Desalination 280 (2011) 391–396

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Desalination

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Determination of inorganic arsenic species by hydride generation atomic absorptionspectrometry in water samples after preconcentration/separation on nano ZrO2/B2O3

by solid phase extraction

Hakan Erdoğan, Özcan Yalçınkaya, Ali Rehber Türker ⁎Gazi University, Faculty of Science, Department of Chemistry, 06500, Ankara, Turkey

⁎ Corresponding author. Tel.: +90 312 2021110; fax:E-mail address: aturker@gazi.edu.tr (A.R. Türker).

0011-9164/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.desal.2011.07.029

a b s t r a c t

a r t i c l e i n f o

Article history:Received 18 February 2011Received in revised form 13 July 2011Accepted 14 July 2011Available online 31 July 2011

Keywords:ArsenicSpeciationPreconcentrationSolid phase extractionNano metal oxidesWater samples

A solid phase preconcentration procedure using hybrid sorbent based on nano zirconium dioxide–boronoxide for the speciation and determination of As(III), As(V) and total As in water samples by hydridegeneration atomic absorption spectrometry (HGAAS) was presented. Experimental parameters including pH,sample volume, flow rate, volume and concentration of eluent that affect the recovery of the arsenic specieshave been optimized. Under optimized experimental conditions, analytical parameters including limit ofdetection, limit of quantification, linear working range, precision and accuracy have also been determined.Interfering effects of matrix constituent on the recovery of the arsenic were studied. The reusability andadsorption capacity of the new hybrid sorbent were also investigated. The hybrid sorbent was successfullyapplied for preconcentration and speciation of arsenic(V) from various samples with recovery of 99±5%. Theanalytical limit of detection was found 9.25 ng/L. The hybrid sorbent was stable up to 100 runs. Adsorptioncapacities of the hybrid sorbent were 98.04 mg/g for As(V). The accuracy of the method was tested byanalyzing certified reference material (SPS-WW1 Waste Water) and spiked real samples. The method hasbeen applied for the determination of analytes in tap water, underground water.

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

In recent years, determination of arsenic species in environmentaland industrial sources has become important due to their toxic effectson human being [1,2]. Arsenic is introduced to the environment andgroundwater from natural and anthropogenic sources and geologicaldeposits containing iron which had trapped arsenic [3,4]. In addition,uncontrolled industrial discharges, use of arsenical agricultural drugssuch as pesticides and herbicides, and power generation from coal orgeothermal sources also contribute to the arsenic contamination [4].Arsenic is known to be one of the most toxic elements and has seriouseffects on plants, animals and human health [5]. Therefore, in nationaland international regulations [6–8], permissible arsenic content ofdrinking water has been reduced from 50 to 10 μg L−1, due to itscarcinogenic nature and other dermal effects. High arsenic concen-trations in natural waters and food samples are now a worldwideproblem. Therefore, many groups are working on remediationtechnologies and determination techniques of total arsenic and/orarsenic species. Arsenic has different chemical forms such as arsenide,arsenate, monomethylarsonic acid, dimethylarsenic acid, arsenobe-taine, arsenocholine, and arsenolipids and arsenosugars [1,5,9].

The actual distribution, mobility, bioavailability, toxicity, bioaccu-mulation, and biodegradability of arsenic depend not only on its totalconcentration but also on its chemical form in the sample. Forexample, while inorganic arsenic species are highly toxic, arsenobe-taine or arsenosugars are harmless to humans. Therefore, to obtaincomplete information on the toxicity, mobility bioavailability, etc. ofarsenic, it is necessary to speciate the different chemical forms oroxidation states. To obtain such information, developing newanalytical methods and strategies are needed due to the speciationinformation is becoming very important.

