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Sensors and Actuators B 162 (2012) 194– 200

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators B: Chemical

j o ur nal homep a ge: www.elsev ier .com/ locate /snb

arbon nanoparticle–chitosan composite electrode with anion, cation, andeutral binding sites: Dihydroxybenzene selectivity

andana Amiria,∗, Shahnaz Ghaffarib, Abolfazl Bezaatpoura, Frank Markenc

Department of Chemistry, University of Mohaghegh Ardabili, Ardabil, IranDepartment of Chemistry, Payame Noor University, Ardabil, IranDepartment of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK

r t i c l e i n f o

rticle history:eceived 2 October 2011eceived in revised form0 December 2011ccepted 19 December 2011vailable online 8 January 2012

eywords:arbon nanoparticleoltammetry

a b s t r a c t

A voltammetric study of dihydroxybenzene isomers has been carried out at the surface of a glassy carbonelectrode modified with a carbon nanoparticle–chitosan high surface area composite film. Generally, theadsorption of analytes into the nanocomposite film is possible based on cation (chitosan), anion (surface-sulfonates of Emperor 2000TM particles), and neutral sites (graphitic carbon). Although all three types ofadsorption are observed in aqueous media, the dominant effect is shown here to be weak adsorption ofneutral molecules such as dihydroxybenzenes, which are bound and detected with good sensitivity andselectivity.

Potential sweep rate and pH effects on the response of the electrode for the oxidation of dihydroxyben-zens are investigated. At pH 7 separate oxidation peak potentials were observed at 0.10, 0.19, and 0.58 V

hitosandsorptionihydroxybenzenesastewater

versus SCE for hydroquinone, catechol, and resorcinol, respectively. Dynamic linear ranges obtainedin differential pulse voltammetry analysis were 8.0 × 10−7–1.0 × 10−4, 8.0 × 10−7–1.0 × 10−4, and8.0 × 10−6–1.0 × 10−3 mol L−1. The detection limits were 2.0 × 10−7, 2.0 × 10−7, and 3.0 × 10−6 mol L−1.Real water samples were analyzed and recoveries from 96% to 108% were obtained. The new low costmethod is proposed for application in the simultaneous determination of dihydroxybenzene isomers forenvironmental analysis.

. Introduction

Phenolic compounds are important and often classified as “sec-nd type” of environment pollutions [1,2]. Hydroquinone (HQ),,4-dihydroxybenzene, catechol (CA), 1,2-dihydroxybenzene, andesorcinol (RS), 1,3-dihydroxybenzene, are three isomers of dihy-roxybenzene that often coexist in environmental samples. Theyre usually employed as industrial reagents in the production ofubber, dyes, plastics, pharmaceuticals, and cosmetics [3,4]. Dueo their similar structures, it was important to develop a simul-aneous and simple analytical procedure for dihydroxybenzenesomer detection in situ. Known methods for the simultaneousetermination of dihydroxybenzene isomers are HPLC [5], cap-

llary electro-chromatography [6], and spectrophotometry [7,8].owever, these techniques have some disadvantages, such as timeonsuming need for pre-separation, complicated operation, or a

arrow linear range. Here a low cost modified-electrode method-logy is proposed based on a carbon nanoparticle–chitosan activelm.

∗ Corresponding author. Tel.: +98 451 5514701; fax: +98 451 5514703.E-mail address: mandanaamiri@yahoo.com (M. Amiri).

925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2011.12.066

© 2011 Elsevier B.V. All rights reserved.

There are several direct electrochemical methods for dihy-droxybenzene isomer determination, for example using poly-(acidchrome blue K)/carbon nanotube–composite electrodes [9], single-wall carbon nanotube electrodes [10], multi-electrode arraysmodified with carbon nanotubes [11], poly-(p-aminobenzene sul-fonic acid) modified glassy carbon [12], boron-doped diamondelectrodes [13], and graphene–chitosan modified electrodes [14].Electrochemical methods offer unique characteristics such as lowmaintenance costs, high accuracy, and excellent sensitivity. Elec-trochemical processes have been proposed also for the preventionand the remedy of pollution problems such as treatment of wastew-ater [15], phenolic compounds pollutants [16], insecticides [17] andpesticides [18].

