Journal of Electroanalytical Chemistry 683 (2012) 80–87

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Journal of Electroanalytical Chemistry

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Selective voltammetric determination of Cu(II) based on multiwalled carbonnanotube and nano-porous Cu-ion imprinted polymer

Hamid Ashkenani a,b,c,⇑, Mohammad Ali Taher a

a Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iranb Department of Chemistry, Minab Branch, Islamic Azad University, Minab, Iranc Young Researchers Society, Shahid Bahonar University of Kerman, P.O. Box 76175-133, Kerman, Iran

a r t i c l e i n f o

Article history:Received 6 June 2012Received in revised form 19 July 2012Accepted 10 August 2012Available online 23 August 2012

Keywords:Cu(II)Nano-porous imprinted polymerCarbon nanotubeModified carbon paste electrodeVoltammetry

1572-6657/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.jelechem.2012.08.010

⇑ Corresponding author at: Department of Chemistrof Kerman, Kerman, Iran. Tel.: +98 3413221452.

E-mail address: Hamid6730@gmail.com (H. Ashke

a b s t r a c t

A very high selective Cu-ion imprinted polymer as a chemical modifier was prepared by formation of1-(2-pyridylazo)-2-naphthol complex for stripping voltammetric determination of copper. Polymeriza-tion was performed with ethylene glycol dimethacrylate, as crosslinking monomer and methacrylic acidas functional monomer; in the presence of 2,20-azobis(isobutyronitrile), as initiator, via bulk polymeriza-tion. The electrochemical method is based on accumulation of copper ions at �0.6 V on the surface of Cu-IIP–CNT-modified carbon paste electrode. After preconcentration, the measurements were carried out ina closed circuit by electrolysis of the accumulated Cu(II) by voltammetric scanning from �0.25 to +0.1 V.Under optimized conditions, a linear response range from 2 to 120 lg L�1 was obtained. The detectionlimit of Cu(II) was 0.34 lg L�1 and RSD for 50.0 lg L�1 was ±2.4%. The modified electrode showed highselectivity, sensitivity and stability and was applied for enrichment and electrochemical detection of ultratrace copper ion in real samples.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction of an effective preconcentration step with pulse measurement

Copper is one of the most widely distributed elements in theenvironment of industrialized countries. It is present in all organ-isms, land and marine. It has been shown that copper is an essen-tial element for many biological processes such as blood formationand function of many important enzymes [1]. Copper is classifiedas biogenic element playing a significant role in photosynthesis,metabolism of nitrogen compounds or regulation of RNA andDNA transcription process [2]. Moreover, the presence of heavymetals such as copper in the aquatic environment is a source ofgreat environmental concern. Traces of this heavy metal is neces-sary as co-factors of enzymatic reactions, but high levels of itmay cause extreme toxicity to living organisms due to inhibitionof metabolic reactions. Two diseases of Cu metabolism in humansare Menkes disease and Wilson disease [3–6]. Therefore, applica-tion of methods to control trace amounts of copper in environmentis necessary. Electrochemical methods are the most favorable tech-niques for the determination of metal ions because of their lowcost, high sensitivity, easy operation and the ability for portability.Electrochemical stripping analysis is still recognized as a powerfultechnique for trace heavy metal detection in environmental sam-ples. Its remarkable sensitivity is attributed to the combination

ll rights reserved.

y, Shahid Bahonar University

nani).

techniques that generates an extremely favorable signal-to-back-ground ratio [7,8]. Development of environmentally friendly andselective chemical sensors has received widespread attention dur-ing the past three decades because of their possibility use in clini-cal and environmental monitoring as they provide a rapid,accurate, and low-cost method of analysis [9–11]. For these pur-poses, a great variety of electrode materials have been reported,such as gold, silver, bismuth, platinum, mercury, iridium, glassycarbon, and carbon ceramic [12–20]. Carbon paste electrode(CPE) is one of the convenient conductive matrixes to preparethe chemically modified electrodes (CMEs) by simple mixing ofgraphite/binder paste and modifier. These kinds of electrodes areinexpensive and non-toxic and posses many advantages such aslow background current, wide range of used potential, easy fabri-cation and rapid renewal [21,22]. The operation mechanism ofchemically modified carbon paste electrodes depends on the prop-erties of the modifier which is used for selectivity towards the tar-get species. Chemical modifiers are able to preconcentrate metallicions on the electrode surface by complexation or electrostaticattraction that lead to electroanalytical procedures with lowerdetection limit [9]. Dispersing materials into a conductive car-bon-based composite graphite or carbon nanotube is another sim-ple way to use their properties in electrochemistry. Unfortunately,more of the used modifiers in sensors have poor ion selectivity,which leads to high interference of other existing species withthe target metal ions. Over the past two decades the idea of im-