Except for highly contaminated samples, speciation of arsenic iseven more difficult because of their low content in environmentalsamples. Speciation analysis of arsenic can involve the measurementof discrete chemical compounds [10,11] (e.g., arsenocholine arseno-betaine) or different oxidation states [5] (e.g. As(III) and As(VI)). Thedetermination of oxidation states is important for elements such asAs, Se, and Cr, because toxicity and reactivity can vary with oxidationstate. Determination of different oxidation states of an element maybe performed by electrochemical analysis [12], and separationmethods such as selective coprecipitation [13,14] and complexationwith ligands that are specific for oxidation-states [15].

Since the concentrations of arsenic in water are very low, sensitiveanalytical techniques are generally required. Electrothermal atomicabsorption spectrometry (ETAAS) appears as an attractive apparatusfor such determination because it is a well-established technique

Table 1Experimental conditions of HGAAS.

Parameters Value

Wavelength, nm 193.7Lamb current, mA 10.0Slit width, nm 0.5Background correction (Deuterium lamp) OnConcentration of NaBH4 solution, % (m/v) 0.6 (in 0.5% (m/v) NaOH solution)Concentration of HCl solution, mol L−1 7.0Air and acetylene flow rate, mL min−1 13.5 and 2.1Inert gas type ArgonAscorbic acid concentration, % (m/v) 5.0Concentration of KI solution, % (m/v) 3.0Reading time, s 10Delay time, s 10Signal measurement Peak height

392 H. Erdoğan et al. / Desalination 280 (2011) 391–396

available in practically all laboratories. However, due to the very lowconcentration of arsenic in waters, direct determination and specia-tion of it is difficult by also ETAAS [16]. Therefore, in speciationstudies, combination of a chromatographic separation with varyinginstrumental detection systems such as liquid chromatographyinductively coupled plasma–mass spectrometry (LC–ICP-MS) [17],liquid chromatography–atomic absorption spectrometry (LC–AAS)[18] and liquid chromatography–atomic fluorescence spectrometry(LC–AFS) [19] has been widely used. These techniques are commonlycalled coupled, hybrid, or hyphenated techniques and they are highlyexpensive. Among the atomic spectrometric techniques, hydridegeneration atomic absorption spectrometry presents desirable char-acteristics, such as low costs, easy operation procedure and goodselectivity. However, the direct determination of trace arsenic speciesby this technique is generally difficult because of low concentration ofspecies and possible matrix interference problems. These problemscan be overcome by using preconcentration and/or separationprocedure before the detection procedure. For this reason, samplesare generally treated with separation/preconcentration methodswhich are frequently used for enrichment of ultra trace metals andmetalloids. A number of separation and preconcentration proceduresinvolving cloud point extraction [20,21], liquid–liquid extraction[22,23], solid phase extraction [5,24–26] and coprecipitation [13,14]have been proposed to overcome this problem. Solid phase extraction(SPE) has been used commonly for selective preconcentration ofspecific oxidation states prior to spectrometric determination due toits advantages such as selectivity, easiness, speed, and low consump-tion of chemicals [26].

In the past decades nano scale materials were frequently offered inSPE processes as a solid phase [27-29]. In this work, synthesized nanozirconium dioxide–boron oxide (ZrO2/B2O3) composite material as asolid phase extractor was used for the preconcentration and/orseparation of arsenic species by a column technique prior to itsdetermination by hydride generation atomic absorption spectrometry(HGAAS). According to our literature survey, nano ZrO2/B2O3 has notbeen used for the speciation of As(III) and As(V). A solid-phaseextraction procedure based on speciation of As(III) and As(V) onZrO2/B2O3 has been established. Experimental parameters includingpH of sample, flow rate of sample, sample volume, eluent type,volume and concentration were optimized. Analytical parameterssuch as accuracy, precision, LOD, LOQ and linear dynamic range werealso studied.

