Determination of Vanadium in Food Samples by Cloud PointExtraction and Graphite Furnace AtomicAbsorption Spectroscopy

Hayati Filik & Duygu Aksu

Received: 23 March 2011 /Accepted: 16 May 2011 /Published online: 28 May 2011# Springer Science+Business Media, LLC 2011

Abstract A preconcentration methodology utilizing thecloud point phenomenon is described for the determinationof total vanadium by graphite furnace atomic absorptionspectrometry. Cloud point extraction method was based onthe formation of a ternary complex between vanadium,2-(2´-thiazolylazo)-p-cresol, and ascorbic acid, with subse-quent extraction–preconcentration of the formed complexesusing Triton X-100. Optimization of different parameterswas evaluated. Under optimal conditions, a calibrationcurve was constructed, showing a linear range of 1.0–60 ng mL−1 and the limit of detection and relative standarddeviation for preconcentration of a 10-mL sample werefound to be 0.05 ng mL−1 and 3.9%, respectively. Thepreconcentration factor was found to be tenfold for 10 mLof water sample. The technique has been applied succes-fully to the determination of vanadium traces in wine, tea,and tomato samples and the recoveries of added vanadiumwere in the range 96–102%.

Keywords Vanadium determination . Cloud point extraction .

Atomic spectroscopy. 2-(2´-thiazolylazo)-p-cresol .

Food analysis

Introduction

Vanadium mainly enters the environment from naturalsources and from the burning of fuel oils and coal. Theburning of petroleum fuels and coal releases vanadium into

the air, that then settles on the soil. Vanadium concen-trations in natural waters can range from 10 to 40 nM (Vegaand van den Berg 1994) and are a good indicator of urbanpollution levels (Ensafi et al. 2008). Vanadium is normallyfound in ultra trace amounts in different food (Bermejo-Barrera et al. 2000). In breast milk, the content (Myron etal. 1978) is between 0.1 and 0.2 μg kg−1, equivalent to anintake of 0.1–0.2 μg/day (López-García et al. 2009a, b).Levels in drinks, fat, oil, fruit juices, and vegetables are inthe range 1–5 μg kg−1. Cereals, fish, meat, and milk-derived products have concentrations of 5–30 μg kg−1.Vanadium levels range from 7.0 to 90.0 μg L−1 in red andfrom 6.6 to 43.9 μg L−1 in white wines (Teissèdret et al.1998). It is important to monitor food and beverages formetallic elements that may be toxic when their concen-trations exceed recognized safe levels.

Several analytical methods have been developed for thedetermination of V at low concentrations, among them,catalytic spectrophotometry and neutron activation analysis,inductively coupled plasma mass spectrometry (ICP-MS),ICP atomic emission spectrometry (AES), and graphitefurnace atomic absorption spectrometry (GFAAS) (Chenand Owens 2008; Pyrzyńska and Wierzbicki 2004).Although ICP-AES or GFAAS are the most used techni-ques in the determination of traces of vanadium, the lowlevel of vanadium concentration in water is not compatiblewith the detection limit of these techniques. In order toachieve accurate, reliable, and sensitive results, preconcen-trations and separations are needed when the concentrationsof analyte elements in the sample are too low to bedetermined directly by GFAAS. Preconcentration proce-dures using several analytical separation techniques havebeen proposed (Chen and Owens 2008; Pyrzyńska andWierzbicki 2004; Moyano et al. 2006; Amina et al. 2009;López-García et al. 2009a, b). Cloud point extraction (CPE)

H. Filik (*) :D. AksuFaculty of Engineering, Department of Chemistry,Istanbul University,34320 Istanbul, Turkeye-mail: filik@istanbul.edu.tr

