The efficiency of Amberlite XAD-4 resin loaded with 1-(2-pyridylazo)-2-naphthol in preconcentration...

Environ Monit Assess (2011) 175:201–212DOI 10.1007/s10661-010-1506-4

The efficiency of Amberlite XAD-4 resin loadedwith 1-(2-pyridylazo)-2-naphthol in preconcentrationand separation of some toxic metal ions by flame atomicabsorption spectrometry

Aminul Islam · Mohammad Asaduddin Laskar ·Akil Ahmad

Received: 26 December 2009 / Accepted: 6 May 2010 / Published online: 28 May 2010© Springer Science+Business Media B.V. 2010

Abstract A selective method has been developedfor the determination of trace amount of metalions after preconcentration on 1-(2-pyridylazo)-2-naphthol loaded Amberlite XAD-4 resin. Thechelating resin was characterized on the basis ofinfra red spectra, thermal and chemical stability,and hydrogen ion capacity. High preconcentrationfactor of 160–400 up to a low preconcentrationlimit of 10 μg L−1 has been achieved for almost allthe metals. The chelating resin was highly selec-tive even in the presence of large concentrationsof alkali and alkaline earth metals and variousmatrix components. Chromatographic separationof metal ions in binary mixtures has been accom-plished. The analytical utility of the resin for metalions was explored by analyzing natural water andstandard reference materials.

Keywords Chelating resin ·1-(2-pyridylazo)-2-naphthol · Toxic metals ·Separation · Preconcentration

A. Islam (B) · M. A. Laskar · A. AhmadDepartment of Chemistry, Aligarh Muslim University,Aligarh, Uttar Pradesh, India 202002e-mail: [email protected]

Introduction

With growing industrialization and urbanization,diversified uses of metals in varied forms havebecome significant source of pollution resultingin environmental deterioration. Metals constitutea major category of persistent, bioaccumulative,and toxic (PBT) chemicals that do not readilybreak down in the environment, are not easilymetabolized, and may accumulate in human orecological food-chains through consumption. APBT chemical, once released to the environment,may present increasing long-term toxic effectsto public health even if the release was of asmall amount and pose a significant threat topublic health through occupational as well asenvironmental exposures (Hayes 1989). Quan-tification of toxic metal ions in industrial effluents,various water resources, environmental and bi-ological samples is important, especially in theenvironment monitoring and assessment of en-vironmental exposure to toxic metals. However,most of the toxic metal ions in real matrices arein very low concentrations and occur togetherwith much higher concentrations of compoundslikely to cause interferences during the analy-sis by conventional analytical methods and evenwith frequently used sophisticated instrumentaltechniques for trace metal determination suchas inductively coupled plasma atomic emissionspectrometry, electrothermal atomic absorption

202 Environ Monit Assess (2011) 175:201–212

spectrometry, etc., without sample enrichmentand cleanup (APHA 1989; Sung and Huang 2003;Sabarudin et al. 2007). Solid-phase extraction(SPE) addresses these two problems. It concen-trates the desired trace elements whereby extend-ing the detection limits and removes interferingconstituents, thereby improving the precision andaccuracy of the analytical results. The main advan-tage of this technique is the possibility of using arelatively simple detection system with flame at-omization instead of a flameless technique, whichrequire more expensive equipment and are usu-ally much more sensitive to interferences frommacro components of various natural matrices(Pyrzynska and Trojanowicz 1999). The use ofchelating resin in SPE as metal ion extractantshas turned out to be an active area of research, inthe field of separation science in the recent years(Kantipuly et al. 1990; Nabi et al. 2005; Rao et al.2004). High surface area of hydrophobic Amber-lite XAD resin, that also possess excellent chemi-cal and physical stability, will retain more ligandsbecause it contains relatively large number of ac-tive aromatic sites that allow π–π interactions andthus, sorption capacity of the chelating resin willbe improved. Its moderate porosity will hold fairamount of water and exhibit a good hydrophiliccharacter which is crucial factor that governs therate of metal ion phase transfer (Wuilloud et al.2000; Islam et al. 2010; Leon-Gonzalez and Perez-Arribas 2000).

Tridentate N-heterocyclic azo ligand contain-ing N atom, 1-(2-pyridylazo)-2-naphthol (PAN)has shown excellent complexing ability for heavyand transition metal ions and analytical appli-cations of this ligand in the spectrophotometricdetermination of the metals are well estab-

lished (Escriche et al. 1983; Chin et al. 1992;Thanasarakhan et al. 2007; Afkhami and Bahram2004; Li et al. 1997).

It was, therefore, thought worthwhile to pre-pare a chelating resin of better sorption capacityby loading PAN on Amberlite XAD-4 (AXAD-4) resin through surface modification and char-acterize in a systematic manner. The resultingchelating resin was used for the preconcentrationand separation of Cd(II), Zn(II), Co(II), Cu(II),Ni(II), Mn(II), and Pb(II) from various real ma-trices prior to their determination by flame atomicabsorption spectrometry (FAAS).

