solid phase extraction of trace amounts of silver (i) using dithizone-immobilized alumina-coated...

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Solid phase extraction of traceamounts of silver (I) using dithizone-immobilized alumina-coated magnetitenanoparticles prior to determination byflame atomic absorption spectrometryMohammad Ali Karimi a b , Abdolhamid Hatefi-Mehrjardi a b ,Sayed Zia Mohammadi a c , Alireza Mohadesi a c , MohammadMazloum-Ardakani d , Asghar Askarpour Kabir b , MaryamKazemipour e & Najmeh Afsahi ea Department of Chemistry, Payame Noor University, P.O. Box19395-4697, Tehran, Iranb Department of Chemistry & Nanoscience and NanotechnologyResearch Laboratory (NNRL), Payame Noor University (PNU),Sirjan, Iranc Department of Chemistry, Payame Noor University (PNU),Kerman, Irand Department of Chemistry, Faculty of Sciences, Yazd University,Yazd, Irane Department of Chemistry, Faculty of Sciences, Islamic AzadUniversity of Kerman, Kerman, IranPublished online: 03 Feb 2012.

To cite this article: Mohammad Ali Karimi , Abdolhamid Hatefi-Mehrjardi , Sayed Zia Mohammadi ,Alireza Mohadesi , Mohammad Mazloum-Ardakani , Asghar Askarpour Kabir , Maryam Kazemipour& Najmeh Afsahi (2012) Solid phase extraction of trace amounts of silver (I) using dithizone-immobilized alumina-coated magnetite nanoparticles prior to determination by flame atomicabsorption spectrometry, International Journal of Environmental Analytical Chemistry, 92:12,1325-1340, DOI: 10.1080/03067319.2011.563385

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Intern. J. Environ. Anal. Chem.Vol. 92, No. 12, 15 October 2012, 1325–1340

Solid phase extraction of trace amounts of silver (I) using dithizone-

immobilized alumina-coated magnetite nanoparticles prior to

determination by flame atomic absorption spectrometry

Mohammad Ali Karimiab*, Abdolhamid Hatefi-Mehrjardiab,Sayed Zia Mohammadiac, Alireza Mohadesiac, Mohammad Mazloum-Ardakanid,

Asghar Askarpour Kabirb, Maryam Kazemipoure and Najmeh Afsahie

aDepartment of Chemistry, Payame Noor University, P.O. Box 19395-4697, Tehran, Iran;bDepartment of Chemistry & Nanoscience and Nanotechnology Research Laboratory (NNRL),

Payame Noor University (PNU), Sirjan, Iran; cDepartment of Chemistry, Payame NoorUniversity (PNU), Kerman, Iran; dDepartment of Chemistry, Faculty of Sciences, Yazd

University, Yazd, Iran; eDepartment of Chemistry, Faculty of Sciences,Islamic Azad University of Kerman, Kerman, Iran

(Received 6 August 2010; final version received 9 February 2011)

A new, simple, fast and reliable solid-phase extraction (SPE) method has beendeveloped to separation/preconcentration of trace amounts of silver ion fromenvironmental water samples using dithizone/sodium dodecyl sulfate immobilizedon alumina-coated magnetite nanoparticles (DTZ/SDS-ACMNPs) and itsdetermination by flame atomic absorption spectrometry. The coating of aluminaon Fe3O4 NPs not only avoids the dissolving of Fe3O4 NPs in acidic solution, butalso extends their application without sacrificing their unique magnetizationcharacteristics. This method avoided the time-consuming column-passing processof loading large volume samples in traditional SPE through the rapid isolation ofDTZ/SDS-ACMNPs with an adscititious magnet. Optimal experimental condi-tions including amount of DTZ/SDS, pH value, standing time, sample volume,type, volume and concentration of eluent and co-existing ions have been studiedand established. Under the optimal experimental conditions, the detection limitfor Ag(I) with enrichment factors of 100 was found to be 0.52 ngmL�1 and itsrelative standard deviations (RSD) was 3.4% (n¼ 10, C¼ 5.0mgmL�1). Thelinear range of calibration curve for Ag(I) was 2–5000 ngmL�1 with a correlationcoefficient of 0.9991. The proposed method was successfully applied to thedetermination of target analyte in different water and wastewater samples. Thevalidity of the method has been checked by applying it to study the recovery ofsilver ion in spiked water and wastewater samples.

