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Sensors and Actuators B 147 (2010) 15–22

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l homepage: www.e lsev ier .com/ locate /snb

evelopment of an optical fibre reflectance sensor for lead detection based onmmobilised arsenazo III

eynep Yanaz, Hayati Filik ∗, Resat Apakstanbul University, Faculty of Engineering, Department of Chemistry, 34320 Istanbul, Turkey

r t i c l e i n f o

rticle history:eceived 15 December 2008eceived in revised form 8 December 2009ccepted 10 December 2009

a b s t r a c t

A fibre-optic sensor based on the use of 2,7-bis(2-arsenophenylazo) 1,8-dihydroxynaphthalene-3,6-disulphonic acid, commonly called Arsenazo III (ASA III) immobilized onto XAD-16, has been developedfor the rapid reflectance spectrometric determination of lead (II). The measurements were carried out at

vailable online 22 December 2009

eywords:eadrsenazo IIIptical sensor

a wavelength of 664.6 nm since it yielded the largest divergence different in reflectance spectra beforeand after reaction with the analyte element. The sensor was found to have an optimum response at pH5.0 with respective measurement repeatability and probe-to-probe reproducibility of 0.23% and 2.3%.The dynamic working response of Pb(II) was found within the concentration range of 0.2–20.7 ppm, witha LOD of 0.01 ppm. The tolerance limits of coexisting ions were also investigated. The sensor can easilybe regenerated by immersion in 0.1 mol/L HNO3. The proposed sensor was applied to the determination

solin

eflectance spectrometry of Pb(II) in commercial ga

. Introduction

The increasing presence of toxic pollutants in the environ-ent is perceived as a major problem in the last decades [1].

ead is one of the most common ions assayed in environmentalamples, and there is an increasing interest in its determinationecause of its toxicological effect. Widely used analytical tech-iques for the detection of lead in various samples include atomicbsorption spectrometry (AAS), inductively coupled plasma atomicmission spectrometry (ICP-AES), and inductively coupled plasma-ass spectrometry (ICP-MS) [2–4]. These techniques can offer good

imits of detection (LODs) and wide linear ranges, but are veryxpensive and require adequate expertise. Therefore, the analysis isften limited to laboratory level only. The rapid and field analysis ofrace heavy metal ions is of tremendous interest in environmentalpplication.

Optical techniques for chemical analysis are well established,nd sensors based on these techniques are now attracting con-iderable attention because of their importance in applicationsuch as environmental monitoring, biomedical sensing, and indus-rial process control. In sensor applications, indicator dyes and

eagents are mostly used in immobilized form [5]. The reagents normally physically entrapped by adsorption, electrostaticallyttracted or chemically bonded to the solid support. Numerouseagents immobilised on polymer matrix for the preparation of

∗ Corresponding author. Tel.: +90 212 473 70 70/17739; fax: +90 212 473 71 80.E-mail address: filik@istanbul.edu.tr (H. Filik).

925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2009.12.024

e after wet ashing of sample with satisfactory results.© 2010 Elsevier B.V. All rights reserved.

lead sensors were previously described. The polymers not only actas solid supports onto (or into) which indicator dyes are immo-bilized, but also can provide permeation selectivity for certainspecies, while rejecting other substances [5]. Optodes based onthe immobilization of various indicator reagents such as xylenolorange [6,7], dithizone (Dz) and fluorinated dithizone (F2H2Dz)[8–10], 2-(5-bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) [11], gallocynine [12,13], 2,3-naphthalocyanine [14],dithioamide carrier and nile blue [15], 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA) [16], quinolinesulphonic acid [17]and tetraphenyl-porphine-tetrasulfonic acid (TPPS) [18] have pre-viously been investigated in relation to the detection of lead.Another lead(II) ion sensor based on optical fibre has alsobeen developed by Malcik et al. [19] by using a series ofimmobilised reagents comprising 1-nitroso-2-napthol (NN), 4-(2-pyridylazo) resorcinol (PAR), 2,4-dinitrosoresorcinol (DNR) and1-(2-pyridylazo)-2-napthol (PAN). Many of these sensors werebased on absorbance [15,16], fluorescence [14], phosphorescence[17], and reflectance [6–8,11–13,18,19] measurement of the com-plex formed between lead and an immobilised reagent. Only sixprocedures have been reported in the literature for the deter-mination of lead in water samples with reflectance detection[6–8,11,12,19]. A comparison of the methodology and figures ofmerit of the newly developed sensor with those of previously

published reflectance sensors for Pb(II) determination is given inTable 1. In recent years, the lead ion-selective electrodes havebeen investigated by using ionophores, which bear oxygen donoratoms such as dibenzo-18-crown-6 [20–22], capric acid [23], diben-zyl phosphate [24], 9,10-anthraquinone derivatives [25], acrylic

16 Z. Yanaz et al. / Sensors and Actuators B 147 (2010) 15–22

Table 1Review of some reflectance sensor systems for the determination of lead.

Reagent and analytical wavelength (�,nm), measurement

Immobilisation method; supportmatrix

Linear range, LOD References

Xylenol orange, 570 nm Reflectance Electrostatic attraction,Polyacrylonitrile, anion exchangers

NR, 20 �M (4.14 ppm) flow mode;kinetic method (10 min), light sensitivereagent.