Materials and methods

Instruments

A Perkin Elmer flame atomic absorption spec-trometer 3100 was employed for the determi-nation of metal ions. Operating parameters setfor the determination of elements are given inTable 1. Infrared (IR) spectra were recordedon a FT-IR Spectrometer-Interspec 2020 usingKBr disc method. A Shimadzu TG/DTA simulta-neous measuring instrument—DTG-60/60H wasused for thermogravimetric analysis (TGA) anddifferential thermal analysis (DTA).

Reagents and solutions

Stock solutions of nitrate salts of Cd(II), Zn(II),Co(II), Cu(II), Ni(II), Mn(II), and Pb(II) (CentralDrug House (P) Ltd., New Delhi) at the concen-tration of 1000 mg L−1 in 1% HNO3 were stan-dardized by complexometric titration (Welcher

Table 1 Operatingparameters set for FAASfor the determination ofelements

Element Wavelength Slit Lamp Working Flame composition

(nm) width current range Air Acetylene(nm) (mA) (μg mL−1) (L min−1) (L min−1)

Cd(II) 228.8 0.7 10 0.02–3.0 9.5 2.3Zn(II) 213.9 0.7 15 0.01–2.0 9.5 2.3Co(II) 240.7 0.2 30 0.05–15.0 9.5 2.3Cu(II) 324.8 0.7 25 0.03–10.0 9.5 2.3Ni(II) 232.0 0.2 15 0.10–20.0 9.5 2.3Mn(II) 279.5 0.2 12 0.02–5.0 9.5 2.3Pb(II) 283.3 0.7 8 0.10–30.0 9.5 2.3

Environ Monit Assess (2011) 175:201–212 203

1958) before use. Amberlite XAD-4 resin, as20–60 mesh particle size with surface area of725 m2g−1 and PAN was procured from Sigma-Aldrich Chemie GmbH (Steinheim, Germany)and used without further purification. All thechemicals were of analytical reagent grade.

Preparation of samples

Natural and sewage water samples

The water samples namely river water (the Ganga,Narora, India), canal water (Kasimpur, Aligarh,India), sewage water (local nickel electroplatingindustry, Aligarh), and tap water (University cam-pus) were immediately filtered through Milliporecellulose membrane filter (0.45 μm pore size),acidified to pH 2 with HNO3, and stored in pre-cleaned polyethylene bottles.

Digestion of standard environmental, biological,and metal alloy samples

A 0.5-g sample of the environmental standardreference material (vehicle exhaust particulatesNIES 8) was dissolved by adding 10 mL of con-centrated nitric acid (15.5 mol L−1), 10 mL of con-centrated perchloric acid (12.2 mol L−1) and 2 mLof concentrated hydrofluoric acid (22.4 mol L−1)in a 100 mL in a Teflon beaker. The solutionwas evaporated to near dryness, redissolved inminimum volume of 2% HCl, filtered and madeup to 50 mL volume in a calibrated flask.

The sample solutions of human hair (NIES 5),chlorella (NIES 3) and tea leaves (NIES 7) wereprepared as proposed by the International AtomicEnergy Agency (Kubová et al. 1997). A 50 mgsample of each of the samples was agitated with25 mL of acetone, and then washed three timeswith distilled water and with 25 mL of acetone.The contact time of the cleaning medium with thesample was 10 min. The samples were finally driedfor 16 h at 100◦C. Then each of the samples wasdissolved in 10–20 mL of concentrated nitric acid.After adding 0.5 mL of 30% H2O2, the solutionwas boiled to dryness. The residue obtained wasdissolved in minimum amount of 2% HCl andmade up to a 50-mL volume in a calibrated flask.

To dissolve the standard reference alloys,Rompin iron ore (JSS 800-3) and zinc base die-casting alloy C (NBS 627)), an amount of 25 mgof the sample was taken into a beaker and dis-solved in 10–50 ml of aqua regia. The solutionwas boiled to near dryness. Finally, the residuewas dissolved in minimum volume of 2% HCl andfiltered through a Whatman filter paper No. 1.The residue was washed with two 5-ml portions ofhot 2% HCl. The aqueous layer was evaporatedto dryness. The residue was redissolved in 5 ml of2% HCl and made up to 50 ml with distilled water.

Preparation of chelating resin (AXAD-4-PAN)

Earlier reported procedures (Hazer et al. 2009;Taher et al. 2004) were further modified for load-ing PAN onto AXAD-4 resin. An amount of5 g of AXAD-4 resin, was pretreated with anethanol–hydrochloric acid–water (2:1:1) solutionovernight. After the pretreatment, the resin wassubsequently rinsed with triply distilled water un-til pH of the supernatant water became neutraland was packed into a column using ethanol.The resin was then saturated with the reagentby passing 0.01% PAN solution in ethanol at aflow rate of 0.5 mmol L−1. In order to ensurecomplete saturation, the effluent collected wasrepeatedly passed through the same column untilthe whole bed of resin gets uniformly loaded withPAN. Hence after, the resin was washed of anyexcess reagent with distilled water. The amountof PAN taken up by the resin was determined bymeasuring the absorbance of the effluent solutionspectrophotometrically at 470 nm.

