- Email: [email protected]
A novel magnetic ion imprinted polymer for selective adsorption of trace amounts of lead(II) ions in environment samples
G Model
JIEC-1647; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
A novel magnetic ion imprinted polymer for selective adsorption of trace amounts of lead(II) ions in environment samples Omid Sayar a, Niloufar Akbarzadeh Torbati b, Hamideh Saravani b, Kheirollah Mehrani c,*, Ali Behbahani d, Hamid Reza Moghadam Zadeh d a
School of Civil & Environmental Engineering, University of New South Wales, NSW 2052, Australia Department of Chemistry, University of Sistan and Baluchestan, Zahedan, Iran Department of Chemistry, Islamic Azad University, Science and Research Branch, Tehran, Iran d Department of Chemical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran b c
A R T I C L E I N F O
Article history: Received 13 September 2013 Accepted 27 October 2013 Available online xxx Keywords: Pb(II) determination Ion imprinted polymer Fe3O4 nano-particles Environmental samples
A B S T R A C T
In this work a novel ion imprinted polymer (IIP) based on 4-(vinylamino)pyridine-2,6-dicarboxylicacid (VPyDC), was coated on Fe3O4 nano-particles. The application of this magnetic sorbent was investigated for preconcentration and determination of trace Pb(II) ions by flame atomic absorption spectrometry. Effects of various parameters such as sample pH, adsorption/desorption time and eluent were investigated during this study. The relative standard deviation and limit of detection of the method were found to be 1.8% and 0.9 ng mL1, respectively. The accuracy of this method was confirmed using various standard reference materials, then it was used for Pb(II) determination in environmental samples. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Trace levels of heavy metals are widely distributed in environment due to industrial and agricultural processes. Lead (Pb) is one of the most toxic heavy metal which is the main source of contamination for human being found in water and food [1]. As lead and its compounds can cause adverse effects on metabolic processes of human beings even at low concentrations, its determination is so important for scientists all over the world [2]. Although determination of lead by flame atomic absorption spectrometry (FAAS) is very simple and easy to operate, its concentration in environmental samples is usually lower than the FAAS limit of detection [3]. Another concerning item in determination of lead ions in environmental samples is high matrix interferences [4]. Therefore, preconcentration step is necessary for determination of lead when we are dealing with environmental samples which are at the ng mL1 level of ions and have high interfering matrix [5]. Several methods have been developed for Pb(II) ions pre-concentration, separation and determination such as liquid–liquid extraction (LLE) [6], solid phase extraction [7–13], co-precipitation [14,15] and cloud point extraction [16,17] which among them, Solid phase extraction (SPE) is more common due to
* Corresponding author. Tel.: +98 9122483395. E-mail address: [email protected] (K. Mehrani).
the higher enrichment factor, minimal costs, environment friendly and easy automation [18]. Different solid phase extractors such as Amberlite XAD resin [19], carbon nano-tube [20], activated carbon [3], silica gel [21] and ion imprinted polymers [22] have been used as sorbents in solid phase extraction which among these materials, ion imprinted polymers (IIP) is more attractive due to their high selectivity, mechanical and chemical stability [23]. But the difficulty in separation is one of the biggest failures in these materials. In this work, a novel Pb(II) ion imprinted polymer was synthesized and immobilized on the surface of Fe3O4 in scope of easy separation by a magnet. This novel IIP was evaluated by IR spectroscopy, TG/DTA and SEM micrograph. The effects of various parameters such as maximum capacity, optimum eluent containing type, concentration and the least amount of it, interfering ions effects and adsorption conditions containing pH and analyte flow rate were also studied. Moreover the accuracy of this method was confirmed using various standard materials. 2. Experimental 2.1. Apparatus A digital pH meter, WTW Metrohm 827 Ion analyzer (Herisau, Switzerland), equipped with a combined glass calomel electrode was used for the pH adjustments at 25 1 8C temperature. AA-680
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.10.052
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 2
O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Shimadzu (Kyoto, Japan) flame atomic absorption spectrometer with a lead hollow cathode lamp at wavelength 283.3 nm resonance line and the spectral band pass at 0.5 nm was used. All measurements were carried out in an air/acetylene flame. Fourier transform infrared (FT-IR) spectra were recorded using Bruker IFS66/S FT-IR (Bruker, Germany) spectrometer in KBr matrix. Scanning electron microscopy
(SEM) was performed using SEM Philips (XL30, Almelo, The Netherlands) instrument. The thermal analysis was performed using a BAHR-Thermoanalyse GmbH (Hu¨llhorst, Germany) employing heating at rates of 10 8C min1 in air atmosphere. X-ray diffraction patterns were obtained on a STOE diffractometer (Darmstadt, Germany) with Cu Ka radiation.
Fig. 1. A schematic diagram for synthesis of sorbent.
