Selective Separation of Aluminum from Biological andEnvironmental Samples Using Glyoxal-bis(2-hydroxyanil)Functionalized Amberlite XAD-16 Resin: Kinetics and EquilibriumStudiesAminul Islam,* Hilal Ahmad, Noushi Zaidi, and Sudesh Yadav†

Analytical Research Laboratory, Department of Chemistry, Aligarh Muslim University, Aligarh, India 202 002

*S Supporting Information

ABSTRACT: A new glyoxal-bis(2-hydroxyanil) anchored Amberlite XAD-16 chelating resin was synthesized and characterizedby elemental analyses and scanning electron microscopy along with energy dispersive X-ray spectroscopy (SEM/EDAX), infraredspectral, and thermal studies. The resin was found to selectively bind aluminum in aqueous medium over a large number ofcompetitive cations, at pH 9. Experimental conditions, for effective sorption of Al(III) were optimized systematically and werefound to have fast kinetics (t1/2 10 min), high preconcentration flow rate (5.0 mL min−1), very high sorption capacity (24.28 mgg−1), regenerability up to 66 sample loading/elution cycles, and low preconcentration limit (3.3 ppb) from test solutions ofdifferent interferent to analyte ratio. The chemisorption and identical, independent binding site behavior were evaluated byDubinin−Radushkevich isotherm and Scatchard plot analysis. Equilibrium data fit well to Langmuir adsorption isotherms (r2 =0.998) indicating a typical monolayer sorption. We confirmed the analytical reliability of the method by the analysis of standardreference materials (SRMs), recovery experiments, and precision expressed as coefficient of variation (<5%). The applicability ofthe proposed method was demonstrated by preconcentration of trace Al(III) in dialysis fluid, packaged drinking water, rum, andsoft drink samples.

■ INTRODUCTION

Al(III) is the third most abundant element of the earth’s crustand clearly shows a probably peerless versatile chemistry,testimony to which is its multitudinous applications fromautomotive to packaging, cosmetics, construction, and spaceindustries.1,2 The present day production of Al(III) is morethan all other nonferrous metals together.3 Al(III) which waspreviously considered benign has been recently found to causebone, neurological, and other disorders.4−8 Such potentialtoxicity of Al(III) to humans and the environment has drawnthe attention of many analysts in determination of traceAl(III).9−11 Therefore, detection of Al(III) is crucial to controlits concentration levels in the biosphere and its impact tohuman health.Direct determination of metal ions at trace levels by

sophisticated analytical techniques is limited, not only due toinsufficient sensitivity, but also to matrix interference. It iscustomary, to employ a separation and/or preconcentrationstep prior to the trace metal quantification; as adjuncts to suchtechniques (including flame atomic absorption spectrometry(FAAS)). FAAS has been widely used for its advantages of lessspectral interference by concomitants and relatively lessrunning costs instead of expensive flameless techniques whichare usually much more sensitive to interference.The focus of much current research in SPE12−14 as metal ion

extractants is the development of insoluble functionalizedpolymers of very high sorption capacity, by increasing thenumber of chelating sites on the material as well as theiraccessibility for metal ions.

Glyoxal-bis(2-hydroxyanil) (GBH) has been established as atetradentate chelate ligand containing imine-N and phenolato-O donor atoms in the deprotonated form15 formingmononuclear complexes with main group, transition metal,and actinide elements.16−20 Introduction of such functionalgroups on Amberlite XAD series resins decreases thehydrophobicity and facilitates better surface contact with theaqueous phase. Such resins with high surface area and porosityafter functionalization leads to high selectivity, improvedsorption capacity, and increased chelating site accessibility forthe metal ions.21,22

According to our literature knowledge, no systematicinvestigation to date has been performed on the complexationof GBH and Al(III), with or without solid phase. The aim ofthis work was to synthesize and characterize a novel Al(III)selective chelating resin by binding GBH to Amberlite XAD-16produced as the diazotization product of the polymer. The resinwas then systematically explored for its application in theseparation/preconcentration and determination of trace Al(III)in real samples using FAAS.