2. Materials and methods

2.1. Apparatus

A Varian (Palo Alto, CA, USA) AA240FS model flame atomicabsorption spectrometer equipped with VGA 77 hydride generationsystem, a deuterium-lamp background corrector, arsenic hallowcathode lamp (Varian) and air acetylene flame was used for thedetermination of As under the conditions suggested by the manufac-turer. The operating conditions for HGAAS were given in Table 1. AllpH measurements were made with a WTW 720 model pH meter(Weilheim, Germany). Thermostat shaker (Nüve ST-402, Ankara,Turkey), ultrasonic bath (Sonicator) (Bandelin electronic RK100H,Berlin, Germany) and peristaltic pomp (Watson Marlow 323, MA,U.S.A.) were used for adsorption experiments.

2.2. Reagents and solutions

All reagents were of analytical grade, unless otherwise stated. Allsolutions were prepared in ultra pure water (18.3 μΩ cm). Arsenic(III)and (V) standard (in various concentrations) and model solutionswere prepared by dilution of single element stock solutions(1000 μg/mL, Merck, Darmstadt, Germany) of As(III) and As(V). For

reducing and oxidizing agents, L(+) ascorbic acid (Carlo Erba, Milano,Italy), KI and NaBH4 (J.T. Baker, NJ, U.S.A.), and KMnO4 (Merck) wereused, respectively. Nitric acid (65%), hydrochloric acid (37%),ammonia solution (25%) and solid NaOH were purchased also fromMerck. The laboratory glassware was washed by 5% nitric acidsolution before every use. Afterwards, it was rinsed thoroughly withwater and dried.

2.3. Preparation of hybrid nano zirconium dioxide–boron oxide sorbent

Hybrid nano ZrO2/B2O3 was synthesized by modifying theprocedure given in the literature [26] given for nano aluminasynthesize and characterized by scanning electron microscope(SEM), transmission electron microscope (TEM) and X-ray diffraction(XRD) method [30]. From the SEM and TEM images of hybrid nanoZrO2/B2O3 composite material the ZrO2/B2O3 particles are very fineand the grain size is below 100 nm. According to the XRD pattern, thenanoparticles are identified as crystalline B2O3 and ZrO2. It can berecognized that the synthesized new nanomaterial consisted mainlyof B2O3 and ZrO2 [30].

2.4. Column preparation

A glass column (150 mm length and 8 mm i.d.) having a stopcockat the bottom and a tank of 250 mL on top of the column was used. Asmall amount of glass wool was placed over its stopcock in order tohold the sorbent. 200 mg dry hybrid nano material (ZrO2/B2O3) wasmade slurry in water and then placed into column. Then, anothersmall glass wool plug was inserted onto the top of the sorbent to avoiddisturbance of the adsorbent during sample passage. The column waspreconditioned by passing blank solution having same pH with thesample solution prior to use. After each use, the nano material in thecolumn was washed with diluted HCl (0.5 mol L−1) and water,respectively and stored in water until the next experiment.

2.5. Preconcentration and determination procedure

For the optimization of column separation, preconcentration andspeciation method, 25 mL of spiked sample solutions containing0.05 μg of arsenic species (As(III) and/or As(V))was used. For the totalarsenic determination, firstly As(III) was oxidized to As(V) by theaddition of 0.2 mL of 0.1 mol L−1 KMnO4 solution in acidic medium(pH=2).

The pH of the solution was adjusted to the desired value (pH 3) atwhich the recovery of one species (As(V)) is the highest (above 95%)and the other one (As(III)) is the lowest (below 30%) by the additionof HCl and/or NH3 solutions. The resulting solution was drawnthrough the column by using a peristaltic pump adjusted to thedesired flow rate (3 mL min−1). After washing the column withdistilled water, retained species (As(V)) was eluted with 5 mL of

0

20

40

60

80

100

120

0 2 4 6 8 10 12

% R

(R

eco

very

)

pH

As(V)

As(III)

Fig. 1. Effect of pH on to recovery of As(III) and As(V) [As(III), 2 μg L−1; As(V), 2 μg L−1;sample volume, 25 mL; amount of nano sorbent, 200 mg].

Table 2The effect of type and volume of elution solutions on the recovery of As(V).

