ORIGINAL PAPER

Iodide-induced adsorption of lead(II) ion on a glassy carbonelectrode modified with ferroferric oxide nanoparticles

Zhousheng Yang & Panpan Dai & Yong You

Received: 26 November 2011 /Accepted: 2 March 2012 /Published online: 28 March 2012# Springer-Verlag 2012

Abstract Spherical Fe3O4 nanoparticles (NPs) were preparedby hydrothermal synthesis and characterized by scanningelectron microscopy and X-ray diffraction. A glassy carbonelectrode was modified with such NPs to result in a sensor forPb(II) that is based on the strong inducing adsorption ability ofiodide. The electrode gives a pair of well-defined redox peaksfor Pb(II) in pH 5.0 buffer containing 10 mM concentrationsof potassium iodide, with anodic and cathodic peak potentialsat −487 mV and −622 mV (vs. Ag/AgCl), respectively. Theamperometric response to Pb(II) is linear in the range from0.10 to 44 nM, and the detection limit is 40 pM at an SNR of3. The sensor exhibits high selectivity and reproducibility.

Keywords Pb2+ . I− . Fe3O4 nanoparticles . Inducingadsorption . Amperometric sensor

Introduction

Nowadays, the pollution caused by heavy metal ions isbecoming more and more severe all over the world. Amongheavy metals, lead is considered a major environmentalpollutant because of its toxic and accumulative biologicaleffects [1, 2]. Many health problems such as memory loss,irritability, anemia, and muscle paralysis arise from inges-tion of lead, due to the use of gasoline antiknock products,paint pigments, fertilizers and pesticides [3–5]. Lead is alsoa potential neurotoxin that can be accumulated in and ulti-mately damage bones and kidneys. It can cause physical/

mental developmental delays in children [6]. Accordingly,extensive attention has been promoted into developing thesensors for rapid and sensitive determination of Pb2+ duringthe last few years.

Among various sensors, electrochemical sensor hasattracted much attention for possessing high sensitivity, goodselectivity, simplicity and easy data read-out. To date, a greatnumber of electrochemical sensors have been developed forPb2+ utilizing all kinds of working electrodes [7–11]. Other-wise, previous reports have proven the fact that anion ions caninduce somemetal ions to adsorb at electrode surface [12–17].The complexes of metal ions with inorganic anions such asCl−, Br−, I−, SCN−, S2O3

2-, etc. are surface-active, whichmake them can be adsorbed on the electrode surface easily[12, 18, 19]. In fact, the adsorption of metal complexes onelectrodes from supporting electrolytes is accompanied by theprocess of the adsorption of inorganic anions on electrodes[14]. Anion-induced adsorption needs to be distinguishedfrom other related processes such as competitive adsorptionof two independent compounds [20], coadsorption [21], oradsorption of irreversibly bound complex species [22]. Inview of the above problems, several proper mechanisms havebeen proposed by M. Lovric [23].

Conventional mercury electrodes have historically beenvery popular for determining metal ions based on the induc-ing of anion ions [12, 13, 24, 25], owe to the predominantproperties of mercury electrode: easy formation of amalgamwith reduced metal, excellent reproducibility, easy surfacerenewal. However, due to its toxicity, numerous attempts todevelop various mercury-free solid electrodes had beenundertaken. Recently, considerable work has proved the factthat modification of electrodes with nanoparticles has beenconsidered as an effective strategy to enhance the detectionlimit of heavy metal ions [26–28]. Therefore, all kinds ofmercury free solid electrodes or chemically modified solid

Z. Yang (*) : P. Dai :Y. YouCollege of Chemistry and Materials Science, Anhui KeyLaboratory of chemo-Biosensing, Anhui Normal University,Wuhu 241000, People’s Republic of Chinae-mail: yzhoushe@mail.ahnu.edu.cn

Microchim Acta (2012) 177:449–456DOI 10.1007/s00604-012-0793-6

electrodes (CMEs) have been reported for the determinationof metal ions based on the inducing of anion ions [7–11]. Itis worth noting that Fe3O4 magnetic nanoparticles (nano-Fe3O4) have attracted an increasing interest in biotechnolo-gy and medicine [29–31]. Due to their good biocompatibil-ity, hydrophilic, low toxicity, easy preparation and highadsorption ability [32, 33], nano-Fe3O4 has been widelyinvestigated as electrode modified material in sensors andbiosensors [34–36]. However, to the best of our knowledge,electrochemical determination of trace levels of Pb2+ basedon the Fe3O4 nanoparticles modified glass carbon electrodeand the inducing adsorption ability of I− has not beenreported.