2. MATERIALS AND METHODS2.1. Reagents and Solutions. All chemicals used were of

analytical reagent grade. All metal salts were procured fromMerck (Mumbai, India). Stock solutions (1000 mg L−1 in 1%

Received: November 29, 2012Revised: March 5, 2013Accepted: March 17, 2013Published: March 17, 2013

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HNO3 and in 1% HCl) of nitrate salts of Co(II), Ni(II),Cu(II), and Al(III) and chloride salts of Zn(II) and Cd(II),respectively, were standardized by complexometric titrationmethod.23 All solutions were prepared in triply distilled water.Working solutions were prepared on a daily basis through serialdilutions of the stock solution with triply distilled water prior touse. The buffer solutions used were KCl−HCl, HCl−C2H5O2N, CH3COOH−CH3COONa, Na2HPO4−C6H8O7,and NH4Cl−NH3 Merck (Mumbai, India) for the pH 2.0−2.8, 3.0−3.6, 4.0−6.0, 7.0−7.8, 8.0, and 9.0−10.0, respectively.The chelating reagent, Amberlite XAD-16 (particle size 20−60,pore size 100 Å, pore volume 1.82 mL g−1, and surface area 900m2 g−1) and glyoxal-bis(2-hydroxyanil) was procured fromSigma-Aldrich (Steinem, Germany) and Otto Chemicals Pvt.Ltd. (Mumbai, India), respectively. Standard referencematerials were obtained from the National Institute ofEnvironmental Studies (Ibaraki, Japan). All the reagents(HNO3, HCl, HClO4, and H2O2) used for wet digestion ofthe samples were procured from Merck (Mumbai, India).2.2. Instruments. The Thermo Electron Corporation

(Cambridge, UK) M series flame AAS equipped with doublebeam optics and dual zeeman correction (conditions for Al: anitrous oxide-acetylene flame, wavelength 309.3 nm, lampcurrent 100 mA, bandpass 0.5 nm, burner height 11 mm, andfuel flow rate 4.3 L min−1) was used for determining metalconcentration. A thermostatted mechanical shaker NSW-133(New Delhi, India) was used for the batch studies. Infrared(IR) spectra were recorded on a Fourier transform-IRSpectrometer from Spectro Lab-Interspec 2020 (Newbury,U.K.) using KBr disk method. A Shimadzu TGA/DTAsimultaneous measuring instrument, DTG-60/60H (Kyoto,Japan) was used for thermogravimetric analysis (TGA) anddifferential thermal analysis (DTA). CHN analysis was carriedout on Flash EA 1112 Organic Elemental Analyzer (ThermoFischer Scientific). Scanning electron microscopy/energydispersive X-ray spectroscopy (SEM/EDAX) analysis wasdone on Jeol JSM-6510LV (Tokyo, Japan). A column (1 ×10 cm), for dynamic studies, was obtained from J-SIL ScientificIndustries (Agra, India).2.3. Functionalization and Characterization. GBH

functionalized XAD-16 resin (XAD-GBH) was preparedthrough azo spacer as per the scheme reported in earlierwork.24 The resin was characterized on the basis of elemental,SEM along with EDAX, Fourier transform infrared (FTIR), andthermal studies. Chemical stability was established bydetermining the sorption capacity after soaking the resin in25 mL of acid (1−7 mol L−1 HCl and HNO3) and alkalinesolution (1−5 mol L−1 NaOH) for 48 h. The potentialregeneration of XAD−GBH was up to 66 cycles; afterward thereusability tends to decrease as 9% loss of analyte uptake wasobserved in further cycles.The dry resin in basic form was stirred in distilled water for

48 h, and then filtered off by suction, dried in air, weighed,dried again at 100 °C overnight, and reweighed in order tocalculate water regain capacity.25

For hydrogen ion capacity, an exactly weighed (0.5 g) resinwas treated with 4.0 mol L−1 HC1, filtered off, and then washedthoroughly with distilled water and dried at 100 °C for 5−6 h.The resin in acidic form was equilibrated with 20 mL of 0.1 molL−1 NaOH solutions for 6 h and the excess alkali was estimatedwith 0.1 mol L−1 HCl.2.4. Recommended Procedure. 2.4.1. Batch Method.

Batch experiments were conducted by equilibrating 50.0 mL of

metal solution of suitable concentration at constant pH with 0.1g XAD−GBH in an Erlenmeyer flask stirred for 3 h at 27 ± 0.2°C. The metal ions were desorbed by shaking with theappropriate eluting agents and measured by FAAS.