Keywords: solid-phase extraction; alumina-coated magnetite nanoparticles;silver(I); flame atomic absorption spectrometry

1. Introduction

In recent years, great attention has been paid to the application of nano-structurematerials, especially nano-sized magnetic particles. These materials have been used in

*Corresponding author. Email: [email protected]

ISSN 0306–7319 print/ISSN 1029–0397 online

� 2012 Taylor & Francis

http://dx.doi.org/10.1080/03067319.2011.563385

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various scientific fields such as biotechnology, engineering, biomedical, environmental andmaterial science [1–10]. A distinct advantage of these is that magnetite nanoparticles(MNPs) can be readily isolated from sample solutions by the application of an externalmagnetic field. Surface modification of MNPs is a challenged key for different applicationsand can be accomplished by physical/chemical adsorption of organic and inorganicspecies [11–15].

Solid phase extraction (SPE) is a routine extraction method for determining trace levelcontaminants in environmental samples [16]. Many research groups have explored theapplication of several nano-sized SPE adsorbents such as nanoparticles (NPs),nanocomposites and nanotubes [7,17,18]. Nanomaterials can offer several advantagesover traditional SPE sorbents such as very high surface areas and a short diffusion route,which result in high extraction capacity and efficiency. However, the use of nanomaterialshas some inherent limitations, especially when applied in the adsorption and separation ofspecies from large volumes of the samples. The nanosized particles packed SPE columnexhibits high backpressure and making it very difficult to adopt high flow rates in mode ofcolumn dynamic extraction. These nanosized SPE adsorbents are also lead to a very lowfiltration rate in the static batch mode. But MNPs can readily be isolated from samplesolutions by the application of an external magnetic field. These NPs are super-paramagnetic, which means that they can readily be attracted by a magnet but do notretain magnetism after the field is removed. Therefore, suspended superparamagneticparticles tagged with organic and/or inorganic species can be removed from the matrix byapplying a magnetic field, but they do not agglomerate after removal of the field. Hence,the NPs may be reused or recycled. In this paper, we will explore the possibility ofdithizone/sodium dodecyl sulfate immobilized on alumina-coated magnetite nanoparticles(DTZ/SDS-ACMNPs) to act as SPE sorbents for the separation and preconcentration oftrace level silver ions from environmental samples.

With the expansion of industrial activities during this century, a large increase in heavymetal quantities has been spread in the environment. The toxicity of these heavy metalsis widely recognized owing to their adverse effects upon human health. Silver compoundsand alloys have been widely used in industry, jewellers and pharmaceutical preparationsbecause of their marked antibacterial properties [19,20]. Recently, silver impregnatedfilters are also used in water disinfection, while silver concentrations up to 200 mgmL�1 ispermitted for antimicrobial activities for human health [21,22]. Moreover, recentinformation about the interaction of silver with essential nutrients, especially vitaminB12, vitamin E, selenium and copper has focused attention on its potential toxicity [23].A variety of methods including spectrometric and electrochemical techniques have beenproposed for the determination of silver in different environmental samples [24–27].However, aforementioned methods except to flame atomic absorption spectrometry(FAAS) involve a greater cost and increased instrumentation complexity, limiting itswidespread application to routine analytical works. Direct determination of trace amountsof metal ions in some samples by FAAS is difficult because of low sensitivity.Thus, preconcentration procedures are often required. Different techniques such ascloud point extraction [28], liquid–liquid extraction [29], dispersive liquid–liquidmicroextraction [30–32] and solid-phase extraction [33–42] have been used to enrich thesilver(I) ion and separate it from the interferences.