Therefore, in this work, a new electrochemical sensorfabricated based on a glassy carbon electrode (GCE) mod-ified with Fe3O4 nanoparticles is developed for the sensitivedetection of lead (II). The electrochemical behavior of Pb2+

was investigated in a 0.10 M pH 5.0 acetate buffer solutionscontaining 0.01 M KI. The prepared sensor gave an excel-lent amperometric response to Pb2+ and possessed severaladvantages such as high sensitivity, fast response time, long-time stability, reproducibility and relative low detectionlimit. The constructed sensor could be applied to determinelow concentration Pb2+ in real water samples.

Experimental

Reagents and apparatus

All reagents were purchased from Shanghai ChemicalReagent Company (http://www.reagent.com.cn) and wereof analytical grade and used without further purification.Stock solution of lead (II) (0.01 M) was prepared by directlydissolving Pb(NO3)2 in water. Working solutions were pre-pared by appropriate dilution of the stock solution. Acetatebuffer solutions (ABS) with various pH values from 4.0 to6.0 were prepared with NaAc and HAc. All solutions wereprepared with doubly distilled water.

Scanning electron microscopy (SEM) was obtained onS-4800 field emission scanning electron microanalyser(Hitachi, Japan). X-ray diffraction (XRD) were performedwith an X-ray diffractometer (Shimadzu, Japan) using a CuKα source (l00.154060 nm) at 40 kV, 30 mA in the range of20°<2θ <70° at a scan rate of 6.0°min-1. All electrochem-ical experiments including cyclic voltammetry (CV), differ-ential pulse voltammetry (DPV) and electrochemicalimpedance spectroscopy (EIS) were performed withCHI660 Electrochemical Analyzer (Shanghai Chenhua Ap-paratus, China). A conventional three-electrode system wasused. A GCE (ϕ03.0 mm) was used as the basal electrodefor fabrication. An Ag/AgCl (KCl, 3.0 M) electrode and aplatinum wire electrode were used as the reference electrode

and the counter electrode, respectively. During all experi-ments, the electrolyte was pre-purged with high purity ni-trogen for 15 min to remove oxygen and a continuous flowof nitrogen was maintained over the solution. All experi-ments were carried out at room temperature.

Synthesis of spherical Fe3O4 nanoparticles

The Fe3O4 nanoparticles were synthesized with a simpleprocess according to the literature [37] with a slight modi-fication. In a typical process, 0.2799 g FeCl3·6H2O wasdissolved in 12 mL of ethylene glycol, followed by theaddition of 0.05 mol NH4Ac under magnetic stirring to forma clear solution. Then the mixture was transformed into a50 mLTeflon-lined autoclave, and heated at 200 °C for 12 h.The autoclave was cooled down to room temperature natu-rally after reaction. The product was collected by centrifug-ing, washed with the deionized water and absolute ethanolbefore drying in vacuum at 60 °C for 6 h.

Fabrication of modified electrodes

Prior to the modification, the GCE was polished to a mirror-like surface with 0.05 μm α-Al2O3, thoroughly rinsed withwater and sonicated in absolute ethanol and water (each for5 min). 5 mg of synthesized Fe3O4 NPs was added into5 mL double distilled water and then ultrasonicated for10 min to create a suspension. A 10 μL of suspensiondispersion was coated onto the surface of GCE and theelectrode was dried in air to form Fe3O4/GCE.

Results and discussion

Characterization of the spherical Fe3O4 and the modifiedelectrode

The morphology and size of the prepared product werecharacterized by SEM as shown in Fig. 1. Figure 1a showedthe representative SEM image of the Fe3O4 nanoparticles,which illustrated that the prepared product consist of a largerquantity of spheres with an average diameter of ca. 400 nm.The magnified image shown in Fig. 1b exhibited detailedmorphology of the obtained products, indicating the infor-mation of uniform and regular microsphere. In addition, itcould also be observed from the surface of the particles thatthe spheres were composed of some much smaller particles.