2.4.2. Column Method. A glass column (10 cm ×1.0 cm),having a porous disc was packed with water soaked XAD−GBH. The resin bed (height 2.5−3.0 cm) was preconditionedwith 5 mL of corresponding buffer solution. Sample solution ofoptimum concentration buffered at suitable pH was passedthrough the column at an optimum flow rate. After the sorptionexperiment, column was washed with triply distilled water toensure that any unretained metal ion was removed from thesystem. A certain volume of suitable eluent was made topercolate through the bed, whereby the retained metal ions geteluted and subsequently determined by FAAS.

2.5. Collection and Digestion of Samples and SRMs.Peritoneal dialysis fluid (2 × 2000 mL), packaged drinkingwater (3 × 1000 mL), rum (3 × 500 mL), and soft drink (3 ×200 mL) of different batches were collected from the localmarket of Aligarh. The required volume of each sample aftermixing all the contents was then pretreated prior to theirapplication to the SPE procedures.The water sample and dialysis fluid (500 mL each) were

filtered through a cellulose membrane filter (Millipore) of 0.45μm pore size while the rum and soft drink (100 mL each)samples were evaporated to about 5 mL on hot plate anddigested by wet oxidation with 10−20 mL each of conc HNO3and HClO4 and 2 mL of 30% H2O2. The residue was dissolvedin 5 mL of 0.5 M HNO3 and finally made up to 50 mL withtriply distilled water. The sample solutions of 2500 mg, and 20mg of rice flour-unpolished NIES-10, and tea leaves NIES 7,respectively, were prepared as reported in earlier work.26 ThepH was optimized accordingly, and all the samples werepreconcentrated by the given column method. The concen-tration of desorbed analyte ion in the eluent was determined byFAAS.

3. RESULT AND DISCUSSION3.1. Characterization of Chelating Resin. The water

regain capacity was estimated to be 24.63 mM g−1. This valuereflects the high hydrophilic character of the resin which isexcellent for column operation. The overall hydrogen ioncapacity amounts to 1.72 mM g−1 of resin. This suggests thepresence of 0.86 mM reagent g−1 resin and 3.44 mM nitrogeng−1 resin, taking into account that each azo-coupled reagentmolecule contains two replaceable hydrogen ions and twonitrogen atoms. The results of elemental analysis of nitrated,aminated, and reagent coupled resin are (C 67.7%; H 5.9%; N4.6%), (C 58.9%; H 4.6%; N 4.0%), and (C 72.3%; H 5.7%; N4.6%), respectively. Comparing theoretical and experimentalCHN data, it could be inferred that there was an incorporationof one group or reagent molecule per two monomer units asthe relative nitrogen percent from the two data for thesubsequent steps (Figure 1) was found to be 83%, 74%, and41% respectively. This also suggests the continuous decrease inconversion efficiency.The chemical stability of the chelating resin was established

up to 5 mol L−1 of mineral acids and alkali. The thermalstability of XAD−GBH resin was found to be up to 350 °Cabove which the degradation commences, as was evident fromTGA curve.XAD−GBH gave visible peaks at 1446, 1707, and 3480 cm−1

in the FTIR spectrum, which were ascribed to NN,

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CN, and phenolic OH groups, respectively, whereasnascent XAD-16 did not offer such peaks. In Al(III) complexedXAD−GBH, the blue shift in NN (1449.8) and CN (1712) and disappearance of phenolic −OH peakconfirmed the chelation of Al(III) on XAD−GBH.SEM/EDAX analysis in the range of 0−20 keV was carried

out for XAD−GBH and XAD−GBH complexed with Al(III).The observation depicted in (Figure 2) confirms the absenceand presence of Al(III) in uncomplexed and complexed resin,respectively.3.2. Optimization. Various experimental variables with the

potential to affect and accordingly optimize the determinationof metal ions using solid phase were studied. A batch methodwas opted to study the effect of pH, sorption kinetics, and

isotherm studies. The rest of the experiments were done bycolumn procedure.