Eluent Recoverya (%)

10 mL of 1 mol L−1 HCl 4010 mL of 2 mol L−1 HCl 4010 mL of 3 mol L−1 HCl 10010 mL of 4 mol L−1 HCl 1055 mL of 3 mol L−1 HCl 9510 mL of 1 mol L−1 HNO3 5010 mL of 2 mol L−1 HNO3 5010 mL of 3 mol L−1 HNO3 8010 mL of 4 mol L−1 HNO3 955 mL of 4 mol L−1 HNO3 85

a Mean of the three replicates.

393H. Erdoğan et al. / Desalination 280 (2011) 391–396

3 mol L−1 hydrochloric acid. The eluent was analyzed for thedetermination of total arsenic concentration by HGAAS. For thispurpose, arsenic(V) in the eluent was reduced to As(III) by theaddition of 0.15 g of KI and 0.25 g of L(+) ascorbic acid andwaited 1 hlater. Then, the resulting As(III) was determined by applying HGAASprocedure.

For the determination of As(V) alone, the above procedure wasapplied directly except the oxidation procedure. Then, the concen-tration of As(III) was calculated by subtracting the concentration of As(V) from total arsenic concentration. The optimum conditions forseparation of As(III) from As(V) and for preconcentration of As(V)have been determined by using the general procedure given above.

The column has been used repeatedly after washing with 10 mL of3 mol L−1 hydrochloric acid and water, respectively. Using the proce-dure described above, the recovery of arsenic species was calculatedfrom the following equation:

analyte concentration in eluent ðfound by AASÞðμg=mLÞ × volumeofeluentðmLÞanalyte concentration insamplesolutionðknownÞðμg=mLÞ × volumeofsamplesolutionðmLÞ

× 100

2.6. Collection and preparation of samples

Tapwater sampleswere collected from the laboratory of chemistrydepartment. Underground hot spring water samples were collectedfrom Ayaş, Beypazarı and Haymana town in Turkey. The temperaturesand pH's of the underground hot spring water samples weremeasured on-site. Temperature and pH values of the water samplesobtained from Ayaş, Beypazarı and Haymana were 52, 50, 44 °C and 7,6.5, 6.5, respectively. The water samples were acidified on-site withnitric acid so that the acid concentration is to be about 1% (v/v). Ayaşhot spring water is used for both drinking and bathing, while theothers are used only for bathing for various sickness such asrheumatism, neuralgia, gynecologic and digestive disorders. Aftertransferring the water samples to the laboratory, they were filteredthrough a membrane filter (Millipore) of 0.45 μm pore size and thegeneral procedure given in Section 2.5 was applied. The levels ofarsenic in the water samples were determined by hydride generationatomic absorption spectrometry (HGAAS). Total arsenic in watersamples was determined as As(V) after oxidizing As(III) to As(V). Theoxidation of As(III) to As(V) was performed in the procedure given inSection 2.5. Sample blanks were also prepared by applying theprocedure given above by taking water instead of sample. Solution ofcertified reference materials (SPS-WW1 Waste Water) were alsoprepared by the procedure given above for water samples.

3. Results and discussion

To demonstrate the nano character and to determine crystallinestructure of synthesized material, the characterization of synthesizedmaterial has been performed first. Then, the applicability of thematerial as solid phase extractor has been tested.

In order to obtain optimum speciation conditions and maximumrecoveries, some experimental parameters such as the pH of samplesolution, type and concentration of elution solution, volume of samplesolution and flow rate of sample solution have been optimized.Interfering effects, reusability of hybrid sorbent and adsorptionisotherms have also been studied. The analytical parameters such aslimit of detection (LOD), limit of quantitation (LOQ), precision,accuracy and linear working range have been determined in optimalexperimental conditions.