[6]

Xylenol orange, 560 nm Reflectance Electrostatic attraction, Wofatit ES,anion exchange resin, entrapment PVC

3–30 �M, 3 �M (0.621 ppm), batchmode, response time 2 min, lightsensitive.

[7]

Dithizone, 650 nm Reflectance Adsorption, XAD-4 3.0 × 10−7 to 1.0 × 10−5 -(0.06–2.07 ppm), 1 × 10−8 M (2 �g L−1),flow mode; kinetic assay; instablereagent

[8]

2-(5-Bromo-2-pyridylazo)-5-(diethylamino)phenol(Br-PADAP),580 nm, Reflectance

Adsorption XAD-4 NR, 0.17 ppm, kinetic assay; responsetime 10 min.

[11]

Gallocynine, 800 nm, Reflectance. Adsorption, XAD-7 and chitosanmembrane.

0.1–1000, 0.06 ppm, 0.075 ppm;response time 5 min.

[12,13]

Tetraphenyl-porphine-tetrasulfonicacid (TPPS)

Covalently immobilized NR [18]

1-Nitroso-2-napthol (NN),2,4-dinitrosoresorcinol (DNR),4-(2-pyridilazo)resorcinol (PAR),1-(2-pyridylazo)-2 napthol(PAN),Reflectance

Adsorption, XAD-4, XAD-7 and Dowex 1–10, 0.1 ppm; kinetic assay; responsetime 5 min.

[19]

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2

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Arsenazo III, Reflectance. Adsorption, XAD-16

mides, and oxamides [26], and sulfur donor atoms such as ben-yldisulfide [27].

The use of immobilised reagents for Pb(II) detection has beenapidly growing nowadays in the area of chemical sensing employ-ng optical fibre sensor. Arsenazo III (ASA III) is a non-specifichromogenic reagent that can be used for the determination of aarge variety of metal cations under different conditions, rangingrom alkaline to strongly acidic media [28]. Several uranium-ensitive optical sensors have been reported in the literature usinghis indicator [29]. ASA III reacts with Pb (II) to form a sensitiveomplex in a weakly acidic solution [28,30], but has not beensed previously as a reflectance sensing layer for the determina-ion of lead. In this work, spectrophotometric reagent ASA III haseen immobilised on copolymer Amberlite XAD-16 as the sens-

ng phase in an optical fibre chemical sensor for lead detection.he optical sensor is then incorporated with the reflectance sys-em in order to enhance the sensing ability. The proposed neweflectance sensor possesses distinct advantages (summarized inable 1) over existing lead reflectance sensors with respect toensitivity [6–8,11,13,14,19], range of determination [6–8,11,19],implicity [6,8,11,19], response time [6,11,13,14,19], and stability6–8]. The proposed sensor system can be applied to the determi-ation of Pb(II) in gasoline samples – after wet ashing of the samplewith satisfactory results.

. Experimental

.1. Reagents

All chemicals used were of analytical grade and deionisedater was used throughout for solution preparation. An arsenazo

II (Merck) solution of 1.0 × 10−3 mol/L was prepared by dissolv-ng 89.24 mg of arsenazo III in 100 ml of ethanol. A stock Pb(II)olution (1.0 × 10−3 mol/L) was prepared by dissolving 33.123 mg

f Pb(NO3)2 (Sigma) in 100 mL of distilled water. Working stan-ard solutions of Pb(II) were prepared by appropriate dilutionf the stock solution before use. Tetraethyl lead was obtainedrom Aldrich Chemical Company Inc. A 0.1 mol/L HNO3 was useds regenerating solution. Buffer solution at pH 5.0 was prepared

0.2–20.7, 0.01 ppm; response time2 min, very stable reagent.

This work

from acetic acid/sodium acetate, at pH 7 from ammonium acetateand at pH 8–10 from ammonia-ammonium chloride. All mea-surements were carried out at room temperature. The AmberliteXAD-16 resin (styrene–divinylbenzene copolymer, surface area:800 m2 g−1, pore diameter: 100 Å and bead size: 20–60 mesh) wassupplied by Aldrich. The resin beads were washed thoroughly withdistilled water, soaked in EtOH, and rinsed again with H2O prior touse.

2.2. Instrumentation

Schematic diagram of the whole system was previouslydescribed in Refs. [31,32]. Experiments were carried out using acommercially available miniature fibre-optic-based spectrometer(Ocean Optics Inc., HG4000CG-UV-NIR) which utilises a small tung-sten halogen lamp (Ocean Optics Inc.) as the light source and aCCD-based detector for reflectance measurements. The spectralresolution declared by the manufacturer was 0.1 nm. Light reflectedfrom the probe surface was transmitted by a bundle of opticalfibres to a miniature fibre-optic spectrophotometer (Ocean OpticHG4000CG-UV-NIR) which on the other hand was connected toa PC (Dell-compatible) and also a printer. For optical isolation,the probe and the detector were kept in a black box to minimiseany interference from ambient light. The spectral deconvolutionwas performed after smoothing the spectra by a 25-point Fouriertransform filter using peak fitting module in OriginPro7.0 software(OriginLab Co., USA). A mechanical shaker (Nüve, Turkey) havingspeed control facility was used for batch equilibration.

