Selective Solid-Phase Extraction and Trace Monitoringof Lead Ions in Food and Water Samples Using NewLead-Imprinted Polymer Nanoparticles

Mohammad Behbahani & Parmoon Ghareh Hassanlou & Mostafa M. Amini &Hamid Reza Moazami & Hamid Sadeghi Abandansari & Akbar Bagheri &Salman Hassan Zadeh

Received: 11 April 2014 /Accepted: 22 June 2014# Springer Science+Business Media New York 2014

Abstract A solid-phase extraction method using Pb2+ ion-imprinted polymer (Pb2+-IIP) nanoparticles combined withflame atomic absorption spectrophotometry (FAAS) was de-veloped for the preconcentration and trace monitoring of leadions in environmental samples. The Pb2+-IIP nanoparticleswere obtained by precipitation polymerization of 4-vinylpyridine (the functional monomer), ethylene glycoldimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile(the initiator), 4-(2-pyridylazo) resorcinol (the lead-bindingligand), and lead ions (the template ion) in acetonitrile solu-tion. The Pb2+-IIP nanoparticles were characterized by Fouriertransformed infrared spectroscopy (FTIR), X-ray diffraction(XRD), thermogravimetric and differential thermal analysis(TGA/DTA), and by scanning electron microscopy (SEM).Different affecting parameters on the adsorption anddesorption of this solid-phase extraction process wereevaluated and optimized. Under the optimized condi-tions, the detection limit for the proposed method wasfound to be 0.9 μg L−1, while the relative standarddeviation (RSD) for five replicate measurements wascalculated to be <4 %. For proving that the proposedmethod is reliable, a range of food and water sampleswith different and complex matrices was used.

Keywords Lead ions . Ion-imprinted polymer .

Nanoparticles . Flame atomic absorption spectrophotometry .

Food and water samples

Introduction

Lead (Pb) is known to be a toxic metal that accumulates in thehuman body throughout the lifetime (Liang and Sang 2008).Typical symptoms of lead poisoning are abdominal pain,anemia, headaches and convulsions, chronic nephritis of thekidney, brain damage, and central nervous system disorders(Korn et al. 2006). The US Environmental Protection Agency(EPA) has classified lead as a group B2 human carcinogen(Wanger 1995). The World Health Organization (WHO) hasestablished the maximum allowable limit of 10μg L−1 for leadin drinking water (World Health Organization 1996).Therefore, highly sensitive determination methods of tracePb in environmental samples need to be established. Flameatomic absorption spectrometry (FAAS) has been widely usedfor the determination of trace metal ions because of the rela-tively simple and inexpensive equipment required. However,direct determination of metal ions at trace levels by FAAS islimited, not only due to insufficient sensitivity, but also tomatrix interference. Under these circumstances, in order todetermine trace levels of Pb, a separation and enrichment stepprior to the determination may be beneficial. Several methodshave been proposed for separation and preconcentration oftrace Pb including liquid–liquid extraction (LLE) (Comitreand Reis 2005), solid-phase extraction (SPE) (Ensafi andShiraz 2008), cloud point extraction (CPE) [Chen et al.2005], and liquid-phase microextraction (LPME) (Cao et al.

M. Behbahani (*) : P. G. Hassanlou :M. M. Amini :H. R. Moazami :H. S. Abandansari :A. BagheriDepartment of Chemistry, Shahid Beheshti University,G.C., Tehran 1983963113, Irane-mail: mohammadbehbahani89@yahoo.com

S. H. ZadehDepartment of Chemical Engineering, University of Birmingham,Birmingham, UK

Food Anal. MethodsDOI 10.1007/s12161-014-9924-5

2008). Solid-phase extraction (SPE) is a popular technique forseparation and preconcentration of metal ions in environmen-tal samples (Bagheri et al. 2012a; Bagheri et al. 2012b;Bagheri et al. 2012c; Nabid et al. 2012; Behbahani et al.2012; Behbahani et al. 2013; Ebrahimzadeh et al. 2013;Tuzen et al. 2005a; Tuzen et al. 2005b; Soylak & Narin2005) due to its simplicity, rapidity, minimal cost, and theability of combination with different detection techniques inthe form of on-line or off-line mode [Fritz 1999]. AlthoughSPE has many practical and operating advantages over otherpreconcentration methods, it suffers from interfering com-pounds which co-extracted with the target analytes on con-ventional sorbents. In order to solve this lack of selectivity, theuse of molecularly imprinted polymers (MIPs) has been sug-gested especially for the clean-up of organic compounds (delSole et al. 2013; Zhong et al. 2013; Junping et al. 2009). TheMIPs are highly selective because molecular imprinting poly-merization is based on the preparation of a highly cross-linkedpolymer around a template in the presence of a suitablemonomer (del Sole et al. 2013). Therefore, imprinted polymershows an affinity for selective extraction of the templatemolecule or template ion over other components in a sample.