XRD analysis was used to determine the structure andphase of the samples. Figure 1c showed the XRD profilestaken from the as-prepared products. All the diffractionpeaks could be well indexed to the Magnetite cubic structureof Fe3O4 (JCPDS Card. No. 89-3854,a08.394 Å). Bymeans of XRD procedure, no obvious peaks due to the

450 Z. Yang et al.

hematite and other impurities were detected in the XRDpatterns, indicating the formation of pure magnetic products.The sharp and strong diffraction peaks also confirmed thewell crystallization of the products.

EIS is a convenient and effective tool to probe the interfaceproperties of the surface-modified electrodes, which can givedetailed information on the impedance changes in the modi-fication process. Curves in Fig. 2 show the Nyquist diagramsof the bare GCE (curve a) and Fe3O4/GCE (curve b) in thepresence of 5.0 mM [Fe(CN)6]

3−/4− containing 0.1 M KCl,respectively. The surface electron-transfer resistance, Ret, de-rived from the semicircle diameter of impedance spectra wasvery small for the bare GCE. As can be seen, the bare GCE(curve a) shows a small semicircle. Compared to bare GCE(curve a), the Fe3O4/GCE (curve b) shows a larger semicirclethan the bare GCE. After the modification of Fe3O4 NPs, theRet increased compared to bare GCE, indicating that the Fe3O4

NPs could block the electron transfer efficiency in somedegree. Here, the changes of Ret manifested that the Fe3O4

nanoparticles were assembled onto the surface of GCE.

Electrochemical behavior of lead ion on Fe3O4/GCE

In order to examine the electrochemical behavior of Pb2+ onthe Fe3O4/GCE, the cyclic voltammetric experiments of10 μM Pb2+ on bare GCE and Fe3O4/GCE were performedin different condition. Firstly, cyclic voltammograms weretaken in different electrolytes in the absence of lead ions. Asshown in Fig. 3, no voltammetric peaks were observed on bareGCE (curve 1) and Fe3O4/GCE (curve 3) in 0.1 M ABS (pH5.0), and also no voltammetric peaks were observed on bareGCE (curve 2) and Fe3O4/GCE (curve 4) in 0.1 M ABS (pH5.0) containing 0.01 M KI. The obtained cyclic voltammetriccurves of Pb2+ on bare GCE and Fe3O4/GCE were also shownin Fig. 3. In 0.1 M ABS (pH 5.0), there was a faint oxidationpeak on a bare GCE (see Fig. 3 curve a) but not had homol-ogous reduction peak scanning between −0.2–−1.0 V, whichindicated the electrochemical process of Pb2+ on bare GCEwas irreversible; while on the Fe3O4/GCE, an obvious anodicpeak (curve c) for Pb2+ on the Fe3O4/GCE was exhibited. The

Fig. 1 SEM images at low magnification (a), high magnification (b)and XRD pattern (c) of the as-prepared spherical Fe3O4 nanoparticles

Fig. 2 EIS of different film modified electrodes in 0.1 M KCl solutioncontaining 5.0 mM K3Fe(CN)6/K4Fe(CN)6 (1:1): bare GCE (a), Fe3O4/GCE(b)

Iodide-induced adsorption of lead(II) ion on Fe3O4 nanoparticles/GCE 451

peak current (22.64μA)was 16.4 fold to that of the bare GCE,which reflected high catalytic effect of the characteristic ofFe3O4 NPs to the oxidation of Pb(0). Compared to curves aand c, in 0.1 M ABS (pH 5.0) containing 0.01 M KI, the CVcurve of Pb2+ on Fe3O4/GCE (curve d) was obtained. Theresults showed that not only the oxidation peak current in-creased to 33.15 μAwith the peak potential of −0.487 V, butalso the cathodic peak of Pb2+ was present at −0.622 V, whichcould be attributed to the excellent catalytic activity of Fe3O4

to the oxidation of Pb(0) and the strong inducing adsorptionability of I−. Furthermore, the anodic peak potentials of curvesb and d (obtained in the presence of KI) have a degree ofnegatively shifting compared to curves a and c (in the absenceof KI), which was attributed to the formation of a specialcomplex between Pb2+ with I−. According to polarographicwave equation, the polarographic half-wave potential of metalcomplex ions was more negative than that of the metal ions.