Characterization of AXAD-4-PAN

Stability

A 0.5-g sample of the resin was stirred in 25 mL ofacid (0.1–5.0 mol L−1 of HCl and HNO3) and al-kaline solution (0.1–5 mol L−1 of NaOH) for 48 h,then filtered off and washed with distilled water.Its resistance to chemical changes was tested bychecking its sorption capacity. The effect of tem-perature was investigated by subjecting the resinto TGA and DTA in the nitrogen atmosphere atheating rate of 25◦C min−1.


Hydrogen ion capacity

For hydrogen ion capacity, an accurately weighed(0.5 g) resin was first treated with 2.0 mol L−1 HC1and then filtered off, washed with distilled waterto make it free from acid and dried at 100◦C for6 h. The acidic form of the resin was equilibratedwith 20.0 ml 0.1 mol L−1 NaOH solution for 6 hat stirring condition and then the excess alkaliwas estimated with 0.1 mol L−1 hydrochloric acidsolution.

Recommended procedure for sorptionand desorption studies of metal ions

Batch ‘static’ method

A weighed amount of AXAD-4-PAN in Erlen-meyer flask (100 mL) was equilibrated at shakingspeed of 80 rpm with 50 mL of metal solution ofsuitable concentration maintained at constant pHat 25 ± 1◦C for 2 h. The resin was filtered andthe sorbed metal ions were desorbed by shakingwith the appropriate solution of eluting agents andsubsequently analyzed by FAAS.

Column ‘dynamic’ method

A sample of AXAD-4-PAN was soaked in waterfor 24 h and then poured into a glass column ofdimensions 1 cm × 10 cm fitted with sintered disc.The resin bed in the column was buffered with5 mL of the buffer solution of pH 9.2. A solutionof metal ions of suitable concentration was passedthrough the column at a flow rate of 2 mL min−1

after adjusting the pH to 9.2. After the sorptionoperation, the column was washed with distilledwater and then a certain volume of eluting agentwas made to percolate (2 mL min−1) through thebed of loaded resin whereby the sorbed metalions get eluted and subsequently determined byFAAS.

Results and discussion

Characterization of AXAD-4-PAN

The optimum pH for loading of PAN on Am-berlite XAD-4 was observed at pH 5.5–6.5. The

amount of PAN loaded on the resin was found tobe 0.24 mmol g−1 at the optimum pH. The resinwas subsequently characterized by IR spectraldata. The FT-IR spectrum of PAN has prominentbands at 3,437 cm−1 and 1,631.12 cm−1 due toν(O–H) and ν(N=N) respectively. On the otherhand, the FT-IR spectrum of AXAD-4-PAN alsoexhibits the same bands besides the bands thatcorrespond to AXAD-4 resin alone. This supportsthe immobilizing of PAN onto AmberliteXAD-4resin. The broadening of the band at 3,437 cm−1

implies the presence of intramolecular hydrogenbonding between the azo group and the orthohydroxyl group of PAN (Kenawy et al. 2001). Theabsence of broadening of the hydroxyl band inthe spectra of the metal-loaded resin proves theabsence of hydrogen bonding that indicates theparticipation of –OH group in the coordinationprocess. The red shifts of the two peaks namely–OH and –N=N– by 10–15 cm−1 for metal-loadedresin further suggest the involvement of both thegroups in retaining the metals through chelation.The resin shows good chemical stability with noloss of capacity up to 5 mol L−1 of all acids used forstripping of metal ions. It can withstand alkalinemedium up to 4 mol L−1. At concentrations higherthan 5 mol L−1 of NaOH, the sorption capacitywas reduced by 3.5%. According to thermogravi-metric analysis, the resin was found to be stable upto 200◦C with no significant loss of weight otherthan the loss due to sorbed water. Weight lossof 1.49% at 252.21◦C and 12.25% at 359.79◦C inTGA which were supported by an endothermicand exothermic peak, respectively, in the DTAcurve indicates the degradation of PAN reagentof the chelating resin. The hydrogen ion capacitywas found to be 0.48 mmol g−1, which furthersupports the fact that 0.24 mmol g−1 of the reagentcomprising of two replaceable hydrogen ions permolecule (contributed by the hydroxyl and theprotonated pyridine moiety) was adsorbed.

Optimum experimental parameters

In order to optimize sorption of metal ions, themultivariate approach was followed to establishall the parameters. Each optimum condition wasestablished by varying one of them and followingthe recommended procedure.


Ef fect of pH for metal ion uptake

Optimum pH of metal ion uptake was determinedby static method. Excess of each metal ion (50 mL,100 μg mL−1) was shaken with 300 mg of resinfor 120 min. The pH of metal ion solution wasadjusted prior to equilibration over a range of pH2–10 with the corresponding buffer system. Theeffect of pH on the sorption of metal ions onAXAD-4-PAN is shown in Fig. 1. As the complexformation is strongly pH-dependent, careful ad-justment of proper pH for the reagent was neces-sary. The nitrogen of the heterocyclic ring of PANgets protonated at lower pH while the phenolicOH group dissociates in the alkaline region. Dueto this fact, the reagent has sufficient solubilityboth in acidic and alkaline solution and reacts withthe metal ions under slightly alkaline condition toform a stable complex. All the metal ions studiedexhibited higher sorption capacity (Table 2) in thepH range 8.5–9.5. Hence, pH 9.2 was adjusted inall further experiments.