Usually, MIPs or IIPs are synthesized by bulk polymeriza-tion making necessary the subsequent crushing and sieving ofthe obtained polymer. This process is tedious, time-consuming, and the obtained particles show a random shapeand size limiting its applicability. During recent years, newpolymerization strategies have been introduced and recentlyreviewed (Turiel & Martin-Esteban 2004) dealing with theobtainment of imprinted beads in order to improve the analyt-ical performance of MIPs. Within the different new polymer-ization strategies, precipitation polymerization (Beltran et al.2009; Li et al. 2003; Wang et al. 2003) seems to be one of themost simple and well-suited methods to obtain spherical par-ticles with the desired characteristics. Basically, this methodconsists on the polymerization of the system (monomer,template and cross-linker) in the presence of a largeramount of porogen than that typically used in the bulkpolymerization method. As a result of this more dilutedreaction system, the growing polymer chains are unableto occupy the entire volume of the vessel leading to adispersion of microgel particles in the solvent. Besidethis, it has been reported that the capacity, affinityconstants, and homogeneity of binding sites associatedto polymers prepared by precipitation polymerization areclearly improved compared to those present in MIPsobtained by bulk polymerization (Tamayo et al. 2003,Cacho et al. 2004).

In this study, a novel Pb2+ ion-imprinted polymer has beensynthesized by precipitation polymerization technique for fastand selective preconcentration and trace determinationof Pb2+ ions from various matrixes. Characterization ofthis polymer was evaluated by Fourier transformed

infrared spectroscopy (FTIR), X-ray diffraction (XRD),thermogravimetric and differential thermal analysis(TGA/DTA), and by scanning electron microscopy(SEM). The effect of several factors such as solutionpH, sorption and desorption time, type, concentrationand volume of eluent, breakthrough volume, maximumadsorption capacity, and the selectivity of this sorbenttoward lead ions were investigated and optimized.Finally, this sorbent was used for preconcentration anddetermination of Pb2+ in different matrixes.

Experimental

Apparatus

Lead concentration was determined by an AA-680 Shimadzu(Kyoto, Japan) flame atomic absorption spectrometer (FAAS)in an air-acetylene flame, according to the user’s manual,provided by the manufacturer. A lead hollow cathode lampwas used as the radiation source with wavelength of 283.3 nm.A home-made microsample introduction system was used foraspiration of the extractant phase in flame atomic absorptionspectrometry. A digital pH meter, WTW Metrohm 827 Ionanalyzer (Herisau, Switzerland), equipped with a combinedglass calomel electrode was used for the pH adjustmentsat 25±1 °C temperature. Heidolph heater stirrer model MR3001 (Germany) was employed for heating and stirring of thesolutions. Fourier transform infrared (FT-IR) spectra (4,000–200 cm−1) in KBr were recorded using Bruker IFS66/S FT-IRspectrometer. High angle X-ray diffraction patterns were ob-tained on a Philips-PW 17C diffractometer with CuKα radia-tion. Scanning electron microscopy (SEM) was performed bygently distributing the powder sample on the stainless steelstubs, using SEM (KYKY, EM3200) instrument. The thermalproperties of synthesized polymers were determined using aBAHR-Thermoanalyse GmbH (Germany) with employing,heating, and cooling rates of 10 °C min−1 and using a con-denser as the coolant. The samples were weighed as a thin filmand carefully packed into a clean aluminum pan (11.5–12.5 mg) and sealed by crimping an aluminum lid on thepan (Shimadzu universal crimper). An Al2O3 empty pansealed with a cover pan was used as a reference sample. Ascanning range of 10 to 800 °C was used for samples at10 °C min−1 in nitrogen gas.

Material and Reagents

4-Vinyl pyridine with high purity was purchased fromMerck (Darmstadt, Germany, www.merck.de). Ethyleneglycol dimethacrylate (EGDMA) and 4-(2-pyridylazo)resorcinol were obtained from Fluka (Buchs SG,Sw i t z e r l a n d , www. s i gma a l d r i c h . c om ) . 2 , 2 ′ -

Food Anal. Methods

Azobisisobutyronitrile (AIBN) was obtained from AcrosOrganics (NJ, USA). NaOH, HCl, HNO3, acetic acid(HOAC), and methanol were purchased from Merck(Darmstadt, Germany, www.merck.de). All the otherreagents used were of analytical grade and purchasedfrom Merck (Darmstadt, Germany, www.merck.de).Stock solutions of Cu2+, Cd2+, Pb2+, Zn2+, Ni2+, andCo2+ were prepared from Titrisol solutions (Merck,Darmstadt, Germany, www.merck.de). Ultrapure waterwas prepared using a Milli-Q system from Millipore(Bedford, MA, USA). Ore polymetallic gold Zidarovo-PMZrZ (206 BG 326) from Bulgaria was used as thereference material.

Real Sample Pretreatment

Fruit Samples (Citrus limetta, Kiwi, and Pomegranate)

Three types of fruits were chosen for analysis. Thesewere C. limetta, kiwi, and pomegranate, which werecollected from the local supermarket. 1.0 g of driedand grounded samples was put into burning cup with15 mL of pure HNO3. The samples were incinerated ina MARS 5 microwave oven at 200 °C. After digestiontreatment, the samples were filtrated through WhatmanNo. 42. After filtration, the obtained clear solution wasdiluted to 50 mL (pH of 6.0) for lead analysis.