3.1. Effect of pH of sample solutions

The pH value plays an important role to adsorption of the ions ontosorbents. It strongly influences the sorption availability of the metal

ions. Therefore, pHwas the first optimized parameter. The recovery ofthe As(III) and As(V) was determined separately by applying thegeneral procedure (Section 2.5) by changing the pH of model solutionin the range of 1–10. pH of the model solutions was adjusted todesired values with diluted hydrochloric acid (0.1 mol L−1) and/orammonia solution (0.1 mol L−1). The variation in recovery of As(III)and As(V) with pH is shown in Fig. 1. These results reveal that at pH2.0–3.0, while the quantitative recovery (above 95%) was achieved forAs(V), the lower recovery (below 5%) was obtained for As(III). Hence,pH 3 was selected as an optimum pH for the speciation of As(III) andAs(V) and solid phase extraction of the As(V) for subsequentexperiments.

3.2. Effect of eluent type and concentration

The type and concentration of eluent are other importantparameters for such studies. In order to determine type and amountof elution solution, 25 mL of model solutions containing 0.05 μg As(V)was used. pH of the solutions was adjusted to 3 and the generalprocedure (Section 2.5) was applied. For the elution process, HCl andHNO3 solutions having various concentrations and various volumeswere tested. As a result of experiments, 5 mL of 3 mol L−1 HClsolution and 10 mL of 4 mol L−1 HNO3 that give maximum recoverywere found as optimal eluent solutions to desorption of As(V) on thehybrid nano sorbent. These results were given in Table 2. Because thevolume of eluent is important for the high concentration factor (thelower eluent volume leads the higher preconcentration factor), 5 mLof 3 mol L−1 HCl was selected as eluent for subsequent experiments.

3.3. Effect of the sample flow rate

The influences of flow rates of sample solution on the recovery ofarsenic species (As(V) and As(III)) were also investigated bycontrolling the flow rate of sample solution with peristaltic pump.Flow rate of sample solution is another important parameter that

0

20

40

60

80

100

0 1 2 3 4 5

% R

(R

eco

very

)

Flow rate (mL/min)

As(III)As(V)

Fig. 2. Effect of the sample flow rate on the recovery As species [As(III), 2 μg L−1; As(V),2 μg L−1; sample volume, 25 mL; amount of nano sorbent, 200 mg].

y = 0.0102x + 0.481R² = 0.9932

0

1

2

3

4

0 50 100 150 200 250

Ce/

Qe

(g/L

)

Ce (mg/L)

Fig. 4. Linearized Langmuir adsorption isotherm of As(V) on hybrid nano ZrO2/B2O3.

394 H. Erdoğan et al. / Desalination 280 (2011) 391–396

affects the retention of the analytes on the sorbent. It does not onlyaffect the retention of the analytes, but also controls the duration ofanalysis. Because a large volume of sample solution is needed forobtaining high preconcentration factor, it is always expected thatsample solution can be passed through the column at higher flowrates without reducing the recovery. Therefore, the effect of flow rateof sample solutions on the recoveries of arsenic species was examinedin the range of 1–4 mL min−1. Under optimum conditions (pH, 3;eluent, 5 mL of 3 mol L−1 HCl), As(V) was quantitatively recovered upto 3 mL min−1 of the flow rates (Fig. 2). Above 3 mL/min the recoverywas decreased gradually due to the lower contact time of analytes andsorbent. This result indicates that As(III) and As(V) could be separatedby applying the sample flow rate of 3 mL min−1. Because the eluentvolume was very low (5 mL), the effect of flow rate of eluent has notbeen studied and selected directly as 1 mL min−1.

3.4. Effect of volume of sample solution

Another parameter investigated to find the best experimentalconditions is the volume of sample solution and/or analyte concen-tration. In order to determine the maximum applicable samplesolution (or minimum analyte concentration), the effect of thevolume of sample solution on the recovery of the As(V) wasinvestigated by using model solutions and by applying generalprocedure mentioned above (Section 2.5). For this purpose, As(V)was preconcentrated from sample volumes of 25, 50, 100, 250 and500 mL containing 0.1 μg As(V) corresponding to concentration of 4.0,2.0, 1.0, 0.4 and 0.2 μg L−1, respectively. The recovery of As(V) wasquantitative (N 95%) for sample volumes up to 100 mL. After thepreconcentration of 100 mL sample solution, if 5 mL of eluent solutionwas used for the analysis, the preconcentration factor was found to be20 for As(V). As a result, it can be concluded that 1 μg L−1As(V) couldbe determined by applying this preconcentration method.