According to previous reports [12, 14], I− exhibits obviousinducing adsorption ability towards some metal ions, andsubsequently induces them to adsorb at mercury electrodesurface. Due to O’Dom and Murray [13], it is assumed thatone particular complex species is formed in the solutionadsorbed onmercury electrode surface to produce an adsorbedspecies. In the current system, Pb2+ forms a special complexwith I− and the complex is easily and efficiently accumulatedat Fe3O4/GCE electrode surface under the strong inducingadsorption ability of I−, which is later reduced to metal andpartly reoxidized in reverse scan. On the other hand, the Fe3O4

NPs modified on the GCE possess larger specific area, whichcan provide more adsorption sites. Finally, according to

literature survey [18, 23, 38], a possible mechanism for theelectrochemical reaction of Pb2+ can be given as following:

Pb2þ þ n I� ! PbInn�2ð Þ� in solutionð Þ ð1Þ

PbInn�2ð Þ� þ Fe3O4=GCE ! In�1PbI½ � n�2ð Þ� � Fe3O4=GCE

ð2Þ

In�1PbI½ � n�2ð Þ� � Fe3O4=GCEþ 2e� ! Pb� Fe3O4=GCE þ n I�

ð3Þ

Pb� Fe3O4=GCE� 2e� ! Pb2þ þ Fe3O4=GCE ð4ÞIn addition, the CV curve of 10 μM Pb2+ on bare GCE

(curve b) in presence of 0.01MKI was also obtained in 0.1 MABS (pH 5.0). Compared to curve a, a pair of well-definedand reversible redox peaks for Pb2+ was observed with theincrease of the oxidation peak current, which can furtherverify the effects of I− to the electrochemical behavior of Pb2+.

Optimization of the Pb2+ determination conditions

To improve the performance of the sensor, the effect of thedetermination conditions such as the pH value, the concen-tration of I− and other anion ions (Br−, Cl−) on the responseof the Fe3O4/GCE electrode to Pb2+ had been examined indetail.

With the concentration of KI fixed at a certain value,theinfluences of the buffer solutions pH on electrochemicalbehaviors of lead ion on Fe3O4/GCE were illustrated in0.1 M ABS at various pH values ranging from 4.0 to 6.5.Figure 4 showed the dependence of anodic peak current onsolution pH. The anodic peak current enhanced with in-creasing the pH value of solutions and reached the highest

Fig. 3 CVs of bare GCE (1), Fe3O4/GCE (3), without lead ion in0.1 M ABS (pH 5.0); CVs of bare GCE (2), Fe3O4/GCE (4) withoutlead ion in 0.1 M ABS (pH 5.0) containing 0.01 M KI; CVs of 10 μMlead ion on bare GCE (a), Fe3O4/GCE (c), in 0.1 M ABS (pH 5.0);CVs of 10 μM lead ion bare GCE (b), Fe3O4/GCE (d) in 0.1 M ABS(pH 5.0) containing 0.01 M KI. Scan rate: 100 mV s−1

Fig. 4 The effects of solution pH on anodic peak current (containing10 μM Pb2+)

452 Z. Yang et al.

at pH 5.0. Afterward, the anodic peak current decreasedwith increasing the pH value of solution. Therefore, pH5.0 was the optimal for Pb2+ redox on Fe3O4/GCE.