Carbon materials are important in electroanalysis. Many typesof carbon including screen printed graphite, glassy carbon, car-bon nanotubes, boron doped diamond, and carbon nanoparticlesprovide electrode materials with a wide range of applications[19]. In contrast to the more recently emerging nano-tubes andfullerenes, carbon nanoparticles are well known for many years

and they have been widely used in industry, for example as fillerand pigments. These carbon nanoparticles are potentially benefi-cial in electrochemical processes, for example due to high surfacearea and high levels of active interfacial edge sites [20]. Recently,

Actuators B 162 (2012) 194– 200 195

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M. Amiri et al. / Sensors and

arbon nanoparticles with sulfonate surface functionality (Emperor000TM from Cabot Corp.) have been successfully used as mod-

fier for chemically modified electrode [20–23]. Ultrathin carbonanoparticle composite films have been prepared in an electro-tatic layer-by-layer deposition process with chemically modifiedydrophilic carbon particles. These negatively charged and water-oluble particles interact preferentially with poly-cationomers likeoly-(diallyldimethylammonium chloride) [23] or chitosan and cane applied and studied as thin carbon nanoparticle–chitosan filmlectrodes [24]. The benefits of these film electrodes have beenbserved mainly in the detection of charged analytes (e.g. triclosan)ith binding interaction predominantly to the poly-electrolyte

inder.In this study a carbon nanoparticle–chitosan composite film

s prepared with medium molecular weight chitosan and car-on nanoparticles of ca. 9–18 nm diameter. The simultaneousensitivity towards anionic, cationic, and neutral analytes (thei-hydroxybenzene isomers) is demonstrated. A thin carbonanoparticle–chitosan film is applied as a modifier in thislectrochemical sensor and a significant interaction with dihy-roxybenzenes is observed. Potential applications are suggested

n environmental monitoring. The main advantages of the car-on nanoparticle-modified electrode compared to a conventionalacro-electrode are a higher effective surface area, accumula-

ion of analyte, and control over local microenvironment to givemproved selectivity. Real sample analysis is demonstrated forihydroxybenzenes.

. Experimental

.1. Apparatus

Voltammetric experiments were performed using a Metrohmomputrace Voltammetric Analyzer model 797 VA. A conventionalhree-electrode system was used with a glassy carbon disk elec-rode (2 mm diameter GCE), a KCl-saturated calomel referencelectrode (SCE), and a Pt wire as the counter electrode. A digitalH/mV/Ion meter (JENWAY) was applied for the preparation ofuffer solutions. The surface morphology of the films was stud-

ed by a Thermo Microscope Autoprobe CP-Research atomic forceicroscope (AFM) in air with a silicon tip of 10 nm radius, in con-

act mode. A microAutolab III potentiostat system (EcoChemie,etherlands) was employed for impedance spectroscopic studiesith a Pt wire counter electrode and a KCl-saturated calomel ref-

rence electrode (Azar electrode).

.2. Reagents

Carbon nanoparticles with surface sulfonate groups werebtained from Cabot (ca. 9–18 nm diameter, Emperor 2000TM,abot Corporation). All other chemicals were analytical reagentrade from Merck. Chitosan was medium molecular weight and5–80% deacetylated (Aldrich, 200–800 cP, 1% in 1% acetic acid). Allqueous solutions were prepared with doubly distilled deionizedater. Voltammetric experiments were carried out in the buffered

olutions, deoxygenated by purging the pure nitrogen. Deionizednd filtered water was taken from a Millipore water purificationystem.

.3. Preparation of modified electrodes

A carbon nanoparticle–chitosan solution was prepared by dis-

ersing 3 mg of medium molecular weight chitosan in 10 cm3 of% acetic acid. From this stock solution 1 cm3 was taken followedy addition of 3 mg of the hydrophilic Emperor 2000TM carbonanoparticles and with further addition of water to give 10 cm3.

