Talanta 50 (2000) 11571162

Potentiometric determination of hydrogen peroxide atMnO2-doped carbon paste electrode

Xingwang Zheng *, Zhihui GuoDepartment of Chemistry, Shaanxi Normal Uni6ersity, Xian 710062, Peoples Republic of China

Received 23 November 1998; received in revised form 20 May 1999; accepted 16 July 1999

Abstract

A novel hydrogen peroxide (H2O2) potentiometric sensor, made with a MnO2-doped carbon paste electrode (CPE),is reported. Under optimum conditions, the electrode gives a Nernstian response for H2O2 in the concentration range3.001073.63104 mol/l, with a slope of 2119.4 mV/pH2O2 and a detection limit of 1.210

7mol/l H2O2.In addition, this sensor offers some analytical characteristics such as sensitivity, good reproducibility and a simplepreparation procedure. The effects of both the components of the electrode and other conditions on the potentialresponse of the sensor, as well as the possible response mechanism, are discussed. 2000 Elsevier Science B.V. Allrights reserved.

Keywords: Hydrogen peroxide; Manganese dioxide; Modified carbon paste electrode; Potentiometric sensor

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1. Introduction

Chemically modified electrodes [13] as usefulanalytical tools have been widely used in differentresearch fields since more analytical possibilities[47] are offered by electrode manufacture. How-ever, only a few analytical applications have em-ployed chemically modified electrodes aspotentiometric sensors [813], and the modifiedmethods of the electrodes often involve covalentattachment and polymeric films to the surface ofbased electrodes [1416], so the preparation ofthese potentiometric sensors often suffers fromthe complex preparation process of the based-

electrodes and are time-consuming. Comparedwith these methods, the fabrication of chemicallymodified carbon paste electrodes (CPE) madewith liquid paraffin oil as the gluing material aresimple and cheap, these modified carbon pasteelectrodes are often applied for this purpose andmany CPE-based potentiometric sensors havebeen reported in the literature [1719], but theseCPE-based sensors often have poor stability andpoor reproducibility since the carbon powder onthe face of the CPE is easy to be omitted.

Recently, some CPE-based potentiometric sen-sors prepared with solid paraffin oil as the gluingmaterial have been reported [20,21], these newtypes of CPE-based electrodes have presentedsome advantages, such as good stability andreproducibility.* Corresponding author. Tel.: +86-29-5235570.

0039-9140/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved.

PII: S0039 -9140 (99 )00223 -4

X. Zheng, Z. Guo / Talanta 50 (2000) 115711621158

Hydrogen peroxide (H2O2) is a very importantintermediate in environmental and biologicalreactions. The monitoring of H2O2 with a re-liable, rapid and economic method is of greatsignificance for numerous processes. Severalanalytical techniques have been employed forits determination [2224], including the man-ganese dioxide-modified CPE amperometric sen-sor [25], but most suffer from interference,complex instrumentation and expensive reagents[2628].

The potentiometric analytical method hasbeen found to be more suitable for determinationof many analytes since it possesses advantagessuch as rapid, simple instrumentation and awide linear range. But until now, to the bestof our knowledge, a potentiometric methodfor the determination of H2O2 has not been re-ported.

In this paper, by doping the CPE with MnO2and using solid paraffin as gluing material, a newCPE-based electrode was prepared and it wasfound that this CPE-based electrode presented theNernstian response for H2O2. Based on this obser-vation, a new potentiometric sensor for the deter-mination of H2O2 was proposed and factorswhich affected the analytical performance of thissensor such as the components of paste and con-dition time were studied. At the same time, thepossible response mechanism of the sensor is dis-cussed. This sensor has been used to detect H2O2in rain water samples and it has some advantagessuch as simple instrumentation, simple prepara-tion procedures and good stability andreproducibility.

2. Experimental

2.1. Reagents

All reagents were of analytical-reagent gradeor better and water doubly-distilled in a fused-silica apparatus was used throughout the ex-periment. A stock solution of H2O2 (0.100 mol/l)was prepared by diluting 5.5 ml of 30% v/vH2O2 (Shanghai Chemical Reagents Plant) to500 ml with water. The solution was standardized

by titration with potassium permanganate.Test standard solutions were prepared daily byappropriate dilution of the stock solution. A0.10 mol/l NH4Cl solution was prepared by dis-solving 5.5 g of NH4CL (Xian ChemicalReagents Plant) in 1 l of water and a 0.10 mol/lNH3H2O solution was prepared by dilutingan appropriate volume of saturated NH3 sol-ution (Xian Chemical Reagents Plant) in 1 l ofwater.