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
2.2. Materials and reagents 4-Aminopyridine-2,6-dicarboxylic acid and Fe3O4 nano-particles have been synthesized according to previous reported procedure [24,25]. 4-(Vinylamino)pyridine-2,6-dicarboxylic acid (VPyDC) was prepared by reaction of 1 mmol of 4-aminopyridine2,6-dicarboxylic acid with 1 mmol of vinyl chloride in presence of 50 mL methanol and triethylamine (1:1, V:V) [26]. Ethylene glycol dimethacrylate (EGDMA) was obtained from Fluka (Buchs, Switzerland). 2,20 -Azo bis isobutyro nitrile (AIBN) was obtained from Acros Organics (New Jersey, USA). All the other reagents used were of analytical grade and purchased from Merck (Darmstadt, Germany). Distilled water was prepared using a Milli-Q system from Millipore (Bedford, MA, USA). Standard Stock solutions (1000 mg L1) were obtained from Aldrich Company. The working standard solutions were prepared by appropriate dilution of the stock solution with double distillated water. All of these solutions were stored in ambient temperature. The standard reference materials (SRM 1515, SRM 1640 and SRM 2709), which used for method validation, were obtained from National Institute of Standards and Technology (www.nist.gov, Gaithersburg, USA). 2.3. Preparation of lead magnetic ions imprinted polymer nanoparticles To prepare vinyl functionalized Fe3O4 nano-particles, 1.0 g Fe3O4 was suspended in 50 mL toluene, afterward 2.0 g of 3vinyletriethoxy silane was added to the solution [27]. After stirring for 48 h, the solid phase was separated from the solvent by a strong magnet and washed with methanol and dried at room temperature. The vinyl functionalization of Fe3O4 nano-particles was confirmed by IR spectroscopy and elemental analysis. Elemental analysis showed 0.68 mmol g1 vinyl group coated on this sorbent (C = 2.44%, H = 0.33%). The Pb(II) complex was prepared same as previous reports [28]. In this approach, 0.193 g (1 mmol) of VPyDC and 0.16 g (1 mmol) bipyridine were dissolved in 20 mL methanol, then 0.165 g (0.5 mmol) Pb(NO3)2 was added to the solution. The resulting purple solution was stirred at room temperature for 4 h until the reaction was completed. In order to synthesize IIP@Fe3O4, 0.5 mmol of Pb(II) complex and 1.5 g of vinyl functionalized Fe3O4 were dispersed in 100 mL of methanol. After addition of 0.1 g of AIBN and 1.1 mL of EGDMA to
3
the mixture, the mixture was heated to 60 8C. At the end of polymerization reaction (after 24 h), the composite was separated by a magnet and the template (Pb(II) ions in polymer structure) was removed by several washing using 0.1 mol L1 Thiourea/ 0.01 mol L1 HCl solution. According to FAAS results, the removal of the template was completed after 8 times washing with 0.1 mol L1 Thiourea/0.01 mol L1 HCl solution. In order to confirm the removal of Pb(II) ions, the amount of Pb(II) ions was determined by FAAS after treatment of this composite with piranha solution (H2SO4 + H2O2). Piranha solution which containing concentrated H2SO4 and 30% solution of H2O2 (3:1, v/v), dissolves organic parts of these particles and release lead ions in solution. The formation of this IIP was confirmed by IR, TG/DT analysis and also SEM photograph. A schematic diagram of this IIP is shown in Fig. 1. 2.4. Extraction procedure The extraction procedure consists of two steps: in the sorption step, pH of sample solution was adjusted at 7, then, 0.01 g of IIP@Fe3O4 was suspended in aqueous solution containing 1 mg L1 of Pb(II) and shakes for 4 min. In desorption step, elution of adsorbed Pb(II) ions was performed by 3 mL of 0.1 mol L1 Thiourea/0.01 mol L1 HCl solution. After 9 min concentration of lead ions in the eluent was determined by FAAS. 2.5. Standard reference materials pretreatment The water samples were obtained from tap water (Tehran, Iran), sea water (Caspian Sea, Iran) and river water (Chaloos, Iran). The samples were collected in cleaned polyethylene bottles and were filtered through a 0.45 mm pore size nylon filter (Millipore) immediately after sampling. The soil samples were collected form seashore (Caspian Sea, Iran) and Chaloos river coast (Chaloos, Iran) and stored in polythene bags and brought to the laboratory for preparation and treatment. To digest the soil samples, 1 g of solid sample was digested with 6 mL of HCl (37%) and 2 mL of HNO3 (65%) in a microwave digestion system. Digestion was carried out for 2 min at 250 W, 2 min at 0 W, 6 min at 250 W, 5 min at 400 W, 8 min at 550 W and then venting for 8 min. Finally the residue was then diluted to 100 mL with deionized water [27]. The standard reference materials (SRM 1515 and SRM 2709) were digested by mentioned method.
Fig. 2. Thermal analysis of synthesized magnetic ion imprinted polymer.
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
4
120
3. Results and discussion
100
Fe3O4 nano-particles have been synthesized according to reported procedure [25]. Formation of these nano-particles was confirmed by SEM and high-angle X-ray. Modification of nano-size Fe3O4 surface with vinyl groups was carried out through the direct method for functionalization of Fe3O4 with triethoxysilan agents reported severally before [27]. The reaction of vinyl functionalized Fe3O4 as a monomer with lead complex as another monomer in presence of an initiator like AIBN and EGDMA as the cross linker lead to the formation of this IIP (Fig. 1). The resulting imprinted nano-particles were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric and differential thermal analysis. The FT-IR spectra of ion imprinted polymer showed following bands: 1268 cm1 (C–O), 1629 cm1 (C5 5N), 1715 cm1 (C5 5O), 2968 cm1 (aliphatic C–H) and 3037 cm1 (aromatic C–H). Thermal stability of this composite was evaluated by TG/DT analysis (Fig. 2). The results showed this composite (IIP@Fe3O4) have high thermal stability, as it is stable up to 300 8C. Moreover according to loosing 40% of the composite weight, it can be concluded that forty percent of this sorbent is consists of polymer. Also the size and morphology of this sorbent were determined by SEM (Fig. 3). According to this micrograph, the sorbent are consists of spherical nano-particles with approximately 70 nm in diameter. It worth mentioning, since the magnetic nano-particles are coated by polymer, they will not destroy in acidic solutions. 3.2. Optimization of the preconcentration method It is evident that extraction and preconcentration of Pb(II) ions on this IIP are strongly affected by experimental conditions such as pH, eluent concentration and volume, extraction and desorption time [26,27]. The influences of these parameters were studied through this study and the optimum conditions were obtained. 3.2.1. Effect of solution’s pH As the pH could change the coordination sites of the ligand, it is one of the most controlling parameters for adsorption of lead ions on IIP. The effect of varying pH values on Pb(II) ions adsorption was investigated by adjusting the pH of sample solutions containing 1 mg L1 of lead in the range of pH = 2–9. After stirring for 4 min, the adsorbed Pb(II) ions were eluted with 3 mL of 0.1 mol L1 Thiourea/0.01 mol L1 HCl, afterward the amount of lead ions in the eluent was determined by FAAS. As it can be seen from Fig. 4, the best pH for adsorption of Pb(II) on this composite is 7.0–8.0. Since the most environmental samples are in natural pH, pH = 7.0
Recovery %
3.1. Sorbent characterization
80 60 40 20 0
0
2
4
6
8
10
pH Fig. 4. Effect of sample pH on the recovery of Pb(II) ions from synthesized magnetic ion imprinted polymer.