Scheme 1 Schematic illustrationof imprinting process for thepreparation of lead-imprintedpolymer nanoparticles byprecipitation polymerizationtechnique

Food Anal. Methods

Water Samples

The polyethylene bottles filled with the samples were cleanedwith detergent, water, diluted nitric acid, and water in se-quence. The samples were immediately filtered through acellulose filter membrane (pore size 0.45 μm) and were acid-ified to pH of 2.0 for storage. Tap water samples (50 mL) weretaken from our research laboratory without pretreatment (pHadjusted to 6.0). Before analysis, the water samples (50 mL)which were taken from Caspian Sea, river (SiahroodRiver (Ghaemshahr, Iran)), and waste (water fish ponds)were adjusted to pH of 6.0 according to optimizedexperimental conditions.

Synthesis of Pb2+ Ion-imprinted Polymer and NonimprintedPolymer Nanoparticles

The nanosized lead-imprinted polymer was prepared byprecipitation polymerization technique. In the first step,3 mmol of 4-vinyl pyridine (functional monomer) and1 mmol of 4-(2-pyridylazo) resorcinol (the lead-bindingligand) were dissolved in 50 mL of acetonitrile in a100-mL glass flask. Subsequently; as the second step,1 mmol of Pb(NO3)2 as an imprinted metal ion(template) was added slowly to a glass flask and theresulted mixture was stirred for 5 h at room tempera-ture. In the third step, 18 mmol of EGDMA and 75 mgof AIBN were added as cross-linker and initiator. Theoxygen of the sample solution was removed by bub-bling nitrogen through the sample for 10.0 min.Polymerization was performed in an oil bath at 65 °Cfor 24 h in the presence of nitrogen under magneticstirring at 400 rpm. The prepared polymer was washedseveral times with 1:4 (v/v) methanol/water to removethe unreacted materials and then with HCl (1 mol L−1)for leaching the imprinted metal ions until the washing

solution was free from lead ions. Finally, it was washedwith double-distilled water until reached a neutral pH(Scheme 1 provides the images of synthesized nanosizedIIP after each step). The resulting fine powder was driedunder vacuum in a desiccator before sorption and de-sorption studies. In the same way, the nonimprintedpolymer (NIP) was also prepared without lead ion.

Extraction Procedure

Batch experiments were used for investigation of factorsin sorption and desorption steps. Extraction of lead ionsfrom solution is followed by two steps: sorption anddesorption. In the sorption step, the pH of samplesolution was adjusted to 6.0 by dropwise addition of2 mol L−1 sodium hydroxide or nitric acid solutions.Then, 20 mg of dried polymer was suspended in aque-ous solution containing 2 mg L−1 of Pb2+ and stirred for5 min with a magnetic stirrer. In desorption step, elutionof lead ions from IIP bead was performed by 0.5 mL of

Fig. 3 The SEM image of lead-imprinted polymer nanoparticlesFig. 1 DTA plot of leached and unleached lead-imprinted polymernanoparticles

Fig. 2 TGA plot of leached and unleached lead-imprinted polymernanoparticles

Food Anal. Methods

HCl (1 mol L−1). After 10 min, the concentration oflead ions in this solution was determined by flameatomic absorption spectrometry (FAAS).

Results and Discussion

Characterization of Synthesized IIP (Colorimetry, SEM,XRD, TGA/DTA, and FT-IR Analysis)

The resulting nanosized imprinted polymer were character-ized by colorimetric studies, scanning electron microscopy

(SEM), X-ray diffraction (XRD), Fourier transformed infraredspectroscopy (FTIR), thermogravimetric analysis (TGA), anddifferential thermal analysis (DTA).

After synthesis of unleached, leached IIP, and NIP (whitecolor) samples, colorimetric studies were carried out to com-pare the changes in the color of prepared powders. An obviouschange in the color from red of unleached IIPs to yellow afterthe leaching process clearly indicated the successful removalof lead ions from the polymeric matrix. Meanwhile, adsorp-tion process caused an instant color change in the leachedsample from yellow to a red color due to fast extractionof lead ions into the imprinted polymeric matrix brownat the desired pH.

Fig. 5 FT-IR spectra of 4-(2-pyridylazo) resorcinol (a), unleached (b), and leached lead-imprinted polymer nanoparticles (c)

Fig. 4 XRD patterns of leached and unleached lead-imprinted polymer nanoparticles