3.2.1. Effect of pH. The solution pH affects the extent ofdissociation of functional groups (especially phenolic hydro-gen), and metal binding ability of dissociated and associatedfunctional groups are expected to be different at different pH.27

It affects both the surface charge of resin and the degree ofionization of the metal in solution.28 The pH of the solutionswas adjusted within a range of 2−10 by using correspondingbuffer solutions. As can be seen from the Figure 3, the

maximum uptake of Al(III) occurs at pH 9 ± 0.01. This may beattributed (i) to the competition between the hydrogen andAl(III) ions on the sorption sites, at low pH, and (ii) to theelectrostatic interaction and the ease of coordination betweenAl(III) and phenoxide ion over that of the phenolic −OHgroup, at high pH. For subsequent experiments, pH 9 ± 0.01was selected as the working pH.Moreover the fact that at pH 9 the uptake of other studied

metal ions [Cu(II), Co(II), Zn(II), Ni(II), and Cd(II)] is verylow compared to that of Al(III) facilitates the effectual selectivedetermination of Al(III) at chosen pH. This selective behavioris due to the competition that exists between the formation of

Figure 1. Immobilization of GBH ligand on Amberlite XAD-16.

Figure 2. EDAX spectra showing elemental analysis for the selected area in SEM picture. (A) EDAX spectra of XAD−GBH (B) EDAX spectra ofXAD−GBH complexed with Al(III).

Figure 3. Dependence of sorption capacity on the pH of the solution(experimental conditions: sample volume 50 mL, metal ion 100 μgmL−1, resin amount 0.1 g).

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more stable Al(III)−ligand complex over other stable forms ofthe studied metal ion species in the solution state.3.2.2. Effect of Shaking Time. The adsorption kinetics that

described the Al(III) uptake rate and governed the contact timeof the adsorption reaction are one of the importantcharacteristics in defining Al(III) adsorption. It was concludedthat the apparent adsorption equilibrium for Al(III) wasestablished in just 15 min29 (with a corresponding loading halftime, t1/2, of merely 10 min) whereas the equilibration time forother studied metals is more than or equal to 60 min. This maybe because of the high complexation rate between hard acidAl(III) and hard base O−30,31 of the functionalized chelatingresin. Thus, an equilibration time of 15 min was set in allfurther experiments.3.2.3. Effect of Resin Amount. To examine the effect of the

resin amount on the sorption of Al(III), an excess of metal ionsolution (250 μg mL−1) was equilibrated with varying amountsof resin buffered at pH 9 ± 0.01. The retention of the metalions per gram resin increased with the increase in resin amountup to 300 mg, after which sorption capacity almost remainsconstant. All further operations were done with 0.3 g of XAD−GBH.3.2.4. Effect of Flow Rate. The sorption flow rate was

optimized by varying the rate (2−10 mL min−1) for maximumsorption. Observations indicated that metal retention on theresin was optimum at a flow rate of 5 mL min−1. The retentionfor Al(III) gradually decreases on further accelerating thesorption flow rate (up to 50% loss at 10 mL min−1). Thedecrease in sorption, with increasing flow rate is due to thedecrease in equilibration time between two phases. In theelution studies, >98% recovery of the sorbed metals from theresin could be achieved at a flow rate of 2 mL min−1. Inconsequence, a flow rate of 5 and 2 mL min−1 was maintainedfor sorption and elution studies, respectively.3.2.5. Type of Eluting Agent. In order to elute Al(III) from

the solid phase, different mineral acids have been tested byvarying their volumes and concentrations. The percent recoveryfor Al(III) by using 5 mL each of 2 M HCl, 2 M HNO3, and 2M H2SO4 were found to be 98.2 ± 1, 72 ± 3, and 68 ± 2,respectively. In all further studies, 5.0 mL of 2 M HCl was usedas eluent.3.2.6. Effect of Sample Loading Volume. To explore the

maximum volume in the SPE beyond which the quantitativerecovery of the metal ion is not feasible, the sample loadingvolume containing 5 μg of Al(III) was constantly increased.Following the column procedure, the recoveries of analyte atdifferent volumes were obtained. The result shows that theanalyte can be preconcentrated up to a concentration of 3.3 μgL−1 corresponding to a high preconcentration factor of 300obtained on using 5.0 mL of eluate.3.3. Sorption Isotherm. A sorption isotherm is funda-

mental in understanding the sorption mode of an adsorbate onsorbent surface once the equilibrium is attained. Theexperimentally obtained adsorption isotherm data were appliedto both Langmuir and Freundlich isotherms. The datatreatment for the linearized form of both isotherm equationsis as follows.32

Langmuir model equation (Figure 4)

= +C Q Q K C Q/ 1/ /e e m b e m (1)

Freundlich model equation (Figure 5)

= +Q k n Cln ln (1/ ) lne e (2)

gave correlation coefficient values >0.9 but resulted in a betterfit to the Langmuir model, as was evidenced from the highervalue of r2 (Table 1).