Since Fig. 3 tells that low concentration of I− can improvethe sensitivity of determining Pb2+, the influence of I−

concentration (C) on the anodic peak current was explored,as shown in Fig. 5a. The anodic peak current firstly in-creased linearly with I− concentration over the range from0 to 8.0×10−3 M, then increased slowly over the range from8.0×10−3 to 10.0×10−3 M and reached the highest at 10.0×10−3 M, because the amount of special surface-active com-plex of Pb2+ with I− on the surface of the modified electrodeincreases correspondingly. Afterward the anodic peak cur-rent of Pb2+ decreased continuously when I− concentrationexceeds 10.0×10−3 M. which obviously indicates that at thehigher I− concentration, in addition to forming complex withPb2+, the redundant I− could develop competitive adsorptionwith the complex at the electrode surface. Therefore,C00.01 M was selected in the subsequent experiments.

Additionally, in order to investigated whether other anionions possess the ability to induce the lead ion to be adsorbed

at the electrode surface, the CV curves of 10 μM Pb2+ onFe3O4/GCE in the presence of 0.01 M KBr or KCl were alsoobtained in 0.1 M ABS (pH 5.0), respectively. The experi-mental results were shown in Fig. 5b. In the presence ofeither KCl or KBr, there was only an oxidation peak (seeFig. 5b curve a and b) but not had homologous reductionpeak scanning between −0.2 and −1.0 V, which indicated theelectrochemical process of Pb2+ irreversible. Compared tocurves a and b, in the presence of 0.01 M KI, the CV curveof Pb2+ on Fe3O4/GCE (curve c) showed that not only theoxidation peak current increased, but also the cathodic peakof Pb2+ was present at −0.622 V. Therefore, 0.1MABS (pH 5)containing 0.01 M KI was selected for Pb2+ analysis.

Amperometric response to lead ion

The determination of lead ion concentration was performedwith the differential pulse voltammetry (DPV) using Fe3O4/GCE modified electrode under optimum conditions. Theanodic peak current (Ipa), ascribed to the oxidation of Pb(0) to Pb2+, was selected as the analytical signal. Before theinitial potential was applied onto the surface of the elec-trode, the concentration of Pb(0) in the cell was zero, whatwas more, the cathodic peak potential of Pb2+ was −0.622 V,so the initial potential was chosen as −1.0 V, which wasnegative enough to reduce the Pb2+ to Pb(0) once the initialpotential was applied. The dependence of Ipa on lead ionconcentration was given in Fig. 6. The linear regressionequation was: Ipa ¼ 12:4107C � 0:9342 (Ipa, the anodicpeak current, μA; C, the concentration of the Pb2+, nM),with a correlation coefficient of 0.999. The amperometric

Fig. 5 a The effects of the concentration of KI on anodic peak currentof 10 μM Pb2+ in 0.1 M ABS (pH 5.0); b CVs of 10 μM lead ion onFe3O4/GCE in 0.1 M ABS (pH 5.0) containing 0.01 M KCl (a), KBr(b) and KI (c), respectively

Fig. 6 The DPV curves of different concentration lead ion (nM) in0.1 M ABS (pH 5.0) containing 0.01 M KI: a:0, b:0.10, c:0.14, d:0.18,e:0.22, f:0.26, g:0.34, h:0.42, i:0.50, j:0.60, k:0.7, l:0.85. Inset showsthe relation between the concentration of lead ion and the anodic peakcurrent

Iodide-induced adsorption of lead(II) ion on Fe3O4 nanoparticles/GCE 453

response to Pb(II) is linear in the range from 0.10 to 44 nM,and the detection limit is 0.04 nM, which was lower thanthat of other modified electrodes [7, 10, 39, 40] (Table 1).

Anti-interference capability, reproducibility and stabilityof the sensor

The interferences of some heavy metal ions on sensor werealso examined with the Fe3O4/GCE, as shown in Table 2.According to the experimental result, these heavy metal ionsdid not interfere to detect Pb2+ within 50 times of Pb2+

concentration. Other potentially interfering ions such asNa+, K+, Ca2+, Mg2+, Cl−, Br−, and NO3

− ions also did notinterfere on determination. It indicated that the preparedsensor possessed high selectivity for Pb2+.