H. Ashkenani, M.A. Taher / Journal of Electroanalytical Chemistry 683 (2012) 80–87 81

printed polymers has been developed and gained immense popu-larity both for molecules and metal ions. Leaching of the templateion/molecule from the obtained sorbent provides active cavitiesretaining spatial geometry of template [2]. Using of ion imprintedtechnique in carbon paste electrode as modifier can develop ahighly selective copper sensor, would enable the fast, easy andlow-cost detection of this element in different samples. Ion im-printed polymers (IIPs) show very interesting characteristics suchas high selectivity, low cost, high surface area, durability and reus-ability. Moreover, the benefits of this polymerization include uni-versality and not require particular skills or sophisticatedequipments. Thus, in recent years, a number of papers dealing withthe preparation of ion selective imprinted polymers for metal ionshave been appeared in the literature [23–28]. Ion imprinting is aversatile technique for preparing polymeric materials that arecapable of high ionic recognition. In general, polymerization is car-ried out in the presence of a print ion or template, which forms acomplex with the constituent monomers [29]. After ion imprintingpolymerization, the imprint metal ion is removed from the poly-meric particles by leaching with mineral acid that leaves cavitiesor ‘‘imprinted sites’’ in the polymeric particles that are comple-mentary in shape and size of the imprint metal ion. Such an im-printed polymeric material shows an affinity for the template ionover other structurally related compounds [29].

Moreover, CNTs have been the subject of numerous investiga-tions in chemical, physical and material areas due to their novelstructural, mechanical, electronic and chemical properties [30,31].The modification of electrode substrates with multiwalled carbonnanotubes (MWCNTs) for use in analytical sensing has been docu-mented to result in low detection limits, high sensitivities, reduc-tion of overpotentials and resistance to surface fouling [32–34].

To the best of our knowledge, there is no previous report in lit-erature on the use of ion imprinted polymer and stripping voltam-metry for preconcentration and determination of Cu(II) ions in realsamples. The aim of the present investigation was to develop a newand economic CPE modified with ion imprinted polymer, for selec-tive preconcentration and quantitation of Cu(II) by differentialpulse anodic stripping voltammetry. The method is reasonablyselective and it has been applied to the determination of tracesof Cu(II) in real samples. The simplicity, high efficiency and low-cost of performance are the other features of the proposed method.

2. Experimental

2.1. Apparatus

Voltammetric experiments were performed using a Metrohmelectroanalyzer (Model 757 VA Computrace, Switzerland). Themeasurements were recorded using VA computrace version 2.0run under windows 98 operating system. All voltammograms wererecorded with a three electrode system consisting of an Ag/AgClelectrode as the reference electrode, a platinum wire as the auxil-iary electrode, and Carbon paste electrode modified with Cu-IIPwas used as the working electrode. FT-IR spectra were recordedon a Tensor-27 spectrometer (Bruker, Ettlingen, Germany). A Scan-ning Electron Microscope (AIS2100, Seron Technology, South Kor-ea) was used for morphological information. A Metrohm 827 pHmeter was used for pH adjustments. All the electrochemical exper-iments were carried out under pure nitrogen atmosphere at roomtemperature.

2.2. Materials and reagents

All chemical reagents were of analytical-reagent grade anddeionized water was used for preparation of the sample solutions.A stock solution of copper (1.0 mg mL�1) were prepared by dissolv-

ing proper amount of Cu(NO3)2�3H2O (Merck, Darmstadt, Ger-many) with deionized water. Working solutions were prepareddaily by appropriate dilution of stock solution. The buffer of phos-phate (0.10 mol L�1, pH 5) was prepared by addition of appropriateamount of phosphoric acid and sodium hydroxide into a 500 mLflask, and diluting to the mark with deionized water. Highly puregraphite Powder and multiwalled carbon nanotubes (MWCNTs)with 3–20 nm diameters, core diameter: 1–10 nm, SBET:350 m2 g�1 and 95% purity were purchased from Merck Co. (Merck,Darmstadt, Germany). Ethylene glycol dimethacrylate (EGDMA),1-(2-pyridylazo)-2-naphthol (PAN), methacrylic acid (MAA) and2,20-azobis(isobutyronitrile) (AIBN) were supplied by Merck(Darmstadt, Germany). Dimethyl sulfoxide (DMSO), acetonitrile(AC) and other chemicals were of analytical grade and were pur-chased from (Merck, Germany).