Food Anal. Methods (2012) 5:359–365DOI 10.1007/s12161-011-9254-9

is one of these. The separations and preconcentrations ofmetal ions, after the formation of sparingly water-solublecomplex, based on CPE have been largely employed inanalytical chemistry. The cloud point procedure offersconvenience and simplicity when compared with liquid–liquid extraction modality, including higher extraction andpreconcentration factors, lower cost, and lower toxicity forthe analyst and the environment. The procedure is based onthe properties of non-ionic or amphoteric surfactants atlevels upper to their critical micellar concentrations (CMC).Above CMC, a system composed by a unique phase isseparated into two isotropic phases if some condition suchas temperature or pressure is changed or if an appropriatesubstance is added to the solution. For a more detaileddiscussion about CPE phenomenon, it is recommended toconsult the literature (Hinze and Pramauro 1993; Stalikas2002; de Almeida Bezerra et al. 2005; Paleologos et al.2005; Silva et al. 2006; Tani et al. 1997; Sanz-Medel et al.1999). To date, CPE as a preconcentration step inconjunction with detection by spectrphotometry (Madrakianet al. 2011), flow injection spectrofluorimetry (Paleologos etal. 2001), flow injection-inductively coupled plasma opticalemission spectrometry (Wuilloud et al. 2002), GFAAS(Ohashi et al. 2007; Khan et al. 2010; Zhu et al. 2008),FAAS (Filik et al. 2008) for the determination of vanadiumhave been reported.

The 2-aminothiazole derivatives, called thiazolylazodyes, are an important class of organic complexingreagents. The main applications of thiazolylazo dyes inchemical operations include spectrophotometry, solid phaseextraction, liquid chromatography, electrochemistry, andliquid–liquid and cloud point extraction. The application ofthiazolylazo dyes in spectrophotometry is based on thecolored compounds resulting from their reaction with mostmetals, especially some transition metals (Lemos et al.2007). Among these compounds, 2-(2′-thiazolylazo)-p-cresol (TAC), 4-(2´-thiazolylazo)resorcinol, and 1-(2′-thiazolylazo)-2-naphthol are the most widely used reagents.In the developed system, TAC was used as the chelatingagent in CPE method. TAC is a bidentate ligand and it isprobable that the VO(TAC)2 complex accepts ascorbic acid(AA) as the sixth ligand forming the VO(TAC)2.AAcomplex. The presence of AA is fundamental to increasethe determination sensitivity and stability (Teixeira et al.1998). Usually, stable chelates are produced.

The aim of this work is to combine CPE with GFAASand developed a new method for the determination of tracevanadium in water samples. This paper proposes a methodfor preconcentration and determination of vanadium byGFAAS based on CPE of the complex of vanadium withTAC in TX-100 surfactant media. The preconcentration andcombination parameters of CPE/GFAAS technique wereinvestigated. The analyte in surfactant-rich phase was

determined by GFAAS with ascorbic acid as the matrixmodifier. The method was applied for the determination oftotal vanadium in several real and spiked samples withsatisfactory results.

Experimental

Apparatus

All atomic absorption spectrometry measurements wereperformed with a graphite furnace atomic absorption spectro-photometer (Model AA-6701-F, Shimadzu, Kyoto, Japan),using deuterium arc background correction, were employed tomeasure V. Argon was used as the purge and protective gas.Measurements were made by using hallow cathode lamps(Shimadzu, Kyoto, Japan) of V at 318.4 nm wavelengths.Pyrolitycally coated tubes without platform were used. Thework condition of graphite furnace atomic absorptionspectrophotometer was listed in Table 1. The pH values ofthe solutions were measured by a Hanna HI 221 pH meterusing the full pH range of 0−14. A thermostated bathmaintained at the desired temperature was used for cloudpoint temperature experiments and phase separation wasassisted using a centrifuge (Hettich, Tuttlingen, Germany).