2.3. Sample preparation

2.3.1. Gasoline analysisCommercial gasoline samples were obtained from a local station

and analyzed (Avcilar, Istanbul, Turkey). A 10 mL portion of gasoline

sample (or sample spiked with tetraethyl lead sample) was treatedwith 5 mL of concentrated HNO3 and heated in a sand bath to dry-ness. The residue was then treated with 2 mL of 30% (v/v) hydrogenperoxide (H2O2), and heated in a sand bath again to dryness. Aftercomplete drying and cooling to room temperature, a second 2-mL

d Actuators B 147 (2010) 15–22 17

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Fig. 1. (a) The reflectance spectrum (as reflectance, %) of the ASA III/XAD-16 reagent

Z. Yanaz et al. / Sensors an

ortion of 30% H2O2 was added and the procedure was repeated.he residue was then treated with 1.0 mL of 0.1 mol/L HNO3 underentle warming to achieve complete dissolution. The volume wasdjusted to 10 mL by water, and finally Pb(II) was quantified usinghe developed sensor system.

.4. Impregnation procedure

Amberlite XAD-16 resin obtained from the supplier containedrganic and inorganic impurities. To remove these contaminants, itas washed successively with ethanol, distilled water, 0.1 M NaOH

nd 0.1 M HCl. The XAD-16 beads were then washed with distilledater until neutral. The sensing material (ASA III) was physically

mmobilised by adsorption onto Amberlite XAD-16 polymer. Theigand-loaded resin beads were dried in an oven at 105 ◦C for 4 h. A.5 g amount of dry resin (Amberlite XAD-16) beads was treatedith 5 mL of 1.0 × 10−3 mol/L ASA III and 2 mL ethanol, and theixture was shaken at room temperature for 10 min. The result-

ng red-violet resin beads were filtered off from the supernatantolution, and were washed with distilled water until the washingsere colourless. Finally, the red-violet resin beads were kept under

.1 mol/L HNO3 when not in use.

.5. Sensor fabrication

The detailed description of the model sensor design was given inur previous papers [31–34]. The probe was built using disposableyringe tubes (i.d. = 10 mm) (SB Medical Center, Kartal, Istanbul). Ayringe column (12 cm length and 1.0 cm diameter), with a nylonembrane and a stopcock, was used for preconcentration of Pb(II).

he syringe tube was filled with 0.3 g (wet substance) AmberliteAD-16-ASA III resin. The filling height of the resin was approxi-ately 5 mm. The prepared probe was later attached to the distal

nd of a bifurcated fibre optic. During measurements, the arbitrarynit and the detector were kept in a black box to minimise any

nterference from ambient light.

.6. Reflectance measurement

The aqueous sample solution containing lead (within the work-ng range of 0.06–20.7 ppm) was buffered to pH 5.0 with aceticcid/sodium acetate. The prepared mixture was then loaded to theensor system. The reflectance measurement was carried out byecording the optical signal 3 min after placement of the bifur-ated optical fibre in the analyte solution. Reflectance spectra wereegistered after 3 min (for full color development). The measure-ents were expressed in the units of relative reflectance, which

s defined as the difference between the reflectance of the ASA III-b(II) complex (Rc) and that of the immobilised reagent alone (Rf),oth recorded at the same wavelength (664.6 ± 0.1 nm).

As the concentration of the analyte increases, the reflec-ion intensity count (at the working wavelength of 664.6 nm) ofhe analyte-adsorbed resin (ASA III/XAD-16) decreases, becauseight absorption increases. When this is converted to percentageeflectance (R,%), this is given as R,% = 100 (Rc − Rf)/Rf, where Rf andc are the reflectance intensities of the reagent blank and com-lex, respectively. Since Rc < Rf (the latter as the reflectance baseline

eing set to 100 arbitrary units), R,% assumes a negative value. How-ver, when the reflectance intensity (R,%) or relative reflectanceRc − Rf) is correlated to some parameter such as analyte concen-ration, then it is more reasonable to take the ‘absolute value’ ofhis relative reflectance.

phase before (Rf) and after reaction with 2.07 (a) and 10.35 ppm (b) Pb(II) at pH 5.0.(b) The reflectance spectrum (as reflectance intensity counts) of the ASA III/XAD-16reagent phase before (Rf) and after reaction with 2.07 (a) and 10.35 (b) ppm Pb(II)at pH 5.0.

3. Results and discussion

3.1. Reflectance spectra of the sensor

The spectral features of both the XAD-16/ASA III and the XAD-16/ASA III-Pb(II) were recorded in solid-phase media. ASA III wasfixed on Amberlite XAD-16 resin showing a red-violet color with areflectance maximum at 571 nm (550 nm in solution). In the pres-ence of Pb(II), ASA III/XAD-16 sensing layer turns from red-violetto blue color with reflectance maxima at 664.6 nm (660 nm in solu-tion). Fig. 1a shows the reflectance spectrum of the immobilizedASA III/XAD-16 reagent phase before and after reaction with (a)2.07 and (b) 10.35 ppm Pb(II) at pH 5.0. The reflectance intensity(Fig. 1b.) was measured at 664.6 nm against a sensing layer blank(ASA III/XAD-16) that was composed of all the chemicals used in themethod except lead. The bathochromic shift resulting from com-plex formation was due to charge-transfer interactions betweenthe metal ion and ligand adsorbed on the solid resin.

