The pH on the Sensitivity of Detection of Hydrogen Peroxide for the Small Electrode Modified with Meldola’s Blue Chi-Wen Lo ( 羅濟玟 ), 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 ABSTRACT. A study was conducted to use the Meldola’s Blue to modify the small carbon paste electrode. Because the Meldola’s Blue possesses the excellent catalytic characteristic, it can be used with the graphite carbon powders which possesses 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 ℃, -300 mV operating potential, 500 rpm stirring rate and in 0.05 M phosphate buffer solution (PBS), the TB (Time Base) graphs for the carbon paste electrode at different pH of buffer solution were plotted to evaluate the effect of pH of buffer solution on the responding current of detection of hydrogen peroxide. At the optimum operating conditions -300 mV operating potential, 500 rpm stirring rate and in 0.05 M PBS buffer solution ( pH = 7.4 ), when the carbon paste electrode was modified with Meldola’s Blue [Meldola’s Blue : carbon powders : carbon paste = 2 ： 15 ： 15 ( weight ratio )], the detection limit was 0.02 mM H 2 O 2, the linear range was 0.02 ～ 1.4 mM H 2 O 2, R 2 = , the sensitivity was µA/cm 2 ． mM H 2 O 2, and the average responding current was 2.54µA. The detection techniques for hydrogen peroxide and glucose are important research subjects. 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 Meldola’s Blue 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 concentration of hydrogen peroxide can be determined. At 30 ℃, -300 mV operating potential, 500 rpm stirring rate and in 0.05 M phosphate buffer solution (PBS), the TB (Time Base) graphs for the carbon paste electrode at different pH of buffer solution were plotted to evaluate the effect of pH of buffer solution 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 Meldola’s Blue.techniquete INTRODUCTION 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 ; Oven (DENG YNG) ; Electric Stirrer(Fargo) ; pH meter (Metrohm 731); Constant Temperature Thermal Bath (Wisdom BC-2DT 10L); 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 Meldola’s Blue ; 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 (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 0.05 cm 0.5 cm (2) Then the Meldola’s Blue powders, graphite carbon powders and carbon paste were mixed with the appropriate ratio [Meldola’s Blue : carbon powders : carbon paste = 2 ： 15 ： 15 ( weight ratio )]. 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. Meldola’s Blue Carbon Powders Mixing with Carbon Paste DEPARTMENT OF CHEMICAL AND MATERIALS ENGINEERING, SOUTHERN TAIWAN UNIVERSITY RESULTS AND DISCUSSION Table 1 The sensitivities, responding currents and R 2 values of different pH of buffer solution for the carbon paste electrode modified with Meldola’s Blue Fig 1. CV graphs for (A) unmodified carbon paste electrode( the range of scanning potential: -0.8 ～ +0.8 V) (B) carbon paste electrode modified with Meldola’s Blue ( 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 pH values of PBS buffer solution [Meldola’s Blue : carbon powders : carbon paste = 2 ： 15 ： 15 ( weight ratio )]; the pH values are [ (A) pH = 4.0 (B) pH = 5.0 (C) pH = 6.0 (D) pH = 7.4 ] Fig. 3 The calibration curves of different pH of buffer solution for the carbon paste electrode modified with Meldola’s Blue[ (A) pH = 4.0 (B) pH = 5.0 (C) pH = 6.0 (D) pH = 7.4 ] Fig. 5 The TB graphs of carbon paste electrode for determining the linear range of H 2 O 2 [Meldola’s Blue : carbon powders : carbon paste = 2 ： 15 ： 15 ( weight ratio )] CONCLUSIONS The showed that the responding current for the carbon paste electrode modified with the Meldola’s Blue was elevated significantly. The TB (Time Base ) graphs at different pH of buffer solution were plotted to evaluate the effect of pH of PBS buffer solution on the responding current of detection of hydrogen peroxide and determine the optimum operating conditions. The results showed that at the optimum operating conditions –300mV 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 0.02~1.4 mM H 2 O 2, R 2 =0.9994, the sensitivity was μA/cm 2 ּmM H 2 O 2 and the average responding current was 2.54µA. REFERENCES 1. L. Mao and K.Yamamoto,“Glucose and Choline On-Line Biosensors Based on Electropolymerized Meldola’s Blue, ”Talanta, Vol. 51, 187 (2000). 2. 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). 3. 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). 4. S. Singh, A. Chaubey, and B. D. Malhotra, “Amperometric Cholesterol Biosensor Based on Immobilized Cholesterol Esterase and Cholesterol Oxidase on Conducting Polypyrrole Films,” Analytica Chimica Acta, Vol. 502, 229 (2004). Fig. 4 The TB graphs of carbon paste electrode electrodes for determining the detection limit of H 2 O 2 [Meldola’s Blue : carbon powders : carbon paste = 2 ： 15 ： 15 ( weight ratio )]