Development of Electrochemical Sensor for the

American Journal of Advanced Drug Delivery www.ajadd.co.uk

Original Article

Development of Electrochemical Sensor for the Detection of Cadmium, Copper and Lead Najet Belkhamsa1, Mohamed Ksibi1 and Abedilah Chtaini*2 1

Université de Sfax, Laboratoire Eau Energie et Environnement L3E-ENIS, Route de Soukra km 4, B.P 1173, 3038 Sfax Tunisie 2 Equipe d’Electrochimie Moléculaire et Matériaux Inorganiques, Université Sultan Moulay Slimane, Faculté des Sciences et Techniques, Beni Mellel Maroc Date of Receipt13/02/2014 Date of Revision- 20/02/2014 Date of Acceptance- 21/02/2014

Address for Correspondence Equipe d’Electrochimie Moléculaire et Matériaux Inorganiques, Université Sultan Moulay Slimane, Faculté des Sciences et Techniques, Beni Mellel Maroc

ABSTRACT A new sensor was developed for simultaneous detection of cadmium, copper and lead, based on the cyclic and square wave voltammetry at a carbon paste electrode modified, respectively, with clay and natural phosphate. Under the optimized working conditions, calibration graph was linear. This method involves coupling a bioanalytical column to an electrochemical sensor. At the level of the column, produces the free radicals which are immediately analyzed in the electrochemical sensor. Keywords: Cyclic and square wave voltammetry, Carbon paste electrode, Clay, Natural phosphate, Heavy metals.

E-mail: [email protected]

INTRODUCTION Industrial activity is responsible for the dissemination of toxic metallic elements, such as lead, copper, cadmium and rivers, oceans and soils in trace amounts. Pollution with lead is highly significant risk factor in predicting higher rates of crime, attention deficit disorder or hyperactivity, and learning disabilities. Exposure and uptake of lead has been associated with industrial pollution, leaded paint and plumbing American Journal of Advanced Drug Delivery

systems in old housing, lead residues in soil. Detection of toxic trace metals in the environment is a challenging analytical problem. The major existing techniques for metal trace analyses are spectroscopic and inductively coupled plasma mass spectroscopy, voltammetry and chronoamperometric. Stripping voltammetric techniques are well known as very powerful techniques for determination of diverse www.ajadd.co.uk

Chtaini et al____________________________________________________ ISSN 2321-547X range of metallic and biological targets in environmental, biological and industrial samples. Their significant sensitivity is due to their unique ability to preconcentrate target species during the preconcentration step and its combination with pulse measurement techniques that generates a highly favorable signal to background ratio. Recently, it has been demonstrated that the chemically modified carbon paste electrodes have received considerable attention due to their numerous advantages, such as easy manufacture, no poison, low prize. Wider operational window, renewable surface, stability in various solvents and longer life time1,2. For trace determination, use of an Hg-film electrode has been shown to be necessary to achieve sub-µg/L detection limits for complex environmental sample3. Because Hg is toxic, however, its incorporation into sensors poses problems, particularly with regard to disposability4. It has made necessary to develop a sensitive and non toxic electrode for the determination of heavy metals. For example, bismuth film electrodes have been shown to offer comparable performance to mercury electrode in anodic stripping voltammetry5-9. It has been shown that bismuth film electrodes maintain all the advantages of mercury electrodes and, at the same time, are environmentally friendly as the toxicity of bismuth and its salts is negligible. In addition to their lower toxicity, bismuth film electrodes resulted in compared to the performance of mercury electrodes were less sensitive to dissolved oxygen and had a wide potential window for analysis. However, the determination of copper using bismuth film electrodes has been relatively ignored due to the similar stripping potentials of copper and bismuth with only a few reports in the open literature10,11. Natural phosphate modified platinum was recently used for the determination of lead with a detection limit 5 x 10-7 mol/L12. AJADD[2][1][2014]000-000