2.3. Sample preparation

2.3.1. Water samplesFour water samples, including tap water (Kerman drinking

water, Kerman, Iran), well water (Shahid Bahonar University ofKerman, Kerman, Iran), dam water (Chahar Gonbad, Sirjan, Iran)and river water (Sarcheshmeh, Sirjan, Iran) were selected and theproposed method was applied to determine the copper content.A 250.0 mL of water sample was adjusted to pH 2.0 with nitric acidso as to prevent adsorption of the metallic ions onto the flask walls.Samples were filtered to remove any suspended material. For nat-ural waters, these waters were exchanged with distilled waterused for the preparation of a phosphate buffer (pH 5) and the gen-eral procedure was used on these resultant solutions.

2.3.2. Human hairA 1.0 g of human hair sample, was washed with acetone, was

decomposed by mixture of 5 mL concentrated HNO3 and 3 mLHClO4 50%. The solution was heated until dried. Deionized waterwas added to residue and the solution was filtered and diluted to10.0 mL. A 200 lL of this solution added to 20 mL of phosphatebuffer with pH 5, and the general procedure was used on the resul-tant solution.

2.4. Preparation of Cu-imprinted polymeric particles

The Cu-IIP particles were prepared by bulk polymerization tech-nique. In order to prepare Cu-IIP, 0.25 mmol of Cu(NO3)2�3H2O,0.25 mmol of PAN and 4 mmol methacrylic acid were dissolvedin 10 mL 1–1 of DMSO-AC. The solution was allowed to be at thiscondition for 1 h in order to ensure the equilibration of the com-plexation reaction. Finally, 20 mmol of cross-linker (EGDMA) and100 mg of free radical initiator (AIBN) was mixed with previoussolution and followed by purging with N2 gas for 10 min to removemolecular oxygen from the mixture, since it traps the radicals andretards the polymerization. The polymerization was carried out ina water bath at 60 �C for 24 h. The obtained polymer was groundedin a mortar. The particles were firstly washed with ethanol to re-move the unreacted materials and then by HCl 3 mol L�1 for leach-ing of the imprint metal ions until the wash solution was free fromCu ions and, finally, by double distilled water until neutral pH isreached and dried at 60 �C. These obtained particles were namedCu-IIP. IIP were characterized by FT-IR and scanning electronmicroscopy (SEM).

2.5. Preparation of the chemically modified carbon paste electrodes

The chemically modified carbon paste electrodes were preparedby thoroughly mixing 50 mg graphite powder, 5 mg carbon nano-tube, 15 mg Cu-IIP and 30 lL of silicon oil. The electrode body

82 H. Ashkenani, M.A. Taher / Journal of Electroanalytical Chemistry 683 (2012) 80–87

was fabricated from a glass tube of i.d. 3 mm and a height of 10 cm.After the mixture homogenization, the paste was packed carefullyinto the tube tip to avoid possible air gaps often enhancing theelectrode resistance. A copper wire was inserted into the oppositeend to establish electrical contact. The external electrode surfacewas smoothed with soft paper. A new surface was produced byscraping out the old surface and replacing the carbon paste.

2.6. Accumulation and voltammetric procedures

For preconcentration step, the Cu-IIP–CNT–MCPE was im-mersed in a stirred 20 mL of 0.10 mol L�1 phosphate buffer solu-tions (pH 5) containing 1.0 lg of Cu(II) for 6 min where the Cu(II)ions were accumulated and reduced onto surface electrode in�0.6 V. Finally the differential pulse voltammogram was recordedby scanning from �0.25 to +0.1 V (with 30 mV s�1 scan rate,

Fig. 1. FTIR spectra of Cu-imprinted polymeric particles obtained v

100 mV pulse amplitude, and 4 ms pulse period). All the measure-ments were carried out at room temperature (23 ± 1 �C).

3. Results and discussion

IR spectra of the unleached (Fig. 1a) and leached Cu(II)-IIP(Fig. 1b) were recorded using KBr pellet method. These polymershave the same backbone; 3441.5 cm�1 for OAH; 3000.3 cm�1 withtwo branches for aromatic and aliphatic CAH; 1721.6 cm�1 forC@O; 1602.9 cm�1 for N@N and C@N; 1437.7 cm�1 for aromaticC@C; 1384.8 cm�1 for CAOAH deformation vibration in unleachedpolymer and 3447.8 cm�1 for OAH; 2991.4 cm�1 with twobranches for aromatic and aliphatic CAH; 1731.4 cm�1 for C@O;1672.5 cm�1 for N@N and C@N; 1457.0 cm�1 for aromatic C@C;1387.8 cm�1 (weak) for CAOAH deformation vibration in leachedpolymer that leads to the presence of the ligand in leached im-printed polymer. Moreover, based on physical property it is quite

ia bulk polymerization method: (a) unleached and (b) leached.