Sorption kinetics and loading halftime

The rate of loading of metal ions on the resinwas determined by static method. Fifty microlitersof each metal ion solution (100 μg mL−1) wasshaken with 300 mg of the resin in a thermo-

pH

0 2 4 6 8 10 12

Sorp

tion

capa

city

(10

-2 m

mol

g-1

)

0

1

2

3

4

5

6

Cd(II)Co(II)Ni(II)Mn(II)Zn(II)Pb(II)Cu(II)

Fig. 1 Dependence of sorption capacity on the pH ofthe solution (experimental conditions 50 mL solution,100 μg mL−1 of metal, pH 9.2, 0.3 g of resin)

Table 2 Kinetics and batch capacity of sorption of metalions on AXAD-PAN (experimental conditions:50 mLsolution, pH 9.2, 0.3 g of resin)

Metal Loading Rate Batchion halftime constant capacity

t1/2 (min) k (min−1) ×10−2 (mmol g−1)

Cd(II) 20 3.4 0.050Co(II) 22 3.1 0.048Ni(II) 20 3.4 0.046Mn(II) 22 3.1 0.044Zn(II) 20 3.4 0.043Pb(II) 24 2.9 0.033Cu(II) 20 3.4 0.030

stat shaker for pre-selected intervals of time. Theloading halftime, t1/2, that is, the time required toreach 50% of the resins total loading capacity wasevaluated from the resulting isotherm. From thekinetics of sorption for each metal (Fig. 2), it wasobserved that 60 min was enough for the sorbentto reach the saturation level for all the metals. Thesorption rate constant k can be calculated usingthe following equation (Pramanik et al. 2006):−ln (1 − F) = kt, where F = Qt/Q and Qt is thesorption amount at sorption time t and Q thesorption amount at equilibrium. Putting the valueof Qt at t1/2 in the above equation we may getthe corresponding value of k for every metal ion(Table 2).

Contact time (min)

0 10 20 30 40 50 60 70 80

Satu

rati

on (

%)

0

20

40

60

80

100

120

Zn(II)Ni(II)Mn(II)Cd(II)Co(II)Pb(II)Cu(II)

Fig. 2 Rate of sorption of metal ions by AXAD-4-PAN(experimental conditions 50 mL solution, pH 9.2, 0.3 g ofresin)


Ef fect of resin amount on the sorption capacity

To investigate the effect of the amount of the resinon the sorption of metal ions, an excess of themetal ion solution corresponding to150 μg mL−1

was equilibrated with varying amounts of resinbuffered at pH 9.2. The retention of the metal ionsper gram of the resin increased with the increasein the amount of the resin. An almost constant andmaximum sorption capacity was observed after300 mg of the resin.

Ef fect of f low rate for sorption and elution

The effect of flow rate on the sorption was studiedby varying the flow rate from 1–8 mL min−1 usingcolumn method. During the sorption studies, itwas observed that at a flow rate greater than3 mL min−1 there was an appreciable reduction inthe exchange capacity of almost all the metals by10–15%. Hence, the optimum flow rate was takento be 2.0 mL min−1 for all the dynamic studies.This decrease in sorption with increasing flowrate may be due to the decrease in equilibrationtime between two phases. In the elution studies,quantitative recovery of the sorbed metals fromthe resin could be achieved up to a flow rate of2 mL min−1.

Types of eluting agents and chromatographicseparation

In order to investigate the most efficient elutingagent, varying concentrations of different volumesof mineral and organic acids such as HNO3, HCl,H2SO4, perchloric, formic, and acetic acid weretried as depicted in Table 3. Distilled water wasfound to be unsuitable for the purpose of elu-tion as <0.5% recovery was achieved indicatingthat the metal ions were retained by the resinby some strong bonding forces. Perchloric acid of2 mol L−1 was found to give >97% recovery ofCu(II) and Ni(II) with 5 and 2.5 mL, respectively,while 2 mol L−1 HNO3 could give >98% recoveryof Zn(II) and Co(II) with 5 mL. Among the min-eral acids, 2.5 mL of 0.5 mol L−1 H2SO4 was foundto be the best eluent for 100% elution of Cd(II),Pb(II), and Mn(II). Organic acids proved to beunsuitable (<89%) for the stripping of any of themetal ions studied. The behavior of these elutingagents for different metal ions may be interpretedon the basis of the HSAB principle and stabilityconstants (Sen and Mingos 1993; Bjerrum et al.1958). Species like SO −2

3 , SO −24 (contributed by

H2SO4), NO −2 , NO −

3 (contributed by HNO3), andClO −

4 (contributed by HClO4) act as Lewis basesthat bind with the metal ions as stable complexes.Thus, the metal ions bound at the chelating sites

Table 3 Elution of metal ions from the AXAD-4-PAN resin (column parameters: elution flow rate 2 mL min−1)