To characterize the reproducibility of the sensor, electro-chemical experiments were repeatedly performed ten timesunder optimized conditions with the same Fe3O4/GCE in thesolution containing 10 μM Pb2+. The experimental resultsshowed a relative standard deviation of 3.6 %, which con-firmed that the reproducibility of the produced sensor wasexcellent. In addition, the stability of the sensor for thedetermination of lead ion on storage was examined bykeeping the electrode in a desiccator at room temperaturewhen not in use and recording a cyclic voltammogram eachday. After sensor was used for approximately 40 times, only

a small decrease of response current (about 4.8 %) for 5 μMPb2+ was observed, which can be attributed to the excellentstability of the modified electrode.

Application to real water samples

To illustrate its applicability and validity of the preparedsensor, the electrode was employed for the determination ofPb2+ in spiked distilled water, tap water and the river watersample using the standard addition method under the opti-mum condition. All real water samples were filtered with a0.22 μm membrane (Millipore), and then added to 0.1 Macetate buffer (pH 5.0) containing 0.01 M KI (two-folddilution). The results can be seen in Table 3. Each value isan average of five measurements and the recoveries of leadion in the three water sample were in the range of 96.6–99.3 %. Furthermore, in order to testify the validity andaccuracy of this method, the typical and common usedmethod: inductive coupled plasma atomic emission spec-trometry (ICP-AES) was used to detect Pb2+ in water sam-ples. From the comparisons listed in Table 3, conclusion canbe made that the prepared sensor could be satisfactorilyapplied to determine lead ion in some real water samples.

Conclusions

We have successfully fabricated a new, high sensitivity, fastresponse and highly selective amperometric Pb2+ sensor

Table 1 Reported details of detection of Pb2+ at various chemically modified electrodes for comparison with this work

Electrode Medium Linear range (nM) Detection limit (nM) Sensitivity (μA nM−1) Ref.

montmorillonite calcium-modified CPE 0.01 M HCl 25–2000 6 – [7]

bismuth-modified zeolite doped CPE Acetate buffer (pH 4.5) 4.8–96 0.48 0.277 [10]

Poly(phenol red)/GCE HNO3 (pH 2.5) 5–500 2.0 0.271 [39]

NH4-Y modified CPE 0.1 M KCl (pH 5.9) 25–100 17.4 0.090 [40]

Fe3O4/GCE Acetate buffer (pH 5.0) 0.10–44 0.04 12.41 This work

Table 2 Effects of interfering substance on the detecting of 10 μMlead ion

Species Maximum tolerableconcentration ratioa

Na+, K+, Ca2+, Mg2+, Cl−, Br−, NO3− 100

Ca2+ 50

Mg2+ 50

Al3+ 50

Bi3+ 50

Ni2+ 50

Cu2+ 50

Hg2+ 50

a Ratio denotes the ratio of the concentration between the interferingsubstance and lead ion

Table 3 Results for determination of Pb2+ in different spiked watersamples

Sample Pb2+ added(nM)

Pb2+ found(nM)

Recovery(%)

Detected byICP-AES (nM)

Distilled water 20.00 19.86 99.3 19.90

20.00 19.71 99.5 19.85

Tap water 20.00 19.75 99.8 19.60

20.00 19.54 99.7 19.56

The River water 20.00 19.50 99.5 19.60

20.00 19.32 99.6 19.53

454 Z. Yang et al.

based on the excellent catalytic activity of Fe3O4 to Pb2+

and the strong inducing adsorption ability of I−. In addition,the use of Fe3O4 NPs has proven to be an efficient method toenlarge the specific area of electrode for providing theadsorption sites to the active-surface complex. And in thepresence of low concentration of I−, Pb2+ in bulk solution iseffectively induced to accumulate at the electrode surface ofFe3O4/GCE. The Fe3O4/GCE exhibited the prominent ac-tivity for redox of Pb2+ ion in the presence of I−, and thefabricated sensor gave a good stability and reproducibility,which could be used as an amperometric sensor for deter-mination of low concentration Pb2+ in real sample.