Reagents and Solutions

The non-ionic surfactant Triton X-100 was obtained fromSigma (St. Louis, MO, USA) and used without futherpurification. Stock standard solution of V(vanadium (IV))(1.0×10−3 mol L−1) was prepared by dissolving vanadylsulfate trihydrate in 1.0×10−2 mol L−1 hydrochloric acid.Stock standard solution of V(V) (1.0×10−3 mol L−1) wasprepared by dissolving ammonium metavanadate in 1.0×10−2 mol L−1 hydrochloric acid. Working standard solutionswere obtained by appropriate dilution of the stock standardsolutions. TAC (Sigma-Aldrich, St. Louis, MO, USA)solution (1.0×10−3 mol L−1) was prepared by dissolvingappropriate amount of this reagent in 1.0×10−2 mol L−1

NaOH. Ascorbic acid solution (1.0%) was prepared by

Table 1 Operating conditions for GFAAS

Wavelength/nm 318.4

Slit/mm 0.4

Hallow cathode lamps (HCL)Current/mA

5

Dry temperature/°C 120 (ramp 10 s, hold 20 s)

Ashing temperature/°C 1,400 (ramp 10 s, hold 20 s)

Atomization temperature/°C 2,700 (ramp 0 s, hold 5 s)

Cleaning temperature/°C 2,700 (ramp 0 s, hold 2 s)

Injected volume/μL 20

360 Food Anal. Methods (2012) 5:359–365

dissolving 1.0 g (Merck) in 100 mL of distilled water. Thefollowing buffers were used to control the pH of thesolutions: sodium acetate-acetic acid (pH 3–6), ammoniumacetate–ammonia (pH 6–8).

Preparation of Samples

Turkish wine samples were obtained from the wineries andjust filtered without any further treatment. The digestion ofwine samples was performed by treating 10 mL winesample with 3 mL conc. HNO3 and 5 mL H2O2. Aftercomplete digestion, the sample was made up to 100 mL.Suitable aliquots (5 mL) of this solution were taken andanalyzed for V(V) using the proposed procedure.

For the analysis of vanadium in food (tea and tomato)samples, about 1.0 g of the dried sample was first ashed for6 h at 500 °C in a crucible. After cooling, the residue wascarefully moistened with 5 mL of 6 mol L−1 HNO3 and themixture were heated on a hotplate to near dryness. Theresidue was dissolved in 25 mL of distilled water and thesolution was filtered using filter paper (Whatman no. 1).The filtration was collected into a 100.0 mL volumetricflask and diluted to the mark with distilled water. Suitablealiquots (5 mL) of this solution were taken and analyzed forV(V) using the proposed procedure.

Analytical Procedure

An aliquot of a V(IV) standard solution (1–60 ng mL−1) wastransferred to a 10 mL centrifuge tube, 2 mL of 1.0×10−3 mol L−1 TAC, 1.0 mL of 1.0% (w/v) AA, 1.0 mL ofacetate buffer solution (pH 5.0) and 1.0 mL of 10% TX-100(v/v) were added. The mixture was diluted with to 10 mL,with distilled water. The resultant solution was heated in aboiling water bath for 5 min (i.e., V(IV)-TAC-AA complexformation). The phase separation was accelerated bycentrifuging the test tubes for 5 min at 4000 rpm. Aftercooling in ice bath, the surfactant-rich phase became aviscous and was retained at the bottom of the tube. In thisway, the bulk aqueous phase was easily decanted and anyresidual aqueous phase was removed with a pipette. Theremaining miceller phase was dissolved in 0.3 mL of amethanolic of 1.0 mol L−1 HNO3 in order to reduce itsviscosity. Of the diluted exract, 20 μL was injected directlyinto the furnace for GFAAS determination of V. A blanksubmitted to the same procedure was measured parellel tothe samples and calibration solutions.

Results and discussion

In order to find the optimum experimental condition, theparameters affecting the proposed reaction, micelle formation,

and the absorbance signal of vanadium in GFAAS analysis,such as pH, surfactant and chelating agent concentration,temperature, incubation time, temperature program ofGFAAS, and nature of modifier were investigated.

