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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 H2O2 , the linear range was 0.02～1.4 mM H2O2 , R2 = 0.9994 , the sensitivity was 159.39 µA/cm2．mM H2O2 , and
the average responding current was 2.54µA.
INTRODUCTION
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
EXPERIMENTAL
RESULTS AND DISCUSSION
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)
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.
Fig. 2 The TB graphs of carbon paste
electrodes for detection of H2O2 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 ]
Table 1 The sensitivities, responding
currents and R2 values of different pH of
buffer solution for the carbon paste
electrode modified with Meldola’s Blue
2. Chemicals and Reagents
Meldola’s Blue ; Hydrochloric Acid (HCl); Sodium Hydroxide (NaOH) ; Hydrogen Peroxide
(H2O2); Graphite Carbon Powder( C ); Carbon Paste; Cyclohexanone(C6H10O); Potassium
Dihydrogenphosphate (KH2PO4); Potassium Chloride (KCl).
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 ]
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 nakeended electric wire and dried in the oven and then we obtained the carbon paste electrode.
Fig. 4 The TB graphs of carbon paste
electrode electrodes for determining the
detection limit of H2O2 [Meldola’s Blue :
carbon powders : carbon paste =
2 ：15：15 ( weight ratio )]
Fig. 5 The TB graphs of carbon paste
electrode for determining the linear
range of H2O2 [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 H2O2, the linear range was 0.02~1.4 mM H2O2 , R2=0.9994,
the sensitivity was 159.39μA/cm2ּmM H2O2 and the average responding current was 2.54µA.
Meldola’s Blue
REFERENCES
Mixing with Carbon Paste
Carbon Powders
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).
DEPARTMENT OF CHEMICAL AND MATERIALS ENGINEERING, SOUTHERN TAIWAN UNIVERSITY