2.2. Apparatus

The potentials were measured with a PHX-215 ION-meter (Shanghai Second AnalyticalInstrument Plant, China).The reference elec-trode was a saturated calomel electrode (SCE)and the 0.10 mol/l NH3NH4Cl buffer solution(pH 8.50) was stirred with a Teflon-coated mag-netic bar during measurement. The electrochemi-cal cell used can be represented byCuMnO2-modified carbon pastesample solution(0.10 mol/, pH 8.50, NH4+NH3 buffer solu-tion)SCE.

2.3. Construction of the sensor

A Teflon rod (11 mm o.d.) with a hole at oneend (7 mm diameter, 3.5 mm deep) for the carbonpaste filling served as the electrode body. Electri-cal contact was made with a copper wire throughthe centre of the rode. Unmodified carbon pastewas prepared by adding 1.58 g of solid paraffin oilto 5.00 g of spectral carbon powder. Modifiedcarbon paste was prepared by replacing corre-sponding amounts of the carbon powder (2.5, 5,10, 15 and 20% m/m) with manganese dioxide andthen adding the solid paraffin oil.The mixtureswere homogenized carefully by heating on anelectric hot-plate and then the hot carbon pastewas packed into the hole of the electrode; after ashorted cooling time, the carbon paste wassmoothed onto paper until it had a shiny appear-ance. Before using the modified paste for poten-tiometric measurements, the electrode waspreconditioned in 0.10 mol/l NH3NH4Cl buffersolution for 72 h until a steady potential responsewas obtained.

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2.4. EMF measurement and selecti6ities

The electrode potential was measured in 50 mlof sample or standard hydrogen peroxide solu-tions (pH 8.50, 0.10 mol/l NH3NH4+ buffer)with stirring at 28C, and potentiometric measure-ment of the steady-state response was carried outin the usual manner. After each measurement, theH2O2 sensor was washed free of residual H2O2and pH buffer solution with water until a stableblank potential was obtained. The selectivity co-efficients of the electrode for H2O2 with respect toother ions were quantified using the mixed solu-tion method [29].

3. Results and discussion

3.1. Electrode response

A typical calibration curve of the electroderesponse for 3.001083.60103 mol/lH2O2 shows that the linear range of electroderesponse is 3.001073.63104 mol/l H2O2and the electrode gives a near-Nernstian responseof 19.4 mV/pH2O2 and a detection limit of 1.20107 mol/l H2O2. The calibration curve is pre-sented in Fig. 1.

3.2. Choice of the modifier on the sensor

The composition of the electrode is an impor-tant aspect to be considered for the analytical

performance of this sensor. The initial testingshowed that an unmodified carbon paste electrodedid not have any potential response to H2O2. Inorder to improve the analytical characteristics ofthe CPE electrode, different metal oxide mi-croparticles of MnO2, NiO, Co2O3 and TiO2 wereemployed as modifiers. Of these modified elec-trodes, the CPE modified with MnO2 showed astable Nernstian response to H2O2, the sensordoped with Co2O3 gave an unstable potentialresponse to H2O2, and sensors prepared withother modifiers did not show any Nernstian re-sponse to H2O2. Thus MnO2 was selected as themodifier for preparing the H2O2 potentiometricsensor.

3.3. Effect of the amount of MnO2 in CPE onthe response

The effect of the amount of MnO2 on thepotential response of the sensor for H2O2 wasinvestigated by altering the ratio of MnO2 tographite powder in the mixture.The resultsshowed that the potentiol response increased withincreasing amounts of MnO2 up to 4.0% and itdecreased above 7%. Thus, an electrode modifiedwith 4% MnO2 was employed in further work.

3.4. Effect of electrode conditioned time on theresponse

The MnO2-doped carbon paste electrode gave astable response to H2O2 after conditioning for asufficient period of time in 0.10 mol/l NH4ClNH3aqueous buffer medium. The response of anewly made electrode drops rapidly with time, butbecomes stable after conditioning for 72 h; Fig. 2shows the response curves after different condi-tioning times. The response is also more rapid(B3 min) than that of a conventional electrode,owing to the low resistance. Fig. 1 shows that theresponse of this electrode conditioned for \72 his Nernstian.

3.5. Effect of pH on the response

Based on the preliminary testing results, noneof the other acid or basic buffer solutions investi-Fig. 1. Typical calibration graph for the H2O2 sensor.

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Fig. 2. Effect of conditioning time of the sensor for 10.0mmol/l H2O2 (pH 8.50, 0.10 mol/l NH4+NH3 solution).

checked by recording the e.m.f. of a standard cellCuMnO2 chemically modified CPE1.00105mol/l H2O2, NH4+NH3 buffer solutionSCE andvarying the acidity by the addition of small vol-umes of HCl and/or ammonium solution (1.0mol/l of each); the concentration of H2O2 was1.00105 mol/l. The results showed that whilethe pH changed in the range 7.08.0, the poten-tial response increased with increasing pH; thisresults may be related to the enhancing of oxidiz-ing ability of H2O2 when pH changed in thisrange. For pH values in the range 8.09.0, theresponse was almost constant; Above pH 9.0, thepotential response dropped, possibly because it isdifficult to oxidize MnO2+ to its higher oxidationstate when pH\9.0. So the potential responsedropped. Thus, pH 8.50 NH4+NH3 buffer solu-tion was selected for the further experiments.