Effect of pH

Depending on the pH, thiazolylazo reagents exist in solutionin certain forms. For example, acidic solutions of TAC containthe water-soluble protonated H2R

+ ion. At neutral andslightly acid or basic solutions, TAC occurs as the neutralHR molecule soluble in organic solvents. In basic solutions,TAC exists as the water-soluble R− anion. The pH plays aunique role on metal chelate formation and subsequentextraction and constitutes the main parameter for CPE. Theeffect of pH on the recovery of the V(IV)-TAC-AA complexsystem using 3.0 mg mL−1 vanadium was investigated in therange of 2.0–8.0 (Fig. 1). Maximum vanadium recovery wasobtained at pH 5.0–6.0. Figure 1 shows the effect of pH onthe extraction recovery of V. In more acidic and morealkaline solutions, recovery decreased because of incompletecomplex formation and possible degradation of the complex(due to fast oxidation of VO(OH)+ species with dissolvedoxygen (O2)) at elevated pH (Wehrli and Stumm 1989),respectively, so the vanadium recovery was lower. Moreover,ascorbic acid, a constituent of the ternary complex, is knownto be most susceptible to oxidative degradation at increasedpH. Owing to these properties, a pH value of 5.0 wasselected as the working value. It has been reported thatoptimal pH range of ternary chelate formation between V(IV), TAC and AA in aqueous solution was 4.6–6.0 (Wehrliand Stumm 1989).

Effect of TAC Concentration

Under the optimum pH, the variation of the analyticalsignal as a function of the chelating agent concentration

3 4 5 6 7 8 90

20

40

60

80

100

Rec

ove

ry %

pH

Fig. 1 Effect of pH on the extraction recovery 3.0 ng mL−1 V(IV),1.0 mL of 10% TX-100 (v/v); TAC, 2.0×10−4 mol L−1; temperature,100 °C

Food Anal. Methods (2012) 5:359–365 361

was evaluated for V(IV) complex formation during the CPEprocedure. Figure 2 shows the variation of recovery overthe TAC concentration range when 10 mL of solutioncontaining a fixed amount of V(IV) at pH 5.0 in thepresence of 1.0 mL of 10% Triton X-100 (v/v) wassubjected to CPE. Concentration of TAC was varied inthe range of 5.0×10−5–5×10−4 mol L−1. The V(IV)recovery increased up to a TAC concentration of 2.0×10−4 mol L−1 for V(IV), thereafter reached a plateau. Theaddition of an excess of chelating agent was required inorder to compensate for the consumption of the usedchelating agent in reaction with other metals, and thisexcess did not have any adverse effect on the CPE system.In this work, 4.0×10−4 mol L−1 was used as optimum TACconcentration.

Effect of TX-100 Concentration

Triton X-100 has been used as surfactant for CPE ofvanadium, after the formation of a complex with TAC.The amount of TX-100 not only affected the extractionefficiency but also the volume of surfactant-rich phase.So, the changes of the extraction efficiency affected byamount of 10% TX-100 solution was investigated withina TX-100 volume range of 0.2–2.0 mL. The experimen-tal results showed that the extraction efficiency in-creased with the amount of TX-100 up to a volume of1.0 mL, a plateau appeared between 1.0 and 1.5 mLwhere the extraction efficiency remained nearly con-stant, and finally above 1.5 mL, efficiency decreased(Fig. 3). Therefore, 1.0 mL of 10% Triton X-100 (v/v)was used in subsequent experiments. An increase in thesurfactant amount also increases the volume of thesurfactant-rich phase obtained after centrifugation of thesamples. This phase is therefore more diluted when higheramounts of surfactants are used, resulting in a loss ofrecovery.

Effect of Ascorbic Acid

Effect of ascorbic acid concentration on the extractionand determination of vanadium was investigated. Thepreconcentration efficiency was evaluated using AAconcentrations ranging from 0.025% to 0.3% (w/v). Thehighest recovery was obtained with 0.1% (w/v) AA. Bydecreasing the AA concentration below 0.1% (w/v), thepreconcentration efficiency was reduced. At higher con-centrations, the efficiency of the ternary complex isconstant. The results are shown in Fig. 4. Thus, an AAconcentration of 0.1% (w/v) was used in further experi-ments. Ascorbic acid behaves as a reductant, thus it mustalways be added before the buffer addition as the acidmedium increases V(V) reduction. AA or vitamin C haslong been used in the wine industry as an anti-oxidant, thereason being the ability of AA to rapidly removemolecular O2 from juice or wine. Measurement ofvanadium in wine samples containing high levels ofascorbic acid. Vanadium(IV), as the vanadyl cation VO2+,may be present in reducing environment.