To the best of our knowledge, this is the first time that alumina-coated MNPs based onimmobilizing a complexing reagent on their surface used for the separation/preconcentra-tion of trace amounts of metallic ions. As a reagent commonly used in spectrophotometry,

1326 M. Ali Karimi et al.

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dithizone (DTZ, 1,5-diphenyl carbazone) can form stable complex with Ag(I) underspecial conditions due to functional groups of –SH– and –NH– [43–45]. In this study, atfirst step the MNPs were synthesized and then coated with alumina subsequently modifiedwith DTZ as extractor, with aid of SDS, based on the ion pair formation and simplephysical adsorption. DTZ was incorporated into the inner hydrophobic part of producedadmicelles in ammoniacal mixture of DTZ, SDS and ACMNPs was acidified to producean assemble suitable for preconcentration and determination of silver(I) ion. Silver ionsare adsorbed on DTZ/SDS-ACMNPs as extractors that were isolated using an adscititiousmagnet. Then adsorbed analyte was eluted with thiourea solution and quantifiedusing FAAS.

2. Experimental

2.1 Apparatus

A flame atomic absorption spectrophotometer (PG Instruments, England) was used with asilver hollow-cathode-lamp, an operating current of 2mA and wavelength and spectralbandwidth of 328.1 and 0.2 nm, respectively. pH measurements were made with aMetrohmModel 780 pH meter with a combination glass electrode. Other instruments usedwere: ultrasonic bath (S60H Elmasonic, Germany), mechanical stirrer (Heidolph,RZR2020), orbital shaker (Ika, KS130 Basic). An electronic analytical balance(Adam, AA220LA) was used for weighting the solid materials. In addition, formagnetic separations a strong neodymium-iron-boron (Nd2Fe12B) magnet (1.2 T,2.5 cm� 5 cm � 10 cm) was used.

The surface morphology of the powders was observed by the scanning electronmicroscope (LEO 1455VP SEM). A Fourier transform infrared spectrometer (IR Prestige-21, Shimadzu) was used to determine the identity of the as-prepared nanoparticles and tocharacterize the coated Fe3O4 nanoparticles. Magnetic properties of the particles weredetermined by vibrating sample magnetometer (VSM 7400 Model Lake-Shore).

2.2 Reagents and solutions

All of the chemicals were of analytical grade and prepared with double distilled water.Dithizone (DTZ), sodium dodecylsulfate (SDS), ferrous chloride (FeCl2 � 4H2O), ferricchloride (FeCl3 � 6H2O), aluminium isopropoxide, ethanol, thiourea, ammonia, hydro-chloric acid and sodium hydroxide were used without further purification processes. All ofthe chemicals were obtained from Merck. A stock solution of silver at a concentration of1000 mgmL�1 was prepared by dissolving appropriate amounts of AgNO3 in deionizedwater containing 1mL concentrated nitric acid and stored in the dark. The pHs of thesolutions were adjusted with phosphate buffer.

2.3 Preparation of alumina-coated Fe3O4 NPs (ACMNPs)

The alumina-coated Fe3O4 NPs (ACMNPs) were prepared according to Li et al. withminor modification [15]. At first step the Fe3O4 NPs (MNPs) were prepared by chemicalco-precipitation procedure [12]. Ferrous chloride (2.0 g), ferric chloride (5.2 g), andhydrochloric acid (12mol L�1, 0.85mL) were dissolved in 25mL pure deionized water. Themixture was added dropwise into 250mL NaOH solution (1.5mol L�1) under vigorous

International Journal of Environmental Analytical Chemistry 1327

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stirring with nitrogen gas passing continuously through the solution during the reaction.

After the reaction, the obtained MNPs precipitate was separated from the reaction

medium under the magnetic field, and rinsed with 200mL pure deionized water four times.

Then, the product was oven dried at 80�C.For preparation of ACMNPs, aluminium isopropoxide (1.0 g) was dissolved in ethanol

(60mL) to form a clear solution. MNPs (0.1 g) were then dispersed in the freshly prepared

solution for 5min with the aid of ultrasonic waves. A mixture of water and ethanol

(1:5, v/v) was added dropwise to the suspension of MNPs with vigorous stirring. The

mixture was stirred for half an hour after the addition. Subsequently, the suspension was

standing for one hour before separating and washing with ethanol. After five cycles of

separation/washing/redispersion with ethanol, the powder obtained was oven dried and

calcined at 500�C for three hours.

