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Synthesis and application of nano-sized ionic imprinted polymer for the selective voltammetric determination of thallium
Author’s Accepted Manuscript Synthesis and application of nano-sized Ionic imprinted polymer for the selective voltammetric determination of thallium Mojtaba Nasiri-Majd, Mohammad Ali Taher, Hamid Fazelirad www.elsevier.com/locate/talanta
PII: DOI: Reference:
S0039-9140(15)30014-X http://dx.doi.org/10.1016/j.talanta.2015.05.058 TAL15650
To appear in: Talanta Received date: 8 March 2015 Revised date: 22 May 2015 Accepted date: 24 May 2015 Cite this article as: Mojtaba Nasiri-Majd, Mohammad Ali Taher and Hamid Fazelirad, Synthesis and application of nano-sized Ionic imprinted polymer for the selective voltammetric determination of thallium, Talanta, http://dx.doi.org/10.1016/j.talanta.2015.05.058 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis and application of nano-sized ionic imprinted polymer for the selective voltammetric determination of thallium Mojtaba Nasiri-Majd a,, Mohammad Ali Taher a, Hamid Fazelirad b Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran b Young Researchers and Elite Club, Kerman Branch, Islamic Azad University, Kerman, Iran a
Abstract A simple and selective thallium imprinted polymer was synthesized as a chemical modifier for the stripping voltammetric determination of Tl ions. The polymerization process (bulk polymerization) was performed with ethylene glycol dimethacrylate (crosslinking monomer) and methacrylic acid (functional monomer) in the presence of 2,20-azobis(isobutyronitrile) (initiator). The electrochemical method was based on the accumulation of thallium ions at the surface of a modified carbon paste electrode with Tl imprinted polymer and multi-walled carbon nanotubes. After preconcentration process, the voltammetric measurements were carried out via electrolysis of the accumulated Tl ions in a closed circuit. Under the optimized conditions, a linear response range from 3.0 to 240 ng mL-1 was obtained. The detection limit and RSD (100.0 ng mL-1 of Tl) were calculated as 0.76 ng mL-1 and ±2.7%, respectively. The suggested modified electrode has good characteristics such as excellent selectivity, high sensitivity and suitable stability. Also, it was successfully applied for the electrochemical determination of trace amounts of Tl in the environmental and biological samples. Keywords: Anodic stripping voltammetry; Modified carbon paste electrode; Ion imprinted polymer; Thallium.
1. Introduction Thallium (Tl) is widely applied in various industries including; production of low temperature thermometers, semi-conductors, mixed crystals for infrared instruments, dyes, jewelry and pigments [1]. Also, it has been recognized as a biologically significant element due to its toxic effects. Thallium is more toxic than mercury, cadmium, lead and copper [2]. It can bind to the sulfhydryil groups of proteins and mitochondrial membranes and prevent the action of some vital enzymes. Moreover, thallium has other toxic effects such as the interaction with riboflavin and riboflavin-based cofactors, inhibition of cellular respiration and distribution of calcium homeostasis [3]. The main mechanism of thallium toxicity is related to the disturbance with the vital potassium-dependent processes, e.g., substitution with potassium in the (Na+/K+)-ATPase. The ability of Tl+ ions to imitating the biological action of K+ ions has been attributed to the significant incapability of cell membranes to discern between thallium and potassium, due to similarity of their ionic charges and radii [4]. Moreover, thallium ions have mutagenic, carcinogenic and teratogenic activities [3]. Whereas the elemental form of Tl does not have toxicity, its monovalent and trivalent salts are extremely toxic. Thallium exists as Tl(I) and Tl(III) ions in the nature and its univalent state is more stable, whereas its trivalent state forms more stable complexes. All these information confirms the importance of the thallium identification and determination to providing the comprehensive data about its properties and human health relevance. In the recent years, ion imprinted polymers (IIPs) have been used as a useful tool for the determination of metals. An ion imprinted polymer is produced in two steps: 1) complex formation between a metal ion and an appropriate ligand in the liquid phase, 2) polymerization process in the presence of cross-linking monomers and initiator. The polymerization is usually performed thermally
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or photochemically. In this step of polymerization, the ligand can trap in the cross-linked polymer network (non-polymerizable ligand) or participate in the polymerization process (polymerizable ligand). Although in the former case, various ligands can be used, but in the latter case, the polymer reusability increases due to the chemical binding of ligand to the polymer network [5]. One of the common applications of modern electrochemistry is the electroanalytical detection of organic and inorganic compounds in various matrices [6-10]. Between different electrochemical techniques, anodic stripping voltammetry plays an important role. It has been identified as one of the most powerful tools for the analysis of diverse species, due to its unique preconcentration ability in association with different electrode materials [11]. There are a few reports about the determination of trace metals using of imprinted polymers and electrochemical methods. Until now, this combination has been used only for the determination of La and Ce [12], Pb [13-15], Cu [16, 17], Hg [18-20] and Cd [21]. To the best of our knowledge, there is no previous report about the use of ion imprinted polymer and anodic stripping voltammetry for the preconcentration and determination of Tl(I) ions in real samples. The purpose of the present investigation is the utilization a simple and sensitive carbon paste electrode (CPE) modified with nano-sized thallium imprinted polymer (Tl-IP) and carbon nanotubes (CNT) for the selective preconcentration and determination of Tl(I) by differential pulse anodic stripping voltammetry (DPASV). In addition, this suggested modified carbon paste electrode with thallium imprinted polymer and multi-walled carbon nanotubes (Tl-IP-MWCNT-CPE) exhibits several advantages, such as the simple preparation, reproducable surface renewal by simple polishing, good stability and an excellent ability for the determination of trace amounts of Tl(I) in water, hair and synthetic samples.