0.0 0.5 1.0 1.5 2.0 2.5 3.00

20

40

60

80

100

Rec

ove

ry %

Triton X-100 (% v/v)

Fig. 3 Effect of TX-100 concentration on the extraction recovery.Reaction conditions, V(IV) 3.0 ng mL−1; TAC, 2.0×10−4 mol L−1;temperature, 100 °C

0 1 2 3 40

20

40

60

80

100

Rec

ove

ry %

TAC concentration (x10-5 mol L-1)

Fig. 2 Effect of TAC concentration on the extraction recovery.Reaction conditions, V(IV) 3.0 ng mL−1; 1.0 mL of 10% TX-100 (v/v); temperature, 100 °C

0.0 0.2 0.4 0.6 0.8 1.00

20

40

60

80

100

Rec

ove

ry %

Ascorbic acid concentration (% w/v)

Fig. 4 Effect of AA concentration on the extraction recovery.Reaction conditions, V(IV) 3.0 ng mL−1; TAC, 2.0×10−4 mol L−1;temperature, 100 °C

362 Food Anal. Methods (2012) 5:359–365

Equilibration temperature and time

The reaction rate of ternary (V(IV)-TAC-AA) complexformation was slow at room temperature, and colordevelopment was complete after 30 min. Warming thesolution in a boiling water bath increased the reactionrate greatly. Excellent recovery of V(IV)-TAC-AA com-plex was obtained for an equilibration temperature from80 to 100 °C. A temperature of 100 °C was selected inorder to accelerate the required metal–ligand complexformation. The dependence of recovery upon incubationor complexing time was studied in the range of 2–10 min, where a complexing time of 5 min was selectedas optimal (Fig. 5). Thus, equilibration at 100 °C for5 min was adequate to achieve quantitative extraction. Thecentrifugation time was examined in the range of 1–10 min at 4000 rpm. A time of 5 min was selected asoptimum, since complete phase separation occurred withinthis time period and no appreciable improvements wereobserved for larger times.

Effect of the Viscosity on the Analytical Signal

Since the surfactant-rich phase obtained after cloud-pointextraction is rather viscous, methanol containing1.0 mol L−1 HNO3 was added to the surfactant-rich phaseafter separation of the phases in order to facilitate itsintroduction into nebulizer of the spectrometer. Anoptimal volume of 0.3 mL of a methanolic solution of1.0 mol L−1 HNO3 was added to the remaining micellerphase (final volume 1.0 mL). This added volume ofmethanol was selected in order to ensure a sufficientvolume of the sample for aspiration. The surfactant-richphase can be easy introduced into the graphite furnaceafter dilution with 0.1 mol L−1 HNO3 and directlydetermined by GFAAS.

Selection of Modifier and Optimum Furnace TemperatureProgram

Vanadium is a refractory element; meanwhile, it is acarbide-forming element and its atomization is carriedout at very high temperatures in the graphite tube. Theatomization efficiency could be obviously improved byincreasing the atomization temperature, but at the sametime, the deterioration of graphite tube occurred andfrequently changes of graphite tubes were required(Khan et al. 2010). In order to attain best conditions(highest sensitivity besides lowest background) for themethodology, studies about the effects of several varia-bles (evaluation of pyrolysis and atomization temper-atures, type of chemical modifier, concentration ofmodifier and pyrolysis time) and the convenient calibra-tion strategy were performed. The use of various chemicalmodifiers for determination of V by GFAAS was studied.In this study, several modifiers, including ascorbic acid,EDTA, citric acid, and NH4NO3 were tested for bestsignals of vanadium. In this paper, ascorbic acid was usedas matrix modifier. Figure 6 shows the pyrolysis andatomization curves for V(IV). Obviously, from Fig. 6, itcould be seen that ascorbic acid and Triton X-100 was aquite effective matrix modifier for the determination ofvanadium. The atomization efficiency could be obvious