was chosen for further experiments. This is because at low pH values there is an excessive protonation of the lone pair of electrons on nitrogen, resulting in a decrease in the Pb(II) ions sorption. Moreover, in the alkaline pHs, the Pb(II) precipitate as Pb(OH)2 which cause reducing in removal efficiency. 3.2.2. Effect of type, concentration and volume of eluent Series of acidic eluent solutions such as HCl, HNO3, HClO4 and H2SO4 in different concentrations and also their mixture with Thiourea as an auxiliary ligand were used to elute Pb(II) ions from this IIP. The experimental results showed that the mixture of HCl and Thiourea in concentrations higher than 0.01 mol L1 and 0.1, respectively, elutes Pb(II) from this sorbent efficiently (Table 1). The investigation of the effect of eluent volume on the recovery of Pb(II) showed 3 mL of the 0.1 mol L1 Thiourea/0.01 mol L1 HCl is the optimum volume for desorption of Pb(II) ions (Table 1). 3.2.3. Optimization of sorption and desorption time Optimization of the time is so important in analytical analysis since the insufficient time reduces the procedure efficiently and extra ones cause increasing analysis time. In order to study the effect of time, 100 mL of solutions containing 1 mg mL1 of Pb(II) were adjusted to pH = 7.0 and 0.01 g magnetic IIP was introduced to the solutions and shake for desired time. Then, the sorbent was separated by placing a magnet and the preconcentrated analyte was determined by FAAS after eluting by 0.1 mol L1 Thiourea/ 0.01 mol L1 HCl. As it can be seen from Fig. 5, 4 min for a completing the extraction and 9 min for eluting is needed. This fast extraction and elution could be attributed to the high surface area dealing with these IIP nano-particles.
Table 1 Effect of type, concentration and volume of eluent on recovery of lead ions.
Fig. 3. SEM micrograph of synthesized magnetic ion imprinted polymer.
Eluent
Volume (mL)
Concentration (mol L1)
Recovery (%)
HCl HNO3 HClO4 H2SO4 HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea
10 10 10 10 10 10 10 8 6 4 2 10
0.01 0.01 0.01 0.01 0.01/0.01 0.01/0.1 0.01/1 0.01/0.1 0.01/0.1 0.01/0.1 0.01/0.1 0.01/0.1
53.1 44.7 28.3 35.9 83.4 98.7 98.3 99.1 97.5 98.5 91.4 97.9
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
5
method under optimum conditions was determined by performing ten replicates. The recovery value for lead ions was found to be 98.3% with relative standard deviation of 1.8% on these IIP. 3.4. Sorbent maximum capacity The maximum adsorption capacity of this IIP@Fe3O4 for Pb(II) ions was established by placing 0.01 g of it in 500 mL of aqueous solutions containing 10 mg of lead ions and the amount of adsorbed ions in eluted solutions have been investigated by FAAS. The maximum adsorption capacity of this IIP was calculated to be 55.89 0.6 mg g1 based on the three replicate measurements. 3.5. Effect of matrix ions
Fig. 5. Effect of adsorption and desorption time on the recovery of Pb(II) ions from synthesized magnetic ion imprinted polymer.
3.3. Figure of merit The detection limit of this method was determined by ten times placing 0.01 g sorbent in 500 mL blank solutions under the optimal experimental conditions. The value of LOD for lead on IIP@Fe3O4 was 0.9 ng mL1. These results were obtained from CLOD = KbSb/m; where the numerical factor, Kb = 3 [29]. Also the precision of the Table 2 The tolerance limit of diverse ions in the determination of lead. Interfering ions +
Na K+ Ca2+ Mg+2 Zn2+ Ni+2 Cu+2 Co+2 Fe+2 Mn+2 Cd+2
Tolerable concentration ratio X/Pb
Recovery (%)
5000 5000 2500 2500 1000 2500 1000 1000 500 500 500
99.3 98.7 99.1 99.3 97.9 96.8 97.4 98.4 97.6 97.3 96.2
As it mentioned in Section 1, the selectivity of sorbent is so important in determination of lead in real samples since there are lots of interfering ions in the matrix. The effect of a variety of cations found in natural samples on the determination of Pb(II) ions was studied by adding various concentrations of Na+, K+, Cs+, Mg2+, Ca2+, Cd2+, Fe2+, Mn2+ and Cr3+ to solutions containing 10 mg L1 of Pb(II) listed in Table 2. The tolerable amount of each ion was determined by comparing the FAAS signal Pb(II) ion in presence and absence of interference ion. The tolerable amount was defined as the maximum concentration could cause a change of less than 5% in signal compared to the signal Pb(II) ion without any interference. As shown in Table 2, the vast majority of transition metals do not interfere the concentrations encountered in nature, and the method is selective toward lead extraction at a pH = 7. Furthermore, extraction is not affected by high concentrations of alkaline and alkaline earth metals. This high selectivity toward Pb(II) ions which could not be seen in common sorbents could be attributed to the printing of Pb(II) ions in sorbent synthesis. By printing the ion, there will be the sites which have suitable size and interaction only for target ion. 3.6. Validation of method In order to investigate the accuracy, this technique was validated by comparison to several reference materials containing a certified lead content. As the results in Table 3 show, this sorbent could be used as a promising solid-phase for extraction and determination of lead ions in environmental samples. Due to its high selectivity and adsorption capacity, this magnetic ion imprinted polymer can be used as a reliable sorbent for
Table 3 Recovery of determination of lead in certified reference materials. Ion
Sample
SRM 1640 (drinking water) (mg g1) SRM 1515 (apple leaves) (ng g1) SRM 2709 (San Joaquin soil) (mg g1)
Concentration
Pb(II) Pb(II) Pb(II)
Certified
Found
27.89 47 17.28
27.55 45.2 17.183
Recovery (%)
Relative error (%)
98.8 96.1 99.4
0.9 3.4 1.2
Table 4 Results for the determination of lead ions in environmental samples. Sample
Found (ng mL1)
Added (ng mL1)
C, found (ng mL1)
Recovery (%)
RSD (%)
Distilled water Tap water River water Sea water Seashore soil River coast soil
ND ND ND ND 16.2 38.4
20.0 20.0 20.0 20.0 20.0 20.0
19.9 19.8 20.3 19.5 35.6 57.9
99.5 99.0 101.5 97.5 97.0 97.5
1.3 1.9 2.4 2.7 3.1 2.8
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
6
Table 5 Comparison of established method with previously reported ones. Sorbent
RSD (%)
Capacity (mg g1)
LOD (ng mL1)
Reference
Tris(2-aminoethyl) amine-silica gel Pyridine-2,6-diamine-Fe3O4 Multiwall carbon nano-tubes Modified activated carbon Amberite XAD-2000 Pyridine-functionalized Fe3O4 Magnetic ion imprinted polymer
4.0 0.6 3.52 4.0 <9.0 1.3 1.8
64.61 172.02 NR1 48.56 NR 38.7 55.9
0.55 1.3 3.52 0.45 3 0.8 0.9
[30] [31] [32] [33] [34] [35] This work
NR: not reported.