2. Experimental 2.1. Materials and reagents Highly pure graphite powder, benzo-15-crown-5, nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, thallium nitrate (TlNO3), thallium standard solution (1000.0 µg mL-1), dimethyl sulfoxide (DMSO), acetonitrile (AN), ethylene glycol dimethacrylate (EGDMA), methacrylic acid (MAA) and 2,2-azobis(isobutyronitrile) (AIBN) were purchased from Merck (Darmstadt, Germany). Thallium working solutions were prepared by appropriate dilution of the stock solution. Also pure nitrogen was used for deaeration. 2.2. Apparatus Voltammetric experiments were performed with a Metrohm electroanalyzer (Model 757 VA Computrace, Switzerland). All voltammograms were recorded with a three electrodes system: an Ag/AgCl electrode as the reference electrode, a platinum wire as the auxiliary electrode, and carbon paste electrode modified with ion imprinted polymer (IIP) or non-imprinted poymer (NIP) as the working electrode. FT-IR spectra were recorded with a Tensor-27 spectrometer (Bruker, Ettlingen, Germany). A Scanning Electron Microscope (AIS2100, Seron Technology, South Korea) was used for the morphological information. All the electrochemical experiments were carried out under the pure nitrogen atmosphere at room temperature. 2.3. Samples preparation 2.3.1. Water samples Three water samples including; tap water (Kerman drinking water, Kerman, Iran), well water (Shahid Bahonar University of Kerman, Kerman, Iran) and wastewater (Copper factory, Sarcheshmeh, Kerman, Iran) were selected and filtered to remove all of the suspended particles. Then, pH was adjusted to pH=2.0 with nitric acid (to prevent the ions adsorption onto the flask walls), stored at 4 °C in a refrigerator and the suggested method was applied. For Tl preconcentration, HCl (0.2 mol L-1) was
chosen as the appropriate medium. 2.3.2. Human hair The human hair sample was immersed in acetone for 30 min, washed with water and dried. An exact amount of sample (5.0 g) was weighed accurately and digested by 30.0 mL a mixture (HClO4 and HNO3, 1:8 v/v). The digested solution was dried and several drops of diluted H2SO4 (1:1 v/v) were added [22]. The residue was transferred to a 100.0 mL volummetric flask and diluted to the mark with deionized water. Finally, an aliquot of this solution was selected and the experiment was carried out according to the mentioned procedure. 2.3.3. Synthetic sample Also, in order to confirm the procedure's validity, this method has been applied for the determination of thallium in a synthetic sample. An aliquot of this sample was poured into the electrochemical cell and thallium content was determined by the suggested method. 2.4. Preparation of nano-sized Tl ion imprinted polymer The nano-sized Tl-IP was prepared via bulk polymerization technique. In order to prepare TlIP, 0.2 mmol TlNO3, 0.2 mmol benzo-15-crown-5 and 0.3 mL methacrylic acid were dissolved in a mixture containing 5.0 mL DMSO and 5.0 mL AN. The solution was stirred for 1 h in order to complete the complex formation process. Then, 4.0 mL EGDMA (cross-linker) and 75 mg AIBN (free radical initiator) were added to the solution. Since the oxygen traps the radicals and retards the polymerization, the Tl-IP preparation process was continued by N2 gas purging for 15 min to remove the molecular oxygen from the mixture. The final step of polymerization was carried out in a water bath at 60 ºC for 10 h. The obtained polymer was powdered with a mortar and pestle. These particles were washed with ethanol and HCl (2.0 mol L-1) to remove the unreacted ligands and the imprint metal ions (until the output solution was free from the Tl ions), respectively. Finally, the obtained polymer was washed with deionized water (10 times) and dried at 60 ºC. This polymer was named TlIP and characterized by FT-IR and scanning electron microscopy (SEM). Also, NIP was prepared via the same procedure, but thallium (as TlNO3) did not exist in the polymerization mixture. 2.5. Preparation of Tl-IP-MWCNT-CPE The modified carbon paste with thallium IP and multi-walled carbon nanotube was prepared by mixing 60 mg graphite powder, 5 mg carbon nanotube, 5 mg Tl-IP (or 5 mg NIP) and 30 µL silicon oil. The mixture was blended for 20 min until a uniform paste was obtained. For the preparation of TlIP-MWCNT-CPE, a portion of this paste was filled into the end of a glass tube (ca. 3.0 mm i.d. and 10 cm long). When necessary, a new surface was obtained by polishing the electrode surface on a smooth paper. The electrical connection was established with a copper wire. 2.6. General procedure For the preconcentration step, the Tl-IP-MWCNT-CPE was inserted in 20.0 mL stirring HCl solution (0.2 mol L-1) containing 100.0 ng mL-1 Tl(I) for 300 s, where the Tl(I) ions were accumulated and reduced at -1.2 V. Then, the differential pulse voltammogram was recorded by scanning from -0.5 to -1.0 V (30 mV s-1 scan rate, 100 mV pulse amplitude and 4 ms pulse period). All of the measurements were carried out at room temperature (~23±1 °C) and the observed peak in -0.69 V was applied for the determination of Tl content.
3. Results and discussion The prepared imprinted nanoparticles were characterized by IR spectroscopy and scanning
electron microscopy. IR spectra of the unleached (Fig. 1a) and the leached (Fig. 1b) Tl-IP were recorded using KBr pellet method. These polymers have the same backbone; 2990.99 cm-1 for aliphatic C-H; 3000.13 cm-1 for aromatic C-H; 1727.89 cm-1 for C=O; 1638.45 cm-1 for aromatic C=C; 1155.50 cm-1 for stretching vibration of C-O in unleached polymer and 2956.58 cm-1 for aliphatic C-H; 3001.30 cm-1 for aromatic CH; 1732.93 cm-1 for C=O; 1637.10 cm-1 for aromatic C=C and 1160.00 cm-1 for stretching vibration of CO in leached imprinted polymer. The similarities between the IR spectra of unleached and leached IIPs, suggest that the leaching process does not affect on the different groups of the polymeric network. Furthermore, the shifts of aromatic C-H, C=O and C-O frequencies to higher regions in the leached IIP, proves the removal of Tl(I). The synthesized Tl-IP structure was investigated by scanning electron microscopy and the SEM image is presented in Fig. 2. In this type of polymerization method, the morphology of the IIP particles depends on the ligand, cross-linking monomer, type and amount of polymerization solvent, metal ion salt, initiator, temperature and time.
3.1. Voltammetric behavior of Tl at the surface of different electrodes The ability of the different modified carbon paste electrodes to preconcentration of Tl(I) ions was investigated. Fig. 3 shows the differential pulse anodic stripping voltammograms of MWCNT-CPE (modified CPE with multi-walled carbon nanotubes) (a), NIP-MWCNT-CPE (modified CPE with nonimprinted polymer and multi-walled carbon nanotubes) (b), Tl-IP-CPE (modified CPE with Tl ion imprinted polymer) (c), Tl-IP-MWCNT-CPE (modified CPE with Tl ion imprinted polymer and multiwalled carbon nanotubes) (d) and Tl-IP-MWCNT-CPE (modified CPE with Tl ion imprinted polymer and multi-walled carbon nanotubes, no Tl(I) in accumulation medium) (e) in HCl 0.2 mol L-1 as the preconcentration and accumulation medium. In MWCNT-CPE case, a small anodic peak (at about -0.69 V) indicates some adsorption of Tl(I) on the surface of this modified electrode. However, this small peak confirms the Tl accumulation process at the surface of MWCNT-CPE is not quantitative. In contrast, when NIP-MWCNT-CPE and TlIP-CPE were applied, two well-defined anodic stripping peaks were appeared in the medium containing 100.0 ng mL-1 Tl(I). These peaks were observed due to the reoxidation of elemental thallium, that were produced by the reduction of accumulated Tl(I) at the negative potentials. As can be seen, the anodic peak current of thallium at Tl-IP-CPE is several times larger than NIP-MWCNT-CPE and MWCNT-CPE. Finally, when Tl-IP-MWCNT-CPE was applied, the peak current showed a well increasing after accumulation in the medium containing 100.0 ng mL-1 Tl(I). Also, when Tl-IP-MWCNTCPE was applied in the absence of Tl(I), only a residual current was observed (Fig. 3(e))