The analytical performances of the method and the phosphate lead interaction were investigated using cyclic voltammetry, differential pulse voltammetry, energy dispersive analysis of X-ray and electrochemical impedance spectroscopy. The incorporation of specially chosen modifiers in the electrodes for collection of the analytes prior to voltammetric analysis gives rise to high selectivity and sensitivity. In the past several modified carbon paste electrodes have been used for lead determination13-15. In the present paper, highly sensitive and simultaneous determination of cadmium (II), lead (II) and copper (II) on a clay and natural phosphate modified (NP) carbon paste electrodes (Clay-CPE and NP-CPE) using square wave voltammetry is reported. These modified electrodes are a valuable alternative for mercury based electrodes for anodic striping voltammetric determination of cadmium (II), lead (II) and copper (II). In this work we develop the electrochemical technology of the trapping of the mineral micro pollutants in solution such as lead, copper and cadmium using the natural phosphate and clay. This method is relatively inexpensive when compared to the spectroscopic techniques and the feasibility of compact portable instruments makes it attractive for field on line monitoring of trace metals16-18. EXPERIMENTAL Reagent CuSO4, PbSO4 and Cd (NO3)2 were dissolved into bi-distilled deionized water to form 10-3 mol/L stock solutions. Working standards for calibration were prepared by diluting the primary stock solution with bidistilled deionized water. Carbon paste was supplied from (Carbone, Lorraine, ref. 9900, French). All chemicals were of analytical grade and used without further purification. Page 2

Chtaini et al____________________________________________________ ISSN 2321-547X Instrumentation and software Square wave voltammetry was performed with a voltalab potentiostat (model PGSTAT 100, Eco Chemie B.V., Utrecht. The Netherlands) driven by the general purpose electrochemical systems data processing software (voltalab master 4 software) connected to computer. The electrochemical cell contains, respectively, clay-CPE and NP-CPE working electrode, a platinum counter electrode and a saturated calomel reference electrode (SCE). An evaluation of the purity of the phosphate and clay powder was carried out by the X-ray diffraction analysis (XRD: Cu Kα radiation, XPERT) produced at 30 kV and 25 mA scanned the diffraction angles (2) between 10 and 70 with a step size of 0.02, 2per second. The volume V of the hexagonal unit cell was determined for each modifier formulation from the relation V = a2.c.sin (2π/3). Preparation of electrode Clay and natural phosphate modified carbon paste electrodes were prepared according the following procedure19. The modified electrodes were prepared by mixing the graphite powder with respectively, clay a NP to give an appropriate ratio modifier (clay and NP).carbon paste. The mixture was grinding in a mortar agate and then a portion of the resulting composite material was housed in PTFE cylinder. The geometric surface area of the working electrode was 0.12 cm2. A bare of carbon vitreous inserted into carbon paste provided the electrical contact. Procedure of voltammetric measurements For the electro analytical determination of the concentration of metals (lead, cadmium and copper) in aqueous samples, a two step procedure was followed. The electrode was first immersed in a preconcentration solution containing the AJADD[2][1][2014]000-000

target analyte at a given concentration and selected pH. Where the accumulation of metal species was achieved chemically by binding to clay or NP at open circuit, the modified electrode was then removed from the accumulation cell, rinsed with bi distilled water, and transferred to separate voltammetric cell containing only a supporting electrolyte. All measurements were carried out at room temperature. The square wave voltammograms were recorded in different metal concentrations using 5 mV of the pulse amplitude, step potential 25 mV and the duration time is 2s at scan rate 1 mV/s. According to Miller and Miller20 the standard deviation of the mean current  measured was calculated for five voltammograms of the blank solution. The calculated  was used in the determination of the detection limit (DL, 3./slope) and the quantification limit (QL, 10./slope). The suitability of the electro analytical working procedure in detecting metal in natural matrices was tested by lake water Sfax Tunisia. RESULTS Characterization of prepared electrodes surfaces The surface structure of natural phosphate and clay was observed using scanning electron microscopy (Figs. 1 and 2). The treatment of NP describes above lead to a fraction between 100 µm and 400 µm that is rich in phosphate and as can be seen that compact natural phosphate appearance was evident (Fig. 2). The treated NP has following chemical composition: CaO (54.12 %), P2O5 (34.24 %), F(3.37 %), SiO2 (2.42 %), SO3 (2.21 %), CO2 (1.13 %), Na2O (0.92 %), MgO (0.68 %), Al2O3 (0.46 %), Fe2O3 (0.36 %), K2O (0.04 %) and several metals in the range of ppm.