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300 350

Qe

(mg

/g)

Ce (mg/L)

Fig. 3. Adsorption isotherm of As(V) on hybrid nano ZrO2/B2O3.

3.5. Reusability of the sorbent

The stability and potential reusability of the hybrid nano nanoZrO2/B2O3 were assessed by monitoring the change in the recoveriesof the As(V) through several adsorption–elution cycles. The passage of25 mL of the 2 μg L−1As(V) solution, 5 mL of 3 mol L−1 HCl and 50 mLof ultra pure water through the column packed with 200 mg of hybridsorbent, respectively, was considered one adsorption–elution cycle.The adsorbent was always stored in water when it was not in use. Itwas observed that the column could be reused up to about 100 timeswithout decrease in the recoveries of the As(V).

3.6. Influence of foreign ions

The preconcentration procedures and thus the recovery of arsenicspecies may be affected by the other constituents of the samples. Forthis reason, the reliability of the proposed method should beexamined in the presence of possible interfering ions of the samples.To investigate the effect of other constituent on the recovery of As(V),the possible interfering elements (Na+, K+, Ca2+, Mg2+, Ni2+, Cu2+,Al3+, Cr3+, Fe3+, Mn2+ and Co2+) were added to 25 mL of modelsolutions containing 0.05 μg of As(V) (2 μg L−1), as their nitrate orchloride salts. Interfering ion concentrations causing±5% deviation inrecovery of the As(V) is considered as the tolerance limit. The resultsshow that there was no any influence below the tolerance limit of50 mg L−1 for K+ ions, 25 mg L−1 for Ca2+, Mg2+, Ni2+, Cu2+, Al3+

and Cr3+ ions, and 5 mg L−1 for Fe3+, Mn2+ and Co2+ ions on therecovery of As(V). It was found that Na+ ions interfere with thedetermination of arsenic at a concentration of above 1 mg L−1 when itwas used as its chloride salt. To increase the tolerance limit, sodiumwas added as its nitrate salt and 10 mL of 4 mol L−1 HNO3was used asan eluent instead of 3 mol L−1 HCl. As a result, the tolerance limit forNa+ ions could be increased up to about 50 mg L−1. Ratio ofconcentration of the elements having lower tolerance limits, such asFe3+, Mn2+ and Co2+ to the concentration of arsenic is about 2500.These results show that the proposed hybrid nano ZrO2/B2O3 as solidphase extractor could be applied for the speciation of As(III) and As(V)and preconcentration of As in the various water samples that containsother metal ions at mg L−1 levels.

Table 3Determination of total arsenic in certified reference material.

Certified reference material Certified valueng mL−1

Found valuea

x±(ts/√N)ng mL−1

Relative error, %

SPS-WW1 Batch 109b 100.0±0.5 95±1 −5.0

a Mean of three replicates at 95% confidence level.b Concentration of elements in SPS-WW1 Wastewater sample: Al, 2000; As, 100.0;

Cd, 20.0; Co, 60.0; Cr, 200; Cu, 400, Fe, 1000; Mn, 400; Ni, 1000; P, 1000; Pb, 100; V, 100;Zn, 600 ng mL−1.

Table 4Determination of arsenic species in various hot spring water and tap water samples.