3.2. Optimization of analytical conditions To optimize the Tl-IP-MWCNT-CPE performance for the electrochemical determination of thallium ions, the important parameters such as HCl concentration, supporting electrolyte type, accumulation time, reduction potential and amounts of ion imprinted polymer and carbon nanotubes were investigated and optimized. 3.2.1. Effect of supporting electrolyte The voltammetric behavior of the suggested modified electrode was examined in the different supporting electrolytes including; H2SO4, HNO3, HClO4 and HCl (in all cases, the concentration
was adjusted to 0.2 mol L-1). Fig. 4 shows the anodic peak in HCl is the most acceptable peak in comparison with the other supporting electrolytes. So, HCl was chosen as supporting electrolyte in the further experiments. 3.2.2. Effect of HCl concentration The effect of HCl concentration as the selected supporting electrolyte on the Tl-IP-MWCNTCPE response was investigated between 0.01 and 0.5 mol L-1. The results show the maximum anodic peak current was obtained in 0.2 mol L-1. Therefore, 0.2 mol L-1 HCl was chosen in the next experiments. 3.2.3. Effect of the electrode composition The effect of the electrode composition on the Tl-IP-MWCNT-CPE response was evaluated by the voltammetric determination of 100.0 ng mL-1 Tl(I) in HCl 0.2 mol L-1. The anodic peak current increased with increasing the amount of Tl-IP and multi-walled carbon nanotubes up to 5% (w/w) and then decreased in further amounts. According to these results, a modified carbon paste electrode with 5% (w/w) Tl-IP and MWCNT was selected for the suggested method. 3.2.4. Effect of reduction potential Reduction potentials between -0.8 and -1.4 V were studied. For this purpose, the preconcentration of Tl(I) ions (100.0 ng mL-1) from 0.2 mol L-1 HCl was performed. Then, Tl(0) was analyzed by the differential pulse voltammetry with 30 mV s-1 scan rate, 100 mV pulse amplitude and 4 ms pulse period. The results show when the potential was increased from -0.8 to -1.2 V, the anodic peak current showed a maximum amount and then decreased. So, -1.2 V was chosen as an optimum reduction potential for Tl(I) determination. 3.2.5. Effect of accumulation-reduction time The effect of time on the anodic peak current for 100 ng mL-1 Tl(I) was investigated. Based on the obtained data, the anodic peak current of Tl(I) increased linearly with increasing time up to 300 s due to the surface saturation and remained constant for longer times. Based on these results, for all subsequent measurements, 300 s was employed. 3.2.6. Performance characteristics Standard solutions containing Tl(I) were prepared in 0.2 mol L-1 HCl and applied for the optimized anodic stripping voltammetric procedure. The calibration graph (Fig. 5) showed a linear relationship in the range of 3.0 and 240 ng mL-1 and the detection limit was calculated as 0.76 ng mL-1. The relative standard deviation (R.S.D.) was obtained as ±2.7% for seven successive measurements of the similar samples containing 100.0 ng mL-1 Tl(I). This result indicates a good reproducibity of the modified electrode construction could be due to the strong adsorption of Tl(I) ions at the electrode surface. 3.2.7. Interferences study The method efficiency for the extraction and preconcentration of thallium ions in the presence of various cations and anions was examined. The tolerance level was defined as the maximum amount of interfering ions can produce an error of ±5% on the Tl(I) current. The tolerance level of each species was tested and if interference occurred, the ratio was reduced until it ceased. The study was performed with 20.0 mL solution containing 100.0 ng mL-1 Tl and different concentrations of concomitant ions. The results of these experiments are summarized in Table 1. As the results indicate, the Tl(I) recoveries were quantitative in the presence of excessive amounts of
possible interference cations and anions. Although, the tolerance limit of Cd(II), Pb(II) and Sn(II) is lower than other ions, but the interferences of these ions (at 500-fold of thallium) are not too high. These results indicate the Tl-IP-MWCNT-CPE electrode is suitable for the selective extraction and determination of Tl(I) from various matrices. 3.2.8. Analytical applications In order to investigate the procedure's validity, the suggested method was applied for the determination of thallium in water samples (tap water, well water and wastewater) and human hair. The reliability of the method was checked by the analysis of the spiked samples with the known amount of thallium. The illustrated results in Table 2 reveal the recoveries of the spiked samples at a high confidence level (95%) are satisfactory. To verify the method accuracy, this procedure was applied for the determination of thallium in a synthetic sample and the analytical results are presented in Table 3. As can be seen, the obtained results are in good agreement with the reference values and there is no significant difference between the results and the accepted values. Thus, the procedure is reliable for the analysis of a wide range of samples. 3.2.9. Comparison with some previously reported Table 4 compares the performance characteristics of the recommended sensor, with some prepared thallium sensors [23-33]. The suggested method has the better, or comparable performance in comparison with the other reported methods and has some advantages such as the high selectivity and environmentally-friendly property. As can be seen in this table, the Tl-IP-MWCNT-CPE shows the lowest detection limit and the best relative standard deviation except the only four cases [24,28,29,33]. Also, this method shows the good reproducibility, simplicity, high accuracy and precision and low toxicity in comparison with the other studies.
4. Conclusion In this work, the anodic stripping voltammetric procedure for the thallium determination was investigated. This work indicated the modified carbon paste electrode with Tl-IP and multi-walled carbon nanotube (Tl-IP-MWCNT-CPE) is a suitable sensor for the analytical determination of Tl(I). The suggested electrode showed the good characteristics such as a wide concentration range (3.0-240 ng mL-1), a very low detection limit (0.76 ng mL-1) and good selectivity. This modified electrode (Tl-IPMWCNT-CPE) coupled with differential pulse anodic stripping voltammetry was applied in water, human hair and synthetic sample with satisfactory results. In addition, some other advantages of this electrochemical sensor are its rapid response, simple operation, precise results, low cost and direct application for the determination of thallium.
References [1] L.B. Escudero, P. Berton, E.M. Martinis, R.A. Olsina, R.G. Wuilloud, Dispersive liquid-liquid microextraction and preconcentration of thallium species in water samples by two ionic liquids applied as ion-pairing reagent and extractant phase, Talanta 88 (2012) 277-283. [2] G. Repetto, A. Del Peso, M. Repetto, Thallium in the Environment, first ed., Wiley, Chichester, England, 1998. [3] N.D. Solovyev, N.B. Ivanenko, A.A. Ivanenko, Whole blood thallium determination by GFAAS with high-frequency modulation polarization Zeeman effect background correction, Biol. Trace Elem. Res. 143 (2011) 591-599. [4] A.L. Peter, T. Viraraghavan, Thallium: a review of public health and environmental concerns,