Food Anal. Methods

Thermal stability of the leached (the imprinted polymer hasbeen washed with optimized elution solvent and became freefrom target ions after washing) and unleached (the imprintedpolymer which is not washed with optimized elution solventand in this condition, the target ions is sorbed in the synthe-sized imprinted polymer) imprinted polymer was evaluated byTGA. Figures 1 and 2 show DTA and TGA plots for leachedand unleached imprinted polymer, respectively. In DTA plotsof lead imprinted polymer, exothermic peaks were observed at369, 468, 499, and 527 °C (for unleached) and 337 and 507 °C(for leached). As can be seen in the DTA plots, the temperaturefor maximum of peaks in lead-IIP was observed at highertemperature of 369 and 527 °C; while this event for theleached IIP was happened in the lower temperature of 337and 507 °C. These events confirm the higher thermal stabilityof the unleached relative to leached polymer, which is due tothe presence of lead ions in the unleached polymer and also itsstrong complexation with 4-(2-pyridylazo) resorcinol in thepolymeric network. As it is shown in TG plot for unleachedion-imprinted polymer, weight loss for lead-IIP was about89.09 %, and this amount of reduction in weight is related tothe presence of lead ions in polymer bead. While decrease inweight for leached imprinted polymer up to 100 %, is due tothe absence of lead ions in polymer. These observationsindicate that the formation of lead-imprinted polymerand elution of lead ions from the polymer was per-formed successfully.

The morphology of the lead-IIP was assessed by scanningelectron microscopy, and the SEM micrograph is shown inFig. 3. The SEM pattern showed particles with the size ofabout 29–42 nm. As a result, lead-IIP can be used as ananosize selective solid phase for very fast extraction of traceamounts of lead ions.

The XRD patterns of the leached and unleached nanosizedIIP are shown in Fig. 4. The XRD patterns of the leached andunleached IIP indicated similar patterns, except for the peaks

corresponding to lead. The two sharp peaks in the curve ofunleached IIP, prove the presence of sorbed lead ions on thesynthesized imprinted polymer, whereas these peaks wereabsent in the curve of leached IIP, indicating the completeremoval of lead ions from the structure of synthesizedimprinted polymer.

FTIR spectra of 4-(2-pyridylazo) resorcinol, unleached-IIPand leached-IIP are given in Fig. 5. Three spectra of pure 4-(2-pyridylazo) resorcinol, unleached IIP and leached IIP have thecharacteristics stretching vibration bands of OH (3,298–3,730 cm−1) and –N═N– group (1,447 cm−1) which provethe presence of 4-(2-pyridylazo) resorcinol in the polymerbead. The –N═N– band at 1,447 cm−1 in leached-IIP wereshifted to 1,431 cm−1 in unleached IIP. This amount of reduc-tion in band frequencies indicates that the lead ions have been

Fig. 7 The effect of sample volume on the recovery of lead ions on thesynthesized ion-imprinted polymer nanoparticles

Fig. 6 The effect of sample pH on the IIP retention efficiency (%) of leadon the IIP (the obtained results are the mean of three measurements)

Table 1 Effect of the type, concentration, and volume of eluent fordesorption of lead ions from lead-imprinted polymer

Eluent Concentration (mol L−1) Volume (mL) Ra (%)±Sb

HNO3 2 10 81.0±1.3

HCl 2 10 99.0±0.5

HNO3:HOAC 2:1 10 84.0±1.0

HCl:HOAC 2:1 10 98.0±1.0

HOAC 2 10 38.0±1.5

HCl 1 10 99.0±0.6

HCl 0.5 10 89.0±0.8

HCl 1 7.5 99.0±0.7

HCl 1 5 99.0±0.5

HCl 1 2.5 99.0±0.6

HCl 1 1 99.0±0.8

HCl 1 0.5 99.0±0.7

HCl 1 0.4 78.0±1.2

a Recoveryb Standard deviation

Food Anal. Methods

coordinated with nonbonding electron pairs of nitrogen in4-(2-pyridylazo) resorcinol, and as a result, it demonstratesthe presence of lead ions in unleached IIP structure. Moreover,in the IR spectrum of unleached relative to leached polymerand pure 4-(2-pyridylazo) resorcinol, the new bands in the 438and 506 cm−1 were assigned to lead–N and lead–O vibrations,respectively, which prove coordination of nitrogen and oxy-gen atoms to lead ions.

Optimization Experiments

Extraction and preconcentration of lead ions by synthesizedion-imprinted polymer nanoparticles were highly dependenton the different parameters such as pH of the sample, extrac-tion time, type, volume and concentration of eluent, desorp-tion time, and sample volume. In this context, the procedurewas optimized for the various analytical parameters.

Effect of Solution’s pH

To evaluate the effect of pH on the extraction efficiency, thepH of 25 mL of sample solutions containing 2 mg L−1 of leadions was adjusted in the range of 2–9. The pH of the suspen-sions was adjusted to desired values by adding sodium hy-droxide or nitric acid. As shown in Fig. 6, the adsorption oflead ions by lead-IIP increased from pH 2.0 to 6.0 but de-creased slightly from pH 7.0 to 9.0. By decreasing the pHvalue of the solution, the quantitative removal of thenanosized sorbent was also decreased due to electrostaticrepulsion of the protonated active sites on the sorbent withthe positively charged lead species. Meanwhile, the observeddecrease in retention percentage of lead ions on the IIP nano-particles at the pH values higher than 6.0, is most probablydue to the precipitation of lead ions in the hydroxide form,which leads to decreasing the concentration of free lead ions insample. Thus, the pH of 6.0 was chosen as the optimum pHfor further experiments.