Type Stripping agents Mean recovery for five replicates (%)

Concentration Volume Cd(II) Co(II) Ni(II) Mn(II) Zn(II) Pb(II) Cu(II)(mol L−1) (mL)

HCl 1 15 65 78 75 77 75 88 773 15 68 80 76 79 76 89 79

HNO3 1 15 76 92 79 78 85 78 722 5 79 99 80 85 98 83 79

H2SO4 0.1 15 78 2 1.5 69 2 87 30.5 5 100 3 5 100 4 100 60.5 2.5 100 3 2 100 2 100 2

HCOOH 1 15 45 60 46 44 70 44 552 2.5 56 69 58 48 79 48 65

CH3COOH 1 15 80 67 65 49 55 49 572 15 88 69 68 55 65 55 59

HClO4 2 2.5 12 55 99 21 34 21 902 5 15 58 99 35 38 25 97


get released. Hence, the relative preference ofthese species may be the result of hard–hard andsoft–soft interactions of acids and bases. The rela-tive hardness or softness of the metal ions dependson their characteristics in the chelated form.

The variation of eluting agents for stripping ofthe studied metal ions has been exploited to ac-complish the separation of several binary mixturesof metal ions as illustrated in Table 4. For this pur-pose, a series of 100 mL of solutions containing bi-nary mixtures of the metal ions (100 μg each) werepassed through the column packed with 0.3 g ofthe resin. Separation was done by eluting sorbedmetal ions with different eluting agents. The se-lectivity factor (Table 4) of each of the binary

Table 4 Separation of binary mixtures by elution tech-nique and the corresponding selectivity factors for eachcouple (experimental conditions: 100 mL solution, 100 μgof each metal ion, 0.3 g of resin)

Binary Eluents Recovery Selectivitymixtures (%) factor

Cd(II) 0.5 mol L−1 H2SO4 100 4.37Cu(II) 2 mol L−1 HClO4 97Zn(II) 2 mol L−1 HNO3 98 1.98Cd(II) 0.5 mol L−1 H2SO4 100Ni(II) 2 mol L−1HClO4 99 1.52Cd(II) 0.5 mol L−1 H2SO4 100Co(II) 2 mol L−1 HNO3 99 2.40Cd(II) 0.5 mol L−1 H2SO4 100Cu(II) 2 mol L−1 HClO4 97 1.07Pb(II) 0.5 mol L−1 H2SO4 100Zn(II) 2 mol L−1 HNO3 98 1.29Ni(II) 2 mol L−1 HClO4 99Pb(II) 0.5 mol L−1 H2SO4 100 9.82Co(II) 2 mol L−1 HNO3 99Cu(II) 2 mol L−1 HClO4 97 2.41Mn(II) 0.5 mol L−1 H2SO4 100Zn(II) 2 mol L−1 HNO3 98 1.09Mn(II) 0.5 mol L−1 H2SO4 100Mn(II) 0.5 mol L−1 H2SO4 100 1.19Ni(II) 2 mol L−1HClO4 99Zn(II) 2 mol L−1 HNO3 98 2.07Pb(II) 0.5 mol L−1 H2SO4 100Ni(II) 2 mol L−1HClO4 99 2.69Pb(II) 0.5 mol L−1 H2SO4 100Co(II) 2 mol L−1 HNO3 99 2.87Ni(II) 2 mol L−1HClO4 99Mn(II) 0.5 mol L−1 H2SO4 100 4.36Co(II) 2 mol L−1HNO3 99Cu(II) 2 mol L−1 HClO4 97 2.21Zn(II) 2 mol L−1 HNO3 98

mixtures was evaluated from the ratios of theirdistribution coefficients (Amara and Kerdjoudj2003) in order to indicate the relative preferencefor one metal over other for each couple of met-al ions.

Resin reusability test

The reusability of the resin was tested by loadingthe metal ions several times on a column from asolution having a concentration 50 μg mL−1 at aflow rate of 2 mL min−1 and eluting by the ap-propriate eluting agent. The sorbent can be usedfor more than 35 times in succession without anyappreciable loss in the sorption efficiency. Afterthe resin had been used for 40 cycles, the sorptioncapacity got reduced by 5%.

Study of interferences

Since the present work deals with the determina-tion of levels of trace metal ions of the naturalwaters, the influences of possible matrix ions inthe environmental samples were examined. Theeffect of cations and anions, which are the mainconstituents of natural waters, namely citrate, ox-alate, tartrate, besides (NO3)

2−, (CO3)2−, (NH4)

+,SO 2−

4 , PO 3−4 , Cl−, K+ and Na+, in the form of

their respective salts, on the sorption of the metalions by AXAD-4-PAN resin was studied. Forevery combination of one of these electrolyteswith each metal ion, a set of binary mixtures con-taining 25 μg of each metal ion in 100 mL and theelectrolytes at different concentration levels wastaken. Dynamic method was employed for thesestudies. The tolerated amounts of each matrix ion,for the preconcentration of trace metal ions, werethe concentration values tested that caused thelowering of recovery by more than 3%. It wasfound that the common ions coexisting in naturalwaters do not interfere under the experimentalconditions (Table 5).