Fig. 1. AFM topography image of a carbon nanoparticle–chitosan film deposit at aglassy carbon electrode.

The black solution was then agitated and dispersed in an ultra-sonicator bath for 1 h. The carbon nanoparticle–chitosan thin filmelectrodes were prepared by casting 10 �L of this solution ontoa polished glassy carbon electrode (2 mm diameter, resulting inca. 3 �g carbon deposit containing 0.3 �g chitosan) and letting thewater evaporate in air. Electrodes were stored under ambient con-ditions. The obtained modified GCE was characterized by atomicforce microscopy (AFM), and cyclic voltammetry techniques (CV).

3. Results and discussion

3.1. Characterization of the modified electrode

3.1.1. AFM imagingTo study the surface topography of the CNP-chitosan nanocom-

posite thin films, atomic force microscopy (AFM) has been utilized.According to this analysis, the approximate surface roughness ofthe films was measured to be about 36 nm. Individual globularfeatures in the AFM image (see Fig. 1) could correspond to aggre-gates of carbon nanoparticles with dispersed chitosan binder. Dueto the porous nature of this film water and electrolyte can read-ily access the film whereas electrical contact and conductivity viacarbon nanoparticles is maintained.

3.1.2. Electrochemical characterization I: capacitive currentsThe surface characteristics and microscopic area of the mod-

ified and the bare GCE were obtained by comparison of the CVresponses in 0.1 M phosphate buffer pH 7 (not shown). Capacitancevalues of ca. 35 �F and 400 �F for a bare glassy carbon electrodeand for a modified glassy carbon electrode (ca. 3 �g carbon) wereestimated. A one order of magnitude increase in capacitive cur-rent suggests a significantly increased active electrode surface area(with ca. 100 Fg−1 CNPs). This increase in area can be further con-trolled by changing the amount of film deposited at the electrodesurface.

3.1.3. Electrochemical characterization II: absorbed redoxsystems at CNP-chitosan modified film electrodes

The presence of anionic and cationic functionalities within

the CNP-chitosan nanocomposite film suggests potential affinitytowards charged or hydrophobic ions. In order to assess this affin-ity initially the oxidation of Fe(CN)6

4− (an anionic redox system),the reduction of methylene blue (a cationic redox system), and the

196 M. Amiri et al. / Sensors and Actuators B 162 (2012) 194– 200

Fig. 2. (A) Cyclic voltammograms (scan rate (i) 0.01; (ii) 0.02; (iii) 0.04; (iv) 0.06;(v) 0.1; (vi) 0.15; and (vii) 0.2 V s−1) for the oxidation of 1 mM Fe(CN)6

4− in 0.1 MKCl. (B) Cyclic voltammogram (scan rate 0.1 is V s−1) for the reduction of methyleneblue adsorbed into CNP-chitosan film (pre-adsorbed from 1 mM methylene blue in02

rp2remri0ab

adtbsevTsbmT0

Table 1The charge under the peaks at scan rate 10 mV s−1 for the pre-adsorbed CA, HQ andRS adsorbed into CNP-chitosan film (pre-adsorbed from 1 mM of each compound in0.1 M phosphate buffer pH 7) and immersed in aqueous 0.1 M phosphate buffer pH 7.Methylene blue and indigo carmine adsorbed into CNP-chitosan film (pre-adsorbedfrom 1 mM of each compound in 0.1 M phosphate buffer pH 2) and immersed inaqueous 0.1 M phosphate buffer pH 7. Ferrocyanide adsorbed into CNP-chitosanfilm (pre-adsorbed from 1 mM ferrocyanide in 0.1 M KCl) and immersed in aqueous0.1 M KCl.

Compound Charge under peak (C)

HQ 1.63 × 10−6

CA 4.72 × 10−6

RS 6.92 × 10−7

−4

Fig. 3A–C indicates the electrochemical behaviour of 1 mM CA,HQ and RS at the bare electrode (dotted line) and at the modifiedelectrode (solid line) using cyclic voltammetry (data recorded in0.1 M pH 7 phosphate buffer solution at a scan rate of 0.1 V s−1).