500 1000 1500 2500 30000.00

0.04

0.08

0.12

Ab

sorb

ance

Temperature (OC )

a b

Fig. 6 Ashing curve (a) and atomization curve (b) for the cloud pointextraction of 3.0 ng mL−1 V(IV). CPE conditions, 1.0 mL of 10% TX-100 (v/v); TAC, 2.0×10−4 mol L−1; temperature, 100 °C

0 2 4 6 8 100

20

40

60

80

100

Rec

ove

ry %

Time (min)

Fig. 5 Effect of extraction time on the extraction recovery. CPEconditions, V(IV) 3.0 ng mL−1, 1.0 mL of 10% TX-100 (v/v); TAC,2.0×10−4 mol L−1; temperature, 100 °C

Table 2 Effect of the interferences ions on the recoveries ofvanadium ion

Ions Tolerable value(μg L−1)

Recovery(%)

Ca(II), Mg(II), 2000 98.7

Zn(II), Cd(II), Ni(II), Pb(II), 350 98.5

Co(II), Ni(II), 300 99.2

Al(III), Cr(III), Fe(III) 200 98.5

F−, SO42− Cl−, PO4

3− >5,000 99.7

Food Anal. Methods (2012) 5:359–365 363

improved by increasing the atomization temperature, butat the same time, the deterioration of the graphite tubewas also very bad. The sensitivity of determination wasenhanced greatly.

Interferences

In the view of the high selectivity provided by GFAAS,the only interferences studied were those related to thepreconcentration step. Cations that may react with TACand are extracted to the micelle phase were studied. Therecoveries of vanadium were almost quantitative in thepresence of all interfering ions under the chosenconditions. The tolerance limits were determined for amaximum error of ±5% and the results from these studiesare collected in Table 2. It can be seen that the majorcations and anions in the water samples have no obviousinfluence on the extraction of V(IV) under the selectedconditions. A high concentration of TAC reagent wasadded in order to guarantee the complete chelation of theanalyte even in the presence of interferents. This provedthe applicability of the proposed CPE method to realsamples. Ascorbic acid (100 μg) eliminated the interfer-ences from NaCl, CaCl2, and FeCl3 salts (Thomaidis andPiperaki 1996).

Analytical Performance of the Method

The equation (n=5) of the analytical calibration curvesobtained (n=5) was A=8.8×10−4 C (ng mL−1)+0.0051 withlinear range of 1–60 ng mL−1 preconcentration factor (PF)was 10. The calibration graph was linear with a correlationcoefficient of 0.9976 and the relative standard deviation was3.7% for vanadium(V) (C=2.0 ng mL−1, n=5). Thedetection limit, calculated as the amount of V required toyield a signal-to noise ratio of (3σ) was 0.05 ng mL−1. Thetheoretical preconcentration factor was calculated as the ratioof the volume of solution used to the surfactant-rich phasevolume. The preconcentration factor was found to be tenfoldfor 10 mL of water sample.

Comparison with the Other Methods

There are some publications on cloud point extraction of V(Madrakian et al. 2011; Paleologos et al. 2001; Wuilloud etal. 2002, Ohashi et al. 2007; Khan et al. 2010; Zhu et al.