Preconcentration factor and breakthroughcapacity

The limit of preconcentration was determined byincreasing the volume of metal ion solution andkeeping the total amount of loaded metal ion


Table 5 Tolerance limitof foreign species(in binary mixtures)on sorption of metal ions(experimental conditions:100 mL solution, pH 9.2,25 μg of each metal ion,0.3 g of resin)

Foreign species Tolerance limit of metal ions

(μg mL−1) Cd(II) Co(II) Ni(II) Mn(II) Zn(II) Pb(II) Cu(II)

NaCl 45,000 35,000 40,000 10,000 25,000 20,000 25,000Na2SO4 60,000 55,000 50,000 45,000 50,000 40,000 65,000NaNO3 45,000 40,000 45,000 40,000 35,000 30,000 45,000Na2PO4 500 6,000 6,000 4,500 500 500 3,000NH4Cl 35,000 45,000 50,000 40,000 40,000 30,000 30,000Sodium citrate 300 350 400 250 300 300 250Sodium oxalate 100 100 100 80 70 60 50Sodium potassium tartrate 150 100 90 120 100 60 50CH3COONa 12,000 11,000 12,000 6,000 7,000 5,000 4,000CaCl2 20,000 15,000 20,000 10,000 12,000 8,000 9,000MgCl2 35,000 40,000 50,000 35,000 30,000 10,000 15,000

constant at 10 μg. The breakthrough volume cor-responds to the volume at which the effluent con-centration of metal ions from the column is about3–5% of the influent concentration. The break-through volume was determined by the dynamicprocedure. The overall capacity, breakthrough ca-pacity and the degree of utilization was deter-mined by the literature method (Helfferich 1962).Figure 3 gives the breakthrough curves for all themetal studied. The overall sorption capacity calcu-lated on the basis of total saturation volume wascompared with the corresponding breakthroughcapacities for each metal. The closeness of thedynamic capacity to the total sorption capacityreflects the applicability of the column techniquefor preconcentration. Quantitative collection of

Volume of effluent (mL)

0 200 400 600 800 1000 1200 1400

C/C

o

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Cd(II)Co(II)Ni(II)Mn(II)Zn(II)Pb(II)Cu(II)

Fig. 3 Breakthrough curves for sorption of metal ions:C/Co is the concentration ratio of the effluent toinfluent (column parameters: pH 9.2, sorption flow rate2 mL min−1, 0.5 g of resin)

metal ions was possible from solutions of concen-tration in the order of 10–12.5 μg L−1 with a re-covery up to 98% resulting in a preconcentrationfactor of 160–400 (Table 6).

Method validation and applications

Prior to analysis of real water samples, validationof the method was performed by analyzing stan-dard reference materials and recoveries of tracemetals after spiking. In order to test the accu-racy of the method, 50 mL of pretreated environ-mental (vehicle exhaust particulates), biological(human hair and tea leaves) and alloys (Rompinhematite and zinc base die-casting alloy C) stan-dard reference material samples were analyzedby recommended column method after adjustingits pH to 9.2. The mean concentration valuesof the metals studied agreed with the certifiedvalues. Calculated Student’s t (t test) values forrespective metal ions were found to be less thancritical Student’s t values at the 95% confidencelevel (Table 7). Hence, the mean values were notstatistically significant from the certified valuesindicating absence of bias in the present method.Analytical recoveries of metal ions were ascer-tained by measuring the recovery of standard ad-ditions (S.A.) from various real water (500 mL)samples which were spiked with Cd(II), Co(II),Ni(II), Mn(II), Zn(II), Pb(II), and Cu(II) of con-centrations 12, 80, 55, 25, 10, 80, and 56 μg L−1,respectively. These concentrations were guidedby middle value of preconcentration limit andmaximum concentration of working range of


Table 6 Preconcentration and breakthrough profiles of metal ions on AXAD-PAN (column parameters: pH 9.2, sorptionflow rate 2 mL min−1, 0.5 g of resin)

Metal Preconcentration studies Breakthrough studies

ions Total Concentration Preconcentration Overall sorption Breakthrough Breakthrough Degree ofvolume limit factor capacity capacity volume column(mL) (ng mL−1) (mmol g−1) × (mmol g−1) × (mL) utilization

10−2 10−2

Cd(II) 1,000 10.0 400 5.80 4.17 855 0.72Co(II) 1,000 10.0 200 5.30 4.00 855 0.72Ni(II) 1,000 10.0 400 5.10 3.83 850 0.71Mn(II) 1,000 10.0 400 5.00 3.67 850 0.71Zn(II) 1,000 10.0 200 4.60 3.58 850 0.71Pb(II) 800 12.5 320 3.35 2.64 765 0.63Cu(II) 800 12.5 160 3.50 2.45 760 0.64

Table 7 Analysis of metal ions in standard reference materials (column parameters: pH 9.2, sorption flow rate 4 mL min−1,elution flow rate 2 mL min−1, 0.3 g of resin)

Samples Certified value Found by proposed method Calculated student’s(μg g−1) (μg g−1)a t valueb