Table 2The charge under the peaks at scan rate 10 mV s−1 for 1 mM solution of CA, HQ and RSpH 7 (0.1 M phosphate buffer) at CNP-chitosan film. 1 mM solution of ferrocyanidein 0.1 M KCl at CNP-chitosan film.

Compound Charge under peak (C)

−4

.1 M phosphate buffer pH 2) and immersed in aqueous 0.1 M phosphate buffer pH

.

eduction of indigo carmine (an anionic redox system) are com-ared (1 mM dissolved in aqueous 0.1 M KCl or phosphate buffer pH). Experiments were carried out (i) in aqueous solution of the testedox reagent and (ii) in pure electrolyte after pre-immersion of thelectrode into the test reagent. Fig. 2A shows a typical set of voltam-ograms for the oxidation of Fe(CN)6

4− in situ as a function of scanate. For pre-adsorption measurements the modified electrode ismmersed for 20 min and then rinsed and transferred into clean.1 M KCl or phosphate buffer solution pH 2 for cyclic voltammetrynalysis. Fig. 2B shows a typical voltammogram for the methylenelue redox system pre-adsorbed into the CNP-chitosan film.

In order to evaluate anionic binding, indigo carmine waspplied. Indigo carmine (5,5′-indigodisulfonate) is a water solubleianionic redox system [24]. The CNP-chitosan composite elec-rode is immersed into 1 mM indigo carmine in 0.1 M phosphateuffer pH 7 and then rinsed and transferred into clean bufferolution 0.1 M phosphate buffer pH 2. The process follows a twolectron–two proton mechanisms [24]. From the charge under theoltammetric peak (see Table 1) anionic binding is clearly evident.his is likely to be associated with the presence of chitosan cationicites. From these data, the number of cationic binding sites cane estimated as 0.2 nmol (taking into account the charge of the

olecule and the number of electrons transferred per molecule).

he theoretically expected number of cationic binding sites for.3 �g chitosan is 2 nmol. Therefore only about 10% of all the

Methylene blue 1.6 × 10Indigo carmine 2.0 × 10−5

Ferrocyanide 5.73 × 10−6

sites (ignoring effects from incomplete deacetylation) appearto be active (or close enough to the carbon nanoparticles). It isinteresting to compare to the value of adsorbed ferrocyanide (seeTable 1) which also suggests ca. 0.2 nmol cationic binding sites(each Fe(CN)6

4− occupying four sites).Methylene blue (a mono-cation) when adsorbed into the CNP-

chitosan films results in a significantly higher current response anda charge corresponding to 1.6 × 10−4 C (see Table 1). Therefore sig-nificant binding to the negatively charge CNP surface seems to occureven at pH 2. The number of active binding sites is estimated as0.8 nmol (assuming a 2-electron process) which suggests ca. 300“free” anionic binding sites per particle (assuming an average of12 nm diameter and the density of graphite 2.2 g cm−3). Some ofthe anionic binding sites are occupied by the chitosan binder. Herea medium molecular weight chitosan is employed (in contrast toearlier reports where low molecular weight chitrosan was used)and this seems to result into a structure where anionic bindingsites remain “free” with chitosan “domains” located probably coiledmostly between carbon particles.

When compared to anion and cation binding, the bindingof hydroquinone, catechol, and resorcinol appears weaker (seeTable 1). However, in spite of this the peak currents observed forthe dihydroxybenzene derivatives is substantial when investigateddirectly in a solution with 1 mM analyte in aqueous 0.1 M phos-phate buffer pH 7 (see Table 2). Under these conditions, the chargeunder the oxidation peak for ferrocyanide is increased by a fac-tor 10, but the responses for dihydroxybenzenes increases by twoorders of magnitude. This effect is beneficial for analytical appli-cations and it is probably caused by weak adsorption to a largenumber of binding sites (rinsed away in previous experiments).In the next section this weak adsorption effect is studied in moredetail.