2.4 Preparation of DTZ/SDS-ACMNPs

A DTZ/SDS solution was prepared by dissolving 80.0mg dithizone and 200.0mg SDS in

50mL of 0.1mol L�1 aqueous ammonia diluted to 100mL with deionized water. Ten

milliliters of DTZ/SDS solution was added to 10mL water containing 0.1 g of ACMNPs.

The pH of this suspension was adjusted to 2.0 by dropwise addition of HNO3 (0.1mol L�1)

solution. The mixed solution was shaken for 15min and then separated from the reaction

medium under the magnetic field, and rinsed with 10mL pure deionized water. This

product was used as sorbent for silver(I) ion.

Figure 1. Procedure for magnetic solid-phase extraction.


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2.5 General procedure

The procedure for the magnetic extraction is presented in Figure 1 and detailsare as follows: 10mL of silver(I) ion solution (5.0 mgmL�1) was added to 0.1 g ofDTZ/SDS-ACMNPs from Section 2.4, subsequently the solution was shaken for 10min tofacilitate adsorption of the metal ions onto the NPs. Then the magnetic adsorbent wasseparated easily and quickly using adscititious magnet. Subsequently, the pH of 5mLthiourea (0.4mol L�1) solution was adjusted to 5.5 with phosphate buffer and added aseluent. Finally, after mixing, magnetite nano-adsorbents were separated magnetically fromsolution by the magnet and were revert to cycle according to Figure 1. The eluate solutionwas also pipetted into a test tube for FAAS analysis.

2.6 Sample preparation

Water and wastewater samples were collected in acid leached polyethylene bottles.The samples were filtered before analysis through a 0.45-mm membrane filter (Millipore)and stored in polyethylene container for subsequent usage after they were acidified to pH2.0 with concentrated HNO3, in order to prevent adsorption of the metal ions on theflask walls.

3. Results and discussion

3.1 Characterization of MNPs, ACMNPs and DTZ/SDS-ACMNPs

To enable practical application of ACMNPs, it is most important that the sorbents shouldpossess superparamagnetic properties. Magnetic properties were characterized bymeasuring the hysteresis and remanence curves by means of a vibrating samplemagnetometer (VSM). The magnetization curves show that both MNPs and ACMNPsexhibit typical superparamagnetic behaviour owing to no hysteresis (Figure 2). The

Figure 2. The magnetic behaviour of magnetite nanoparticles (a) and alumina-coated magnetitenanoparticles (b).


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remanence and coercivity are zero, illustrating that the NPs respond magnetically to anexternal magnetic field, and redisperse rapidly when the magnetic field is removed.Another key parameter is the values of large saturation magnetization of 56.72 and9.34 emu g�1 for MNPs and ACMNPs, respectively. The large saturation magnetizationfor MNPs; and compared with ACMNPs due to Al2O3 coating on the Fe3O4 NPs resultsin the decrease of Fe3O4/Al2O3 NPs in the magnetic strength. However, these ACMNPsare sufficient for magnetic separation with a conventional magnet. Figure 3 displays theSEM images of MNPs and ACMNPs, which illustrates the uniform size distribution ofthe nanospheres.

The modified ACMNPs were also confirmed by FT-IR analysis, as shown in Figure 4.As can be seen in Figure 4(a), a broad band exists around 644.22 cm�1, assignable to theFe–O–Fe of the MNPs. The peak at about 1602.85 cm�1 can be assigned to the stretchingvibration of N2 adsorbed on the surfaces of the nanoparticles. The flexing vibration peakof hydroxyl, resulting from the adsorbed water, can be observed at 3497.15 cm�1 [46].

Figure 3. SEM images of Fe3O4 nanoparticles (a) and alumina-coated Fe3O4 nanoparticles (b).