The molecule of arsenazo III (ASA III) contains two functionalgroups which form a part of two partially isolated conjugated sys-tems. As the two chromophoric centres of an ASA III molecule are

in different ionic states, two absorption bands of different inten-sity appear in the visible range of the spectrum. ASA III may act asN,O-donor bidentate ligand toward Pb(II) via the –N N–C C–O–and –N–C C–AsO(OH)–O– groups. Since in a 1:1 complex, onlyone of the functional groups of ASA III ligand participates in com-

18 Z. Yanaz et al. / Sensors and Actuators B 147 (2010) 15–22

Fli

pmathcimmbhodF

3

m3btaits5srobi

diitan

Fig. 3. The effect of reagent amounts used during immobilisation of ASA III onXAD-16 (0.5 g of resin) on the response of Pb(II). The inset shows the reflectance

ig. 2. The effect of pH on the probe response using 5 × 10−3 mmol ASA III immobi-

ized on XAD-16 (0.3 g of resin) measured at 664.6 nm with [Pb(II)] = 2.07 ppm. Thenset shows the intensity profile of the original reflectance spectra.

lex formation, this leads to the disruption of symmetry in the dyeolecule giving rise to the 665 nm band [35]. In the case of ligand

dsorption onto a resin surface, an additional strain is placed onhe ligand-metal complex system causing a distortion from tetra-edral toward planarity, which would lower the symmetry of theomplex and lead to a splitting of degenerate d-orbitals of the metalon. This enhanced splitting of d-orbitals may further interact with

etal-to-ligand (M → L) charge-transfer transitions giving rise to aore complex spectrum. Since some of the filled d-orbitals would

e destabilized by distortion, the energy difference between theighest occupied metal orbital and the lowest unoccupied ligandrbital (i.e., difference between HOMO-LUMO energy levels) willecrease, resulting in a batochromic shift [36]. This is observable inig. 1a.

.2. Effect of variables

One of the effective variables on the sensor response was theedium pH, and therefore, the influence of pH over the range

.0–8.0 on the response of optode was studied. The pH was adjustedy addition of appropriate buffer solutions. As can be seen in Fig. 2,he maximum system response was obtained in the presence ofcetate buffer at pH 5.0. This is advantageous, as at this pH, Pb2+

s not hydrolyzed significantly. The obtained results were similaro those reported studies on formation of Pb(II)-ASA III complex inolution [28,30]. The greatest relative reflectance occurred at pH.0; therefore a pH of 5.0 was fixed with the use of acetate bufferolution. The Pb(II)-ASA III complex leaching occurred in alkalineegion at pH > 8.0. According to literature reports on investigationf the Pb(II)-ASA III complex in solution phase, complex formationegins at pH ≥ 2, and is maximal between pH 4 and 6; the complex

s not stable at pH > 8 [30].The effect of the optimum reagent amount on the response of the

eveloped sensor was studied by using different amounts of ASA III−4 −3

n the range 5.0 × 10 to 7.0 × 10 mmol/0.5 g of resin during its

mmobilisation. The immobilized reagent was later used for reac-ion with 2.07 ppm Pb(II). Fig. 3 shows that the higher the reagentmount used for immobilization, the higher the reflectance sig-al obtained for the same concentration of lead. The reflectance

intensity (%) profile of the original reflectance spectra. [Pb(II)] = 2.07 ppm; � =664.6 nm.

intensity increased with increase in amount of ASA III up to5.0 × 10−3 mmol, and then remained constant between 5.0 and7.0 × 10−3 mmol/0.5 g of resin. Thus, 5.0 × 10−3 mmol was selectedto ensure a sufficient excess of the reagent throughout the experi-ments.

The influence of time of immobilization on optical properties ofthe sensor was important because of the subsequent response timeand dynamic range of sensor [14]. The resin bed (0.5 g of resin) wasinserted into the solutions for different times (5–30 min). Then, thesensing layer was inserted into 2.07 ppm Pb(II) solutions at pH 5.0,and the reflectance signal of the sensor was measured at 664.6 nm.The best signal was achieved for 10 min immobilization as a suit-able time with 5.0 × 10−3 mmol ASA III. Since the original ASA IIIspectrophotometry in aqueous solution is strongly dependent onthe mixing ratio of metal-to-ligand and solution conditions yieldingchelates of varying stoichiometries [37], it was strictly importantto maintain the same conditions for analytical variables in order toobtain reproducible results.

3.3. Regeneration and reusability of the optode

A good sensor should fully regenerate in a short time. For thispurpose, the effect of HNO3 was studied as possible regeneratingagent. Thus, the effect of HNO3 concentration within 0.01–1 mol L−1

as well as its corresponding volume for the elution of Pb(II) wereinvestigated. As a result, a solution of 0.1 M HNO3 provided a shortresin regeneration time lower than 2 min without any leachingof the reagent. With 2 mL of 0.1 mol/L HNO3, the sorbed Pb(II)could be completely eluted from the resin, so the resin couldbe repeatedly used. As shown in Fig. 4 the sensor is reversiblewhen regenerated by using 2 mL of 0.1 M HNO3 solution. About∼20 repetitive measurements were allowed for a single immo-bilized phase. The response of the sensor after 20 cycles variedby less than 10%. But for trace analyses, the use of fresh sen-

sors were recommended for each measurement. For the ensuingexperiments, 5 mL of 0.1 mol L−1 HNO3 was employed for regener-ation.