3.2. Voltammetric study of dihydroxybenzene isomers at thesurface of modified electrodes

HQ 2.73 × 10CA 1.82 × 10−4

RS 9.19 × 10−5

Ferrocyanide 5.46 × 10−5

M. Amiri et al. / Sensors and Actuators B 162 (2012) 194– 200 197

F (B) HQg . (E) T

Torouco

amtatp�taa

3

t

ig. 3. Cyclic voltammograms (scan rate is 0.1 V s−1) for oxidation of 1 mM (A) CA,

lassy carbon (dotted line) and modified glassy carbon (solid line) in 0.1 M PBS pH 7

he increase in the capacitive current by approximately one orderf magnitude is observed (vide supra), but also the Faradaic currentesponses are substantially increased. As can be seen, the electro-xidation of RS at bare electrode is sluggish. On the other hand,sing the modified electrode, a well-defined anodic wave with aonsiderable enhancement in the peak current and decrease inxidation potential are obtained.

Fig. 3D shows the CV for a solution containing 1 mM CA, HQnd RS at pH 7.0 for a bare electrode (dotted line) and for aodified electrode (solid line). At the bare glassy carbon elec-

rode, three relatively weak and poorly resolved anodic wavesre observed. On the other hand, when using the modified elec-rode three well-resolved voltammetric waves are observed. Theeak-to-peak separation observed for HQ-CA and for CA-RS areEp = 373 mV and 130 mV, respectively. With increasing scan rate

he separation of the waves is further improved. The film may offer strategy for the simultaneous voltammetric detection of smallmounts of mixed dihydroxybenzene isomers.

.3. The effect of pH

Voltammetric investigations with the chitosan-carbon nanopar-icle modified electrode were performed in the pH range between

, (C) RS, and (D) a mixture solutions of 1 mM CA, HQ and RS at the surface of barehe plot of Ep,a versus pH for solutions of catechol, hydroquinone, and resorcinol.

3 and 7 in solutions containing 1 mM HQ, CA, and RS. A system-atic negative shift in the anodic peaks occurred for all compoundswhen increasing the pH of the buffer solution. This confirms that H+

participates in the oxidation process in the electro-oxidation of thethree isomers. A good linear relationship was observed between Ep

and pH values in the range of 3–7 (Fig. 3E). These relationships canbe described by the following equations:

HQ Ep = 0.568 − (0.0631 pH) (1)

CA Ep = 0.693 − (0.0649 pH) (2)

RS Ep = 0.926 − (0.0471 pH) (3)

These equations are consistent with Nernstian behaviour exceptfor RS where additional kinetic effects are likely to cause a devi-ation. A pH 7 phosphate buffer solution was selected as thesupporting electrolyte for the quantification studies as it gavemaximum peak current at pH 7. In addition, the maximum peakseparation was also obtained at pH 7.

3.4. The effect of scan rate

Voltammetric data for the oxidation of 1 mM HQ, CA and RSwere recorded at the surface-modified electrode in pH 7 buffer

198 M. Amiri et al. / Sensors and Actuators B 162 (2012) 194– 200

Fv

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3m

3

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Fig. 5. DPV of various concentrations down to up: 8 × 10−7, 1 × 10−6, 8 × 10−6,3 × 10−6, 1 × 10−5, 8 × 10−5, 3 × 10−5, 1 × 10−5, 8 × 10−4, 3 × 10−4, 1 × 10−4 M of (A)

−6 −6 −5 −5 −5 −5 −4

ig. 4. Log–log plot of peak current for oxidation of 1 mM (�) CA, (�) HQ and (*) RSersus the scan rate.

olution at potential sweep rates between 20 and 200 mV s−1. ForS, no cathodic peak is observed on the reverse scan independentf potential sweep rates. Such a behaviour confirms an irreversibleC-type mechanism. For CA and HQ, cathodic and anionic peaks arebserved for all scan rates.