Fig. 2. Scanning electron micrograph of the Cu-imprinted polymeric particlesobtained via bulk polymerization method: (a) unleached and (b) leached.

Fig. 3. DP anodic stripping voltammograms in 0.10 mol L�1 phosphate buffer pH 5:(a) Cu-IIP–CNT–MCPE, with 50.0 lg L�1 Cu(II), (b) Cu-IIP–MCPE, with 50 lg L�1

Cu(II), (c) CNT–MCPE (without Cu-IIP), with 50 lg L�1 Cu(II) and (d) Cu-IIP–CNT–MCPE (without Cu(II) in accumulation medium). Other conditions; accumulation-reduction time: 6 min, accumulation-reduction potential: �0.6 V, scan rate:30 mV s�1, pulse amplitude: 100 mV, pulse period: 4 ms.

Fig. 4. The effect of Cu-IIP amount on the sensor response. Accumulation-reductiontime: 6 min, accumulation–reduction potential: �0.6 V, scan rate: 30 mV s�1, pulseamplitude: 100 mV, pulse period: 4 ms, CNT: 5%.

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obvious that in leaching process, only copper is removed from thepolymeric networks (the violet color of unleached IIP changes toorange after leaching process while the polymer without ligandis white). Furthermore, The change in C@O, C@N and N@N stretch-ing frequency to a higher region in the leached IIP proves the re-moval of Cu(II).

The morphology of the Cu-IIP produced by the bulk method wasassessed by scanning electron microscopy, and the resulting SEMpatterns are shown in Fig. 2. The respective micrographs indicatesthe formation of polymer particle with porosity and excessive sur-face area of the leached rather than unleached polymer. Createdcavities in leaching polymer can be related to the removal of tem-plate ions from polymer particles after leaching process. In poly-merization procedure, the morphology of the individual particlesdepends on type and amount of polymerization solvent, cross-link-ing monomer, ligand, imprint metal ion salt, initiator, polymeriza-tion temperature and time and stirring speed of polymerizationduring polymerization process.

3.1. Principle of the method

The principle of the method involves the chelation of Cu(II) ionsfrom basic solution with PAN onto the network of the Cu-IIP–CNT–MCPE at closed circuit where the applied potential was �0.6 V (1)simultaneously, accumulated Cu(II) ions were reduced to Cu0 (2)forming a thin film on the electrode surface at this sufficiently neg-ative potential (‘‘aq’’, and ‘‘net’’ subscript means that compound isin solution or network of IIP on the electrode surface):

Cu2þaq þ PANnet ! Cu2þPANnet ð1Þ

Cu2þPANnet þ 2e� ! Cu0net þ PANnet ð2Þ

In the next step the differential pulse waveform, is used to elec-trochemically strip the Cu0 back into Cu2+. (3) The resulting oxida-tion peak constitutes the analytical signal.

Cu0net ! Cu2þ

aq þ 2e� ð3Þ

Fig. 5. The effect of different supporting electrolyte on the sensor response.Accumulation-reduction time: 6 min, accumulation-reduction potential: �0.6 V,scan rate: 30 mV s�1, pulse amplitude: 100 mV, pulse period: 4 ms.

Fig. 6. The effect of supporting electrolyte pH on the sensor response. Accumula-tion-reduction time: 6 min, accumulation-reduction potential: �0.6 V, scan rate:30 mV s�1, pulse amplitude: 100 mV, pulse period: 4 ms.

84 H. Ashkenani, M.A. Taher / Journal of Electroanalytical Chemistry 683 (2012) 80–87

Whenever regeneration of the electrode was required (afterevery measurement), a thin layer of the surface was removed witha spatula and replaced by fresh paste.

Fig. 7. (A) DP anodic stripping voltammograms of Cu-IIP–CNT–MCPE, Cu(II)concentrations (lg L�1): (a) 2.0; (b) 5.0; (c) 10.0; (d) 20.0; (e) 50.0; (f) 80.0; (g)120.0. (B) The related calibration graph. Other conditions were the same as in Fig. 2.