Z. Yanaz et al. / Sensors and Actuators B 147 (2010) 15–22 19

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3

rat5wNsc

3

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Fig. 6. The response curve of the sensor towards different concentration of Pb(II)

ig. 4. Variation of the reflectance (%) of the sensor at 664.6 nm for repeatedly expos-ng the adsorbed 2.07 ppm Pb(II) solution to 0.1 mol L−1 HNO3 regeneration solution.a) 5 cycles, (b) 10 cycles, (c) 15 cycles, (d) 20 cycles, (e) 25 cycles. Rf = the spectrumf the reflecting layer at 571 nm after five regeneration cycles.

.4. Response time

The sensing time of the probe is a very important parameter forapid measurement. Fig. 5 shows the result of steady state responsenalysis of the sensing probe at 664.6 nm as a function of time whenhe sensing layer was exposed to 1.035 and 2.07 mg L−1 Pb(II) at pH.0. It was observed that the reflectance intensity initially increasedith increasing reaction time, but remained constant after 1 min.evertheless, a 3-min system response time was chosen in this

tudy since it yielded a more stable response for a wider Pb(II)oncentration range.

.5. Lifetime of optical sensor

The reflectance signals at 664.6 nm for the sensing layer in con-act with 2.07 ppm Pb(II) were recorded over a period of 3 h. Theeflectance of the single sensing layer remained constant for ateast 3 h when the pH of the solution was maintained at 5.0. Duringhis period, there was no evidence of leakage of reagent from theesin phase. When the sensing layer was exposed to light, no drift

n signal occurred and the optode was stable under the selectedxperimental conditions with no leaching of the ASA III. However,repared sensing layers were kept under 0.1 mol L−1 HNO3 solu-ion when not in use to prevent them from drying out. When the

Fig. 5. Response curves for Amberlite XAD-16/ASA III with Pb(II).

(error bars shown). Data were collected as the mean value of three measurements.The inset shows the intensity profile of the original reflectance spectra. (a) 0.01 (asLOD), (b) 0.06, (c) 0.103, (d) 0.207, (e) 1.035, (f) 2.07, (g) 4.14, (h) 6.21, (i) 8.28, and(j) 10.35 ppm.

prepared layer was immersed in 0.1 mol L−1 HNO3 for a month, thesignal value of the sensor system did not change appreciably.

3.6. Stability of the sensor

A study on photostability of the sensor was carried out to detectany possible photobleaching or photodecomposition of the reagentphase when it was continuously exposed to a light source for a longperiod of time. In this test, it was demonstrated that the reagentphase is stable and no photodecomposition occurred. The leachingof the immobilized reagent was evaluated by monitoring the sen-sor response continuously for 3 h when the prepared sensor wasimmersed in acetate buffer solution. For this duration of time, thesystem response was observed to be quite stable with a R.S.D. of1.4%.

3.7. Calibration range and detection limit

The analytical parameters of the proposed method were eval-uated after the system was optimized. Calibration graphs wereobtained according to the procedure described above, using Pb(II)standard solutions of varying concentration. A typical analyticalcurve of signal response as a function of Pb(II) concentration isshown in Fig. 6. This figure shows that the sensor produced asemi-logarithmic response when the Pb(II) concentration is withinthe range of 0.2 and 20.7 ppm. The calibration curve drawn asreflectance versus log Pb(II) concentration is shown in Fig. 7. Theregression equation was Rf − Rc = 0.1117 log C + 0.1494 when theconcentration of Pb(II) was expressed in ppm, with a correla-tion coefficient, r, of 0.9958. The reproducibility of the sensor waschecked by five replicate determinations at 2.07 ppm level of Pb(II).The reflectance measurements were highly reproducible as the rel-ative standard deviation (RSD) for the 2.07 ppm Pb(II) solution was

found to be 0.23%. The RSD of the measurement repeatability wasfound to be 0.23% while for probe-to-probe reproducibility it was2.3%. The limit of detection (LOD) of Pb(II), defined as the concen-tration equivalent to a signal of blank plus three times the standarddeviation of the blank, was calculated to be 0.01 ppm (Fig. 6-inset

20 Z. Yanaz et al. / Sensors and Actuators B 147 (2010) 15–22

Table 2Effect of interference for the determination of 2.07 ppm of Pb(II) (n = 3).

Metal ions Tolerance limit (ppm) Reflectance (%) RSD (%) Error (%) Recovery (%)

Pb2+ 2.07 18.29 ±0.32 – –Al3+ 20.2 18.73 ±0.07 0.44 102Mn2+ 54.8 18.36 ±0.08 0.07 100Co2+ 58.9 18.23 ±0.04 −0.06 100Cd2+ 84.3 18.05 ±0.21 −0.24 99Ni2+ 44.0 18.26 ±0.24 −0.03 100Zn2+ 65.3 18.44 ±0.19 0.15 101Mg2+ 18.2 18.16 ±0.17 −0.13 99Ca2+ 0.4 18.59 ±0.17 0.30 101Fe(III) 0.55 18.94 ±0.06 0.65 103Cu(II) 0.63 18.90 ±0.25 0.61 103Cr(VI) 0.51 18.17 ±0.13 −0.12 99Cr(III) 0.51 18.75 ±0.09 0.46 102Cl− 354.0 18.44 ±0.21 0.15 101NO3

− 620.0 18.39PO4

3− 712.0 18.15SO4

2− 960.0 18.55F− 18.9 18.00

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sintp

constant (as log ˇ ) of 1:1 complexes of ASA III with Ca(II) and

TA

a

ig. 7. The semi-logarithmic calibration curve for determination of Pb(II) usinghe Amberlite XAD-16-ASA III sensor (error bars shown). Correlation coefficientf semi-logarithmic plot: r = 0.9958, linear calibration range: 0.2–20.7 ppm Pb(II),epeatability RSD = 0.23%, probe-to-probe reproducibility as RSD ≤ 2.3%.

hows this value as minimum detectable concentration). This values lower than that of Yusof and Ahmad [12] who used a gallocy-ine sensor for Pb. In validating the performance of the method,he detection limit (LOD) was determined by the analysis of sam-les with known low concentrations of Pb(II). According to IUPAC

able 3nalysis of gasoline samples (n = 3).