A plot of the logarithm of the peak current versus the logarithmf the scan rate is expected to result in two linear regions: (i) ainear region with slope 1 due to thin film behaviour of adsorbededox material (see Eq. (4)) and (ii) a region with slope 0.5 due toiffusion of redox material towards the electrode (see Eq. (5)).

p,thin film = n2F2

4RT�Vc = n2F2

4RT�Aıc (4)

p,diffusion = 0.446nFc

√nF�D

RT(5)

In these equations, the peak current is related to the number ofransferred electrons per molecule, n; the Faraday constant, F; theas constant, R; the absolute temperature, T; the scan rate, v; thelectrode area, A; the film thickness, ı; and the concentration ofedox active material, c. Diffusional transport should dominate atower scan rates. Plots of peak current data are shown in Fig. 4.

The slope at lower scan rate is closer to one (adsorption) andnly at higher scan rates the slope becomes 0.5 (diffusion). The plotn Fig. 4 clearly shows a transition between thin film and diffusionharacteristics at a transition scan rate of ca. �trans = 0.04 V s−1. Theharper peak features observed at faster scan rates are beneficialor analytical detection and employed in the following section alongulse techniques with a similar benefit of adsorption on sensitivity.

.5. Electroanalysis of dihydroxybenzene isomers at the surface ofodified electrodes

.5.1. Analytical results I: test samplesThe differential pulse voltammetry (DPV) technique was applied

or quantitative determination of the dihydroxybenzene isomersFig. 5). Under the optimum conditions, calibration curves of dihy-roxybenzene isomers were obtained. The oxidation peak currentas linearly proportional to the concentration of HQ, CA, andS in the range of 8.0 × 10−7–1.0 × 10−4, 8.0 × 10−7–1.0 × 10−4,.0 × 10−6–1.0 × 10−3 mol L−1, respectively. Additional experi-

ents were performed with mixtures of these compounds and

he same calibration characteristics were observed. The limit ofetection for HQ, CA, and RS was 2.0 × 10−7, 2.0 × 10−7, and.0 × 10−6 mol L−1, respectively. Table 3 compares the new results

HQ, (B) CA and 8 × 10 , 3 × 10 , 1 × 10 , 8 × 10 , 3 × 10 , 1 × 10 , 8 × 10 ,3 × 10−4, 1 × 10−4, 8 × 10−3, 3 × 10−3, 1 × 10−3 M (C) RS in 0.1 M PBS (pH 7.0), 50 mVpulse amplitude, 5 mV step potential, 0.05 s step time.

for the determination of dihydroxybenzene isomers to literaturedata obtained with similar electrochemical procedures.

3.5.2. Analytical results II: real samplesWater samples were tested with this new modified electrode.

Water sample no. 1 was obtained from local river water (Balekhlochai River, Ardabil, Iran). The results demonstrated that no dihy-droxybenzene was detected with the modified electrode. Thestandard solution was added to the water sample to determine

M. Amiri et al. / Sensors and Actuators B 162 (2012) 194– 200 199

Table 3Comparison of some electrochemical methods previously used for the determination of dihydroxybenzene isomers.

Electrode LOD (M) DLR (M) �Ep (mV)

[10] SWCNT GCE HQ: 1.2 × 10−7 4 × 10−7–1 × 10−5 HQ, CA 111CA: 2.6 × 10−7 4 × 10−7–1 × 10−5 CA, RS 399RS: 3 × 10−7 4 × 10−7–1 × 10−5

[11] Nano array carbon nanotube HQ: 3 × 10−7 1 × 10−6–1 × 10−4 HQ, CA 109CA: 2 × 10−7 1 × 10−6–1 × 10−4 CA, RS 382RS: 6 × 10−7 6 × 10−6–1 × 10−4

[14] Graphen-chitosan composite HQ: 7.5 × 10−7 1 × 10−6–3 × 10−4 HQ, CA 96CA: 7.5 × 10−7 1 × 10−6–4 × 10−4 CA, RS 388RS: 7.5 × 10−7 1 × 10−6–5.5 × 10−4

[25] Carbon-atom-wire electrode – 1 × 10−5–1 × 10−2 HQ, CA 1511 × 10−5–1 × 10−2

1 × 10−5–1 × 10−2

[26] Graphite–epoxy composite HQ: 1 × 10−6 1 × 10−6–1 × 10−4 HQ, CA 481CA: 2 × 10−6 CA, RS 343RS: 5 × 10−6