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In the spectrum of ACMNPs (Figure 4(b)), compared with the spectrum of MNPs, afterbinding alumina, and the broadening of the peak at 638.07 cm�1 can be assigned to Al–O,that overlapped with Fe–O characteristic peak. Comparison of the FT-IR spectra ofACMNPs and DTZ/SDS-ACMNPs (Figure 4(c)) is also shows a new sharp peak at1375.96 cm�1 appeared, it was due to that the C–N stretching peak of DTZ stabilized onACMNPs. Consequently, the FT-IR data suggest that DTZ are successfully immobilizedon the ACMNPs surface.

3.2 Amounts of SDS and DTZ

ACMNPs have positively charged surfaces in highly acidic solutions that can stronglyadsorb a negatively charged surfactant such as SDS. A concentration of SDS, below itscritical micellar concentration (CMC, 8mmol L�1), was used. Above this concentration,the excess of SDS would form micelles in the aqueous solution, which were not adsorbedon alumina surfaces. When the solution was acidified, the ad-micelles could trap DTZhomogeneously along with a change in color from red to gray-blue. The influence ofamounts of DTZ/SDS on the adsorption of the silver ions on ACMNPs was investigated.The results obtained are presented in Figures 5 and 6. It could be seen that with theincrease of SDS concentration, the absorbance increases and a maximum is obtained afterthe SDS concentration approaches to 7.8� 10�2mmol L�1 and remains constant up toCMC (Figure 5) and then decreased, because above this point micelles form strongly.Therefore, 0.1mmol L�1 SDS concentration was employed for further experiments.

Figure 4. FTIR spectra of the Fe3O4 nanoparticles (a), ACMNPs (b), and DTZ/SDS-ACMNPs (c).


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In order to study the effect of DTZ concentration on the adsorption of silver ions onthe ACMNPs, ammoniacal solutions of DTZ/SDS with constant concentration of SDSand different concentrations of DTZ were used (Figure 6). At DTZ concentrations lessthan 3.0 � 10�2mmol L�1, the amount of DTZ molecules immobilized into SDS coresare too low to completely complex all silver ions, so recoveries less than 100 were observed.At concentrations more than 3.0� 10�2mmol L�1 of DTZ, the sorbent sites are too rich,

Figure 5. Effect of SDS concentration on adsorption of silver. Conditions: ACMNPs (0.1 g), DTZ(10mL, 4� 10�2mmol L�1, pH 2.0) and Ag(I) solution (10mL, 5.0mgmL�1, pH 5.5).

Figure 6. Effect of DTZ concentration on adsorption of silver. Conditions: ACMNPs (0.1 g), SDS(10mL, 1� 10�1mmol L�1, pH 2.0) and Ag(I) solution (10mL, 5.0mgmL�1, pH 5.5).


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with respect to DTZ molecules, to allow silver ions to be adsorbed by formation ofits DTZ complex. Therefore, 4.0� 10�2mmol L�1 of DTZ was selected as the optimumconcentration for further studies.

3.3 Effect of solution pH

pH is the main investigated factor for the all extraction studies. The effect of pH wasstudied for the recovery of 10mL silver ion (5 mgmL�1) on 0.1 g of DTZ/SDS-ACMNPs.A series of silver ion solutions with different pH values from 1.5 to 12 were used, and theadsorbed silver was eluted with 5mL of 0.4mol L�1 thiourea solution. The results arepresented in Figure 7. As can be seen from the figure, it is evident that the adsorption ofsilver is quantitative (498%) in the pH range of 3.5–8. A pH of 5.5, in the middle of thepH range was selected as the optimum pH to avoid any abrupt changes in pH that mayoccur during accumulation step and could consequently affect the precision. At the pHvalues below 3.5, the recovery decreased, due to adsorption competition of Hþ ions withAgþ on DTZ/SDS-ACMNPs. At the pH values above 8.0, DTZ and/or SDS would bewashed out from surface of sorbent. Consequently, the capacity of the silver adsorption onACMNPs will be decreased; this gives a lower percent recovery for silver ions, as can beobserved in Figure 7.