determination of lead ions in real samples with high matrix interfere. 3.7. Environmental samples analysis The mentioned method was applied for the determination of lead ions concentration in various environmental samples including soil and water. In this regard, after sample preparation by the procedure mentioned in sample preparation section, the sample solution was adjusted to pH = 7 and then the amount of lead ions was determined in eluent by flame atomic adsorption spectroscopy after preconcentration by magnetic ion imprinted polymer. As the results in Table 4 show, this method can be considered to be a reliable and fast method for Pb(II) determination in an environmental sample. The figure of merits for this sorbent was compared to previously reported papers in Table 5. As it can be seen, the ion imprinted polymer has higher detection limit and lower preconcentration factors in some cases. However, the high selectivity of ion imprinted polymer and the possibility of easy separation is the advantages of this sorbent. 4. Conclusion Novel magnetic IIP have been achieved by coating an IIP on Fe3O4 nano-particles. Selectivity of this ion imprinted polymer has made it a suitable and selective sorbent for extraction and preconcentration of lead ions in real samples. The high selectivity of this IIP toward lead ions, easy separation and the high adsorption capacity factor are the advantages of this novel sorbent. References [1] J.B. Stevens, Environmental Science & Technology 25 (1991) 1289. [2] L. Zaijun, T. Jian, P. Jiaomai, Food Control 15 (2004) 565. [3] M. Ghaedi, A. Shokrollahi, A.H. Kianfar, A.S. Mirsadeghi, A. Pourfarokhi, M. Soylak, Journal of Hazardous Materials 154 (2008) 128. [4] S. Tokahoglu, S. Kartal, Microchimica Acta 162 (2008) 1. [5] H. Tian, X.J. Chang, Z. Hu, K. Yang, Q. He, L.N. Zhang, Z.F. Tu, Microchimica Acta 171 (2010) 225.
[6] S. Abe, K. Fuji, T. Sono, Analytica Chimica Acta 293 (1994) 325. [7] M. Ghaedi, M. Montazerozohori, M. Sajedi, M. Roosta, M. Nickoosiar Jahromi, A. Asghari, Journal of Industrial and Engineering Chemistry 19 (2013) 1781. [8] A.A. Lothman, M. Habila, E. Yilmaz, M. Soylak, Microchimica Acta 177 (2012) 397. [9] M. Tuzen, K.O. Saygi, M. Soylak, Journal of Hazardous Materials 152 (2008) 632. [10] M. Tuzen, O.D. Uluozlu, C. Usta, M. Soylak, Analytica Chimica Acta 581 (2007) 241. [11] M. Ghaedi, J. Tashkhourian, M. Montazerozohori, M. Soylak, International Journal of Environmental Analytical Chemistry 93 (2013) 386. [12] M. Ghaedi, M. Montazerozohori, M.N. Biyareh, K. Mortazavi, M. Soylak, International Journal of Environmental Analytical Chemistry 93 (2013) 528. [13] M. Ghaedi, M. Montazerozohori, M. Tabatabie, H. Noormohamadi, A.B. Haghighi, AOAC Journal 95 (2012) 1761. [14] U. Divrikli, L. Elci, Analytica Chimica Acta 452 (2002) 231. [15] D. Citak, M. Tuzen, Food and Chemical Toxicology 48 (2010) 1399. [16] S. Yavuz, N. Ibrahim, S. Mustafa, Y. Huseyin, D. Mehmet, Microchimica Acta 157 (2007) 193. [17] M. Tuzen, M. Soylak, Journal of Hazardous Materials 162 (2009) 724. [18] E. Melek, M. Tuzen, M. Soylak, Analytica Chimica Acta 578 (2006) 213. [19] E. Latif, A.K. Aslihan, S. Mustafa, Journal of Hazardous Materials 153 (2008) 454. [20] M. Ghaedi, M. Montazerozohori, N. Rahimi, M. Nejati Biysreh, Journal of Industrial and Engineering Chemistry 19 (2013) 1477. [21] A. Goswami, A.K. Singh, Talanta 58 (2002) 669. [22] T.P. Rao, S. Daniel, J.M. Gladis, TrAC Trends in Analytical Chemistry 23 (2004) 28. [23] G.Z. Fang, J. Tan, X.P. Yan, Analytical Chemistry 77 (2005) 1734. [24] H.J. Hertog, J.P. Wibaut, Recueil des Travaux Chimiques des Pays-Bas 55 (1936) 122. [25] X. Liu, Z. Ma, J. Xing, H. Liu, Journal of Magnetism and Magnetic Materials 270 (2004) 1. [26] H. Ebrahimzadeh, E. Moazzen, M.M. Amini, O. Sadeghi, Chemical Engineering Journal 215 (2013) 315. [27] H. Ebrahimzadeh, E. Moazzen, M.M. Amini, O. Sadeghi, Analytical Methods 4 (2012) 3232. [28] M. Rafizadeh, V. Amani, B. Neumu¨ller, Zeitschrift fu¨r anorganische und allgemeine Chemie 632 (2006) 2383. [29] A. Bagheri, M. Behbahani, M.M. Amini, O. Sadeghi, A. Tootoonchi, Z. Dahaghin, Microchimica Acta 178 (2012) 261. [30] X. Huang, X. Chang, Q. He, Y. Cui, Y. Zhai, N. Jiang, Journal of Hazardous Materials 157 (2008) 154. [31] H. Ebrahimzadeh, E. Moazzen, M.M. Amini, O. Sadeghi, International Journal of Cosmetic Science 35 (2013) 176. [32] A. Duran, M. Tuzen, M. Soylak, Journal of Hazardous Materials 169 (2009) 466. [33] R. Gao, Z. Hu, X. Chang, Q. He, L. Zhang, Journal of Hazardous Materials 172 (2009) 324. [34] A. Narin, M. Soylak, L. Elci, M. Dogan, Analytical Letters 34 (2001) 1935. [35] O. Sayar, H.R. Lotfi Zadeh Zhad, O. Sadeghi, V. Amani, E. Najafi, N. Tavassoli, Biological Trace Element Research 150 (2012) 403.