Environ. Int. 31 (2005) 493-501. [5] M. Shamsipur, J. Fasihi, K. Ashtari, Anal. Chem. 79 (2007) 7116-7123. [6] S. Jahandari, M.A. Taher, H. Fazelirad, I. Sheikhshoai, Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes, Microchim. Acta 180 (2013) 347-354. [7] P.S. Liew, B. Lertanantawong, S.Y. Lee, R. Manickam, Y.H. Lee, W. Surareungchai, Electrochemical Genosensor Assay Using Lyophilized Gold Nanoparticles/Latex Microsphere Label for Detection of Vibrio cholerae, Talanta 139 (2015) 167-173. [8] A. Cantalapiedra, M.J. Gismera, J.R. Procopio, M.T. Sevilla, Electrochemical sensor based on polystyrene sulfonate-carbon nanopowders composite for Cu (II) determination, Talanta 139 (2015) 111-116. [9] D. Merli, D. Zamboni, S. Protti, M. Pesavento, A. Profumo, Electrochemistry and analytical determination of lysergic acid diethylamide (LSD) via adsorptive stripping voltammetry, Talanta 130 (2014) 456-461. [10] M.S. Qureshi, A.R. bin Mohd Yusoff, A. Shah, A. Nafady, Sirajuddin, A new sensitive electrochemical method for the determination of vanadium(IV) and vanadium(V) in Benfield sample, Talanta 132 (2015) 541-547. [11] S. Cheraghi, M.A. Taher, H. Fazelirad, Voltammetric sensing of thallium at a carbon paste electrode modified with a crown ether, Microchim. Acta 180 (2013) 1157-1163. [12] X.Z. Li, Y.P. Sun, Evaluation of ionic imprinted polymers by electrochemical recognition of rare earth ions, Hydrometallurgy 87 (2007) 63-71. [13] T. Alizadeh, S. Amjadi, Preparation of nano-sized Pb2+ imprinted polymer and its application as the chemical interface of an electrochemical sensor for toxic lead determination in different real samples, J. Hazard. Mater. 190 (2011) 451-459. [14] Z. Wang, Y. Qin, C. Wang, L. Sun, X. Lu, X. Lu, Preparation of electrochemical sensor for lead(II) based on molecularly imprinted film, Appl. Surf. Sci. 258 (2012) 2017-2021. [15] A. Bahrami, A. Besharati-Seidani, A. Abbaspour, M. Shamsipur, A highly selective voltammetric sensor for sub-nanomolar detection of lead ions using a carbon paste electrode impregnated with novel ion imprinted polymeric nanobeads, Electrochim. Acta 118 (2014) 92-99. [16] W. Zhihua, L. Xiaole, Y. Jianming, Q. Yaxin, L. Xiaoquan, Copper(II) determination by using carbon paste electrode modified with molecularly imprinted polymer, Electrochim. Acta 58 (2011) 750756. [17] M. Mazloum-Ardakani, M.K. Amini, M. Dehghan, E. Kordi, M.A. Sheikh-Mohseni, Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II), J. Iran. Chem. Soc. 11 (2014) 257-262. [18] T. Alizadeh, M.R. Ganjali, M. Zare, Application of an Hg2+ selective imprinted polymer as a new modifying agent for the preparation of a novel highly selective and sensitive electrochemical sensor for the determination of ultratrace mercury ions, Anal. Chim. Acta 689 (2011) 52-59. [19] X.C. Fu, X. Chen, Z. Guo, C.G. Xie, L.T. Kong, J.H. Liu, X.J. Huang, Stripping voltammetric detection of mercury(II) based on a surface ion imprinting strategy in electropolymerized microporous poly(2-mercaptobenzothiazole) films modified glassy carbon electrode, Anal. Chim. Acta 685 (2011) 21-28. [20] X.C. Fu, J. Wu, L. Nie, C.G. Xie, J.H. Liu, X.J. Huang, Electropolymerized surface ion imprinting films on a gold nanoparticles/single-wall carbon nanotube nanohybrids modified glassy carbon electrode for electrochemical detection of trace mercury(II) in water, Anal. Chim. Acta 720 (2012) 29-37. [21] T. Alizadeh, M.R. Ganjali, P. Nourozi, M. Zare, M. Hoseini, A carbon paste electrode impregnated with Cd2+ imprinted polymer as a new and high selective electrochemical sensor for
determination of ultra-trace Cd2+ in water samples, J. Electroanal. Chem. 657 (2011) 98-106. [22] H. Fazelirad, M.A. Taher, M. Nasiri-Majd, GFAAS determination of gold with ionic liquid, ion pair based and ultrasound-assisted dispersive liquid-liquid microextraction, J. Anal. Atom. Spectrom. 29 (2014) 2343-2348. [23] A.A.A. Gaber, New thallium (I) ion selective electrode based on indeno pyran compound, Sens. Actuators B 96 (2003) 615-620. [24] M.M. Hassanien, K.S. Abou-El-Sherbini, G.A.E. Mostafa, A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III), Talanta 59 (2003) 383392. [25] K.S. Park, S.O. Jung, S.S. Lee, J.S. Kim, Thallium (I)-selective electrodes based on calix [4] pyrroles, Bull. Korean Chem. Soc. 21 (2000) 909-912. [26] M.B. Saleh, A novel PVC membrane sensor for potentiometric determination of thallium (I), J. Electroanal. Chem. 448 (1998) 33-39. [27] S.V. Kharitonov, V.I. Zarembo, Ion-selective electrode for determining thallium (III) as its complexonate, J. Anal. Chem. 60 (2005) 1056-1061. [28] H. Bagheri, A. Afkhami, A. Shirzadmehr, H. Khoshsafar, A new nano-composite modified carbon paste electrode as a high performance potentiometric sensor for nanomolar Tl (I) determination, J. Mol. Liq. 197 (2014) 52-57. [29] K. Vytřas, E. Khaled, J. Ježková, H.N.A. Hassan, B.N. Barsoum, Studies on the potentiometric thallium (III)-selective carbon paste electrode and its possible applications, Fresenius J. Anal. Chem. 367 (2000) 203-207. [30] H. Dong, H. Zheng, L. Lin, B. Ye, Determination of thallium and cadmium on a chemically modified electrode with Langmuir-Blodgett film of p-allylcalix[4]arene, Sens. Actuators B 115 (2006) 303308. [31] V.A. Tarasova, Voltammetric determination of thallium(I) at a mechanically renewed Bi-graphite electrode, J. Anal. Chem. 62 (2007) 157-160. [32] C. Kokkinos, A. Economou, Disposable microfabricated 3-electrode electrochemical devices with integrated antimony working electrode for stripping voltammetric determination of selected trace metals, Sens. Actuators B 192 (2014) 572-577. [33] E.O. Jorge, M.M. Neto, M.M. Rocha, A mercury-free electrochemical sensor for the determination of thallium(I) based on the rotating-disc bismuth film electrode, Talanta 72 (2007) 1392-1399.
Highlights There are only a few reports on the voltammetric determination of ions by IIPs. It is the first report on the voltammetric determination of Tl with Tl-IP-CNT-CPE. The CPE was modified with Tl-IP and CNT and used for the determination of Tl. Tl-IP-CNT-CPE was successfully applied for Tl determination in real samples.
Table 1 Effect of interfering ions Foreign Recovery ion (%) Ni(II) 96.3 Pb(II) 74.5 Zn(II) 99.1 Mg(II) 96.1 Co(II) 97.4 Na(I) 102.1 Bi(III) 98.5 Fe(III) 98.3 K(I) 102.5 Hg(II) 99.3 Cu(II) 96.4 Ba(II) 97.1 Cd(II) 85.3 Sn(II) 83.8 NO3100.6 97.8 F Br98.4 Mole ratio of ion/thallium:500-fold
Table 2 Determination of thallium in real samples. Sample Spiked Founda -1 (ng mL ) Tap waterb 0.0 N.D.c 50.0 48.2±1.4 Well waterd 0.0 N.D. 50.0 47.7±1.2 Waste watere 0.0 3.8±0.1 10.0 14.1±0.4 -1 (ng g ) Human hair 0.0 76.2±2.2 25.0 101.8±3.1
Recovery (%) 96.4 95.4 103.0 102.4
a
Mean ± standard deviation (n=3) Kerman drinking water, Kerman, Iran c N.D.: Not Detected d Shahid Bahonar University of Kerman, Kerman, Iran e Copper factory, Sarcheshmeh, Kerman, Iran b
Table 3 Analysis of thallium in synthetic sample Sample Composition Synthetic Ca;15.0,Cu;8.0,Mn;20.0 sample Mg;40.0,Co;5.0,Pb;50.0 Ni;22.0,Cd:2.0,Zn;70.0 Hg;300.0,K; 35.0,Na;300.0 Tl;200.0 (ng mL-1) a
Mean ± Standard deviation (n=3)
Founda 194.3±5.8
Recovery (%) 97.2
Table 4 Comparison of the proposed method with other reported electrochemical methods for the thallium determination Analysis R.S.D. Linear range LOD Ref. method (%) (ng mL-1) (ng mL-1) Pa 204.4-20.4×106 145 [23] P 1.4 817.5-20.4×104 408.8 [24] -6 P 654.2-20.4×10 204.38 [25] P 1×10-5-1×10-1 654 [26] P 1144.5-20.4×106 30 [27] p <1 1.74-2×106 1.1 [28] P 1.1-1.7 204.4-10.2×105 204.38 [29] b [30] SV 7.2-8.2 4.9-245.3 1.0 SV 2-4 10.2-1022 1.0 [31] SV 3.9 10-80 0.9 [32] ASVc 0.2 2.5-30.6 2.2 [33] 2.70 3.0-240 0.76 This work DPASV a
Potentiometry Stripping voltammetry c Anodic stripping voltammetry b
Figure captions: Fig. 1. FTIR spectra of the thallium imprinted polymer obtained via bulk polymerization method: (a) unleached and (b) leached. Fig. 2. SEM image of the thallium imprinted polymer obtained via bulk polymerization method. Fig. 3. Differential pulse stripping voltammograms in HCl 0.2 mol L-1: (a) MWCNT-CPE with 100.0 ng mL-1 Tl(I), (b) NIP-MWCNT-CPE with 100.0 ng mL-1 Tl(I), (c) Tl-IPCPE with 100.0 ng mL-1 Tl(I), (d) Tl-IP-MWCNT-CPE with 100.0 ng mL-1 Tl(I) and (e) Tl-IP-MWCNT-CPE, no Tl(I) in accumulation medium. Other conditions: accumulation time: 300 s, reduction potential: -1.2 V, pulse amplitude: 100 mV, pulse period: 4 ms.
Fig. 4. The effect of the supporting electrolyte type on the Tl-IP-MWCNT-CPE response. Other conditions were the same as in Fig. 3 except the supporting electrolyte type. Fig. 5. Differential pulse stripping voltammograms of Tl-IP-MWCNT-CPE, concentrations of (a-j): 3.0, 10.0, 20.0, 30.0, 40.0, 50.0, 100.0, 150.0, 200.0 and 240.0 ng mL-1 of Tl(I).
Fig. 1.
Fig. 2.
Tl-IP-MWCNT-CPE Tl-IP-CPE NIP-MWCNT-CPE
100 MWCNT-CPE
I (µA)
Tl-IP-MWCNT-CPE,no Tl in accumulation medium
50
d 0 -0.72
-0.67 E (V) vs. Ag/AgCl
Fig. 3.
100
I (µA)
Nitric acid Perchloric acid Sulfuric acid Hydrochloric acid
50
Fig. 4.
0 -0.72
-0.67 E (V) vs Ag/AgCl
200
j 150 I (µA)
Fig. 5.