Acknowledgments We thank the National Natural Science Founda-tion of China (grant no. 20775002) for financial support. The work wassupported by Program for Innovative Research Team in Anhui NormalUniversity

References

1. Bridgewater BM, Parkin G (2000) Lead poisoning and the inacti-vation of 5-aminolevulinate dehydratase as modeled by the tris(2-mercapto-1-phenylimidazolyl)hydroborato lead complex, {[TmPh]Pb}[ClO4]. J Am Chem Soc 122:7140

2. Chen JR, Xiao SM, Wu XH, Fang KM, Liu WH (2005) Determi-nation of lead in water samples by graphite furnace atomic absorp-tion spectrometry after cloud point extraction. Talanta 67:992

3. Wang HL, Ou LML, Suo YR, Yu HZ (2011) Computer-readableDNAzyme assay on disc for ppb-level lead detection. Anal Chem83:1557

4. Di Nezio MS, Palomeque ME, Fernández Band BS (2004) Asensitive spectrophotometric method for lead determination byflow injection analysis with on-line preconcentration. Talanta63:405

5. Rifai N, Cohen G, Wolf M, Cohen L, Faser C, Savory J, DepalmaL (1993) Incidence of lead poisoning in young children from inner-city, suburban, and rural communities. Ther Drug Monit 15:71

6. Lanphear BP, Hornung R, Khoury J, Yolton K, Baghurst P, BellingerDC, Canfield RL, Dietrich KN, Bornschein R, Greene T, RothenbergSJ, Needleman HL, Schnaas L, Wasserman G, Graziano J, Roberts R(2005) Low-level environmental lead exposure and children’s intel-lectual function: an international pooled analysis. Environ HealthPersp 113:894

7. Sun D, Wan C, Li G, Wu KB (2007) Electrochemical determina-tion of lead(II) using a montmorillonite calcium-modified carbonpaste electrode. Microchim Acta 158:255

8. Krasnodebska-Ostrega B, Piekarska J (2005) Determination oflead and cadmium at silver electrode by subtractive anodic strip-ping voltammetry in plant materials containing Tl. Electroanalysis17:815

9. Wan QJ, Yu F, Zhu LN, Wang XX, Yang NJ (2010) Bucky-gelcoated glassy carbon electrodes, for voltammetric detection offemtomolar leveled lead ions. Talanta 82:1820

10. Cao L, Jia J, Wang Z (2008) Sensitive determination of Cd and Pbby differential pulse stripping voltammetry with in situ bismuth-modified zeolite doped carbon paste electrodes. Electrichim Acta53:2177

11. Hwang GH, Han WK, Park JS, Kang SG (2008) Determination oftrace metals by anodic stripping voltammetry using a bismuthmo-dified carbon nanotube electrode. Talanta 76:301

12. Anson FC, Barclay DJ (1968) Anion induced adsorption of cad-mium(II) on mercury from iodide and bromide media. Anal Chem40:1791

13. O’Dom GW, Murray RW (1968) Chronocoulometric measurementof indium (III) adsorption from thiocyanate medium. J ElectroanalChem 16:327

14. Barclay DJ, Anson FC (1970) Some aspects of anion-inducedadsorption of white metal cations on mercury. J Electroanal Chem28:71

15. Li G, Wan CD, Ji ZM, Wu KB (2007) An electrochemical sensorfor Cd2+ based on the inducing adsorption ability of I−. Sensorsand Actuators B 124:1

16. Li G, Ji ZM, Wu KB (2006) Square wave anodic stripping voltam-metric determination of Pb2+ using acetylene black paste electrodebased on the inducing adsorption ability of I−. Anal Chim Acta577:178

17. Girija TC, Sangaranarayanan MV (2005) Anion-induced adsorp-tion of thallium complex on silver electrodes. J Colloid InterfaceSci 282:92

18. Murray RW, Gross DJ (1966) Inhibition of electrode reactions byadsorbed lead iodide, bromide, and thiocyanate. Anal Chem38:393

19. Anson FC, Christie JH, Osteryoung RA (1967) Anion inducedadsorption of cadmium(II) on mercury from iodide and bromideMedia. J Electroanal Chem 13:343

20. Parsons R (1951) General equations for the kinetics of electrodeprocesses. Trans Faraday Soc 47:1332

21. Hepel T (1984) Lateral exchange interactions in sub-monolayerfilms of co-adsorbed species. J Electroanal Chem 175:15

22. Weaver MJ, Anson FC (1975) Electrode kinetics with specificallyadsorbed reactants: the reduction of some isothiocyanato com-plexes of Cr(III) on mercury electrodes. J Electroanal Chem 58:95