The experimentally obtained sorption capacity for Al(III)was found to be 24.28 mg g−1 of resin, this agrees well with thecapacity determined by Langmuir model. It further confirmsthe Langmuir fit to the present data.From the Langmuir model, the separation factor RL can be

obtained from the Langmuir sorption constant (Kb)

= +R K C1/(1 )L b o (3)

where Co is the initial Al(III) concentration. Table 2 lists thecalculated RL values at various initial Al(III) concentrations. Forall the tested Al(III) concentrations, RL values (0 < RL < 1)elucidate the favorability of XAD−GBH as a good Al(III)sorbent.The Dubinin−Radushkevich (DR) isotherm was studied to

interpret the sorption on a single type of uniform pores. Itslinear expression is27

= −Q Q Kln lne m2

(4)

The mean free energy E used to estimate the sorption type canbe calculated from constant K:

= − −E K( 2 ) 0.5(5)

This K is obtained from the linear plot of ln Qe against 2

(Figure 6). Since the numerical value of E in the range of 1−8and 8−16 kJ mol−1 forecasts the physical sorption and chemical

Figure 4. Langmuir sorption isotherm of Al(III) on XAD−GBH.

Figure 5. Freundlich sorption isotherm of Al(III) on XAD−GBH.

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sorption, respectively. The E value obtained in our work is infull agreement with the chemisorption of Al(III) by XAD−GBH.The Scatchard plot analysis is also used to investigate the

sorption process and nature of binding sites in solid phase. TheScatchard equation is represented as27

= −Q C Q K Q K/e e m b e b (6)

The type of the interactions of analyte with adsorbent is relatedto the shape of the Scatchard plot. The presence of a deviationfrom linearity on a plot based on Scatchard analysis usuallypoints out the presence of more than one type of binding site,while the linearity of the Scatchard plot indicates that thebinding sites are identical and independent. The Qe/Ce versusQe plot of Al(III) is linear with a negative slope (Figure 7).The applied adsorption isotherms, Scatchard plot analysis,

and software run inferred that the chemical interaction betweenAl(III) and the identical binding sites of XAD−GBH follows atypical uniform and monolayer sorption, as well as ourconclusions from other studies that Al(III) ions are adsorbedthrough complexation with the tetradentate ligand.3.4. Study on Nonspectroscopic Interference. The

preconcentration procedures can be substantially affected byvarious potential concomitants through precipitate formation,redox reactions, or competing complexation reactions; either ofinterferent anions with the analyte metal ion or of the metalions in matrix with the sorbent. The effect of somenonspectroscopic interference was investigated (Table 3). Nointerference was observed for the most common matrix anionsowing to the group-specific character of the XAD−GBH. TheAl(III) preconcentration was not significantly affected even inthe presence of alkali and alkaline earth metals and common

Table 1. Isotherm Models for Al(III) Sorption by XAD−GBH

sorption capacity from column experiment Langmuir isotherm Freundlich isotherm DR isotherm

Q (mg g−1) Q (mg g−1) kb (mL mg) r2 Q (mg g−1) r2 Q (mg g−1) K (mol2 kJ2) E (kJ mol) r2

24.28 25.64 0.055 0.998 11.65 0.994 22.12 0.007 8.45 0.992

Table 2. RL Values for Al(III) Sorption Obtained from theLangmuir Equation

Coa = 97.12 Co

a = 118.71 Coa = 140.29 Co

a = 161.88

RL 0.16 0.13 0.11 0.10aInitial Al(III) concentration (mg L−1).

Figure 6. Dubinin−Radushkevich isotherm of Al(III) on XAD−GBH.

Figure 7. Scatchard plot for sorption of Al(III) on XAD−GBH.