100
50
a
0 -0.75
-0.7 -0.65 E (V) vs. Ag/AgCl
Accumulation of Tl(I) at the surface of Tl-IP-MWCNT-CPE and determination by DPASV
PII: DOI: Reference:
S0039-9140(15)30014-X http://dx.doi.org/10.1016/j.talanta.2015.05.058 TAL15650
To appear in: Talanta Received date: 8 March 2015 Revised date: 22 May 2015 Accepted date: 24 May 2015 Cite this article as: Mojtaba Nasiri-Majd, Mohammad Ali Taher and Hamid Fazelirad, Synthesis and application of nano-sized Ionic imprinted polymer for the selective voltammetric determination of thallium, Talanta, http://dx.doi.org/10.1016/j.talanta.2015.05.058 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis and application of nano-sized ionic imprinted polymer for the selective voltammetric determination of thallium Mojtaba Nasiri-Majd a,, Mohammad Ali Taher a, Hamid Fazelirad b Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran b Young Researchers and Elite Club, Kerman Branch, Islamic Azad University, Kerman, Iran a
Abstract A simple and selective thallium imprinted polymer was synthesized as a chemical modifier for the stripping voltammetric determination of Tl ions. The polymerization process (bulk polymerization) was performed with ethylene glycol dimethacrylate (crosslinking monomer) and methacrylic acid (functional monomer) in the presence of 2,20-azobis(isobutyronitrile) (initiator). The electrochemical method was based on the accumulation of thallium ions at the surface of a modified carbon paste electrode with Tl imprinted polymer and multi-walled carbon nanotubes. After preconcentration process, the voltammetric measurements were carried out via electrolysis of the accumulated Tl ions in a closed circuit. Under the optimized conditions, a linear response range from 3.0 to 240 ng mL-1 was obtained. The detection limit and RSD (100.0 ng mL-1 of Tl) were calculated as 0.76 ng mL-1 and ±2.7%, respectively. The suggested modified electrode has good characteristics such as excellent selectivity, high sensitivity and suitable stability. Also, it was successfully applied for the electrochemical determination of trace amounts of Tl in the environmental and biological samples. Keywords: Anodic stripping voltammetry; Modified carbon paste electrode; Ion imprinted polymer; Thallium.
1. Introduction Thallium (Tl) is widely applied in various industries including; production of low temperature thermometers, semi-conductors, mixed crystals for infrared instruments, dyes, jewelry and pigments [1]. Also, it has been recognized as a biologically significant element due to its toxic effects. Thallium is more toxic than mercury, cadmium, lead and copper [2]. It can bind to the sulfhydryil groups of proteins and mitochondrial membranes and prevent the action of some vital enzymes. Moreover, thallium has other toxic effects such as the interaction with riboflavin and riboflavin-based cofactors, inhibition of cellular respiration and distribution of calcium homeostasis [3]. The main mechanism of thallium toxicity is related to the disturbance with the vital potassium-dependent processes, e.g., substitution with potassium in the (Na+/K+)-ATPase. The ability of Tl+ ions to imitating the biological action of K+ ions has been attributed to the significant incapability of cell membranes to discern between thallium and potassium, due to similarity of their ionic charges and radii [4]. Moreover, thallium ions have mutagenic, carcinogenic and teratogenic activities [3]. Whereas the elemental form of Tl does not have toxicity, its monovalent and trivalent salts are extremely toxic. Thallium exists as Tl(I) and Tl(III) ions in the nature and its univalent state is more stable, whereas its trivalent state forms more stable complexes. All these information confirms the importance of the thallium identification and determination to providing the comprehensive data about its properties and human health relevance. In the recent years, ion imprinted polymers (IIPs) have been used as a useful tool for the determination of metals. An ion imprinted polymer is produced in two steps: 1) complex formation between a metal ion and an appropriate ligand in the liquid phase, 2) polymerization process in the presence of cross-linking monomers and initiator. The polymerization is usually performed thermally
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or photochemically. In this step of polymerization, the ligand can trap in the cross-linked polymer network (non-polymerizable ligand) or participate in the polymerization process (polymerizable ligand). Although in the former case, various ligands can be used, but in the latter case, the polymer reusability increases due to the chemical binding of ligand to the polymer network [5]. One of the common applications of modern electrochemistry is the electroanalytical detection of organic and inorganic compounds in various matrices [6-10]. Between different electrochemical techniques, anodic stripping voltammetry plays an important role. It has been identified as one of the most powerful tools for the analysis of diverse species, due to its unique preconcentration ability in association with different electrode materials [11]. There are a few reports about the determination of trace metals using of imprinted polymers and electrochemical methods. Until now, this combination has been used only for the determination of La and Ce [12], Pb [13-15], Cu [16, 17], Hg [18-20] and Cd [21]. To the best of our knowledge, there is no previous report about the use of ion imprinted polymer and anodic stripping voltammetry for the preconcentration and determination of Tl(I) ions in real samples. The purpose of the present investigation is the utilization a simple and sensitive carbon paste electrode (CPE) modified with nano-sized thallium imprinted polymer (Tl-IP) and carbon nanotubes (CNT) for the selective preconcentration and determination of Tl(I) by differential pulse anodic stripping voltammetry (DPASV). In addition, this suggested modified carbon paste electrode with thallium imprinted polymer and multi-walled carbon nanotubes (Tl-IP-MWCNT-CPE) exhibits several advantages, such as the simple preparation, reproducable surface renewal by simple polishing, good stability and an excellent ability for the determination of trace amounts of Tl(I) in water, hair and synthetic samples.
2. Experimental 2.1. Materials and reagents Highly pure graphite powder, benzo-15-crown-5, nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, thallium nitrate (TlNO3), thallium standard solution (1000.0 µg mL-1), dimethyl sulfoxide (DMSO), acetonitrile (AN), ethylene glycol dimethacrylate (EGDMA), methacrylic acid (MAA) and 2,2-azobis(isobutyronitrile) (AIBN) were purchased from Merck (Darmstadt, Germany). Thallium working solutions were prepared by appropriate dilution of the stock solution. Also pure nitrogen was used for deaeration. 2.2. Apparatus Voltammetric experiments were performed with a Metrohm electroanalyzer (Model 757 VA Computrace, Switzerland). All voltammograms were recorded with a three electrodes system: an Ag/AgCl electrode as the reference electrode, a platinum wire as the auxiliary electrode, and carbon paste electrode modified with ion imprinted polymer (IIP) or non-imprinted poymer (NIP) as the working electrode. FT-IR spectra were recorded with a Tensor-27 spectrometer (Bruker, Ettlingen, Germany). A Scanning Electron Microscope (AIS2100, Seron Technology, South Korea) was used for the morphological information. All the electrochemical experiments were carried out under the pure nitrogen atmosphere at room temperature. 2.3. Samples preparation 2.3.1. Water samples Three water samples including; tap water (Kerman drinking water, Kerman, Iran), well water (Shahid Bahonar University of Kerman, Kerman, Iran) and wastewater (Copper factory, Sarcheshmeh, Kerman, Iran) were selected and filtered to remove all of the suspended particles. Then, pH was adjusted to pH=2.0 with nitric acid (to prevent the ions adsorption onto the flask walls), stored at 4 °C in a refrigerator and the suggested method was applied. For Tl preconcentration, HCl (0.2 mol L-1) was