Samples FAAS (ppm) Lead spike (as ppm Pb in the form o

Gasoline Aa 12.8 ± 0.2 01020

Gasoline Bb 11.7 ± 0.5 01020

Gasoline Cc 14.3 ± 1.0 01020

,b,cGasoline samples collected from different gas station of the city of Istanbul, Turkey.

±0.10 −0.10 101±0.13 −0.14 99±0.08 0.26 101±0.24 −0.29 98

(International Union of Pure & Applied Chemists) definition of LODand LOQ (limit of quantification), the concentrations correspondingto LOD and LOQ are accepted to be 3 and 10 times, respectively, ofthe standard deviation of a blank, divided by the slope of the calibra-tion curve. In this respect, the LOQ was calculated to be 0.034 ppm.However, the minimum concentration level at which the analytecould be reliably quantified was 0.11 ppm (Figs. 6 and 7), and thedynamic linear range started from 0.2 ppm.

3.8. Effect of diverse ions

Under optimum conditions, the effects of various foreign ions onthe determination of 2.07 ppm Pb(II) were examined separately.With a relative error less than ±0.13%, the tolerance limits forvarious foreign ions are listed in Table 2, showing 99–102% recov-eries for the lead analyte. Fe3+, Al3+, and Cu2+ were indicated tobe the major interferents in the reflectance spectrophotometricPb(II) determination with ASA III in aqueous solution [11]. How-ever, in the gasoline samples, concentrations of trace metals weregenerally very low. Thus, the proposed procedure can be appliedto the determination of lead in gasoline samples without any priorseparations.

The possible interferent ions listed in Table 2 were chosenbecause of they are commonly found in soil and groundwater andhave the largest chance of accompanying lead(II) in natural envi-ronments. Calcium(II) interfered, because the conditional stability

1Pb(II) were reported as 6 and 5, respectively [35,38]. Furthermore,the molar absorptivities (ε, in L mol−1 cm−1) for the ASA III-metalion chelates with Ca(II) and Pb(II) were reported as 1.0 × 103 and2.8 × 104, respectively [30,39].

f Pb(C2H5)4) Proposed method (ppm) Recovery (%)

13 –22.8 9832.3 97.5

12 ± 3.3 –21.9 10232 102

13 ± 2.8 –24 9734 98.5

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.9. Analytical applications

The proposed sensor was applied to the determination of Pb(II)n gasoline samples. Three commercial gasoline samples deliveredy different suppliers were analyzed by the proposed method andy comparative procedure. It is well known that organic lead com-ounds are added to gasoline as an anti-knock agent. Tetraalkylleadompounds in the gasoline samples are converted into water-oluble species. The results obtained are shown in Table 3, whichre in accordance with the results obtained by comparative methodFAAS). No statistical differences were found between the encoun-ered values by both methods by applying the t-test at the 95%onfidence level.

. Conclusion

The results obtained showed good reproducibility and accuracy,nd the method is suitable for routine analysis of gasoline. Thistudy has shown that upon reaction with Pb(II) ions, ASA III-XAD-6 produces a reproducible and reversible reflectometric response,ith a low limit of detection. The analytical figures of merit of

he developed sensor for Pb(II) were: repeatability RSD 0.23%, LOD0 ppb, and response time 2 min. The sensor can be readily regener-ted with dilute HNO3. It is reversible and has a long lifetime. Theesponse of the optode is reproducible, and the sensor presentsood sensitivity toward lead. This assay method allows the quan-itative determination of lead content of gasoline after wet ashingf sample.

In general, ASA III may be regarded as a sensitive but ratheron-selective reagent for metal ions, but this reagent providesxcellent repeatability and reproducibility for lead(II) [40]. Thisigh precision obtained in solution studies was confirmed inhe current work, as probe-to-probe reproducibility was 2.3%.SA also provides a high sensitivity for lead determination, as

he molar absorptivity reported for Pb(II) was sufficiently high,.e., ε = 2.8 × 104 L mol−1 cm−1 [30]. Quantitative formation of theb(II)–ASA III complex in weakly acidic solution is also an advan-age, because sensors working only in the neutral range may sufferrom metal ion loss by hydrolysis. If all spectrophotometric meth-ds for the determination of lead are considered, it may be seenhat the interference from common first row transition metal ionss relatively minimal to the ASA III method [41]. Due to disruptionf symmetry in the ASA III dye molecule, the batochromic shift inbsorption spectra of the complex relative to that of the dye is andvantage [35], added to the fact that adsorption of the ASA III lig-nd to a resin surface brings a further advantage via charge-transfernteractions to this batochromic shift in lead determination [36].his enables reflectance measurements at a relatively high wave-ength of the visible spectrum, i.e., 664.6 nm, away from possiblenterferent wavelengths of other weakly coloured species and plantigments.

cknowledgements

The authors gratefully acknowledge Istanbul University Scien-ific Research Fund (BAP Grand no: 1482 and BYP Grand no: 3489,490, 3494 and 4384) for financial support.

eferences

[1] S.Y. Bae, X. Zeng, G.M. Murray, Photometric method for the determinationof Pb2+ following separation and preconcentration using a templated ion-exchange resin, J. Anal. Atom. Spectrom. 13 (1998) 1177–1180.