Vehicle exhaust particulates Cd: 1.1, Pb: 219, Cd: 1.04 (4.80), Pb: 215.00 (2.00), 2.68,2.08, 2.61,NIES 8c Co: 3.3, Cu: 67, Co: 3.17 (3.50), Cu: 68.00 (2.70), 1.22, 0.74

Ni: 18.5 Ni: 18.80 (4.80)Human hair NIES 5 Mn: 5.2, Zn: 169, Mn: 5.10 (2.50), Zn: 167.00 (2.10), 1.75,1.28, 0.43,

Cu: 16.3, Ni: 1.8, Cu: 16.30 (3.20), Ni: 1.74 (4.20), 1.84, 0.99Pb: 6.0 Pb: 6.10 (3.70)

Tea leaves NIES 7 Mn: 700, Zn: 33, Mn: 699.00 (6.64), Zn: 31.94 (2.90), 0.34,2.55,Cu: 7.0, Ni: 6.5 Cu: 6.75 (3.80),Ni: 6.40 (2.20) 2.18,1.59

Chlorella NIES 3 Zn: 20.5,Cu:3.5, Zn: 19.89 (3.5), Cu: 3.42 (4.3), 1.96, 1.22,Co: 0.87,Pb: 0.60 Co: 0.86 (1.6), Pb: 0.58 (4.8) 1.62, 1.61

Rompin hematite, Mn: 2200, Cu: 640, Mn: 2197.00 (1.50), Cu: 638.00 (2.60), 0.20,0.27,JSS (800–3)d Zn: 1030, Pb: 210 Zn: 1027.00 (2.8), Pb: 209.00 (2.90) 0.23, 0.37

Zinc base die-casting Cu: 1320, Pb: 82, Cu: 1318.00 (1.60), Pb: 81.58 (1.80), 0.21,1.34, 1.85,alloy C NBS 627e Cd: 51, Mn: 140, Cd: 51.58 (2.80), Mn: 138.95 (4.60), 0.37, 2.22

Ni: 29 Ni: 28.00 (1.0)aRelative standard deviation, n = 5bAt 95% confidence levelcNational Institute of Environmental Studies (NIES)dIron and Steel Institute of Japan (JSS)eNational Bureau of Standards (NBS)

Table 8 Determination of metal ions in natural waters collected from various locations after preconcentration by AXAD-4-PAN column (column parameters: pH 9.2, sorption flow rate 2 mL min−1, 0.5 g resin)

Samples Method Metal ion found by proposed method μg L−1 (RSD)a

Cd(II) Co(II) Ni(II) Mn(II) Zn(II) Pb(II) Cu(II)

Canal water Direct N.D.b 3.3 (3.4) 3.4 (2.2) 4.6 (3.5) 5.2 (2.9) 3.3 (4.6) 12.9 (2.9)(Kasimpur, U.P., India) S.Ac 1.7 (3.9) 3.1 (2.8) 3.5 (2.4) 4.5 (3.5) 5.5 (2.8) 3.5 (4.1) 12.6 (2.6)

Tap water Direct N.D.b 6.9 (2.5) 5.5 (2.1) 11.3 (4.1) 17.4 (3.1) 12.7 (4.9) 10.3 (2.9)(University Campus, Aligarh) S.A. 1.5 (4.8) 7.0 (2.9) 5.4 (2.2) 11.4 (3.7) 16.7 (3.2) 12.5 (3.3) 10.0 (3.1)

Sewage water (Ni plating Direct 3.6 (1.8) 5.1 (3.9) 12.4 (3.0) 5.9 (2.8) 7.1 (4.2) 6.0 (4.6) 8.2 (4.9)industrial area, Aligarh, India) S.A. 3.6 (1.9) 5.2 (4.7) 12.6 (3.2) 5.7 (2.6) 7.1 (4.4) 6.3 (4.5) 8.4 (3.7)

River water Direct 2.5 (2.4) 3.1 (3.3) 3.9 (2.5) 4.5 (4.2) 4.1 (4.3) 3.2 (2.1) 14.0 (3.2)(The Ganga Narora, U.P., India) S.A. 2.6 (2.2) 3.3 (3.8) 3.8 (2.8) 4.3 (2.9) 4.4 (3.4) 3.1 (4.3) 14.4 (2.9)

aRelative standard deviation, n = 3bNot detectedcStandard addition method


Tab

le9

Com

pari

son

ofpr

evio

usw

orks

usin

g1-

(2-p

yrid

ylaz

o)-2

-nap

htho

las

the

chel

atin

glig

and

Typ

eof

Met

alio

nsSo

rpti

onca

paci

tyP

reco

ncen

trat

ion

Pre

conc

entr

atio

nD

etec

tion

limit

Ref

eren

ces

supp

ort

(mm

olg−

1 )fa

ctor

limit

(ng

mL

−1)

(ng

mL

−1)

Am

berl

ite

Cd(

II),

Co(

II),

Ni(

II),

Mn(

II),

0.05

0,0.

048,

0.04

6,0.

044,

400,

200,

400,

400,

10,1

0,10

,10,

0.09

,0.5

4,1.