23. Lovric M (2010) Stripping voltammetry. In: Scholz F (ed) Elec-troanalytical methods, 2nd edn. Springer, Berlin/New York, pp201–221

24. Komorsky-Loric S, Loric M, Branica M (1988) Coadsorption of Bi(III) and Cl− at a mercury electrode. J Electroanal Chem 241:329

25. Lovric M (1989) Influence of anion-induced adsorption on D.C.polarography of metal ions. Anal Chim Acta 218:7

26. Yin ZJ, Wu JJ, Yang ZS (2010) A sensitive mercury (II) sensorbased on CuO nanoshuttles/poly(thionine) modified glassy carbonelectrode. Microchim Acta 170:307

27. Chen BH, Wang LS, Huang XJ, Wu PX (2011) Glassy carbonelectrode modified with organic–inorganic pillared montmorillon-ites for voltammetric detection of mercury. Microchim Acta172:335

28. Sánchez A, Morante-Zarcero S, Pérez-Quintanilla D, Sierra I,Hierro ID (2010) Development of screen-printed carbon electrodesmodified with functionalized mesoporous silica nanoparticles: Ap-plication to voltammetric stripping determination of Pb(II) in non-pretreated natural waters. Electrochim Acta 55:6983

29. Dobson J (2006) Magnetic nanoparticles for drug delivery. DrugDev Res 67:55

30. Mornet S, Vasseur S, Grasset F, Duguet E (2004) Magnetic nano-particle design for medical diagnosis and therapy. J Mater Chem14:2161

31. Mirzabekov T, Kontos H, Farzan M, Marasco W, Sodroski J(2000) Paramagnetic proteoliposomes containing a pure, native,and oriented seven-transmembrane segment protein, CCR5. J NatBiotechnol 18:649

32. Woo K, Hong J, Choi S, Lee H, Ahn J, Kim CS, Lee SW (2004)Easy synthesis and magnetic properties of iron oxide nanopar-ticles. Chem Mater 16:2814

33. Hogemann D, Ntziachristos V, Josephson L, Weissleder R (2002)High throughput magnetic resonance imaging for evaluating. Bio-conjugate Chem 13:116

Iodide-induced adsorption of lead(II) ion on Fe3O4 nanoparticles/GCE 455

34. Cheng Y, Liu Y, Huang J, Li K, Xian Y, Zhang W, Jin L (2009)Amperomeric tyrosinase biosensor based on Fe3O4 nanoparticles-coated carbon nanotubes nanocomposite for rapid detection ofcoliforms. Electrochim Acta 54:2588

35. Zhang ZX, Zhu H, Wang XL, Yang XR (2011) Sensitiveelectrochemical sensor for hydrogen peroxide using Fe3O4 mag-netic nanoparticles as a mimic for peroxidase. Microchim Acta174:183

36. Yina HS, Zhou YL, Ma Q, Ai SY, Chen QP, Zhu LS (2010)Electrocatalytic oxidation behavior of guanosine at graphene, chi-tosan and Fe3O4 nanoparticles modified glassy carbon electrodeand its determination. Talanta 82:1193

37. Hu P, Yu LJ, Zuo AH, Guo CY, Yuan FL (2009) Fabrication ofmonodisperse magnetite hollow spheres. J Phys Chem C 113:900

38. Herman HB, McNeely RL, Surana P, Elliott CM, Murray RW(1974) Surface solubility and reaction inhibition in lead bromideand iodide adsorbed on mercury electrodes. Anal Chem 46:1258

39. Yang GJ, Qu XL, Shen M, Wang CY, Qu QS, Hu XY (2008)Electrochemical behavior of lead(II) at poly(phenol red) modifiedglassy carbon electrode, and its trace determination by differentialpulse anodic stripping voltammetry. Microchim Acta 160:275

40. Senthilkumar S, Saraswathi R (2009) Electrochemical sensing ofcadmium and lead ions at zeolite-modified electrodes: optimizationand field measurements. Sensors Actuators B 141:65

456 Z. Yang et al.