[2] W. Chuachuad, J.F. Tyson, Determination of lead by flow injection hydride gen-eration atomic absorption spectrometry with tetrahydroborate immobilizedon an anion-exchange resin, J. Anal. Atom. Spectrom. 20 (2005) 282–288.

[

[

ators B 147 (2010) 15–22 21

[3] M.C. Yebra-Biurrun, A. Moreno-Cid Barinaga, Literature survey of on-line spec-troscopic methods for lead determination in environmental solid samples,Chemosphere 48 (2002) 511–518.

[4] L. Polo-Díez, J. Hernández-Méndez, F. Pedraz-Penalva, Analytical applicationsof emulsions: determination of lead in gasoline by atomic-absorption spec-trophotometry, Analyst 105 (1980) 37–42.

[5] I. Oehme, O.S. Wolfbeis, Optical sensors for determination of heavy metal ions,Mikrochim. Acta 126 (1997) 177–192.

[6] L.M. Trutneva, O.P. Shvoeva, S.B. Savvin, Immobilized Xylenol Orange as sen-sitive element for fiber optics sensors for thorium(IV) and lead(II), Zh. Anal.Khim. 44 (1989) 1804–1808.

[7] I. Klimant, M. Otto, A fiber optical sensor for heavy metal ions based on immo-bilized xylenol orange, Mikrochim. Acta 108 (1992) 11–17.

[8] W.A. De Oliveira, R. Narayanaswamy, A flow-cell optosensor for lead based onimmobilized dithizone, Talanta 39 (1992) 1499–1503.

[9] A.M. Kiwan, M.S. El-Shahawi, S.M. Aldhaheri, M.H. Saleh, Sensitive detec-tion and semiquantitative determination of mercury(II) and lead(II) inaqueous media using polyurethane foam immobilized 1,5-di-(2-fluorophenyl)-3-mercaptoformazan, Talanta 45 (1997) 203–211.

10] S.B. Savvin, T.G. Dzherayan, T.V. Petrova, A.V. Mikhailova, Sensitive opticalsensors for uranium(VI), mercury(II), and lead, J. Anal. Chem. 52 (1997) 136–140.

11] A.A. Vaughan, R. Narayanaswamy, Optical fibre reflectance sensors for thedetection of heavy metal ions based on immobilised Br-PADAP, Sens. ActuatorsB 51 (1998) 368–376.

12] N.A. Yusof, M. Ahmad, A flow-through optical fibre reflectance sensor for thedetection of lead ion based on immobilised gallocynine, Sens. Actuators B 94(2003) 201–209.

13] N.A. Yusof, M. Ahmad, A flow cell optosensor for lead based on immobilizedgallocynin in chitosan membrane, Talanta 58 (2002) 459–466.

14] G.A. Casay, N. Narayanan, L. Evans, T. Czuppon, G. Patonay, Near-infrared tetra-substituted aluminum 2,3-naphthalocyanine dyes for optical fiber applications,Talanta 3 (1996) 1997–2005.

15] M. Lerchi, E. Reitter, W. Simon, E. Pretsch, D.A. Chowdhury, S. Kamata, Bulkoptodes based on neutral dithiocarbamate ionophores with high selectivityand sensitivity for silver and mercury cations, Anal. Chem. 66 (1994) 1713–1717.

16] A.A. Ensafi, Z.N. Isfahani, Determination of lead ions by an optical sensorbased on 2-amino-cyclopentene-1-dithiocarboxylic acid, Sens. J. IEEE 7 (2007)1112–1117.

17] B.S.V. de la Riva, J.M. Costa-Fernández, R. Pereiro, A. Sanz-Medel, Flow-throughroom temperature phosphorescence optosensing for the determination of leadin sea water, Anal. Chim. Acta 395 (1999) 1–9.

18] R. Czolk, J. Reichert, H.J. Ache, An optical sensor for the detection of heavy metalions, Sens. Actuators B 7 (1992) 540–543.

19] N. Malcik, O. Oktar, M.E. Ozser, P. Caglar, L. Bushby, A. Vaughan, B. Kuswandi, R.Narayanaswamy, Immobilised reagents for optical heavy metal ions sensing,Sens. Actuators B 53 (1998) 211–221.

20] L.K. Shpigun, E.A. Novikov, Y.A. Zolotov, Synthetic macrocyclic compounds asactive membrane components of a lead selective electrode, Zh. Anal. Khim. 41(1986) 617–621.

21] M.F. Mousavi, S. Sahargi, N. Alizadeh, M. Shamsipour, Lead ion-selective mem-brane electrode based on 1,10-dibenzyl-1,10-diaza-18-crown-6, Anal. Chim.Acta 414 (2000) 189–194.

22] M.M. Zareh, A.K. Ghoneom, M.H.A. E1-Aziz, Effect of presence of 18-crown-6 onthe response of 1-pyrrolidine dicarbodithioate-based lead selective electrode,Talanta 54 (2001) 1049–1057.