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Chtaini et al____________________________________________________ ISSN 2321-547X The observed scanning electron microscopy micrograph of clay showed dense surfaces and interparticle pores (Fig. 2). The cyclic voltammograms (CVs) of the clay-CPE and CPEs were recorded in the supporting electrolyte Na2SO4 (0.1M). In cycles between -1.5 and 1.5 V, no redox peaks were observed with CPE (Fig. 3-a). The CVs obtained from, respectively, the clay modified CPE (Fig. 3-b) and NP-CPE have a different appearances, suggesting that the both electrodes are effectively modified (Fig. 4-b). Electrochemical detection of studied metals The experimental conditions have been optimized and the response characteristics determined in a previous work21. The results obtained are:  pH  7.2  Preconcentration time = 15 min In order to avoid the strong residual of reduction, the starting potential was fixed at 1.5 V versus SCE. Fig. 5 shows a cyclic voltammograms performed between-1.5 V and 1.5 V for, respectively, CPE (curve a) and NP-CPE (curve b), obtained after exposure to 4.5.10-6 mol/L Cd2+ for 15 min in a stirred solution. The reversible system could be observed at NP-CPE, with cathodic potential value, of -1.4 V and anodic potential value of -0.5 V. The response peaks observed at CPE are smaller and not well definite. The performance of the NP-CPE is based on the preconcentration of Pb2+ from aqueous solution. As can be seen from Fig. 6, two peaks appears in SQW voltammogram, the first one attributed to Cd2+ reduction, at 0.9 V, the second at -0.7 V corresponding to the oxidation of Cd2+. The concentration range from 1.10-7 to 8.10-7 mol/L was examined for proportionality of the NP-CPE signal with concentration of cadmium by analyzing model solutions containing appropriate AJADD[2][1][2014]000-000

additions of Cd2+. The linear calibration plot (Fig. 7) was obtained under optimal conditions. The regression straight line has the following equation: IReduction = 177.26. [Cd2+] + 400.43 Where IReduction is expressed in µA and the concentration in µmol/L and the correlation coefficient was 0.9738. Interference studies The SQWs (Figs. 8 and 9) have been recorded, respectively, at NP-CPE and clayCPE after the preconcentration of modified electrodes in aqueous solutions of the sulfate of lead, cadmium and copper. In the both cases, the cathodic reduction of the three studied metals occurs to the potentials lower. The clean separation of the three potential peaks offers the possibility of the simultaneous determination of lead, cadmium and copper. Comparison of the activities of prepared electrodes Figs. 10, 11 and 12 shows the SQW voltammograms recorded, respectively, at clay-CPE and NP-SPE, after preconcentration in different solutions containing the studied metals. The result confirms the electrocatalytic activity of NP and clay were also exerted on the redox of cadmium, lead and copper. As we can see the degree of sensitivity/electo-catalytic response for clay CPE is best that NP-CPE. CONCLUSIONS The simultaneous detection of lead, copper and cadmium using a carbon paste electrode modified, respectively, with natural phosphate and clay was improved when compared to unmodified CPE. NP and clay modified CPE has been successfully fabricated by the mechanical method. These prepared electrodes are shown to be able mediated effectively in redox of the studied Page 4