30,0

.20,

Pre

sent

wor

kX

AD

-4Z

n(II

),P

b(II

),C

u(II

)0.

043,

0.03

3,0.

030

200,

320,

160

10,1

2.5,

12.5

0.28

,1.1

0,0.

42A

mbe

rlit

eC

u(II

),C

d(II

),P

b(II

)0.

108,

0.02

3,0.

007

5025

,20,

505.

7,0.

8,23

.2B

erm

ejo-

Bar

rera

XA

D-2

etal

.(20

03)

Am

berl

ite

Ni(

II)

0.00

187

2527

5–

Fer

reir

aet

al.(

1999

)X

AD

-2A

mbe

rlit

eC

u(II

)0.

0024

296

0.06

Yeb

raet

al.(

2001

)X

AD

-4A

mbe

rlit

eN

i(II

),C

d(II

),C

u(II

),P

b(II

),20

030

,30,

15,1

5,Y

ebra

etal

.(20

02)

XA

D-4

Cr(

II),

Mn(

II)

15,1

0A

mbe

rlit

eP

b(II

)0.

0009

612

000

–5.

0T

uzen

etal

.(20

05)

XA

D-4

Am

berl

ite

Ni(

II),

Cd(

II),

Co(

II),

0.08

,0.0

435,

0.07

97,

200

max

imum

10to

200.

161,

0.05

6,0.

072,

Nar

inan

dSo

ylak

(200

3)X

AD

-16

Cu(

II),

Pb(

II),

Cr(

III)

0.07

87,0

.023

1,0.

0961

0.07

9,0.

121,

0.26

8A

mbe

rlit

eC

u(II

),N

i(II

),F

e(II

),P

b(II

),0.

02,0

.02,

0.02

,0.0

4,10

0,10

0,10

0,10

0,20

,20,

20,4

0,0.

19,1

.2,2

.7,0

.13,

Tok

alio

glu

etal

.(20

06)

1180

Cr(

III)

,Cd(

II),

Mn(

II)

0.05

,0.0

033,

0.00

677

80,1

50,1

5050

,3.3

,6.6

74.

1,0.

06,0

.13

Am

berl

ite

Cd(

II),

Ni(

II)

0.04

7,0.

062

30,3

020

,83

0.7,

3.1

Haz

eret

al.(

2009

)X

AD

-118

0A

mbe

rlit

eN

i(II

),C

u(II

),P

b(II

),C

r(II

)–

250

8.0

–N

arin

etal

.(20

01)

XA

D-2

000


calibration curve of FAAS for each metal ionin order to ensure complete sorption and avoiddilution of the final eluate during determination.It was found that the mean percentage recoveriesof all the metal ions studied were 98.8–100.2%at 95% confidence level. The detection limits forFAAS were calculated as the concentration cor-responding to the signal equal to three times thestandard deviation of the mean blank signal for20 determinations of the blank (including buffer)and were found to be 0.09, 0.54, 1.30, 0.20, 0.28,1.10 and 0.42 μg L−1 for Cd(II), Co(II), Ni(II),Mn(II), Zn(II), Pb(II), and Cu(II), respectively.Precision of the proposed method is reflectedby low relative standard deviation (<5%) in theanalysis of SRMs as well as various water samples(Tables 6 and 7). Applicability of the presentmethod for preconcentration and determinationof metal ions was accomplished by analyzing river,canal, sewage, and tap water. A 500 mL of each ofthe sample volume was adjusted to pH of 9.2 byadding 5 ml of ammonia buffer and loaded on tothe column of AXAD-4-PAN. The concentrationsof metal ions were determined by following rec-ommended method using FAAS (direct method).The metal determinations were also confirmedusing the S.A. method. The closeness of resultsof direct and S.A. method (Table 8) indicatesthe reliability of the present method for metalanalyses in water samples of various matrices.

Conclusion

The chelating ability of chromogenic ligand, PAN,has been utilized in developing chelating sorbentsfor the purpose of separation and preconcentra-tion of trace metal ions. To assess the credibility ofthe present work a comparative data from previ-ous works on preconcentration studies using PANare summarized in Table 9. The results reflectits promising nature for trace metal ion analysisin various natural water resources, environmentaland biological samples. The main advantages ofthis procedure are: the simple and fast prepara-tion of the chelating resin and no requirement oforganic solvents in the metal elution step. More-over, this resin is applicable to quantitative chro-matographic separation of metal ions in binary

mixtures. Comparison of sorption capacities andpreconcentration factor of metal ions on PAN-functionalized resinwith different polymeric sup-port showed that AXAD-4-PAN surface modifiedresin has greater value of sorption capacity andpreconcentrationfactor. This method shows rela-tively higher tolerance for common matrix ionsexcept for KNO3 and NaCl for Ni(II) (Ferreiraet al. 1999). The detection limit for all the metalswas found to be lower than previously reportedsorbent modified with PAN except for Cd(II)(Yebra et al. 2001). Breakthrough studies hasalso been presented and found to be suitable forcolumn operation. The reusability of the presentmethod is comparable with other works.

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