Samples Added,μg L−1

Founda, μg L−1 Relative error, %

As(V)

As(III)

As(V) As(III)b Total As As(V)

As(III)

TotalAs

Beypazarı – – 4.03±0.05 3.77±0.05 7.8±0.2 – –

Springwater

2 2 6.21±0.05 5.1±0.2 11.3±0.2 +3 −12 −4

Ayaş – – 2.11±0.02 12.2±0.6 14.3±0.6 – –

Springwater

2 2 4.3±0.1 14.7±0.3 19.0±0.3 −5 +4 +4

Haymana – – 0.97±0.03 1.25±0.06 2.22±0.05 – –

Springwater

2 2 3.09±0.09 3.3±0.1 6.37±0.06 +4 +2 +2

Tap water – – 0.52±0.03 0.81±0.09 1.33±0.09 – –

2 2 2.7±0.1 2.6±0.1 5.32±0.08 +7 −7 −1

a Mean of three determinations±standard deviation.b Calculated value.

Table 5Comparison of some reported procedures.

Method Technique pH PF LOD, ng L−1 Ref.

ETAAS CPE 2.0 52.5 10 [20]ETAAS SPE 10.0 50 24 [33]FI-HGAAS SPE 3.0–10.0 7 150 [34]HGAFS SPE 10.0–11.0 33.3 1 [35]HGAAS SPE 2.5 10 20 [36]HGAAS SPE 6.0 36 13 [5]HGAAS SPE 3.0 20 9.25 This study

PF: Preconcentration factor, LOD: Limit of detection, CPE: Cloud point extraction, SPE:Solid phase extraction, ETAAS: Electrothermal atomic absorption spectrometry, FI-HGAAS: Flow Injection hydride generation atomic absorption spectrometry, HGAFS:Hydride generation atomic fluorescence spectrometry, HGAAS: Hydride generationatomic absorption spectrometry.

395H. Erdoğan et al. / Desalination 280 (2011) 391–396

3.7. Adsorption isotherm and adsorption capacity

The adsorption isotherm of the arsenic(V) onto hybrid nanoZrO2/B2O3 composite material was also investigated by the batchtechnique described in Ref. [31]. The adsorption isotherms were usedto characterize the interaction of each analyte ions with theadsorbent. Among the several isotherm equations, Langmuir adsorp-tion isotherm which is valid for monolayer adsorption onto a surfacewith a finite number of identical sites and based on the assumption ofsurface homogeneity was investigated. The adsorption isotherm andadsorption capacity of the synthesized nano hybrid sorbent for As(V)were studied by using the batch method. To obtain adsorptionisotherm and determine the adsorption capacity, the followingexperimental parameters were used: Amount of resin, 50 mg; pH ofthe solution, 3; volume of sample solution, 50 mL; arsenic concen-trations, 5, 10, 25, 50, 100, 200 and 300 mg L−1. The solutions wereshaken for 2 h at 120 rpm at room temperature to reach equilibrium.Then, 10 mL of solution was taken from each solution and the amountof residual arsenic(V) in the solution was determined by HGAAS. Thedata of the isotherm reveal that the adsorption process conforms tothe Langmuir model. In Fig. 3, the graph demonstrated an excellent fitto the data in the concentration interval studied in all cases for theLangmuir model. A modified Langmuir equation conformed to thiskind of adsorption isotherm as represented below:

CE

QE=

CE

Q0+

1Q0 b

Where, Qo (mg g−1) is the maximum amount of the sorbed ionsper unit mass of sorbent (capacity parameter) to form a completemonolayer coverage on the surface, CE (mg L−1) is the equilibriumconcentration of analytes, QE (mg g−1) is the amount of analyte ionsadsorbed per unit mass of sorbent at equilibrium and b (L mg−1) isthe Langmuir constant related to the affinity of binding sites and ameasure of the stability of the bond formed between metal ions andadsorbent under specified experimental conditions.

Based on the linear form of the adsorption isotherm derived fromplots of Ce/Qe versus Ce, the constant Q0 values were calculated fromthe slope of the graph given in Fig. 4. The value of Q0 is found to be98.04 mg g−1. The Langmuir constant is 0.021 L mg−1 and r is 0.9997.