Equilibrium Sorption Time

In a typical uptake kinetics test, 20 mg of the sorbent wasadded to 25 mL of 2 mg L−1 Pb2+ aqueous solution at pH 6.0.The resulting suspension was stirred in different times (i.e.,

from 2 to 10 min) under magnetic stirring. Consequently, anoptimum equilibration time of 5 min was obtained for quan-titative removal of lead ions from solution into the solid phase.

Choice of Eluent and Desorption Time

A series of selected eluents, including HCl, HNO3,HNO3:HCl, HCl:HOAC, HNO3:HOAC, and HOACwere used for elution of lead ions from imprinted poly-mer. As shown in Table 1, it is found that HCl(1 mol L−1) provided the most effective elution of leadions from imprinted sorbent.

The effect of eluent volume on the recovery of lead ionswas also studied. As Table 1 shows, quantitative recovery canbe obtained with 0.5 mL of HCl (1 mol L−1). Therefore,volumes of 0.5 mL of eluent for desorption of lead ions wereused in the next experiments.

In order to investigate the optimum desorption time, vari-ous times were examined in the range of 2 to 15 min, whileother parameters were kept in optimum conditions. Accordingto measurements, extraction recovery was increased up to10 min and it was constant in longer times. Therefore,10 min can be considered to be the best quantitative time forthe elution of lead ions from the imprinted polymer.

Effect of Sample Volume

In the analysis of real samples, the sample volume is one of theimportant parameters influencing the preconcentration factor.

Table 3 The tolerance limits of the diverse ions

Foreign ion Tolerable concentrationratio X/Pb

Ion-imprinted polymerRa (%)±Sb (template ion)

K+ 10,000 98.0±2.0

Na+ 10,000 99.0±1.0

Cu2+ 1,000 97.0±1.2

Cd2+ 1,000 98.0±1.1

Ni2+ 1,000 98.0±1.2

Zn+2 1,000 98.0±0.9

Co+2 1,000 98.0±1.1

Table 2 Distribution ratio (Kd),selectivity coefficient (k), and rel-ative selectively coefficient (k′)values of IIP and NIP for differentcations

Interfering ion Kd (IIP) (mL g−1) Kd (NIP) (mL g−1) K (IIP) K (NIP) k′

Pb2+ 47500.0 725.8 – – –

Cu2+ 277.8 833.3 170.9 0.9 189.8

Cd2+ 131.6 625.0 360.9 1.2 300.8

Zn2+ 202.7 530.3 234.3 1.4 167.4

Ni2+ 173.8 441.2 273.3 1.6 170.8

Co2+ 247.2 494.0 192.2 1.5 128.1

Food Anal. Methods

Therefore, the effect of sample volume on quantitative adsorp-tion of lead ion was investigated. For this purpose, 50 mg ofIIP was suspended in different sample volumes (25, 50, 100,200, 300, 400, 450, 475, 500, 525, 550, and 600 mL) con-taining 0.001 mg of lead ions. All solutions were extractedunder the optimum condition by the method. The results inFig. 7 demonstrate that the dilution effect was not significantfor sample volumes up to 500 mL for lead ions.

Sorption Capacity of the Nanosized Imprintedand Nonimprinted Polymer

The sorption capacity defined as the maximum amount ofmetal ions sorbed per gram of the polymer is an importantfactor for evaluation of the synthesized nanosized imprintedpolymer. To evaluate this factor, 10 mL of a solution contain-ing 0.1 mg of lead ions was applied to the extraction methodand the sorption capacity was calculated at the optimizedextraction conditions. In order to evaluate the maximum ad-sorption capacity, the difference between concentration of thesolution before extraction and the concentration of the solu-tion after extraction was calculated. The sorption capacities ofthe ion imprinted polymer and nonimprinted polymer werecalculated to be 9.8 and 2.4 mg g−1, respectively. Obviously,the adsorption capacity of imprinted polymers for lead ionswas larger than that of nonimprinted polymers.

Selectivity Study

The distribution ratio (mL g−1) of target ions between the IIPparticles and aqueous solution was also calculated by follow-ing equation:

Kd ¼ Ci − Cf

Cf

� �V

mð1Þ

where, Ci (mg L−1) and Cf (mg L−1) are concentrations beforeand after extraction, respectively, V is the volume of initial

solution, and m is mass of IIP nanoparticles. Selectivity coef-ficients and relative selectivity coefficients (k′) for lead ionsrelative to potentially interfering ions in the solution are de-fined as follows:

KPb2þ

=Mnþ ¼ Kd Pb

2þ� �=Kd M

nþð Þ ð2Þ

k 0 ¼ KIIP=KNIP ð3Þ

where Kd (Pb2+) and Kd (M

n+) are the distribution ratios of leadand potentially interfering ions, respectively.