chosen as the appropriate medium. 2.3.2. Human hair The human hair sample was immersed in acetone for 30 min, washed with water and dried. An exact amount of sample (5.0 g) was weighed accurately and digested by 30.0 mL a mixture (HClO4 and HNO3, 1:8 v/v). The digested solution was dried and several drops of diluted H2SO4 (1:1 v/v) were added [22]. The residue was transferred to a 100.0 mL volummetric flask and diluted to the mark with deionized water. Finally, an aliquot of this solution was selected and the experiment was carried out according to the mentioned procedure. 2.3.3. Synthetic sample Also, in order to confirm the procedure's validity, this method has been applied for the determination of thallium in a synthetic sample. An aliquot of this sample was poured into the electrochemical cell and thallium content was determined by the suggested method. 2.4. Preparation of nano-sized Tl ion imprinted polymer The nano-sized Tl-IP was prepared via bulk polymerization technique. In order to prepare TlIP, 0.2 mmol TlNO3, 0.2 mmol benzo-15-crown-5 and 0.3 mL methacrylic acid were dissolved in a mixture containing 5.0 mL DMSO and 5.0 mL AN. The solution was stirred for 1 h in order to complete the complex formation process. Then, 4.0 mL EGDMA (cross-linker) and 75 mg AIBN (free radical initiator) were added to the solution. Since the oxygen traps the radicals and retards the polymerization, the Tl-IP preparation process was continued by N2 gas purging for 15 min to remove the molecular oxygen from the mixture. The final step of polymerization was carried out in a water bath at 60 ºC for 10 h. The obtained polymer was powdered with a mortar and pestle. These particles were washed with ethanol and HCl (2.0 mol L-1) to remove the unreacted ligands and the imprint metal ions (until the output solution was free from the Tl ions), respectively. Finally, the obtained polymer was washed with deionized water (10 times) and dried at 60 ºC. This polymer was named TlIP and characterized by FT-IR and scanning electron microscopy (SEM). Also, NIP was prepared via the same procedure, but thallium (as TlNO3) did not exist in the polymerization mixture. 2.5. Preparation of Tl-IP-MWCNT-CPE The modified carbon paste with thallium IP and multi-walled carbon nanotube was prepared by mixing 60 mg graphite powder, 5 mg carbon nanotube, 5 mg Tl-IP (or 5 mg NIP) and 30 µL silicon oil. The mixture was blended for 20 min until a uniform paste was obtained. For the preparation of TlIP-MWCNT-CPE, a portion of this paste was filled into the end of a glass tube (ca. 3.0 mm i.d. and 10 cm long). When necessary, a new surface was obtained by polishing the electrode surface on a smooth paper. The electrical connection was established with a copper wire. 2.6. General procedure For the preconcentration step, the Tl-IP-MWCNT-CPE was inserted in 20.0 mL stirring HCl solution (0.2 mol L-1) containing 100.0 ng mL-1 Tl(I) for 300 s, where the Tl(I) ions were accumulated and reduced at -1.2 V. Then, the differential pulse voltammogram was recorded by scanning from -0.5 to -1.0 V (30 mV s-1 scan rate, 100 mV pulse amplitude and 4 ms pulse period). All of the measurements were carried out at room temperature (~23±1 °C) and the observed peak in -0.69 V was applied for the determination of Tl content.
3. Results and discussion The prepared imprinted nanoparticles were characterized by IR spectroscopy and scanning
electron microscopy. IR spectra of the unleached (Fig. 1a) and the leached (Fig. 1b) Tl-IP were recorded using KBr pellet method. These polymers have the same backbone; 2990.99 cm-1 for aliphatic C-H; 3000.13 cm-1 for aromatic C-H; 1727.89 cm-1 for C=O; 1638.45 cm-1 for aromatic C=C; 1155.50 cm-1 for stretching vibration of C-O in unleached polymer and 2956.58 cm-1 for aliphatic C-H; 3001.30 cm-1 for aromatic CH; 1732.93 cm-1 for C=O; 1637.10 cm-1 for aromatic C=C and 1160.00 cm-1 for stretching vibration of CO in leached imprinted polymer. The similarities between the IR spectra of unleached and leached IIPs, suggest that the leaching process does not affect on the different groups of the polymeric network. Furthermore, the shifts of aromatic C-H, C=O and C-O frequencies to higher regions in the leached IIP, proves the removal of Tl(I). The synthesized Tl-IP structure was investigated by scanning electron microscopy and the SEM image is presented in Fig. 2. In this type of polymerization method, the morphology of the IIP particles depends on the ligand, cross-linking monomer, type and amount of polymerization solvent, metal ion salt, initiator, temperature and time.
3.1. Voltammetric behavior of Tl at the surface of different electrodes The ability of the different modified carbon paste electrodes to preconcentration of Tl(I) ions was investigated. Fig. 3 shows the differential pulse anodic stripping voltammograms of MWCNT-CPE (modified CPE with multi-walled carbon nanotubes) (a), NIP-MWCNT-CPE (modified CPE with nonimprinted polymer and multi-walled carbon nanotubes) (b), Tl-IP-CPE (modified CPE with Tl ion imprinted polymer) (c), Tl-IP-MWCNT-CPE (modified CPE with Tl ion imprinted polymer and multiwalled carbon nanotubes) (d) and Tl-IP-MWCNT-CPE (modified CPE with Tl ion imprinted polymer and multi-walled carbon nanotubes, no Tl(I) in accumulation medium) (e) in HCl 0.2 mol L-1 as the preconcentration and accumulation medium. In MWCNT-CPE case, a small anodic peak (at about -0.69 V) indicates some adsorption of Tl(I) on the surface of this modified electrode. However, this small peak confirms the Tl accumulation process at the surface of MWCNT-CPE is not quantitative. In contrast, when NIP-MWCNT-CPE and TlIP-CPE were applied, two well-defined anodic stripping peaks were appeared in the medium containing 100.0 ng mL-1 Tl(I). These peaks were observed due to the reoxidation of elemental thallium, that were produced by the reduction of accumulated Tl(I) at the negative potentials. As can be seen, the anodic peak current of thallium at Tl-IP-CPE is several times larger than NIP-MWCNT-CPE and MWCNT-CPE. Finally, when Tl-IP-MWCNT-CPE was applied, the peak current showed a well increasing after accumulation in the medium containing 100.0 ng mL-1 Tl(I). Also, when Tl-IP-MWCNTCPE was applied in the absence of Tl(I), only a residual current was observed (Fig. 3(e))
3.2. Optimization of analytical conditions To optimize the Tl-IP-MWCNT-CPE performance for the electrochemical determination of thallium ions, the important parameters such as HCl concentration, supporting electrolyte type, accumulation time, reduction potential and amounts of ion imprinted polymer and carbon nanotubes were investigated and optimized. 3.2.1. Effect of supporting electrolyte The voltammetric behavior of the suggested modified electrode was examined in the different supporting electrolytes including; H2SO4, HNO3, HClO4 and HCl (in all cases, the concentration