3.8. Analytical figures of merits

As analytical figures of merit, limit of detection (LOD), limit ofquantitation (LOQ), precision and accuracy for the proposed pre-concentration and speciation method have been determined. In orderto determine the instrumental detection limit for As(V), 50 mL ofblank solution was passed through the column under the optimumexperimental conditions (pH=3; eluent, 5 mL of 3 mol L−1 HCl, flowrate, 3 mL min−1). Blank solutions were prepared by adding aminimum amount of the As(V) to the water in order to obtainreadable signal. The sorbed As(V) was eluted by 50 mL of 3 mol L−1

HCl solution (there is no preconcentration) and signal of this blanksolution were measured about 20 times. The instrumental detectionlimit of the As(V) based on the ratio of three standard deviation of theblank signal to slope of the calibration curve (3 s/m) was found as0.185 μg L−1. The analytical detection limit calculated by dividing theinstrumental detection limits by the preconcentration factor (20) was9.25 ng L−1. The limit of quantitation (LOQ) based on 10 s/m was30.85 ng L−1 for As(V) [32].

The linearworking ranges for theAs(V)was foundas0.03–40 μg L−1

by considering the LOQ values as lower limit with a correlationcoefficient of about 0.9998. Regression equation was A=0.07478C+1.5254 (A: absorbance, C: concentration of arsenic(V) in μg L−1).

The precision of proposed method evaluated as the standarddeviations of recovery obtained from five replicates under optimumexperimental conditions (amount of As(V), 0.05 μg; volume of modelsolution, 25 mL; pH, 3.0; elution solution, 5 mL of 3 mol L−1 HCl; flowrate, 3 mL/min) were 99±5% for As(V).

The accuracy of the proposed method was tested by determiningthe content of arsenic(III) and arsenic(V) ions in the certifiedreference materials (SPS-WW1 Waste Water (batch 109)) underoptimal experimental conditions. As seen in Table 3, the determinedvalues were in good agreement with the certified values. The relativeerror was found about 5%.

3.9. Application of proposed method

The proposed preconcentration and/or speciation method wasapplied for determination of As(III) and As(V) in tap water andunderground water samples, under optimal experimental conditions.The accuracy of method was also checked by measuring the recoveryof As(III) and As(V) in spiked real samples. A good agreement wasobtained between added and found value of the arsenic species andtotal arsenic. The results obtained are given in Table 4. Relative errorsbelow 10%, demonstrate the applicability and feasibility of presentedspeciation method, and independence frommatrix constituents of thesamples. These results show that the present speciationmethod couldbe applied for the determination of total arsenic as As(V).

4. Conclusion

A simple, accurate, rapid, precise and economic preconcentrationand/or speciation procedure for arsenic ions (As(III) and AS(V)) basedon the sorption on hybrid nano ZrO2/B2O3 for the hydride generationatomic absorption spectrometric (HGAAS) determination is described.

396 H. Erdoğan et al. / Desalination 280 (2011) 391–396

The speciation of inorganic arsenic ions is possible only by adjusting thepH and flow rate of sample solution. Hybrid nano ZrO2/B2O3 sorbent isenvironment-friendly, low-cost and having sufficiently high adsorptioncapacity. The hybrid nano sorbent was stable up to 100 cycles, withoutmajor loss in its quantities and arsenic(V) recovery property. Thematrixeffects appeared with the use of the proposed method reasonablytolerable. Quantitative recoveries sufficient for analytical purposeswereobtained with using this method. Another advantage of the method ispermitting to study in acidicmedia thatminimize possible precipitationof metal hydroxides. The enrichment factor, detection limit andadsorption capacity of the new sorbents for As(V) are also satisfactory.The analytical performance of the hybrid nano sorbent is comparablewith the other conventional sorbents (Table 5).

Acknowledgment

The authors are grateful for the financial support of Gazi UniversityScientific Research Projects Unit (Project No. 05/2009-18).

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