In order to evaluate the selectivity of the synthesized lead-IIP, during several batch experiments, pairs of lead and poten-tially interfering ions with close atomic radius and identicalchemical properties were extracted by 20.0 mg of IIP at a pHof 6.0. Competitive adsorption of lead ion over the selectedinorganic ions such as Cu2+, Ni2+, Cd2+, Zn2+, and Co2+ forIIP and NIP particles from their binary mixture was investi-gated under optimum conditions and then the distributionratios (Kd), selectivity coefficients (k), and relative selectivitycoefficients (k′) for lead ion relative to foreign ions werecalculated using Eqs. (1)–(3), respectively. The results aresummarized in Table 2. As seen in Table 2, the competitiveadsorption capacity of lead-IIP nanoparticles for lead ions ishigher than nonimprinted polymer (NIP). Ion imprinting ef-fect is clearly observed by comparing the selectivity results ofimprinted and material (NIP) in terms of relative selectivitycoefficients (k′) in Table 2. The imprinted polymer was pre-pared with lead ion complex as the template, so three-dimensional void of cavities formed in the imprinted polymerwas more selective for lead ion than the control polymer(NIP), which only was prepared with 4-(2-pyridylazo) resor-cinol ligand as the template.

However, other cations could form complexes with4-(2-pyridylazo) resorcinol, the size of the cavitiesformed in the polymer was more suitable for the leadion. The cavities act as specific holes in the imprinted

Table 4 Statistical and calibration parameters for the proposed method

Analyte LOD (μg L−1) LOQ (μg L−1) DLR (μg L−1) Regression equation r2 PF Extraction recoverya (%)

Lead 0.9 3 3-600 Y=1.301 C+0.001 0.997 92.9 98.7

a Extraction recovery was found for 100 μg L−1 of lead

Table 5 Determination of leadions in certified reference material(validation of the proposedmethod)

Sample Element Concentration (mg g−1) Relative error (%)

Certified Founded

Ore polymetallic goldZidarovo-PMZrZ(206 BG 326)

Lead 5.4 5.3 −1.8

Food Anal. Methods

polymer, which allows selective adsorption of target ion.Since there were no imprinting effects on the NIP, itexhibited no selectivity. On the other hand, the cavitiesformed in the imprinted polymers had a specific shapeand size of the template, so they could not easily absorbother interfering ions. By considering the high selectiv-ity coefficients obtained by IIP particles and a signifi-cant difference between the binding of lead ion andcompetitor ions to the imprinted sorbent versusnonimprinted polymer, clearly it could be suggested that theprepared IIP can be applied as a selective sorbent for separa-tion of lead ion in the presence of other metal cations invarious real samples with different complex matrices. Thetolerance limits of the diverse ions on the extraction of targetion (lead ions) are summarized in the Table 3.

Statistical and Calibration Parameters

The performance of lead-IIP nanoparticles was investigated atthe optimum conditions. The limit of detection (LOD), regres-sion equations, coefficient of determination (r2), linear dy-namic ranges (LDRs), preconcentration factors (PFs), andextraction recoveries (R%) were obtained. The limits of de-tection, defined as CLOD=3 Sb/m, where Sb is the standarddeviation of seven replicate blank signals andm is the slope ofthe linear section of calibration curve after preconcentrationfor a sample volume of 50 mL. Calibration curves wereplotted using spiked levels of lead ions in the concentrationsranging from 3 to 600 μg L−1. Precision was expressed as amean percentage of the relative standard deviation (RSD%).Also, the preconcentration factor calculated as the ratio

Table 7 Comparison of synthe-sized IIP with literatures Method LOD (μg L−1) RSD (%) Extraction time (min) Ref.

Polymeric resine-FAAS 0.15 10 45 Nagihan et al. 2010

IIP-ICP/OES/MS 0.18 8 – Otero-Romani et al. 2009

IIP-AAS 50.2 3.8 60 Esen et al. 2009

Imprinted polymer-FAAS 15 1.5 50 Liu et al. 2010

IIP nanoparticles-FAAS 0.42 2.1 5 Behbahani et al. 2013

IIP nanoparticles-FAAS 0.9 3.4 5 This work

Table 6 Determination of leadions in different real samples(N=3)

Food Sample Cadded (μg kg−-1) Cfound (μg kg−-1) RR (%) RSD (%)

_ 4.9 _ _

Citrus limetta 10 14.6 97.0 3.1

100 104.2 99.3 3.4

_ 4.1 _ _

Kiwi 10 13.9 98.0 3.2

100 103.1 99.0 3.5

_ 5.1 _

Pomegranate 10 14.8 97.0 3.6

100 104.3 99.2 3.8

Water sample Cadded (μg L-1) Cfound (μg L-1) RR (%) RSD (%)

_ _ _ _

Tap water 10 9.9 99.0 1.9

100 99.1 99.1 2.1

Caspian sea water 10 15.5 97.0 3.1

100 104.9 99.1 3.7

_ 5.1 _ _

River water 10 14.9 98.0 3.5

100 104.1 99.0 3.7

_ 10.1 _ _

Waste water 10 19.8 97.0 3.5

100 108.9 98.8 3.7

Food Anal. Methods

between the slopes of the calibration curves acquired by theproposed method (Y=1.301 X+0.001) and through the directanalysis of lead ions by FAAS (Y=0.014 X+0.006), wasfound to be 92.9 (1.301/0.014=92.9). The analytical perfor-mances of the proposed method are summarized in Table 4.