was adjusted to 0.2 mol L-1). Fig. 4 shows the anodic peak in HCl is the most acceptable peak in comparison with the other supporting electrolytes. So, HCl was chosen as supporting electrolyte in the further experiments. 3.2.2. Effect of HCl concentration The effect of HCl concentration as the selected supporting electrolyte on the Tl-IP-MWCNTCPE response was investigated between 0.01 and 0.5 mol L-1. The results show the maximum anodic peak current was obtained in 0.2 mol L-1. Therefore, 0.2 mol L-1 HCl was chosen in the next experiments. 3.2.3. Effect of the electrode composition The effect of the electrode composition on the Tl-IP-MWCNT-CPE response was evaluated by the voltammetric determination of 100.0 ng mL-1 Tl(I) in HCl 0.2 mol L-1. The anodic peak current increased with increasing the amount of Tl-IP and multi-walled carbon nanotubes up to 5% (w/w) and then decreased in further amounts. According to these results, a modified carbon paste electrode with 5% (w/w) Tl-IP and MWCNT was selected for the suggested method. 3.2.4. Effect of reduction potential Reduction potentials between -0.8 and -1.4 V were studied. For this purpose, the preconcentration of Tl(I) ions (100.0 ng mL-1) from 0.2 mol L-1 HCl was performed. Then, Tl(0) was analyzed by the differential pulse voltammetry with 30 mV s-1 scan rate, 100 mV pulse amplitude and 4 ms pulse period. The results show when the potential was increased from -0.8 to -1.2 V, the anodic peak current showed a maximum amount and then decreased. So, -1.2 V was chosen as an optimum reduction potential for Tl(I) determination. 3.2.5. Effect of accumulation-reduction time The effect of time on the anodic peak current for 100 ng mL-1 Tl(I) was investigated. Based on the obtained data, the anodic peak current of Tl(I) increased linearly with increasing time up to 300 s due to the surface saturation and remained constant for longer times. Based on these results, for all subsequent measurements, 300 s was employed. 3.2.6. Performance characteristics Standard solutions containing Tl(I) were prepared in 0.2 mol L-1 HCl and applied for the optimized anodic stripping voltammetric procedure. The calibration graph (Fig. 5) showed a linear relationship in the range of 3.0 and 240 ng mL-1 and the detection limit was calculated as 0.76 ng mL-1. The relative standard deviation (R.S.D.) was obtained as ±2.7% for seven successive measurements of the similar samples containing 100.0 ng mL-1 Tl(I). This result indicates a good reproducibity of the modified electrode construction could be due to the strong adsorption of Tl(I) ions at the electrode surface. 3.2.7. Interferences study The method efficiency for the extraction and preconcentration of thallium ions in the presence of various cations and anions was examined. The tolerance level was defined as the maximum amount of interfering ions can produce an error of ±5% on the Tl(I) current. The tolerance level of each species was tested and if interference occurred, the ratio was reduced until it ceased. The study was performed with 20.0 mL solution containing 100.0 ng mL-1 Tl and different concentrations of concomitant ions. The results of these experiments are summarized in Table 1. As the results indicate, the Tl(I) recoveries were quantitative in the presence of excessive amounts of
possible interference cations and anions. Although, the tolerance limit of Cd(II), Pb(II) and Sn(II) is lower than other ions, but the interferences of these ions (at 500-fold of thallium) are not too high. These results indicate the Tl-IP-MWCNT-CPE electrode is suitable for the selective extraction and determination of Tl(I) from various matrices. 3.2.8. Analytical applications In order to investigate the procedure's validity, the suggested method was applied for the determination of thallium in water samples (tap water, well water and wastewater) and human hair. The reliability of the method was checked by the analysis of the spiked samples with the known amount of thallium. The illustrated results in Table 2 reveal the recoveries of the spiked samples at a high confidence level (95%) are satisfactory. To verify the method accuracy, this procedure was applied for the determination of thallium in a synthetic sample and the analytical results are presented in Table 3. As can be seen, the obtained results are in good agreement with the reference values and there is no significant difference between the results and the accepted values. Thus, the procedure is reliable for the analysis of a wide range of samples. 3.2.9. Comparison with some previously reported Table 4 compares the performance characteristics of the recommended sensor, with some prepared thallium sensors [23-33]. The suggested method has the better, or comparable performance in comparison with the other reported methods and has some advantages such as the high selectivity and environmentally-friendly property. As can be seen in this table, the Tl-IP-MWCNT-CPE shows the lowest detection limit and the best relative standard deviation except the only four cases [24,28,29,33]. Also, this method shows the good reproducibility, simplicity, high accuracy and precision and low toxicity in comparison with the other studies.
4. Conclusion In this work, the anodic stripping voltammetric procedure for the thallium determination was investigated. This work indicated the modified carbon paste electrode with Tl-IP and multi-walled carbon nanotube (Tl-IP-MWCNT-CPE) is a suitable sensor for the analytical determination of Tl(I). The suggested electrode showed the good characteristics such as a wide concentration range (3.0-240 ng mL-1), a very low detection limit (0.76 ng mL-1) and good selectivity. This modified electrode (Tl-IPMWCNT-CPE) coupled with differential pulse anodic stripping voltammetry was applied in water, human hair and synthetic sample with satisfactory results. In addition, some other advantages of this electrochemical sensor are its rapid response, simple operation, precise results, low cost and direct application for the determination of thallium.
References [1] L.B. Escudero, P. Berton, E.M. Martinis, R.A. Olsina, R.G. Wuilloud, Dispersive liquid-liquid microextraction and preconcentration of thallium species in water samples by two ionic liquids applied as ion-pairing reagent and extractant phase, Talanta 88 (2012) 277-283. [2] G. Repetto, A. Del Peso, M. Repetto, Thallium in the Environment, first ed., Wiley, Chichester, England, 1998. [3] N.D. Solovyev, N.B. Ivanenko, A.A. Ivanenko, Whole blood thallium determination by GFAAS with high-frequency modulation polarization Zeeman effect background correction, Biol. Trace Elem. Res. 143 (2011) 591-599. [4] A.L. Peter, T. Viraraghavan, Thallium: a review of public health and environmental concerns,
Environ. Int. 31 (2005) 493-501. [5] M. Shamsipur, J. Fasihi, K. Ashtari, Anal. Chem. 79 (2007) 7116-7123. [6] S. Jahandari, M.A. Taher, H. Fazelirad, I. Sheikhshoai, Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes, Microchim. Acta 180 (2013) 347-354. [7] P.S. Liew, B. Lertanantawong, S.Y. Lee, R. Manickam, Y.H. Lee, W. Surareungchai, Electrochemical Genosensor Assay Using Lyophilized Gold Nanoparticles/Latex Microsphere Label for Detection of Vibrio cholerae, Talanta 139 (2015) 167-173. [8] A. Cantalapiedra, M.J. Gismera, J.R. Procopio, M.T. Sevilla, Electrochemical sensor based on polystyrene sulfonate-carbon nanopowders composite for Cu (II) determination, Talanta 139 (2015) 111-116. [9] D. Merli, D. Zamboni, S. Protti, M. Pesavento, A. Profumo, Electrochemistry and analytical determination of lysergic acid diethylamide (LSD) via adsorptive stripping voltammetry, Talanta 130 (2014) 456-461. [10] M.S. Qureshi, A.R. bin Mohd Yusoff, A. Shah, A. Nafady, Sirajuddin, A new sensitive electrochemical method for the determination of vanadium(IV) and vanadium(V) in Benfield sample, Talanta 132 (2015) 541-547. [11] S. Cheraghi, M.A. Taher, H. Fazelirad, Voltammetric sensing of thallium at a carbon paste electrode modified with a crown ether, Microchim. Acta 180 (2013) 1157-1163. [12] X.Z. Li, Y.P. Sun, Evaluation of ionic imprinted polymers by electrochemical recognition of rare earth ions, Hydrometallurgy 87 (2007) 63-71. [13] T. Alizadeh, S. Amjadi, Preparation of nano-sized Pb2+ imprinted polymer and its application as the chemical interface of an electrochemical sensor for toxic lead determination in different real samples, J. Hazard. Mater. 