3.2. Voltammetric behavior of Cu(II) on different carbon pasteelectrode

Fig. 3 presents the differential pulse stripping voltammogramsobtained with different carbon paste electrodes in 0.10 mol L�1

phosphate buffer pH 5. No peaks were observed in the potentialrange �0.25–+0.1 V (vs. Ag/AgCl) in the phosphate buffer at theCu-IIP–CNT–MCPE (curve d). when the accumulation process wascarried out for 6 min at �0.6 V in a solution containing 50.0 lg L�1

Cu(II), at the CNT–MCPE a small Cu(II) anodic peak appears at�0.05 V (curve c) and the Cu-IIP–MCPE shows higher Cu(II) anodicpeak than CNT–MCPE (curve b). However, the MCPE with CNT andCu-IIP (curve a) exhibits an anodic peak at �0.05 V, with higherintensity of the anodic current in comparison to that observed atthe other electrodes. The increase in anodic current at the Cu-IIP–CNT–MCPE demonstrates that the CNT and Cu-IIP plays animportant role in the accumulation process of Cu(II) on the elec-trode surface. Use of non-conductive imprinted polymer in elec-trode composition to increase selectivity, causes some reductionin the sensitivity of the electrode (because of reduction in conduc-tivity of the electrode). The presence of carbon nanotube due to itshigh surface and conductivity, it causes to increase the conductiv-ity, in other word, sensitivity of the electrode.

3.3. Electrode composition effect

The effect of the carbon paste composition in the voltammetricresponse of the electrode modified with Cu-IIP–CNT was evaluated

by differential pulse anodic stripping voltammetry of 50.0 lg L�1

Cu(II) in 0.10 mol L�1 phosphate buffer (pH 5). As it is visualizedin Fig. 4, the anodic peak current increased with the amount ofCu-IIP in the paste up to 15% (mass/mass). This maximum valuemay be related to the increase in surface area of the PAN layer.

Table 1The effect of co-existing metal ions.

Co-existing ion Recovery (%)

Ni(II) 77.3Pb(II) 98.3Co(II) 96.6Mg(II) 102.4Zn(II) 84.3Na(I) 99.5Bi(III) 101.8Fe(III) 98.7K(I) 99.2Hg(II) 98.5Cd(II) 88.5Ba(II) 99.0F� 98.8Br� 97.2

Table 2Determination of Cu in real samples.

Sample Added Founda Recovery (%) GFAAS

Cu (lg L�1) (lg L�1) (lg L�1)Tap waterb – 5.2 ± 0.1 – 4.9 ± 0.4

10.0 14.9 ± 0.4 97.0 –Well waterc – N.D. – N.D.

10.0 9.8 ± 0.3 98.0 –Dam waterd – N.D. – N.D.

10.0 10.2 ± 0.0.2 102.0 –River watere – 8.2 ± 0.3 – 8.6 ± 0.3

10.0 18.0 ± 0.2 98.0 –

Cu (lg g�1) (lg g�1)Hair – 13.4 ± 0.4 – 13.1 ± 0.7

10.0 23.0 ± 0.3 96.0 –

a Mean of three experiments, ±standard deviation.b Kerman drinking water, Kerman, Iran.c Shahid Bahonar University of Kerman, Kerman, Iran.d Chahar gonbad, Sirjan, Iran.e Sarcheshmeh, Sirjan, Iran.

Table 3Comparison of the proposed method with other reported methods for preconcentration o

Separation method Detection method RSD (%)

MCPEa DPASVb 2.9MCPE SWAdSVc –SA/Aud DPASV 1.06MCPE SWAdSV –MCPE DPASV 2.22MCPE Potentiometry 5SbF-CPEe DPASV –

MCPE DPASV 3.7MGEf LASVg –MCPE DPASV 3.1MCPE DPASV –MCPE DPASV –HMDEh AdSVi 0.9Cu-IIP–CNT–MCPEj DPASV 2.4

a Modified carbon paste electrode.b Differential pulse anodic stripping voltammetry.c Square wave adsorptive stripping voltammetry.d Self-assembled gold electrode.e Antimony film carbon paste electrode.f Modified gold electrode.g Linear anodic stripping voltammetry.h Hanging mercury drop electrode.i Adsorptive stripping voltammetry.j Cu(II)-ion imprinted polymer-carbon nanotube-modified carbon paste electrode.

H. Ashkenani, M.A. Taher / Journal of Electroanalytical Chemistry 683 (2012) 80–87 85

The anodic peak current decreased significantly when more than15% is used in the electrode preparation. This probably occursdue to the decrease in the conductive area at the electrode surface.

Moreover, the effect of CNT and graphite amount in carbonpaste composition was evaluated. The results showed that the bestanodic peak with higher sensitivity obtained with 5% (mass/mass)for CNT and 50% (mass/mass) for graphite powder. According tothese results a carbon-paste composition of 15% Cu-IIP, 5% CNT,50% graphite and 30% (mass/mass) silicone oil was used in furtherstudies.