Certified Reference Material Analysis

Ore polymetallic gold Zidarovo-PMZrZ (206 BG 326) fromBulgaria was used for the validation of the method. As Table 5shows, a good correlation was obtained between the certifiedamounts and the amounts found by the method. Therefore,nanosized lead-imprinted polymer can be used as a reliableselective solid-phase for extraction and trace determination oflead in food, environmental, and water samples.

Real Sample Analysis

To evaluate the capability of this sample preparation techniquefor trace analysis of lead in real samples with different matri-ces containing various amounts of diverse ions, the methodwas used for the extraction of lead ions from different samples(Table 6). The recoveries of lead ions from the real and spikedsamples varied in the range of 97.0–99.3 %. The resultsclearly indicate the suitability of the synthesized imprintedpolymer for the preconcentration and determination of leadions at trace levels in real samples.

Comparison of the Synthesized IIP Nanoparticleswith Literature

The proposed method was compared with other reportedmethods in literatures. According to Table 7, LOD and RSDare similar to the other synthesized IIPs. This method is clearlydifferent from other reports in preconcentration factor (PF)and extraction time (Nagihan et al. 2010; Otero-Romani et al.2009; Esen et al. 2009; Liu et al. 2010). Furthermore, theselectivity of the proposed method was significantly betterthan other sample preparation methods.

Conclusion

The ion-imprinted polymer is a selective sample preparationtechnique for preconcentration of metal ions such as lead fromaqueous solutions. We describe here, a robust method forselective separation and determination of lead ions at tracelevels. The nanosized lead-imprinted polymer has been syn-thesized by precipitation polymerization technique. The pre-pared imprinted polymer has an increased selectivity towardlead ion over a range of potentially interfering ions with thesame charge and similar ionic radius. The synthesized lead-

imprinted polymer can be used repeatedly (10 times) with nosignificant decrease in its binding affinities. Due to relativelyhigh preconcentration factor, trace lead ions at microgram perliter levels can be determined and separated by lead-imprintedpolymer.

Conflict of Interest Mohammad Behbahani declares that he has noconflict of interest. Parmoon Ghareh Hassanlou declares that he has noconflict of interest. Mostafa M. Amini declares that he has no conflict ofinterest. Hamid RezaMoazami declares that he has no conflict of interest.Hamid Sadeghi Abandansari declares that he has no conflict of interest.Akbar Bagheri declares that he has no conflict of interest. This articledoes not contain any studies with human or animal subjects.

References

Bagheri A, BehbahaniM, AminiMM, Sadeghi O, TaghizadeM, BaghayiL, SalarianM (2012a) Simultaneous separation and determination oftrace amounts of Cd(II) and Cu(II) in environmental samples usingnovel diphenylcarbazide modified nanoporous silica. Talanta 89:455–461

Bagheri A, Taghizadeh M, Behbahani M, Asgharinezhad AA, SalarianM, Dehghani A, Ebrahimzadeh H, Amini MM (2012b) Synthesisand characterization of magnetic metal-organic framework (MOF)as a novel sorbent, and its optimization by experimental designmethodology for determination of palladium in environmentalsamples. Talanta 99:132–139

Bagheri A, Behbahani M, Amini MM, Sadeghi O, Tootoonchi A,Dahaghin Z (2012c) Preconcentration and separation of ultra-tracepalladium ion using pyridine-functionalizedmagnetic nanoparticles.Microchim Acta 178:261–268

Behbahani M, Taghizadeh M, Bagheri A, Hosseini H, Salarian M,Tootoonchi A (2012) A nanostructured ion-imprinted polymer forthe selective extraction and preconcentration of ultra-trace quantitiesof nickel ions. Microchim Acta 178:429–437

Behbahani M, Bagheri A, Taghizadeh M, Salarian M, Sadeghi O,Adlnasab L, Jalali K (2013) Synthesis and characterization of nanostructure lead (II) ion-imprinted polymer as a new sorbent forselective extraction and preconcentration of ultra-trace amounts oflead ions from vegetables, rice, and fish samples. Food Chem 138:2050–2056

Beltran A, Marcé RM, Cormack PAG, Borrull F (2009) Synthesis byprecipitation polymerisation of molecularly imprinted polymer mi-crospheres for the selective extraction of carbamazepine andoxcarbazepine from human urine. J Chromatogr A 1216:2248–2253

Cacho C, Turiel E,Martin-Esteban A, P´erez-Conde C, C´amara C (2004)Characterisation and quality assessment of binding sites on apropazine-imprinted polymer prepared by precipitation polymeriza-tion. J Chromatogr B 802:347–353

Cao J, Liang P, Liu Y (2008) Determination of trace lead in water samplesby continuous flow microextraction combined with graphite furnaceatomic absorption spectrometry. J Hazard Mater 152:910–914

Chen JR, Xiao SM, Wu XH, Fang KM, Liu WH (2005)Determination of lead in water samples by graphite furnaceatomic absorption spectrometry after cloud point extraction.Talanta 67:992–996

