1. The Operating Conditions for the Sensitivity of Detection of Hydrogen Peroxide for the Electrode Modified with Copper Hexacyanoferrate Chia-Cheng Hsiao( 蕭佳政 ), Chung-Min Lien( 連崇閔 ), Hau Lin( 林浩 ) Department of Chemical and Materials Engineering, Southern Taiwan University ABSTRACT 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 copper( Ⅱ ) hexacyanoferrate 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 Coprecipitation method to prepare the Copper( Ⅱ ) Hexacyanoferrate(Cu( Ⅱ )HCF) [Cu( Ⅱ )HCF : graphite carbon powders = 3 : 7(weight ratio)]. The Cu( Ⅱ )HCF was used to modify the carbon paste electrode because the Cu( Ⅱ )HCF possessed the excellent catalytic characteristic and it could be used with the graphite carbon powders and carbon paste to make the carbon paste electrode to elevate the responding current of the hydrogen peroxide at different operating conditions. The TB (Time Base ) graphs for different operating potentials, stirring rates, and pH values were plotted to determine the optimum operating conditions. At the optimum operating conditions - 0.2 V operating potential, 500rpm 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 0.02~2.6 mM H 2 O 2, R 2 =0.9945 and the sensitivity was 121.606 μA/cm 2 ּmM H 2 O 2. Fig 1. The theory of detection of glucose for the biosensor CuSO 4 ． 5H 2 O (aq) (MERCK ） 3(CuSO 4 ． 5H 2 O)+ 2 〔 K 3 [Fe(CN) 6 ] 〕 Cu 3 [Fe(CN) 6 ] 2 + 3K 2 SO 4 + 15H 2 O Coprecipitation method ： K 3 Fe(CN) 6(aq) （ MERCK ） Cu 3 [Fe(CN) 6 ] 2 (aq) Separation of side product Drying at 60 ℃ (48 hours) copper( Ⅱ ) hexacyanoferrate Stoichiometry 3 ： 2 (mole ratio) INTRODUCTIO N EXPERIMENTAL RESULTS AND DISCUSSION Fig 2. CV graphs for (A) carbon paste electrode modified with Cu( Ⅱ )HCF ( stirring by homogenizer ) (B) carbon paste electrode modified with Cu( Ⅱ )HCF (stirring by magnetic stirrer) (C) unmodified carbon paste electrode CONCLUSIONS The results showed that the responding current for the carbon paste electrode modified with the Copper( Ⅱ ) Hexacyanoferrate was elevated significantly. The TB (Time Base ) graphs for different operating potentials, stirring rates, and pH values were plotted to determine the optimum operating conditions. At the optimum operating conditions –0.2V operating potential, 500rpm 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 0.02~2.6 mM H 2 O 2, R 2 =0.9945 and the sensitivity was 121.606 μA/cm 2 ּmM H 2 O 2. This research can be further applied to the glucose biosensor in the future. 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, 309, 35 (1995). 2. Y. -M. Uang and T.-C. Chou, “Criteria for Designing a Polypyrrole Glucose Biosensor by Galvanostatic Electropolymerization, ” Electroanalysis, 14, 1564 (2002). 3. M. A. Kim and W. -Y. Lee, “Amperometric Phenol Biosensor Based on Sol-Gel Silicate/Nafion Composite Film,” Analytica Chimica Acta, 479, 143 (2003). REFERENCES Preparation of Copper( Ⅱ ) Hexacyanoferrate(Cu( Ⅱ )HCF) ： N2N2 Temperature at 30 ℃ CounterElectrode PtPt Working Electrode ReferenceElectrode Ag/AgCl pH 7.4 之 0.05 M PBS Buffer Solution ※ Three Electrodes System ： Preparation of the working electrode : 1. 7 cm 0.5 cm 0.05 cm Surface area of electrode=0.0805cm 2 The mixing of Cu( Ⅱ )HCF and carbon powders was evenly Mixing with equal amount of carbon paste 銅 芯 電 線 2. Then the Copper( Ⅱ ) Hexacyanoferrate powders, graphite carbon powders and carbon paste were mixed with the appropriate ratio (Copper( Ⅱ ) Hexacyanoferrate : 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. (A) (B) (C) Fig. 3 The TB graphs of carbon paste electrode for detection of H 2 O 2 at different operating potentials (Cu( Ⅱ )HCF : graphite carbon powders = 3 : 7); the operating potentials are [ (A) 0V (B) –0.05V (C) –0.1V (D) –0.2V (E) – 0.3 V ] Fig. 5 The TB graphs of carbon paste electrode for detection of H 2 O 2 at different pH values of PBS buffer solution (Cu( Ⅱ )HCF : graphite carbon powders = 3 : 7); the pH values are [ (A) pH = 4.0 (B) pH = 5.0 (C) pH = 6.0 (D) pH = 7.4 (E) pH = 8.0 ] Fig. 6 The TB graphs of carbon paste electrode for detection of H 2 O 2 (pH=7.4) Fig. 7 The TB graphs of carbon paste electrode for detection of H 2 O 2, 10μL of 100mM H 2 O 2 is injected per 100 seconds (pH=7.4) Fig. 4 The TB graphs of carbon paste electrode for detection of H 2 O 2 at different stirring rates (Cu( Ⅱ )HCF : graphite carbon powders = 3 : 7); the stirring rates are [ (A) 200 rpm (B) 300 rpm (C) 400 rpm (D) 500 rpm (E) 600 rpm ]