3.6. Selecti6ity of the electrode

The selectivity of the sensor was evaluated bythe mixed solution method. The results are pre-sented in Table 1 and show that the sensor offereda good selectivity for H2O2, and that many poten-tially interfering ionic species, excepting Co2+andPO43, do not interfere in the determination ofH2O2.

3.7. The performance of the sensor

3.7.1. The response timeWhen the hydrogen peroxide concentration was

above 1.00105 mol/l, the response time wasshorter than 3 min; when the H2O2 concentrationwas 3.00107 mol/l, the response time was 5min.

3.7.2. The reproducibility of the sensorThe reproducibility of the sensor was examined

using the reference method [30]. The results areshown in Table 2 and reveal that the sensor had agood reproducibility for determination of H2O2.

3.7.3. The life time of the sensorAfter the new sensor had been conditioned for

a given time, it showed a stable response for H2O2when it was used continually for 20 days; the

Table 1Interferences of various ions for the H2O2 sensor

Interfering ions

C2O42 7.2103

Co2+ 3.0102

CO32 2.4104

PO43 1.1102

SO42 1.6104

3.0104SO32

NO2 2.5104

gated, such as H2SO4, HCl, NaOH, NaHCO3 andN2B4O7 (their concentrations were 0.10 mol/l, re-spectively), proved to be better than 0.10 mol/lNH4+NH3 buffer solution for H2O2 determina-tion. So the NH4+NH3 buffer solution was cho-sen for controlling the pH values of samplesolutions.

The effect of pH values of sample solutions onthe potential readings of the H2O2 sensor was

Table 2Results of examination of the sensor reproducibilitya

1.00106 mol/lNumber of repeats 1.00105 mol/lH2O2H2O2for determination of

H2O2 response

163.91 183.2164.1182.62

3 163.8182.54 164.0183.1

a Results are given in mV.

X. Zheng, Z. Guo / Talanta 50 (2000) 11571162 1161

response slope and linear range of the sensor forH2O2 kept from any obvious various. The sensorappeared the poor stability and long responsetime after it was continually used over such a longtime as 30 days; at the same time, the responselinear range of the sensor for H2O2 was also poor.But the sensor regained its good response perfor-mance after it was smoothed and conditionedwhen it was first prepared.

3.8. Discussion on the possible responsemechanism of the sensor

When the sensor was conditioned in 0.10 mol/lNH3NH4+ buffer solution, the e.m.f. increasedwith time at first and then gave a constant re-sponse over a long time.While a few of H2O2presented in the testing buffer solution, the re-sponse of this sensor was faster than that of blanktesting buffer solution. Based on those experimen-tal phenomena and some of MnO2 chemicallyproperties, we proposed the possible responsemechanism of this sensor as follows. First, a fewof the solvated MnO2 was formed on the face ofthe sensor when the sensor was inserted in thetesting solution. Second, H2O2 can oxidize MnO2to produce MnO42 [31], so the sensor appearedresponse for H2O2. Third, the response resultsshowed that the e.m.f. became more positive withincreasing H2O2 concentration and the sensor re-gained its blank e.m.f. response after it was againinserted in the blank solution (not containedH2O2). The possible reason is that the organicmaterials which existed in parallin oil reduced the

MnO42 to produce MnO2. So the possible re-sponse mechanism of this sensor is attributed tothe following procedures and reactions:

MnO2 (in CPE)+H2O

MnO2H2O (in solventing film) (1)

MnO2H2OMnO(OH)2 (in solventing film)(2)

MnO(OH)2

MnO2+ +OH (in solventing film) (3)

MnO2+ +H2O2+OH

MnO42 +H2O (in solventing film) (4)

MnO42 +R (in parallin)MnO2+Ox (5)

So the potentiometric response of this sensormy be a mixture redox potentiol between theMnO42 and MnO2+; at the same time, the ratioof [MnO42]/[MnO2+] (in the solvent film) is ad-justed by the concentration of H2O2 in buffersolution, so the electrode gives the Nernstian re-sponse for the H2O2.

3.9. The sample analysis

The utility of this sensor was checked by usingit for the quantitative determination of H2O2 inrainwater samples collected on different days (inXian, China) and comparing the results with thatof the chemiluminescence (CL) method [32]. Theresults (shown in Table 3) clearly show that theproposed method performs exceptionally well andthe results obtained are in agreement with the CLmethod.