Table 3. Effect of Interfering Ions on the Recovery of Al(III)(Resin Amount 300 mg, Sample Volume 100 mL, Amount ofAl(III) Loaded 5 μg, N = 3) on XAD−GBH in AqueousSamples Using SPE−FAAS

interferingions added as

amount added(× 103 μg)

Al(III)recovery (%) RSD

Cl− NaCl 750 100.0 0.91500 99.7 1.6

Br− NaBr 25 100.0 0.450 98.6 0.7

I− NaI 25 100.1 0.750 100.2 1.1

F− NaF 25 100.8 1.950 97.5 1.8

PO42− Na2HPO4 5 98.3 2.7

10 97.6 1.1SO4

2− Na2SO4 50 96.4 1.4100 95.8 0.4

CO32− Na2CO3 50 96.9 1.0

100 98.5 2.8C2O4

2− Na2C2O4 25 100.0 0.750 99.8 0.9

CH3COO− CH3COONa 50 99.4 1.4

100 99.8 0.7C6H5O7

3− Na3C6H5O7 5 98.8 1.412.5 99.1 1.5

C4H4O62− Na2C4H4O6 5 99.6 0.9

12.5 97.8 0.7Na+ NaCl 500 100.4 1.2

1000 100.3 1.5K+ KCl 100 100.4 0.8

200 100.1 0.9Ca2+ CaCl2 50 100.4 1.7

100 97.3 0.9Mg2+ MgCl2 50 100.3 1.4

100 100.0 0.9

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matrix anions, attributed to the fast kinetics of the presentsystem. This suggested that the structure of the chelate is notsuitable for recognition of these anions. The selectivity of theresin toward Al(III) was further ascertained by the competitiveexperiment. The XAD−GBH resin was treated with Al(III) inthe presence of Co2+, Mn2+, Ni2+, Cr3+, Pb2+, Cu2+, and Zn2+ atthe concentrations 25 times that of the Al3+. No interferencewas observed for the determination of Al(III) undercompetitive and noncompetitive conditions. This uniqueselectivity of XAD−GBH toward Al(III) can be interpretedin terms of the smaller ionic radius and higher charge density ofthe Al(III). The smaller radius of the Al(III) permits suitablecoordination geometry for the chelating resin and the largercharge density allows strong coordination ability betweenXAD−GBH and Al(III).3.5. Method Validation. The bias of the outlined

separation/preconcentration method was estimated by theanalysis of trace amount of Al(III) present as major and minorcomponent in studied SRMs. The mean concentration valuesfor Al(III) obtained by the proposed method (Table 4) werestatistically insignificant from the certified values indicatingabsence of systematic method errors. The method also hadgood precision for the analysis of trace Al(III) in samplesolutions, as the coefficient of variation for 5 replicatemeasurements of 5 μg of Al in 100 mL was <5%.The calibration curve with the regression equation and

correlation coefficient (r2) for Al(III) determination, obtainedby the method of least-squares, was A = 0.0042C + 0.0002 (r2 =0.9966), where A is the absorbance and C is the metal ionconcentration (mg L−1). The linearity of the calibration curve isapparent from the correlation coefficient (r2) which lies wellabove 0.99. According to IUPAC,33 the detection limit andlimit of quantification evaluated as 3s and 10s of the mean blanksignal (absorbance) for 20 replicate measurements (100 mLeach) were found to be 1.3 (−0.00125) and 4.4 μg L−1,respectively.3.6. Proposed Method of Al(III) Determination and its

Applications. The proposed separation/preconcentrationmethod, after being optimized in terms of the parametersdescribed above, was applied for the determination of Al(III) inthe pretreated sample solutions spiked with known amount ofAl(III). Sample solution of 100 mL (500 mL for PDW anddialysis fluid) buffered at pH 9 was passed through the columnat a flow rate of 5 mL min−1. Sorbed Al(III) was eluted with 5mL of 2 M HCl at a flow rate of 2 mL min−1 and collected in 5mL volumetric flask for the subsequent determination byFAAS. The presence of constant errors in our procedure wasruled out by varying the sample size and henceforth proves theapplicability of reported method for Al(III) determination withgood efficacy (Table 5).3.7. Comparison with Other Solid Phase Extraction

Methods. Some previous work done on Al(III) is comparedwith the proposed separation/preconcentration method (Table6). The comparative data clearly suggests the superiority of our

work over the reported comparisons mainly on parameters ofpreconcentration factor, selectivity, sorption capacity, and fastkinetics. A 5.0 mL portion of eluent was efficient to eluteAl(III) from the column. XAD−GBH was used as a selectivechelating resin for Al(III) in the presence of most competingmetal ions.