Comitre ALD, Reis BF (2005) Automatic flow procedure based onmulticommutation exploiting liquid–liquid extraction forspectrophotometric lead determination in plant material.Talanta 65:846–852

Food Anal. Methods

del Sole R, Scardino A, Lazzoi MR, Mergola L, Scorrano S, Vasapollo G(2013) A molecularly imprinted polymer for the determination ofneopterin. Microchim Acta 180:1401–1409

Ebrahimzadeh H, Behbahani M, Yamini Y, Adlnasab L, AsgharinezhadAA (2013) Optimization of Cu (II)-ion imprinted nanoparticles fortrace monitoring of copper in water and fish samples using a Box-Behnken design. React Funct Polym 73:23–29

Ensafi AA, Shiraz AZ (2008) On-line separation and preconcentration oflead(II) by solid-phase extraction using activated carbon loaded withxylenol orange and its determination by flame atomic absorptionspectrometry. J Hazard Mater 150:554–559

Esen C, Andaç M, Bereli N, Say RI, Henden E, Denizli A (2009) Highlyselective ion-imprinted particles for solid-phase extraction of Pb2+

ions. Mat Sci Eng C 29:2464–2470Fritz JS (1999) Analytical solid-phase extraction. Wiley-VCH, NewYorkJunpingW, Mingfei P, Guozhen F, ShuoW (2009) Preparation of a novel

molecularly imprinted polymer by a sol-gel process for on-linesolid-phase extraction coupled with high performance liquid chro-matography to detect trace enrofloxacin in fish and chicken samples.Microchim Acta 166:295–302

Korn MG, de Andrade JB, de Jesus DS, Lemos VA, Bandeira MLSF, dosSantos WNL, Bezerra MA, Amorim FAC, Souza AS, Ferreira SLC(2006) Separation and preconcentration procedures for the determi-nation of lead using spectrometric techniques: a review. Talanta 69:16–24

Li P, Rong F, Yuan C (2003) Morphologies and binding characteristics ofmolecular imprinted polymers prepared by precipitation polymeri-zation. Polym Int 52:1799–1806

Liang P, Sang HB (2008) Determination of trace lead in biological andwater samples with dispersive liquid–liquid microextractionpreconcentration. Anal Biochem 380:21–25

Liu Y, Liu Z, Wang Y, Dai J, Gao J, Xie J, Yan Y (2010) A surface ion-imprinted mesoporous sorbent for separation and determination ofPb(II) ion by flame atomic absorption spectrometry. MicrochimActa 172:309–317

Nabid MR, Sedghi R, Bagheri A, Behbahani M, Taghizadeh M, OskooieHA, Heravi MM (2012) Preparation and application of poly(2-amino thiophenol)/MWCNTs nanocomposite for adsorption and

separation of cadmium and lead ions via solid phase extraction. JHazard Mater 203–204:93–100

Nagihan M, Karaaslan B, Senkal F, Cengiz E, Yaman M (2010) Novelpolymeric resin for solid phase extraction and determination of leadin waters. Clean Soil Air Water 38(11):1047–1054

Otero-Romaní J, Moreda-Piñeiro A, Bermejo-Barrera P, Martin-EstebanA (2009) Inductively coupled plasma-optical emissionspectrometry/mass spectrometry for the determination of Cu Ni,Pb and Zn in seawater after ionic imprinted polymer based solidphase extraction. Talanta 79:723–729

Soylak M, Narin I (2005) An On-Line Preconcentration System ForCadmium Determination In Environmental Samples By FlameAtomic Absorption Spectrometry. Chem Anal 50:705–715

Tamayo FG, Casillas JL, Martin-Esteban A (2003) Lanthanide sensitizedchemiluminescence determination of grepafloxacin in tablets andhuman urine. Anal Chim Acta 482:165–173

Turiel E, Martin-Esteban (2004) A molecularly imprinted poly-mers: towards highly selective stationary phases in liquidchromatography and capillary electrophoresis. Anal BioanalChem 378:1876–1886

Tuzen M, Parlar K, Soylak M (2005a) Enrichment/separation ofcadmium(II) and lead(II) in environmental samples by solid phaseextraction. J Hazard Mater 121:79–87

Tuzen M, Soylak M, Elci L (2005b) Multi-element pre-concentration ofheavy metal ions by solid phase extraction on Chromosorb 108.Anal Chim Acta 548:101–108

Wagner HP (1995) Determination of lead in beer using Zeeman back-ground corrected graphite furnace atomic absorption spectrometry. JAm Soc Brew Chem 53:141–144

Wang J, Cormack PAG, Sherrington DC, Khoshdel E (2003)Monodisperse, molecularly imprinted polymer microspheres pre-pared by precipitation polymerization for affinity separation appli-cations. Angew Chem 115:5494–5496

World Health Organization, Health Criteria and Other SupportingInformation, World Health Organization, Geneva, 1996

Zhong XW, Deng F, Wang YH, Luo XB (2013) A molecularly imprintedpolymer for solid phase extraction of allantoin. Microchim Acta180:1453–1460

Food Anal. Methods