References

[1] R.A. Durst, A.J. Baumner, R.W. Murray, R.P. Buck,C.P. Andrieux, Pure Appl. Chem. 69 (1997) 13171323.

[2] J.A. Cox, M.E. Tess, T.E. Cummings, Rev. Anal. Chem.15 (1996) 173223.

[3] T.E. Mallouk, H.-N. Kim, P.J. Ollivier, S.W. Keller, in:G. Alberti, T. Bein (Eds.), Comprehensive Supramolecu-lar Chemistry, Elsevier, Oxford, 1996, pp. 189217.

[4] I.G. Casella, M.R. Guascito, A.M. Salvi, E. Desimoni,Anal. Chim. Acta 354 (1997) 333341.

[5] P.V.A. Pamidi, J. Wang, Electrolysis 8 (1996) 244247.[6] J. Liu, W. Zhoui, T. You, F. Li, E. Wang, S. Dong, Anal.

Chem. 68 (1996) 33503353.

Table 3Analytical concentrations (mol/l) of H2O2 in rainwater sam-ples

Sample Concentration as deter- Concentration as de-termined by CLmined by proposed

methoda methodb

2.61061 (2.590.3)106

2 (3.790.4)106 3.6106

(0.890.4)1063 0.8106

(0.990.3)1064 0.9106

a Mean of four determinations (9R.S.D., %).b Mean of three replications.

X. Zheng, Z. Guo / Talanta 50 (2000) 115711621162

[7] M.E.G. Lyons, Analyst 119 (1994) 805826.[8] J. Kankare, L.A. Vinokurov, Anal. Chem. 69 (1997)

23372342.[9] Y.B. Shim, D.E. Stilwell, S.M. Park, Electrolysis 3 (1991)

3136.[10] J.M. Teresa, A. Lewenstam, Anal. Chim. Acta 322 (1996)

141149.[11] R.K. Meruva, M.E. Meyerhoff, Anal. Chim. Acta 341

(1997) 187194.[12] H.S. Yim, M.E. Meyerhoff, Anal. Chem. 64 (1992) 1777

1784.[13] R.K. Meruva, M.E. Meyerhoff, Electrolysis 7 (1995)

10201027.[14] G.G. Guibaultt, R.A. Durst, M.S. Frantt, H. Freiser,

E.H. Hansen, T.S. Light, E. Pungor, G.A. Rechnittz,X.M. Rice, T.J. Bohm, W. Simon, J.D.R. Thomas, PureAppl. Chem. 48 (1976) 127.

[15] S. Dong, Z. Sun, Z. Lu, Analyst 113 (1988) 1525.[16] S. Dong, Z. Sun, Z. Lu, Analyst 113 (1988) 1525.[17] X.-Y. Hu, Z.-Z. Leng, Anal. Proc. 32 (1995) 12).[18] X.-Y. Hu, Z.-Z. Leng, Fenxi Huaxue 24 (5) (1996) 595

598.[19] X.-Y. Hu, Z.-Z. Leng, Anal. Lett. 28 (13) (1995) 2263

2274.

[20] Q.-L. Mao, S.-G. Wu, H.-C. Zhang, Fenxi Huaxue 23 (6)(1995) 648651.

[21] J.-P. Li, B.-B. Liu, B.-G Wu, Fenxi Huaxue 26 (3) (1998)279282.

[22] A.A. Karyakin, O.V. Gitelmacher, E.E. Karyakina, Anal.Chem. 67 (1995) 2419.

[23] Q. Chin, S. Dong, Anal. Chim. Acta 310 (1995) 429.[24] Yuji, M., Junko, M., Kenichi, M., Sanae, I., Anal. Chim.

Acta (in press).[25] K. Schachl, H. Alemu, K. Kalcher, J. Jezkova, Analyst

122 (1997) 985989.[26] A.L. Vogel, Textbook of Inorganic Analysis, 4th ed.,

Longman, New York, 1981, p. 381.[27] C. Matsubura, N. Kawamoto, K. Takamura, Analyst 117

(1992) 1781.[28] W. Oungpipat, P. Alexander, P. Southwell-Kelly, Anal.

Chim. Acta 309 (1995) 35.[29] P.-D. Hong, Z.-P. Sheng, G.-L. Wu, The Application and

Principle of ISO, New Time Press, Beijing, 1982, p. 51.[30] P.-D. Hong, Z.-P. Sheng, G.-L. Wu, The Application and

Principle of ISE, New Time Press, Beijing, 1982, p. 64.[31] Beijing Normal University, Inorganic Chemistry, 2nd ed.,

High Education Press, Beijing, 1986.[32] C. Niu, J. Li, Environ. Chem. 00 (1988) 634638.

.