide for Electrode Modified with Chromium Hexacyanoferrate Chen-Hsun Hu ( 胡真熏 ), 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 RESULTS INTRODUCTION EXPERIMENTAL ABSTRAC T Because hydrogen peroxide plays an important role in industry and also because sometimes hydrogen peroxide is used in the food industry for the purpose of preservation, a rapid and convenient sensor for detecting the hydrogen peroxide is an important research subject. 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 ) graphs 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 pH of buffer solutions were plotted to evaluate the effect of the pH of buffer solutions 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 H 2 O 2, the linear range was 0.02 ～ 2.8 mM H 2 O 2, R 2 = 0.9999 and the sensitivity was 242.57µA/cm 2 ． mM H 2 O 2. 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. In recent years, the diabetes has become one of the top ten causes of death for the people in our country. Therefore, developing a glucose biosensor which can detect the glucose rapidly and conveniently is also an important research subject. The glucose and oxygen can be catalyzed by the glucose oxidase to produce the gluconic acid and hydrogen peroxide, and therefore, as the concentration of hydrogen peroxide can be determined, the concentration of glucose can also be determined. Because the Chromium Hexacyanoferrate possesses the excellent catalytic characteristic it can be used with the carbon paste and carbon powders which possess the high 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 sensitivity of detection of hydrogen peroxide can be determined. A study of the TB (Time Base) graphs for the carbon paste electrode at different pH of buffer solutions was conducted to evaluate the effect of pH of buffer solution on the responding current of detection of hydrogen peroxide. 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 ; 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 (CrCl 3 ． 6H 2 O) ; Potassium Hexacyanoferrate( Ⅱ )( K 4 [Fe(CN) 6 ] ． 3H 2 O ) ; Hydrochloric Acid (HCl); Sodium Hydroxide (NaOH) ; Hydrogen Peroxide (H 2 O 2 ); Graphite Carbon Powder ; 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 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. 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 ; 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 (CrCl 3 ． 6H 2 O) ; Potassium Hexacyanoferrate( Ⅱ )( K 4 [Fe(CN) 6 ] ． 3H 2 O ) ; Hydrochloric Acid (HCl); Sodium Hydroxide (NaOH) ; Hydrogen Peroxide (H 2 O 2 ); Graphite Carbon Powder ; 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 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. 7 cm 0.05 cm 0.5 cm chromium hexacyanoferrate Carbon Powders Mixing with Carbon Paste 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. 5 The TB graphs of carbon paste electrodes for determining the linear range of H 2 O 2 (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 H 2 O 2 is injected per 100 seconds CONCLUSIONS REFERENCES The TB (Time Base) graphs for the carbon paste electrode at different pH of buffer solutions were plotted to evaluate the effect of pH of buffer solution on the responding current of detection of hydrogen peroxide. The results of TB (Time Base) graphs showed that when pH=8 the responding current was the highest. Because the pH value of human blood is about 7.4, the buffer solution of pH=7.4 was used in this research. The results showed that the optimum operating conditions for this research were operating potential = –200mV, stirring rate = 700 rpm, and pH = 7.4. Also the results showed that at –200mV operating potential, 700 rpm stirring rate and in 0.05M PBS buffer solution (pH=7.4), the detection limit was 0.02 mM H 2 O 2, the linear range was 0.02~2.8 mM H 2 O 2, R 2 =0.9999 and the sensitivity was 242.57μA/cm 2 ּmM H 2 O 2. 1.M. A. Kim and W.-Y. Lee, “Amperometric Phenol Biosensor Based on Sol-Gel Silicate/Nafion Composite Film,” Analytica Chimica Acta, 479, 143 (2003). 2. L. Qian and X. Yang, “Composite Film of Carbon Nanotubes and Chitosan for Preparation of Amperometric Hydrogen Peroxide Biosensor,” Talanta, 68, 721(2006). 3. D. Odaci, A. Telefoncu and S. Timur, “Pyranose Oxidase Biosensor Based on Carbon Nanotube (CNT)-Modified Carbon Paste Electrodes,” Sensors and Actuators B, 132, 159 (2008). 4. L. Shi, X. Liu, W. Niu, H. Li, S. Han, J. Chen and G. Xu,, “Hydrogen Peroxide Biosensor Based on Direct Electrochemistry of Soybean Peroxidase Immobilized on Single-Walled Carbon Nanohorn Modified Electrode,” Biosensors and Bioelectronics, 24, 1159 (2009). DEPARTMENT OF CHEMICAL AND MATERIALS ENGINEERING, SOUTHERN TAIWAN UNIVERSITY Table 1 The sensitivities, responding currents, and R 2 values of different pH of buffer solutions for the carbon paste electrode modified with chromium hexacyanoferrate ( Ⅱ ) Fig. 2 The TB graphs of carbon paste electrodes for detection of H 2 O 2 at different pH of buffer solutions (chromium hexacyanoferrate ( Ⅱ ) : graphite carbon powders = 3 : 7); the pH values are [ (A) pH=4 (B) pH=5 (C) pH=6 (D) pH=7.4 (E) pH=8 ] Fig. 3 The calibration curves of different pH of buffer solutions for the carbon paste electrode modified with chromium hexacyanoferrate ( Ⅱ ) [ (A) pH=4 (B) pH=5 (C) pH=6 (D) pH=7.4 (E) pH=8 ] (A) (B) Fig. 4 The TB graphs of carbon paste electrodes for determining the detection limit of H 2 O 2 (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 )