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
JIEC-1647; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
A novel magnetic ion imprinted polymer for selective adsorption of trace amounts of lead(II) ions in environment samples Omid Sayar a, Niloufar Akbarzadeh Torbati b, Hamideh Saravani b, Kheirollah Mehrani c,*, Ali Behbahani d, Hamid Reza Moghadam Zadeh d a
School of Civil & Environmental Engineering, University of New South Wales, NSW 2052, Australia Department of Chemistry, University of Sistan and Baluchestan, Zahedan, Iran Department of Chemistry, Islamic Azad University, Science and Research Branch, Tehran, Iran d Department of Chemical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran b c
A R T I C L E I N F O
Article history: Received 13 September 2013 Accepted 27 October 2013 Available online xxx Keywords: Pb(II) determination Ion imprinted polymer Fe3O4 nano-particles Environmental samples
A B S T R A C T
In this work a novel ion imprinted polymer (IIP) based on 4-(vinylamino)pyridine-2,6-dicarboxylicacid (VPyDC), was coated on Fe3O4 nano-particles. The application of this magnetic sorbent was investigated for preconcentration and determination of trace Pb(II) ions by flame atomic absorption spectrometry. Effects of various parameters such as sample pH, adsorption/desorption time and eluent were investigated during this study. The relative standard deviation and limit of detection of the method were found to be 1.8% and 0.9 ng mL1, respectively. The accuracy of this method was confirmed using various standard reference materials, then it was used for Pb(II) determination in environmental samples. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Trace levels of heavy metals are widely distributed in environment due to industrial and agricultural processes. Lead (Pb) is one of the most toxic heavy metal which is the main source of contamination for human being found in water and food [1]. As lead and its compounds can cause adverse effects on metabolic processes of human beings even at low concentrations, its determination is so important for scientists all over the world [2]. Although determination of lead by flame atomic absorption spectrometry (FAAS) is very simple and easy to operate, its concentration in environmental samples is usually lower than the FAAS limit of detection [3]. Another concerning item in determination of lead ions in environmental samples is high matrix interferences [4]. Therefore, preconcentration step is necessary for determination of lead when we are dealing with environmental samples which are at the ng mL1 level of ions and have high interfering matrix [5]. Several methods have been developed for Pb(II) ions pre-concentration, separation and determination such as liquid–liquid extraction (LLE) [6], solid phase extraction [7–13], co-precipitation [14,15] and cloud point extraction [16,17] which among them, Solid phase extraction (SPE) is more common due to
* Corresponding author. Tel.: +98 9122483395. E-mail address: [email protected] (K. Mehrani).
the higher enrichment factor, minimal costs, environment friendly and easy automation [18]. Different solid phase extractors such as Amberlite XAD resin [19], carbon nano-tube [20], activated carbon [3], silica gel [21] and ion imprinted polymers [22] have been used as sorbents in solid phase extraction which among these materials, ion imprinted polymers (IIP) is more attractive due to their high selectivity, mechanical and chemical stability [23]. But the difficulty in separation is one of the biggest failures in these materials. In this work, a novel Pb(II) ion imprinted polymer was synthesized and immobilized on the surface of Fe3O4 in scope of easy separation by a magnet. This novel IIP was evaluated by IR spectroscopy, TG/DTA and SEM micrograph. The effects of various parameters such as maximum capacity, optimum eluent containing type, concentration and the least amount of it, interfering ions effects and adsorption conditions containing pH and analyte flow rate were also studied. Moreover the accuracy of this method was confirmed using various standard materials. 2. Experimental 2.1. Apparatus A digital pH meter, WTW Metrohm 827 Ion analyzer (Herisau, Switzerland), equipped with a combined glass calomel electrode was used for the pH adjustments at 25 1 8C temperature. AA-680
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.10.052
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 2
O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Shimadzu (Kyoto, Japan) flame atomic absorption spectrometer with a lead hollow cathode lamp at wavelength 283.3 nm resonance line and the spectral band pass at 0.5 nm was used. All measurements were carried out in an air/acetylene flame. Fourier transform infrared (FT-IR) spectra were recorded using Bruker IFS66/S FT-IR (Bruker, Germany) spectrometer in KBr matrix. Scanning electron microscopy
(SEM) was performed using SEM Philips (XL30, Almelo, The Netherlands) instrument. The thermal analysis was performed using a BAHR-Thermoanalyse GmbH (Hu¨llhorst, Germany) employing heating at rates of 10 8C min1 in air atmosphere. X-ray diffraction patterns were obtained on a STOE diffractometer (Darmstadt, Germany) with Cu Ka radiation.
Fig. 1. A schematic diagram for synthesis of sorbent.