4. CONCLUSION

The approach adopted in this work has proved to be fairlysuccessful and meets the best analytical requirements such assimple design and instrumentation with an easy functioning anda low cost of acquisition and maintenance. FAAS, as a single-element technique, is ideally suited for the determination of asingle analyte, Al(III). The XAD−GBH resin shows highselectivity for Al(III), as a function of pH control, thusminimizing the nonspectroscopic interferences in successiveFAAS determination. The sorption equilibrium for Al(III) wasachieved within 15 min (t1/2; 10 min) by using XAD−GBH,resulted in short analysis time and allows the possibility ofworking with large sample volumes. The selectivity ofaluminum over other metals was also favored for fast kineticreasons. The mentioned procedure promises a simple to use,accurate, sensitive, selective, repeatable, and environmentallyinnocuous method for efficient separation/preconcentrationFAAS of Al(III), along with low preconcentration limit (3.3 μgL−1). These results show that this technique can be a viablealternative over other existing preconcentration methods forAl(III). The application of the proposed procedure for Al(III)preconcentration/determination in various real samples and incertified reference materials validate the reliability of theproposed method with good accuracy and precision.

Table 4. Validation of Proposed Separation/Preconcentration Method by Analysis of SRMs for Al Concentration

SRM composition (μg g−1)certified value

(μg g−1)founda (μg g−1) ±standard deviation

calculatedstudent’s t-valueb

NIES 10(c)c Al: 1.5, Ca: 95 ± 2, Mn: 40.1 ± 2.0, Zn: 23.1 ± 0.8, Fe: 11.4 ± 0.8, Cu: 4.1 ± 0.3,Ni: 0.30 ± 0.03, Cd: 1.82 ± 0.06

1.5 1.48 ± 0.02 3.89

NIES 7d Al: 775, Mn: 700, Zn: 33, Cu: 7, Ni: 6.5, Ba: 5.7, Sr: 3.7, Na: 15.5 775 773.8 ± 0.7 3.01aN = 3. bAt 95% confidence level. cAl as minor component. dAl as major component.

Table 5. Determination of Al(III) in Spiked Real Samplesafter Column Preconcentration on XAD−GBH by FAAS

sampleadded

(μg L−1)founda (μg L−1) ± standard

deviationrecovery(%)

PDWb 0 22.68 ± 0.054 26.41 ± 0.48 99.010 32.49 ± 0.25 99.4

soft drink 0 55.66 ± 0.1320 75.73 ± 0.38 100.150 106.37 ± 0.29 100.7

rum 0 28.37 ± 0.1420 48.63 ± 0.38 102.750 78.50 ± 0.50 101.5

dialysis fluid 0 24.07 ± 0.404 28.43 ± 0.15 101.310 34.36 ± 0.36 100.9

aCL = X̅ ± (ts/√N), N = 3 at 95% confidence level. bPackageddrinking water.

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■ ASSOCIATED CONTENT

*S Supporting InformationDetailed description for characterization of XAD−GBHchelating resin: (1) CHN data of nitrated XAD, aminatedXAD, and GBH functionalized XAD. (2) TGA and DTA dataof XAD−GBH. (3) FTIR spectra of XAD−GBH and Al(III)complexed XAD−GBH. This material is available free of chargevia the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATION

Corresponding Author*Tel.: +91 9358979659. E-mail address: aminulislam.ch@amu.ac.in.

Present Address†School of Environmental Sciences, Jawaharlal Nehru Uni-versity, New Mehrauli Road, New Delhi 110067, India.

NotesThe authors declare no competing financial interest.

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Table 6. Summary of Some Previous Solid Phase Extraction Studies about Aluminum

adsorbent complexing media pH capacity (mg g−1) PF DL (μg L−1) RSD (%) ref

vinyl polymer gel 8-hydroxyquinoline 5−5.5 0.004 34AG l-X8 Chromotrope 2B 7 10 10.7 358-Q-CPG 8-quinolinol 9.3 15.40 4 36XAD-4 salicylic acid 4 4.4 ± 0.3 37XAD-7 8-hydroxyquinoline 8.5 50 0.23 2.4 38controlled-pore glass 8-hydroxyquinoline 10 76 3.00 <10 39activated carbon cupferron 5 150 40Chelex-100 7−8 2.22 41silica gel 8-hydroxyquinoline 5−8 0.2 4.2 42201 × 8 anion exchange resin Tiron 4−6 5.6 20 0.3 <10 43AXAD-16 GBH 9 24.28 ± 0.24 300 1.3 <5 this work

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