Chtaini et al____________________________________________________ ISSN 2321-547X metals, with significant current enhancement. These modified electrodes can be used as sensors for detection of the traces of heavy metals such as cadmium, lead or copper in different solutions. REFERENCES 1. K. Kalcher, J. M. Kauffmann, J. Wang, I. Svacara, K. Vytras, C. Nruhold, Z. Yang, Electroanalysis, 7(1995)5. 2. I. Svancara, K. Vytlas, J. Barek, J. Zima, J. Barek, Rev., Anal. Chem., 31(2001)311. 3. R. O. Kadara, J. D. Newman, I. E. Tothil, Anal. Chem. Acta, 23(2003)95104. 4. R. Kadara, I. E. Tothil, Talanta 66(2005)1089-1093. 5. D. Demetriades, A. Economou, Anal, Chim. Acta, 519(2004)167-172. 6. L. Baldrianova, I. Svancara,M. Vlcek, Electrochim. Acta, 52(2006)481-490. 7. J. Wang, J. M. Lu, U. A. Kirgoz, S. B. Hocevar, B. Ogorevc, Anal. Chim. Acta, 434(2001)29. 8. 9. L. Badrianova, I. Svancara, S. Sotiropoulos, Anal. Chem. Acta, 599(2007)249-255. 10. M. A. Baldo, S. Daniele, Anal. Lett. 37(2004)995.

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11. C. Prior, C. E. Lenehan, G. S. Walker, Electroanalysis 18(2006)2486. 12. H. Zejli, K.R. Temsamani, J.L. Hidalgo Hidalgo de Cisneros, C.I. Naranjo Rodriguez, P. Sharrock, Electrochem. Commun., 8(2006)15441548. 13. S.V. Prabhu, R.P. Baldwin, L. Kryger, Electroanalysis 1(1089)13. 14. J. Wang, Z. Taha, N. Naser, Talanta, 38(1991)81. 15. T. Molina Holdago, J.M. Pinilla Macias, L. Hernbdez, Anal. Acta 309(1995)117-122. 16. J. Wang, B. Tian, Anal. Chel., 64(1992)1706. 17. M.A. Baldo, S. Danele, G.A. Mazzochin, Electroanalysis 10(1998) 410. 18. K.Z. Brainina, L.V. Kubysheva, E.G. Miroshnikova, S.I. Parshakov, Y.G. Maksimov, A.E. Volkonsky, Anal. Chem. Technol., 5(2001)260. 19. M. El Mhammedi, M. Bakasse, A. Chtaini, Electroanalysis 19(2007) 17271733. 20. J.C. Miller, J.N. Miller, Analyst 113(1988)1351-1356. 21. Valery Hambate Gomdje, Thérèse Rosie Lauriane Ngono, Salah Eddine El quoatli, Rachida Najih, Abdelilah Chtaini. Acta Technica Corviniensis 6(2013) 139-142.

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Figure 1. Scanning electron micrograph of NP

Figure 2. Scanning electron micrograph of the clay

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Figure 3. Cyclic voltammograms in Na2SO4 (0.1M) recorded for, a- carbon paste electrode (CE) and b- clay modified CPE at 100 mV/s

Figure 4. Cyclic voltammograms in Na2SO4 (0.1M) recorded for, a- carbon paste electrode (CPE) and b- NP modified CPE at 100 mV/s

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Figure 5. Cyclic voltammograms in Na2SO4 (0.1M) recorded for, a- carbon paste electrode (CE) and b- clay modified CPE at 100 mV/s. pH 7.2, 15 min of preconcentration

Figure 6. Square wave voltammogram of 4.5.10-6 mol/L of cadmium (pH 7.2) in 0.1M Na2SO4, accumulation time: 15 min

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Figure 7. Influence of concentration of cadmium on the reduction peaks at NP-CPE under the optimized conditions

Figure 8. SQWs of 4.5 mol/L of lead, cadmium and copper at NP-CPE, pH 7.2, 15 min of preconcentration time

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Figure 9. SQW voltammograms of 4.5 mol/L of lead, cadmium and copper at clay-CPE, pH 7.2, 15 min of preconcentration time

Figure 10. SQW voltammograms of 4.5 mol/L of Cu2+, at aclay-CPE and b- NP-CPE, pH 7.2, 15 min of preconcentration time

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Figure 11. SQW voltammograms of 4.5 mol/L of Cd2+, at aclay-CPE and b- NP-CPE, pH 7.2, 15 min of preconcentration time

Figure 12. SQW voltammograms of 4.5 mol/L of Pb2+, at aclay-CPE and b- NP-CPE, pH 7.2, 15 min of preconcentration time

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