3.4. Effect of supporting electrolyte

The voltammetric behavior of the proposed modified carbonpaste electrode was examined in different supporting electrolytesas 0.10 mol L�1 HCl, HNO3, CH3COOH, H2SO4, H3PO4, acetate bufferpH 5 and phosphate buffer pH 5. As it is seen from Fig. 5, the anodicpeak in phosphate buffer is higher than others and this supportingelectrolyte was chosen in all subsequent experiments.

3.5. Effect of supporting electrolyte pH

The effect of supporting electrolyte pH on the voltammetric re-sponse of the Cu-IIP–CNT–MCPE was studied over a pH range be-tween 2.0 and 7.0 in a solution containing 50 lg L�1 Cu(II) in0.10 mol L�1 phosphate and is presented in Fig. 6. The maximumanodic peak current was observed at pH 5.0. The sensitivity de-crease in acidic solution could be related to the protonation ofthe N atom in the PAN at the polymer network. The anodic peakpotentials are also pH dependent (see Fig. 6). Therefore, only a0.10 mol L�1 phosphate buffer pH 5.0 was used in the furtherstudies.

3.6. Effect of accumulation-reduction potential

Accumulation-reduction potentials between �1.0 and �0.3 Vwere investigated. For this purpose, preconcentration of Cu(II) ions(50 lg L�1) from 0.10 mol L�1 phosphate buffer (pH 5.0) were per-formed. Then, Cu(0) was analyzed by differential pulse voltamme-

f Cu(II).

Linear range (lg L�1) DL (lg L�1) Ref.

4.45–63.5 1.46 [35]10–200 0.5 [36]3–225 1.26 [37]3.18–12.7 0.19 [38]3.17–317 0.95 [39]6.34–6.34 � 105 5.08 [40]Up to 100 1.10 [41]Up to 120 1.454.77–159 1.97 [42]127.1–1271 8.3 [43]5.02–1017 0.64 [44]3.17–101.7 0.70 [45]50.8–635.5 12.7 [46]0.5–100 0.4 [47]2–120 0.34 This work

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try with 30 mV s�1 scan rate, 100 mV pulse amplitude, and 4 mspulse period. Increasing the potential from �0.3 to �0.5 V, the ano-dic peak current increased successively, and then leveled off after�0.5 V. The potentials more negative than �0.8 V led to decreasedpeak currents. Hence, �0.6 V was employed as an optimum accu-mulation-reduction potential for copper(II) determination studies.

3.7. Effect of accumulation-reduction time

The dependence of anodic peak current with the accumulation-reduction time for 50 lg L�1 Cu(II) was also investigated. Based onthe resulting data, the anodic peak current of Cu(II) was found toincrease linearly with increasing time up to 5 min due to the sur-face saturation. Hence for all subsequent measurements accumula-tion time of 6 min was employed.

3.8. Calibration plot, detection limit and reproducibility

Standard solutions containing Cu(II) were prepared in0.10 mol L�1 phosphate buffer pH 5.0 and subjected to the opti-mized anodic stripping voltammetric procedure. As can be seenin Fig. 7, the calibration plot was found to be linear between 2and 120 lg L�1 with slopes of 0.9012 lA lg�1 L. The detection limitwas calculated by making replicate current measurements at�0.6 V for a blank solution; the detection limit based on threetimes the mean of these measurements gave a value of 0.34 lg L�1

Cu(II). The relative standard deviation was determined by perform-ing seven replicate measurements on solutions containing50.0 lg L�1; the calculated value was ±2.4.

3.9. Interferences study

The selectivity and utility of the proposed method were investi-gated in the presence of various cations and anions either presentin real sample or forming complex with PAN. For this purpose, theeffect of diverse ions, at an initial mole ratio of 500-fold (ion/cop-per), on the recovery of 50.0 lg L�1 of Cu(II) from 20 mL of aqueoussolution was studied. The results of these experiments are summa-rized in Table 1. As the results indicate, the recovery of Cu(II) wasquantitative in the presence of excessive amount of possible inter-ferences cations and anions. Although, the tolerance limit of Ni(II),Zn(II) and Cd(II) is lower than other ions, but the interference ofthis ions at 500-fold of cadmium with recoveries 77.3, 84.3 and88.5, respectively is not too high. This indicates that the Cu-IIP–CNT–MCP electrode is more selective for Cu(II) than the tested po-tential interfering ions. Although, PAN is not a selective chelate, ionimprinted technique can provide the high selectivity toward theanalyte of interest. In the other words, under the optimum condi-tions, the synthesized Cu-IIP acts as a selective sorbent for Cu(II).Thus, the method is suitable for separation and determination ofCu(II) from various matrices.