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
2.2. Materials and reagents 4-Aminopyridine-2,6-dicarboxylic acid and Fe3O4 nano-particles have been synthesized according to previous reported procedure [24,25]. 4-(Vinylamino)pyridine-2,6-dicarboxylic acid (VPyDC) was prepared by reaction of 1 mmol of 4-aminopyridine2,6-dicarboxylic acid with 1 mmol of vinyl chloride in presence of 50 mL methanol and triethylamine (1:1, V:V) [26]. Ethylene glycol dimethacrylate (EGDMA) was obtained from Fluka (Buchs, Switzerland). 2,20 -Azo bis isobutyro nitrile (AIBN) was obtained from Acros Organics (New Jersey, USA). All the other reagents used were of analytical grade and purchased from Merck (Darmstadt, Germany). Distilled water was prepared using a Milli-Q system from Millipore (Bedford, MA, USA). Standard Stock solutions (1000 mg L1) were obtained from Aldrich Company. The working standard solutions were prepared by appropriate dilution of the stock solution with double distillated water. All of these solutions were stored in ambient temperature. The standard reference materials (SRM 1515, SRM 1640 and SRM 2709), which used for method validation, were obtained from National Institute of Standards and Technology (www.nist.gov, Gaithersburg, USA). 2.3. Preparation of lead magnetic ions imprinted polymer nanoparticles To prepare vinyl functionalized Fe3O4 nano-particles, 1.0 g Fe3O4 was suspended in 50 mL toluene, afterward 2.0 g of 3vinyletriethoxy silane was added to the solution [27]. After stirring for 48 h, the solid phase was separated from the solvent by a strong magnet and washed with methanol and dried at room temperature. The vinyl functionalization of Fe3O4 nano-particles was confirmed by IR spectroscopy and elemental analysis. Elemental analysis showed 0.68 mmol g1 vinyl group coated on this sorbent (C = 2.44%, H = 0.33%). The Pb(II) complex was prepared same as previous reports [28]. In this approach, 0.193 g (1 mmol) of VPyDC and 0.16 g (1 mmol) bipyridine were dissolved in 20 mL methanol, then 0.165 g (0.5 mmol) Pb(NO3)2 was added to the solution. The resulting purple solution was stirred at room temperature for 4 h until the reaction was completed. In order to synthesize IIP@Fe3O4, 0.5 mmol of Pb(II) complex and 1.5 g of vinyl functionalized Fe3O4 were dispersed in 100 mL of methanol. After addition of 0.1 g of AIBN and 1.1 mL of EGDMA to
3
the mixture, the mixture was heated to 60 8C. At the end of polymerization reaction (after 24 h), the composite was separated by a magnet and the template (Pb(II) ions in polymer structure) was removed by several washing using 0.1 mol L1 Thiourea/ 0.01 mol L1 HCl solution. According to FAAS results, the removal of the template was completed after 8 times washing with 0.1 mol L1 Thiourea/0.01 mol L1 HCl solution. In order to confirm the removal of Pb(II) ions, the amount of Pb(II) ions was determined by FAAS after treatment of this composite with piranha solution (H2SO4 + H2O2). Piranha solution which containing concentrated H2SO4 and 30% solution of H2O2 (3:1, v/v), dissolves organic parts of these particles and release lead ions in solution. The formation of this IIP was confirmed by IR, TG/DT analysis and also SEM photograph. A schematic diagram of this IIP is shown in Fig. 1. 2.4. Extraction procedure The extraction procedure consists of two steps: in the sorption step, pH of sample solution was adjusted at 7, then, 0.01 g of IIP@Fe3O4 was suspended in aqueous solution containing 1 mg L1 of Pb(II) and shakes for 4 min. In desorption step, elution of adsorbed Pb(II) ions was performed by 3 mL of 0.1 mol L1 Thiourea/0.01 mol L1 HCl solution. After 9 min concentration of lead ions in the eluent was determined by FAAS. 2.5. Standard reference materials pretreatment The water samples were obtained from tap water (Tehran, Iran), sea water (Caspian Sea, Iran) and river water (Chaloos, Iran). The samples were collected in cleaned polyethylene bottles and were filtered through a 0.45 mm pore size nylon filter (Millipore) immediately after sampling. The soil samples were collected form seashore (Caspian Sea, Iran) and Chaloos river coast (Chaloos, Iran) and stored in polythene bags and brought to the laboratory for preparation and treatment. To digest the soil samples, 1 g of solid sample was digested with 6 mL of HCl (37%) and 2 mL of HNO3 (65%) in a microwave digestion system. Digestion was carried out for 2 min at 250 W, 2 min at 0 W, 6 min at 250 W, 5 min at 400 W, 8 min at 550 W and then venting for 8 min. Finally the residue was then diluted to 100 mL with deionized water [27]. The standard reference materials (SRM 1515 and SRM 2709) were digested by mentioned method.
Fig. 2. Thermal analysis of synthesized magnetic ion imprinted polymer.
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
4
120
3. Results and discussion
100
Fe3O4 nano-particles have been synthesized according to reported procedure [25]. Formation of these nano-particles was confirmed by SEM and high-angle X-ray. Modification of nano-size Fe3O4 surface with vinyl groups was carried out through the direct method for functionalization of Fe3O4 with triethoxysilan agents reported severally before [27]. The reaction of vinyl functionalized Fe3O4 as a monomer with lead complex as another monomer in presence of an initiator like AIBN and EGDMA as the cross linker lead to the formation of this IIP (Fig. 1). The resulting imprinted nano-particles were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric and differential thermal analysis. The FT-IR spectra of ion imprinted polymer showed following bands: 1268 cm1 (C–O), 1629 cm1 (C5 5N), 1715 cm1 (C5 5O), 2968 cm1 (aliphatic C–H) and 3037 cm1 (aromatic C–H). Thermal stability of this composite was evaluated by TG/DT analysis (Fig. 2). The results showed this composite (IIP@Fe3O4) have high thermal stability, as it is stable up to 300 8C. Moreover according to loosing 40% of the composite weight, it can be concluded that forty percent of this sorbent is consists of polymer. Also the size and morphology of this sorbent were determined by SEM (Fig. 3). According to this micrograph, the sorbent are consists of spherical nano-particles with approximately 70 nm in diameter. It worth mentioning, since the magnetic nano-particles are coated by polymer, they will not destroy in acidic solutions. 3.2. Optimization of the preconcentration method It is evident that extraction and preconcentration of Pb(II) ions on this IIP are strongly affected by experimental conditions such as pH, eluent concentration and volume, extraction and desorption time [26,27]. The influences of these parameters were studied through this study and the optimum conditions were obtained. 3.2.1. Effect of solution’s pH As the pH could change the coordination sites of the ligand, it is one of the most controlling parameters for adsorption of lead ions on IIP. The effect of varying pH values on Pb(II) ions adsorption was investigated by adjusting the pH of sample solutions containing 1 mg L1 of lead in the range of pH = 2–9. After stirring for 4 min, the adsorbed Pb(II) ions were eluted with 3 mL of 0.1 mol L1 Thiourea/0.01 mol L1 HCl, afterward the amount of lead ions in the eluent was determined by FAAS. As it can be seen from Fig. 4, the best pH for adsorption of Pb(II) on this composite is 7.0–8.0. Since the most environmental samples are in natural pH, pH = 7.0
Recovery %
3.1. Sorbent characterization
80 60 40 20 0
0
2
4
6
8
10
pH Fig. 4. Effect of sample pH on the recovery of Pb(II) ions from synthesized magnetic ion imprinted polymer.