23] M.F. Mousavi, M.B. Barzegar, S. Sahari, A PVC-based capric acid membranepotentiometric sensor for lead(II) ions, Sens. Actuators B: Chem. 73 (2001)199–204.

24] D. Xu, T. Katsu, Lead-selective membrane electrode based on dibenzyl phos-phate, Anal. Chim. Acta 401 (1999) 111–115.

25] N. Tavakkoli, Z. Khojasteh, H. Sharghi, M. Shamsipour, Lead ion-selective mem-brane electrodes based on some recently synthesized 9,10-anthraquinonederivatives, Anal. Chim. Acta 360 (1998) 203–208.

26] S. Malinowska, Lead-selective membrane electrodes based on neutral carriers.Part 1. Acyclic amides and oxamides, Analyst 115 (1990) 1085–1087.

27] A. Abbaspour, F. Tavakoli, Lead-selective electrode by using benzyl disulphideas ionophore, Anal. Chim. Acta 378 (1999) 145–149.

28] M. Zenki, K. Minamisawa, T. Yokoyama, Clean analytical methodology forthe determination of lead with Arsenazo III by cyclic flow-injection analysis,Talanta 68 (2005) 281–286.

29] L.C. Baylor, B.R. Buchanan, Reflectance probe for uranium(VI) based onthe colorimetric indicator arsenazo III, Appl. Spectrosc. 49 (1995) 547–687.

30] V. Michaylova, N. Kuleva, Arsenazo III as a spectrophotometric reagent fordetermination of lead, Talanta 27 (1980) 63–66.

31] H. Filik, M. Hayvalı, E. Kılıc, R. Apak, D. Aksu, Z. Yanaz, T. Cengel, Developmentof an optical fibre reflectance sensor for p-aminophenol detection based onimmobilised bis-8-hydroxyquinoline, Talanta 77 (2008) 103–109.

32] H. Filik, D. Aksu, R. Apak, I. Sener, E. Kılıc, An optical fibre reflectance sensor forp-aminophenol determination based on tetrahydroxycalix[4]arene as sensingreagent, Sens. Actuators B 136 (2009) 105–112.

33] H. Filik, D. Aksu, R. Apak, I. Boz, Rapid sensing of molybdenum by combinedcolorimetric solid-phase extraction—reflectance spectroscopy, Sens. ActuatorsB 141 (2009) 491–497.

2 d Actu

[

[

[

[

[

[

[

[

2 Z. Yanaz et al. / Sensors an

34] H. Filik, Z. Yanaz, A sensitive method for determining total vanadium in watersamples using colorimetric-solid-phase extraction-fiber optic reflectance spec-troscopy, J. Hazard. Mat. 172 (2009) 1297–1302.

35] E.E. Kostenko, Determination of lead by solid-phase spectrophotometry usingarsenazo III, J. Anal. Chem. 55 (2000) 645–648.

36] M.A. Ditzler, H. Pierre-Jacques, S.A. Harrington, Immobilization as a mechanismfor improving the inherent selectivity of photometric reagents, Anal. Chem. 58(1986) 195–200.

37] S.B. Savvin, Analytical use of Arsenazo III. Determination of thorium, zirconium,uranium and rare earth elements, Talanta 8 (1961) 673–678.

38] P.L Dorogi, E. Neumann, Spectrophotometric determination of reaction sto-ichiometry and equilibrium constants of metallochromic indicators. II. TheCa2+-arsenazo III complexes, Biophys. Chem. 13 (1981) 125–131.

39] I.P. Alimarin, S.B. Savvin, Application of arsenazo III and other azo compoundsin the photometric determination of certain elements, Pure Appl. Chem. 13(1966) 445–456.

40] M. Zenki, K. Minamisawa, T. Yokoyama, Clean analytical methodology for thedetermination of lead with arsenazo III by cyclic flow-injection analysis, Talanta68 (2005) 281–286.

41] Z. Li, Z. Zhu, Y. Chen, C.-G. Hsu, J. Pan, Spectrophotometric determination oflead in biological samples with dibromo-p-methylsulfonazo, Talanta 48 (1999)511–516.

ators B 147 (2010) 15–22

Biographies

Hayati Filik obtained his Ph.D. degree in analytical chemistry from the IstanbulUniversity, Istanbul, Turkey in 1993. He is currently a Professor of Chemistry ofIstanbul University. His fields of interest are analytical chemistry and environmentalchemistry and fiber optic chemical sensors.

Zeynep Yanaz graduated from the Department of Chemistry, Istanbul University in2006. She is currently a Master of Science student in the Department of AnalyticalChemistry in Istanbul University. Her current research interest is in optical chemicalsensors.

Resat Apak graduated in 1976 from the Chemical Engineering Department of Istan-bul University, Faculty of Chemistry, received Ph.D. from the same faculty in 1982,and was appointed to full professorship (analytical chemistry) in 1993. As admin-

istrative tasks, he became faculty dean (1996–1999) and institute director (2007–.) in Istanbul University. He is the author of 104 peer-reviewed SCI journal articles,7 encyclopedia chapters, and three textbooks, and received about 1300 citationsto his journal articles. He is the Editorial Board member of Talanta and Turkish J.Chem. He received the science prize in 2004 from Turkish Chemical Society for hiscontributions to the advancement of chemistry.