[27] Nanogold glassy carbon HQ: 5 × 10−7 2.5 × 10−6–8.5 × 10−4 HQ, CA 100CA: 6.5 × 10−7 1 × 10−6–6.5 × 10−4 CA, RS 399RS: 9 × 10−7 3 × 10−6–4 × 10−4

[28] Amino-functionalized SBA-15 mesoporous silica-modified carbon paste electrode HQ: 3.0 × 10−7 8 × 10−7–1.6 × 10−4 HQ, CA 115CA: 5.0 × 10−7 1 × 10−6–1.4 × 10−4 CA, RS 396RS: 8.0 × 10−7 2 × 10−6–1.6 × 10−4

This work CNP-chitosan −7 −7 −4

Table 4Recovery data observed for spiked resorcinol in diluted river water sample.

1 2

Isomer HQ CA RS HQ CA RSSpiked ×10−5 (M) 1.00 1.00 1.00 5.00 5.00 5.00Found ×10−5 (M) 0.96 0.98 1.08 4.98 4.86 5.08

a

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pwfvmotcrwswfs

4

dsinah

Recovery% 96.0 98.0 108.0 99.6 97.2 101.6

Average of five replicate measurements (rounded).

he recovery rate of dihydroxybenzene. Recoveries from 96% to08%were obtained. The average values of five replicate measure-ents are summarized in Table 4.Water sample no. 2 was obtained from a local Rubber Com-

any. It contained low levels of resorcinol. This waste water sampleas diluted 5 times. The standard addition method was applied

or determination of the calibration curves of the peak currentersus the resorcinol concentration. Also, recoveries were deter-ined by spiking of resorcinol into the water samples. The precision

f method for resorcinol determination in water samples, based onhe five replicates of analysis, was 3.9%. The slope of the calibrationurve, which was obtained with the spiked standard solution ofesorcinol in the range of 1 × 10−5–1 × 10−3 M, was 0.0242 �A/�Mith a correlation coefficient of (R2) 0.993. Compared with the

tandard curve, 0.0262 �A/�M, a recovery of 92.36% was obtainedith the new method, revealing that the method is appropriate

or accurate determination of resorcinol in real and complex wateramples.

. Conclusions

It has been shown that carbon nanoparticle–chitosan filmeposits interact with cationic, anionic and with neutral redoxystems. Although weaker, the interaction with dihydrobenzene

somers (in combination with a large active surface of carbonanoparticles) has been shown to be effective in improving thenalytical signal and allowing simultaneous determination ofydroquinone, catechol, and resorcinol. The simultaneous binding

[

HQ: 2 × 10 8 × 10 –1 × 10 HQ, CA 131CA: 2 × 10−7 8 × 10−7–1 × 10−4 CA, RS 373RS: 3 × 10−6 8 × 10−6–1 × 10−3

of different types of ionic and non-ionic analytes into different“domains” in the nano-composite could be beneficial in someanalytical problems. The low-cost nature of the nano-compositematerial could be exploited for a wider range of analytes andpotentially on a bigger scale, for example for the removal anddestruction of impurities in industrial water streams.

Acknowledgement

The authors gratefully acknowledge the support of this work byArdabil Payame Noor University research council, Ardabil, Iran.

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Biographies

Mandana Amiri received her PhD degree in 2007 from Sharif University of Technol-ogy, Tehran, Iran. At present, she is Assistant Professor of Chemistry at University ofMohaghegh Ardabili, Ardabil, Iran.

Shahnaz Ghaffari received her BS degree in 2006 from Payame Noor University(PNU), Iran. At present, she received her MS degree in 2011 from Department ofPNU, Ardabil, Iran.

Abolfazl Bezaatpour received his PhD degree in 2007 from Sharif University of Tech-

nology, Tehran, Iran. At present, he is Assistant Professor of Chemistry at Universityof Mohaghegh Ardabili, Ardabil, Iran.

Frank Marken received his PhD in 1992 at the RWTH Aachen, Germany and is nowworking as a Professor at the Department of Chemistry at the University of Bath.