was chosen for further experiments. This is because at low pH values there is an excessive protonation of the lone pair of electrons on nitrogen, resulting in a decrease in the Pb(II) ions sorption. Moreover, in the alkaline pHs, the Pb(II) precipitate as Pb(OH)2 which cause reducing in removal efficiency. 3.2.2. Effect of type, concentration and volume of eluent Series of acidic eluent solutions such as HCl, HNO3, HClO4 and H2SO4 in different concentrations and also their mixture with Thiourea as an auxiliary ligand were used to elute Pb(II) ions from this IIP. The experimental results showed that the mixture of HCl and Thiourea in concentrations higher than 0.01 mol L1 and 0.1, respectively, elutes Pb(II) from this sorbent efficiently (Table 1). The investigation of the effect of eluent volume on the recovery of Pb(II) showed 3 mL of the 0.1 mol L1 Thiourea/0.01 mol L1 HCl is the optimum volume for desorption of Pb(II) ions (Table 1). 3.2.3. Optimization of sorption and desorption time Optimization of the time is so important in analytical analysis since the insufficient time reduces the procedure efficiently and extra ones cause increasing analysis time. In order to study the effect of time, 100 mL of solutions containing 1 mg mL1 of Pb(II) were adjusted to pH = 7.0 and 0.01 g magnetic IIP was introduced to the solutions and shake for desired time. Then, the sorbent was separated by placing a magnet and the preconcentrated analyte was determined by FAAS after eluting by 0.1 mol L1 Thiourea/ 0.01 mol L1 HCl. As it can be seen from Fig. 5, 4 min for a completing the extraction and 9 min for eluting is needed. This fast extraction and elution could be attributed to the high surface area dealing with these IIP nano-particles.
Table 1 Effect of type, concentration and volume of eluent on recovery of lead ions.
Fig. 3. SEM micrograph of synthesized magnetic ion imprinted polymer.
Eluent
Volume (mL)
Concentration (mol L1)
Recovery (%)
HCl HNO3 HClO4 H2SO4 HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea HCl + Thiourea
10 10 10 10 10 10 10 8 6 4 2 10
0.01 0.01 0.01 0.01 0.01/0.01 0.01/0.1 0.01/1 0.01/0.1 0.01/0.1 0.01/0.1 0.01/0.1 0.01/0.1
53.1 44.7 28.3 35.9 83.4 98.7 98.3 99.1 97.5 98.5 91.4 97.9
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
5
method under optimum conditions was determined by performing ten replicates. The recovery value for lead ions was found to be 98.3% with relative standard deviation of 1.8% on these IIP. 3.4. Sorbent maximum capacity The maximum adsorption capacity of this IIP@Fe3O4 for Pb(II) ions was established by placing 0.01 g of it in 500 mL of aqueous solutions containing 10 mg of lead ions and the amount of adsorbed ions in eluted solutions have been investigated by FAAS. The maximum adsorption capacity of this IIP was calculated to be 55.89 0.6 mg g1 based on the three replicate measurements. 3.5. Effect of matrix ions
Fig. 5. Effect of adsorption and desorption time on the recovery of Pb(II) ions from synthesized magnetic ion imprinted polymer.
3.3. Figure of merit The detection limit of this method was determined by ten times placing 0.01 g sorbent in 500 mL blank solutions under the optimal experimental conditions. The value of LOD for lead on IIP@Fe3O4 was 0.9 ng mL1. These results were obtained from CLOD = KbSb/m; where the numerical factor, Kb = 3 [29]. Also the precision of the Table 2 The tolerance limit of diverse ions in the determination of lead. Interfering ions +
Na K+ Ca2+ Mg+2 Zn2+ Ni+2 Cu+2 Co+2 Fe+2 Mn+2 Cd+2
Tolerable concentration ratio X/Pb
Recovery (%)
5000 5000 2500 2500 1000 2500 1000 1000 500 500 500
99.3 98.7 99.1 99.3 97.9 96.8 97.4 98.4 97.6 97.3 96.2
As it mentioned in Section 1, the selectivity of sorbent is so important in determination of lead in real samples since there are lots of interfering ions in the matrix. The effect of a variety of cations found in natural samples on the determination of Pb(II) ions was studied by adding various concentrations of Na+, K+, Cs+, Mg2+, Ca2+, Cd2+, Fe2+, Mn2+ and Cr3+ to solutions containing 10 mg L1 of Pb(II) listed in Table 2. The tolerable amount of each ion was determined by comparing the FAAS signal Pb(II) ion in presence and absence of interference ion. The tolerable amount was defined as the maximum concentration could cause a change of less than 5% in signal compared to the signal Pb(II) ion without any interference. As shown in Table 2, the vast majority of transition metals do not interfere the concentrations encountered in nature, and the method is selective toward lead extraction at a pH = 7. Furthermore, extraction is not affected by high concentrations of alkaline and alkaline earth metals. This high selectivity toward Pb(II) ions which could not be seen in common sorbents could be attributed to the printing of Pb(II) ions in sorbent synthesis. By printing the ion, there will be the sites which have suitable size and interaction only for target ion. 3.6. Validation of method In order to investigate the accuracy, this technique was validated by comparison to several reference materials containing a certified lead content. As the results in Table 3 show, this sorbent could be used as a promising solid-phase for extraction and determination of lead ions in environmental samples. Due to its high selectivity and adsorption capacity, this magnetic ion imprinted polymer can be used as a reliable sorbent for
Table 3 Recovery of determination of lead in certified reference materials. Ion
Sample
SRM 1640 (drinking water) (mg g1) SRM 1515 (apple leaves) (ng g1) SRM 2709 (San Joaquin soil) (mg g1)
Concentration
Pb(II) Pb(II) Pb(II)
Certified
Found
27.89 47 17.28
27.55 45.2 17.183
Recovery (%)
Relative error (%)
98.8 96.1 99.4
0.9 3.4 1.2
Table 4 Results for the determination of lead ions in environmental samples. Sample
Found (ng mL1)
Added (ng mL1)
C, found (ng mL1)
Recovery (%)
RSD (%)
Distilled water Tap water River water Sea water Seashore soil River coast soil
ND ND ND ND 16.2 38.4
20.0 20.0 20.0 20.0 20.0 20.0
19.9 19.8 20.3 19.5 35.6 57.9
99.5 99.0 101.5 97.5 97.0 97.5
1.3 1.9 2.4 2.7 3.1 2.8
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052
G Model
JIEC-1647; No. of Pages 6 O. Sayar et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
6
Table 5 Comparison of established method with previously reported ones. Sorbent
RSD (%)
Capacity (mg g1)
LOD (ng mL1)
Reference
Tris(2-aminoethyl) amine-silica gel Pyridine-2,6-diamine-Fe3O4 Multiwall carbon nano-tubes Modified activated carbon Amberite XAD-2000 Pyridine-functionalized Fe3O4 Magnetic ion imprinted polymer
4.0 0.6 3.52 4.0 <9.0 1.3 1.8
64.61 172.02 NR1 48.56 NR 38.7 55.9
0.55 1.3 3.52 0.45 3 0.8 0.9
[30] [31] [32] [33] [34] [35] This work
NR: not reported.