190 (2011) 451-459. [14] Z. Wang, Y. Qin, C. Wang, L. Sun, X. Lu, X. Lu, Preparation of electrochemical sensor for lead(II) based on molecularly imprinted film, Appl. Surf. Sci. 258 (2012) 2017-2021. [15] A. Bahrami, A. Besharati-Seidani, A. Abbaspour, M. Shamsipur, A highly selective voltammetric sensor for sub-nanomolar detection of lead ions using a carbon paste electrode impregnated with novel ion imprinted polymeric nanobeads, Electrochim. Acta 118 (2014) 92-99. [16] W. Zhihua, L. Xiaole, Y. Jianming, Q. Yaxin, L. Xiaoquan, Copper(II) determination by using carbon paste electrode modified with molecularly imprinted polymer, Electrochim. Acta 58 (2011) 750756. [17] M. Mazloum-Ardakani, M.K. Amini, M. Dehghan, E. Kordi, M.A. Sheikh-Mohseni, Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II), J. Iran. Chem. Soc. 11 (2014) 257-262. [18] T. Alizadeh, M.R. Ganjali, M. Zare, Application of an Hg2+ selective imprinted polymer as a new modifying agent for the preparation of a novel highly selective and sensitive electrochemical sensor for the determination of ultratrace mercury ions, Anal. Chim. Acta 689 (2011) 52-59. [19] X.C. Fu, X. Chen, Z. Guo, C.G. Xie, L.T. Kong, J.H. Liu, X.J. Huang, Stripping voltammetric detection of mercury(II) based on a surface ion imprinting strategy in electropolymerized microporous poly(2-mercaptobenzothiazole) films modified glassy carbon electrode, Anal. Chim. Acta 685 (2011) 21-28. [20] X.C. Fu, J. Wu, L. Nie, C.G. Xie, J.H. Liu, X.J. Huang, Electropolymerized surface ion imprinting films on a gold nanoparticles/single-wall carbon nanotube nanohybrids modified glassy carbon electrode for electrochemical detection of trace mercury(II) in water, Anal. Chim. Acta 720 (2012) 29-37. [21] T. Alizadeh, M.R. Ganjali, P. Nourozi, M. Zare, M. Hoseini, A carbon paste electrode impregnated with Cd2+ imprinted polymer as a new and high selective electrochemical sensor for
determination of ultra-trace Cd2+ in water samples, J. Electroanal. Chem. 657 (2011) 98-106. [22] H. Fazelirad, M.A. Taher, M. Nasiri-Majd, GFAAS determination of gold with ionic liquid, ion pair based and ultrasound-assisted dispersive liquid-liquid microextraction, J. Anal. Atom. Spectrom. 29 (2014) 2343-2348. [23] A.A.A. Gaber, New thallium (I) ion selective electrode based on indeno pyran compound, Sens. Actuators B 96 (2003) 615-620. [24] M.M. Hassanien, K.S. Abou-El-Sherbini, G.A.E. Mostafa, A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III), Talanta 59 (2003) 383392. [25] K.S. Park, S.O. Jung, S.S. Lee, J.S. Kim, Thallium (I)-selective electrodes based on calix [4] pyrroles, Bull. Korean Chem. Soc. 21 (2000) 909-912. [26] M.B. Saleh, A novel PVC membrane sensor for potentiometric determination of thallium (I), J. Electroanal. Chem. 448 (1998) 33-39. [27] S.V. Kharitonov, V.I. Zarembo, Ion-selective electrode for determining thallium (III) as its complexonate, J. Anal. Chem. 60 (2005) 1056-1061. [28] H. Bagheri, A. Afkhami, A. Shirzadmehr, H. Khoshsafar, A new nano-composite modified carbon paste electrode as a high performance potentiometric sensor for nanomolar Tl (I) determination, J. Mol. Liq. 197 (2014) 52-57. [29] K. Vytřas, E. Khaled, J. Ježková, H.N.A. Hassan, B.N. Barsoum, Studies on the potentiometric thallium (III)-selective carbon paste electrode and its possible applications, Fresenius J. Anal. Chem. 367 (2000) 203-207. [30] H. Dong, H. Zheng, L. Lin, B. Ye, Determination of thallium and cadmium on a chemically modified electrode with Langmuir-Blodgett film of p-allylcalix[4]arene, Sens. Actuators B 115 (2006) 303308. [31] V.A. Tarasova, Voltammetric determination of thallium(I) at a mechanically renewed Bi-graphite electrode, J. Anal. Chem. 62 (2007) 157-160. [32] C. Kokkinos, A. Economou, Disposable microfabricated 3-electrode electrochemical devices with integrated antimony working electrode for stripping voltammetric determination of selected trace metals, Sens. Actuators B 192 (2014) 572-577. [33] E.O. Jorge, M.M. Neto, M.M. Rocha, A mercury-free electrochemical sensor for the determination of thallium(I) based on the rotating-disc bismuth film electrode, Talanta 72 (2007) 1392-1399.
Highlights There are only a few reports on the voltammetric determination of ions by IIPs. It is the first report on the voltammetric determination of Tl with Tl-IP-CNT-CPE. The CPE was modified with Tl-IP and CNT and used for the determination of Tl. Tl-IP-CNT-CPE was successfully applied for Tl determination in real samples.
Table 1 Effect of interfering ions Foreign Recovery ion (%) Ni(II) 96.3 Pb(II) 74.5 Zn(II) 99.1 Mg(II) 96.1 Co(II) 97.4 Na(I) 102.1 Bi(III) 98.5 Fe(III) 98.3 K(I) 102.5 Hg(II) 99.3 Cu(II) 96.4 Ba(II) 97.1 Cd(II) 85.3 Sn(II) 83.8 NO3100.6 97.8 F Br98.4 Mole ratio of ion/thallium:500-fold
Table 2 Determination of thallium in real samples. Sample Spiked Founda -1 (ng mL ) Tap waterb 0.0 N.D.c 50.0 48.2±1.4 Well waterd 0.0 N.D. 50.0 47.7±1.2 Waste watere 0.0 3.8±0.1 10.0 14.1±0.4 -1 (ng g ) Human hair 0.0 76.2±2.2 25.0 101.8±3.1
Recovery (%) 96.4 95.4 103.0 102.4
a
Mean ± standard deviation (n=3) Kerman drinking water, Kerman, Iran c N.D.: Not Detected d Shahid Bahonar University of Kerman, Kerman, Iran e Copper factory, Sarcheshmeh, Kerman, Iran b
Table 3 Analysis of thallium in synthetic sample Sample Composition Synthetic Ca;15.0,Cu;8.0,Mn;20.0 sample Mg;40.0,Co;5.0,Pb;50.0 Ni;22.0,Cd:2.0,Zn;70.0 Hg;300.0,K; 35.0,Na;300.0 Tl;200.0 (ng mL-1) a
Mean ± Standard deviation (n=3)
Founda 194.3±5.8
Recovery (%) 97.2
Table 4 Comparison of the proposed method with other reported electrochemical methods for the thallium determination Analysis R.S.D. Linear range LOD Ref. method (%) (ng mL-1) (ng mL-1) Pa 204.4-20.4×106 145 [23] P 1.4 817.5-20.4×104 408.8 [24] -6 P 654.2-20.4×10 204.38 [25] P 1×10-5-1×10-1 654 [26] P 1144.5-20.4×106 30 [27] p <1 1.74-2×106 1.1 [28] P 1.1-1.7 204.4-10.2×105 204.38 [29] b [30] SV 7.2-8.2 4.9-245.3 1.0 SV 2-4 10.2-1022 1.0 [31] SV 3.9 10-80 0.9 [32] ASVc 0.2 2.5-30.6 2.2 [33] 2.70 3.0-240 0.76 This work DPASV a
Potentiometry Stripping voltammetry c Anodic stripping voltammetry b
Figure captions: Fig. 1. FTIR spectra of the thallium imprinted polymer obtained via bulk polymerization method: (a) unleached and (b) leached. Fig. 2. SEM image of the thallium imprinted polymer obtained via bulk polymerization method. Fig. 3. Differential pulse stripping voltammograms in HCl 0.2 mol L-1: (a) MWCNT-CPE with 100.0 ng mL-1 Tl(I), (b) NIP-MWCNT-CPE with 100.0 ng mL-1 Tl(I), (c) Tl-IPCPE with 100.0 ng mL-1 Tl(I), (d) Tl-IP-MWCNT-CPE with 100.0 ng mL-1 Tl(I) and (e) Tl-IP-MWCNT-CPE, no Tl(I) in accumulation medium. Other conditions: accumulation time: 300 s, reduction potential: -1.2 V, pulse amplitude: 100 mV, pulse period: 4 ms.
Fig. 4. The effect of the supporting electrolyte type on the Tl-IP-MWCNT-CPE response. Other conditions were the same as in Fig. 3 except the supporting electrolyte type. Fig. 5. Differential pulse stripping voltammograms of Tl-IP-MWCNT-CPE, concentrations of (a-j): 3.0, 10.0, 20.0, 30.0, 40.0, 50.0, 100.0, 150.0, 200.0 and 240.0 ng mL-1 of Tl(I).
Fig. 1.
Fig. 2.
Tl-IP-MWCNT-CPE Tl-IP-CPE NIP-MWCNT-CPE
100 MWCNT-CPE
I (µA)
Tl-IP-MWCNT-CPE,no Tl in accumulation medium
50
d 0 -0.72
-0.67 E (V) vs. Ag/AgCl
Fig. 3.
100
I (µA)
Nitric acid Perchloric acid Sulfuric acid Hydrochloric acid
50
Fig. 4.
0 -0.72
-0.67 E (V) vs Ag/AgCl
200
j 150 I (µA)
Fig. 5.
100
50
a
0 -0.75
-0.7 -0.65 E (V) vs. Ag/AgCl
Accumulation of Tl(I) at the surface of Tl-IP-MWCNT-CPE and determination by DPASV