3.10. Application

The reliability of the recommended procedure was examined byapplying the proposed method to the determination of Cu(II) infour water samples, including tap water (Kerman drinking water,Kerman, Iran), well water (Shahid Bahonar University of Kerman,Kerman, Iran) dam water (Chahar gonbad, Sirjan, Iran), river water(Sarcheshmeh, Sirjan, Iran) and human hair. The accuracy of themethod was verified by the recovery experiments from samplesspiked with the known amount of copper and comparing the re-sults with data obtained by graphite furnace atomic absorptionspectrometry (GFAAS). The results of this investigation are givenin Table 2. As the results demonstrate, the recoveries of spikedsample is good, and at 95% confidence levels there is no significant

differences between the results of the developed method andGFAAS analysis. These results indicate that the method is suitablefor determination of Cu(II) in wide range of matrices.

4. Conclusions

The development of selective chemical sensor has receivedwidespread attention during the past three decades because oftheir possibility use in clinical and environmental monitoring, asthey provide a rapid, accurate and low cost method of analysis.In stripping voltammetry, the accumulation step preceding themeasurement can be performed with or without an applied poten-tial (closed or open circuit condition). Closed circuit condition isfaster than opened circuit but less selective, because in spite ofopened circuit, the stripping medium is not exchanged after accu-mulation step. In the present work, combining the advantages ofvery high selectivity from the IIP technique, high sensitivity fromCNT–CPE detection and rapidity of closed circuit condition, a selec-tive, sensitive and rapid MCPE sensor has been developed for thedetermination of Cu(II). Therefore, the proposed MCPE is not inter-fered strongly by other metals and the detection limit of 0.34 al-lows the determination of copper in various matrixes. Table 3shows the comparison of the performance characteristics of theproposed sensor with those of the best previously prepared coppersensors [35–47]. The figure of merit of the proposed method is bet-ter or comparable than/to the other reported methods (see Table 3)and additionally, the method has the advantage of high selectivityand environment-friendly property. Also, our work shows a goodreproducibility, simplicity, accuracy, precision, being operativeand cheap and low toxicity as compared to other studies. These re-sults are promising for further development of new selective sen-sors based on the preconcentration of trace metals using ionimprinted polymer.

References

[1] M. Mazloum-Ardakani1, Z. Akrami1, H. Kazemian, H.R. Zare, Int. J. Electrochem.Sci. 4 (2009) 308–319.

[2] A. Tobiasz, S. Walas, L. Landowska, J. Konefał-Goral, Talanta (2012), http://dx.doi.org/10.1016/j.talanta.2012.02.005.

[3] P.C. Bull, D.W. Cox, Trends Genet. 10 (1994) 246–252.[4] M. Schaefer, G.D. Gitlin, Am. J. Physiol. 276 (1999) 311–314.[5] S.S. Saei-Dehkordi, A.A. Fallah, Microchem. J. 98 (2011) 156–162.[6] J.C. Cypriano, M.A.C. Matos, R.C. Matos, Microchem. J. 90 (2008) 26–30.[7] E. Tesarovaa, L. Baldrianova, S.B. Hocevar, I. Svancara, K. Vytras, B. Ogorevca,

Electrochim. Acta 54 (2009) 1506–1510.[8] S. Legeai, S. Bois, O. Vittori, J. Electroanal. Chem. 591 (2006) 93–98.[9] M.R. Ganjali, M. Asgari, F. Faridbod, P. Norouzi, A. Badiei, J. Gholami, J. Solid

State Electrochem. 14 (2010) 1359–1366.[10] Z.-Q. Zhao, X. Chen, Q. Yang, J.-H. Liu, X.-J. Huang, Chem. Commun. 48 (2012)

2180–2182.[11] Y. Wei, R. Yang, Y-X. Zhang, L. Wang, J-H. Liu, X-J. Huang, Chem. Commun. 47

(2011) 11062–11064.[12] G. Riveros, R. Henrıquez, R. Córdova, R. Schrebler, E.A. Dalchiele, H. Gómez, J.