determination of lead ions in real samples with high matrix interfere. 3.7. Environmental samples analysis The mentioned method was applied for the determination of lead ions concentration in various environmental samples including soil and water. In this regard, after sample preparation by the procedure mentioned in sample preparation section, the sample solution was adjusted to pH = 7 and then the amount of lead ions was determined in eluent by flame atomic adsorption spectroscopy after preconcentration by magnetic ion imprinted polymer. As the results in Table 4 show, this method can be considered to be a reliable and fast method for Pb(II) determination in an environmental sample. The figure of merits for this sorbent was compared to previously reported papers in Table 5. As it can be seen, the ion imprinted polymer has higher detection limit and lower preconcentration factors in some cases. However, the high selectivity of ion imprinted polymer and the possibility of easy separation is the advantages of this sorbent. 4. Conclusion Novel magnetic IIP have been achieved by coating an IIP on Fe3O4 nano-particles. Selectivity of this ion imprinted polymer has made it a suitable and selective sorbent for extraction and preconcentration of lead ions in real samples. The high selectivity of this IIP toward lead ions, easy separation and the high adsorption capacity factor are the advantages of this novel sorbent. References [1] J.B. Stevens, Environmental Science & Technology 25 (1991) 1289. [2] L. Zaijun, T. Jian, P. Jiaomai, Food Control 15 (2004) 565. [3] M. Ghaedi, A. Shokrollahi, A.H. Kianfar, A.S. Mirsadeghi, A. Pourfarokhi, M. Soylak, Journal of Hazardous Materials 154 (2008) 128. [4] S. Tokahoglu, S. Kartal, Microchimica Acta 162 (2008) 1. [5] H. Tian, X.J. Chang, Z. Hu, K. Yang, Q. He, L.N. Zhang, Z.F. Tu, Microchimica Acta 171 (2010) 225.
[6] S. Abe, K. Fuji, T. Sono, Analytica Chimica Acta 293 (1994) 325. [7] M. Ghaedi, M. Montazerozohori, M. Sajedi, M. Roosta, M. Nickoosiar Jahromi, A. Asghari, Journal of Industrial and Engineering Chemistry 19 (2013) 1781. [8] A.A. Lothman, M. Habila, E. Yilmaz, M. Soylak, Microchimica Acta 177 (2012) 397. [9] M. Tuzen, K.O. Saygi, M. Soylak, Journal of Hazardous Materials 152 (2008) 632. [10] M. Tuzen, O.D. Uluozlu, C. Usta, M. Soylak, Analytica Chimica Acta 581 (2007) 241. [11] M. Ghaedi, J. Tashkhourian, M. Montazerozohori, M. Soylak, International Journal of Environmental Analytical Chemistry 93 (2013) 386. [12] M. Ghaedi, M. Montazerozohori, M.N. Biyareh, K. Mortazavi, M. Soylak, International Journal of Environmental Analytical Chemistry 93 (2013) 528. [13] M. Ghaedi, M. Montazerozohori, M. Tabatabie, H. Noormohamadi, A.B. Haghighi, AOAC Journal 95 (2012) 1761. [14] U. Divrikli, L. Elci, Analytica Chimica Acta 452 (2002) 231. [15] D. Citak, M. Tuzen, Food and Chemical Toxicology 48 (2010) 1399. [16] S. Yavuz, N. Ibrahim, S. Mustafa, Y. Huseyin, D. Mehmet, Microchimica Acta 157 (2007) 193. [17] M. Tuzen, M. Soylak, Journal of Hazardous Materials 162 (2009) 724. [18] E. Melek, M. Tuzen, M. Soylak, Analytica Chimica Acta 578 (2006) 213. [19] E. Latif, A.K. Aslihan, S. Mustafa, Journal of Hazardous Materials 153 (2008) 454. [20] M. Ghaedi, M. Montazerozohori, N. Rahimi, M. Nejati Biysreh, Journal of Industrial and Engineering Chemistry 19 (2013) 1477. [21] A. Goswami, A.K. Singh, Talanta 58 (2002) 669. [22] T.P. Rao, S. Daniel, J.M. Gladis, TrAC Trends in Analytical Chemistry 23 (2004) 28. [23] G.Z. Fang, J. Tan, X.P. Yan, Analytical Chemistry 77 (2005) 1734. [24] H.J. Hertog, J.P. Wibaut, Recueil des Travaux Chimiques des Pays-Bas 55 (1936) 122. [25] X. Liu, Z. Ma, J. Xing, H. Liu, Journal of Magnetism and Magnetic Materials 270 (2004) 1. [26] H. Ebrahimzadeh, E. Moazzen, M.M. Amini, O. Sadeghi, Chemical Engineering Journal 215 (2013) 315. [27] H. Ebrahimzadeh, E. Moazzen, M.M. Amini, O. Sadeghi, Analytical Methods 4 (2012) 3232. [28] M. Rafizadeh, V. Amani, B. Neumu¨ller, Zeitschrift fu¨r anorganische und allgemeine Chemie 632 (2006) 2383. [29] A. Bagheri, M. Behbahani, M.M. Amini, O. Sadeghi, A. Tootoonchi, Z. Dahaghin, Microchimica Acta 178 (2012) 261. [30] X. Huang, X. Chang, Q. He, Y. Cui, Y. Zhai, N. Jiang, Journal of Hazardous Materials 157 (2008) 154. [31] H. Ebrahimzadeh, E. Moazzen, M.M. Amini, O. Sadeghi, International Journal of Cosmetic Science 35 (2013) 176. [32] A. Duran, M. Tuzen, M. Soylak, Journal of Hazardous Materials 169 (2009) 466. [33] R. Gao, Z. Hu, X. Chang, Q. He, L. Zhang, Journal of Hazardous Materials 172 (2009) 324. [34] A. Narin, M. Soylak, L. Elci, M. Dogan, Analytical Letters 34 (2001) 1935. [35] O. Sayar, H.R. Lotfi Zadeh Zhad, O. Sadeghi, V. Amani, E. Najafi, N. Tavassoli, Biological Trace Element Research 150 (2012) 403.
Please cite this article in press as: O. Sayar, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.10.052