Table 3 Comparison of the proposed CPE method with some of the methods reported in literature

Reagent Technique Linear range(ng mL−1)

LOD(ng mL−1)

Sample volume/PF Reference

8-Hydroxyquinoline GFAAS 2–50 0.042 50 mL/125 Khan et al. (2010)

1-(2-pyridylazo)-2-naphthol (PAN) FAAS 10–120 0.6 10 mL/33 Filik et al. (2008)

Methylene blue GFAAS 4.3–130 0.7 5 mL/10 Zhu et al. (2008)

8-Quinolinol derivatives GFAAS NR NR 20 mL/57.7 Ohashi et al. 2007

5-Br-PADAP ICP-OES 0–50 0.016 50 mL/250 Wuilloud et al. (2002)

Pyronine B-H2O2 Fluorimetry 0.02–10 0.020 10/50 Paleologos et al. (2001)

Bromopyrogallol red Uv/vis 3.0–50 0.5 10 mL/20 Madrakian et al. 2011)

1-(2′-thiazolylazo)-2-naphthol (TAN) GFAAS 1.0–60 0.05 10 mL/20 This work

LOD detection limit, ICP-OES inductively coupled plasma optical emission spectrometry, PF preconcentration factor, NR not reported

Table 4 Vanadium determination in wine samples (n=3) by GFAASemploying CPE

Sample Addedng mL−1

Foundng mL−1

Recovery (%) Foundμg L−1

White wine – 2.8±0.04 – 285 7.9±0.07 101

10 12.7±0.06 96

Red wine – 7.5±0.03 – 755 12.5±0.03 97

10 17.5±0.07 96

Table 5 Vanadium determination in tea and tomato samples (n=3) byGFAAS employing CPE

Sample Addedng mL−1

Foundng mL−1

Recovery (%) Foundμg g−1

TomatoA – 4.5±0.05 – 0.455 9.4±0.04 98

10 14.3±0.02 98

Tomato B – 3.7±0.08 – 0.375 8.6±0.07 98

10 13.6±0.04 99

Tea A – 2.5±0.03 – 0.255 7.6±0.03 102

10 12.6±0.06 101

Tea B – 1.7±0.05 – 0.175 6.6±0.04 96

10 11.5±0.07 98

364 Food Anal. Methods (2012) 5:359–365

2008; Filik et al. 2008). The preconcentration factor of ourmethod is similar (i.e., PF=10) to that reported in Zhu et al.(2008), and our detection limit is better than that reported inthese references. Ohashi et al. (2007) and Khan et al. (2010)obtained larger enrichment factors (57.7 and 125), but theyused a larger volume of initial solution (20 and 50 mL). Itshould be mentioned that the enrichment factor of ourmethod can be improved by using larger volumes of initialsolutions. A comparison of the results is given in Table 3.

Applications

The accuracy of the proposed method was examined byanalyzing total vanadium in a reference material (TMDA-61).The achieved result (342.0±0.2 ng mL−1) was in goodagreement with the certified value (343.0±3.5 ng mL−1).Using 100 μg ascorbic acid and aqueous calibration stand-ards excellent agreement was found with certified values.

The proposed method has been applied to the determina-tion of V in wine (Table 4), tomato and tea samples (Table 5)collected in Istanbul, Turkey. In addition, standard additionmethod was used for the determination of V in thesesamples. The recovery experiments of different amounts ofV(IV) were carried out, and the results were shown inTables 4 and 5. The results indicated that the recoveries werereasonable for trace analysis, ranging from 96% to 102%. Ascan be seen in Table 3, the vanadium content of red wine ismuch higher than that of white wine. These results were inagreement with the literature (Teissèdret et al. 1998).

Conclusions

This fundamental preconcentration technique was appliedsuccessfully to the determination of V in wine, tomato, andtea samples and the recoveries of added vanadium were inthe range 96–102%. The results of this method showed thecouple of CPE and GFAAS was utility and validity methodfor the selective determination of vanadium at trace levels.The methodology offers a good extraction efficiency andlower toxicity than those using organic solvents. Environ-mental pollution is limited to a small amount of surfactant.The fundamental cloud point extraction of vanadium fromwine, tea, and tomato samples coupled with GFAAS wasinvestigated.

Acknowledgment The authors gratefully acknowledge The Scientificand Technological Research Council of Turkey (TÜBİTAK) (Project No:109T856).

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