Electroanal. Chem. 504 (2001) 160–165.[13] B. Bas, M. Jakubowska, M. Je _z, F. Ciepiela, J. Electroanal. Chem. 638 (2010) 3–8.[14] H. Xu, L. Zeng, D. Huang, Y. Xian, L. Jin, Food Chem. 109 (2008) 834–839.[15] A.N. Golikand, L. Irannejad, Electroanalysis 20 (2008) 1121–1127.[16] X.H. Xia, H.-D. Liess, T. Iwasita, J. Electroanal. Chem. 437 (1997) 233–240.[17] Ü.T. Yilmaz, G. Somer, J. Electroanal. Chem. 624 (2008) 59–63.[18] I.A. Ges, K.P.M. Currie, F. Baudenbacher, Biosens. Bioelectron. 34 (2012) 30–36.[19] V. Saumya, K.P. Prathish, S. Dhanya, T.P. Rao, J. Electroanal. Chem. 663 (2011)

53–58.[20] Q. Sheng, H. Yu, J. Zheng, J. Electroanal. Chem. 606 (2007) 39–46.[21] Y.H. Li, H.Q. Xie, F.Q. Zhou, Talanta 67 (2005) 28–33.[22] W.T. Suarez, L.H. Marcolino Jr., O. Fatibello-Filho, Microchem. J. 82 (2006) 163–

167.[23] M. Soleimani, S. Ghaderi, M.G. Afshar, S. Soleimani, Microchem. J. 100 (2012)

1–7.[24] T. Alizadeh, M.R. Ganjali, P. Nourozi, M. Zare, M. Hoseini, J. Electroanal. Chem. 7

(2011) 98–106.[25] H. Ashkenani, M.A. Taher, Microchim. Acta 178 (2012) 53–60.[26] A. Gómez-Caballero, A. Ugarte, A. Sánchez-Ortega, N. Unceta, M.A. Goicolea,

R.J. Barrio, J. Electroanal. Chem. 638 (2010) 246–253.[27] T. Alizadeh, S. Amjadi, J. Hazard. Mater. 190 (2011) 451–459.

H. Ashkenani, M.A. Taher / Journal of Electroanalytical Chemistry 683 (2012) 80–87 87

[28] X.-C. Fu, X. Chen, Z. Guo, C.-G. Xie, L.-T. Kong, J.-H. Liu, X.-J. Huang, Anal. Chim.Acta 685 (2011) 21–28.

[29] C. Lin, H. Wang, Y. Wang, Z. Cheng, Talanta 81 (2010) 30–36.[30] P.M. Ajayan, Chem. Rev. 99 (1999) 1787–1799.[31] H. Hassani Nadiki, M.A. Taher, H. Ashkenani, I. Sheikhshoai, Analyst 137 (2012)

2431–2436.[32] N. Chauhan, C. Shekhar Pundir, Anal. Chim. Acta 701 (2011) 66–74.[33] H. Beitollahi, I. Sheikhshoaie, Electrochim. Acta 56 (2011) 10259–10263.[34] X. Liu, H. Feng, X. Liu, D.K.Y. Wong, Anal. Chim. Acta 689 (2011) 212–218.[35] W. Zhihua, L. Xiaole, Y. Jianming, Q. Yaxin, L. Xiaoquan, Electrochim. Acta 58

(2011) 750–756.[36] W. Yantasee, Y. Lin, G.E. Fryxell, B.J. Busche, Anal. Chim. Acta 502 (2004) 207–

212.[37] A. Mohadesi, M.A. Taher, Talanta 72 (2007) 95–100.

[38] M. Etienne, J. Bessiere, A. Walcarius, Sens. Actuators B 76 (2001) 531–538.[39] S.K. Alpat, U. Yuksel, H. Akcay, Electrochem. Commun. 7 (2005) 130–134.[40] M. Javanbakht, A. Badiei, M.R. Ganjali, P. Norouzi, A. Hasheminasab, M.

Abdouss, Anal. Chim. Acta 601 (2007) 172–182.[41] A.M. Ashrafi, K. Vytras, Electrochim. Acta 73 (2012) 112–117.[42] R.M. Takeuchi, A.L. Santos, P.M. Padilha, N.R. Stradiotto, Talanta 71 (2007)

771–777.[43] X. Dai, R.G. Compton, Electroanalysis 17 (2005) 1835–1840.[44] B.C. Janegitza, L.H. Marcolino-Juniorb, S.P. Campana-Filhoc, R.C. Fariaa, O.

Fatibello-Filho, Sens. Actuators B 142 (2009) 260–266.[45] E.C. Canpolat, E. Sar, N.Y. Coskun, H. Cankurtaran, Electroanalysis 19 (2007)

1109–1115.[46] I. Cesarino, G. Marino, J.R. Matos, E.T.G. Cavalheiro, Talanta 75 (2008) 15–21.[47] A. Babaei, M. Babazadeh, E. Shams, Electroanalysis 19 (2007) 978–985.