3.4 Adsorption isotherm

The equilibrium isotherm of silver ions adsorption by the SDS/DTZ-ACMNPs inphosphate buffer solution at pH 5.5 and 25�C is shown in Figure 8(a). The adsorptionbehaviour could be described by the Langmuir adsorption equation:

C

Q¼

1

Kqmþ

C

qm

Figure 7. Effect of pH on adsorption of silver. Conditions: ACMNPs (0.1 g), DTZ/SDS solution(10mL, 4� 10�2mmol L�1/1� 10�1mmol L�1, pH 2.0) and Ag(I) solution (10mL, 5.0 mgmL�1).


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where Q is the equilibrium adsorption amount of Ag(I) (mg g�1), C is the equilibriumsilver ion concentration in the solution (mgmL�1), qm is the maximum adsorption amountof Ag(I) per gram of adsorbent (mg g�1) and K is the Langmuir adsorption equilibriumconstant (mLmg�1). A plot of C/q vs. C yielded a straight line (Figure 8(b)). From theslope and intercept of the line, the values of qm and K can be estimated to be 10.84mg g�1

and 1.04mL mg�1, respectively.

3.5 Standing and magnetic separation time

In the SPE process, we found that the standing time had obvious effect on the targetanalyte extraction. When the MNPs were isolated immediately without a standing process,the recovery of Ag(I) ions was only 46%. However, when the standing time were adjustedto 5, 10 and 15min, recoveries improved to 87, 93 and 98.6%; respectively. 15min was

Figure. 8. Adsorption isotherm of Ag(I) on SDS/DTZ-ACMNPs (a) and plot of C/q against Cfor the adsorption of Ag(I) on SDS/DTZACMNPs (b). Conditions: ACMNPs (0.1 g), DTZ/SDSsolution (10mL, 4� 10�2mmolL�1/1� 10�1mmol L�1, pH 2.0), Ag(I) solution (50mL,0.5–50.0 mgmL�1); equilibrium time: 10 h, temperature: 25�C.


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sufficient to achieve satisfactory adsorption and better recovery of silver ion. Meanwhile,in the experiment, DTZ/SDS-ACMNPs possessed superparamagnetism properties andlarge saturation magnetization, which enabled them to be completely isolated at the leasttime (less than 1min) by a strong magnet.

3.6 Effect of the type, concentration, volume and pH of the desorbing solution

In order to choose a proper eluent for desorbing silver ion from the adsorbent surface,we investigated a series of selected eluent solutions such as thiourea (0.01–2.0molmL�1),nitric acid (0.01–2.0molmL�1), acetate (0.1–4.0molmL�1) and phosphate (0.1–4.0molmL�1). The most effective eluent for the quantitative recovery of silver ion couldbe chosen. 50.0mg of silver ion, adsorbed on 0.1 g of sorbent (DTZ/SDS-ACMNPs),different concentrations of eluents have been investigated. Recovery of silver ions as afunction of the eluents concentration was plotted. The results show that maximumrecoveries of obtained in the optimum concentrations, 97.6, 83.5, 87.4 and 81.0% forthiourea, nitric acid, acetate and phosphate, respectively. Recovery of desorbed silver ionsas a function of thiourea concentration is represented in Figure 9. As is shown, atconcentrations of more than 0.3mol L�1 thiourea, silver ions were completely desorbedfrom sorbent surfaces. Therefore, a concentration of 0.4mol L�1 thiourea as the mostsuitable eluent was selected for further studies.

Acidity of the thiourea solution influences on the desorption of silver ions from sorbentsurfaces. The results show that recoveries of silver ions at pH5 6.0 are maximum. By thisobservation, it was proposed as an idea that at acidic pH, i.e. at pH range of 2.0 to 6.0 thehydronium ion could compete with silver ion for being adsorbed on the sorbent surfaces.

Figure 9. Effect of thiourea concentration on recovery of silver. Conditions: ACMNPs (0.1 g), DTZ/SDS solution (10mL, 4� 10�2mmol L�1/1� 10�1mmol L�1, pH 2.0) and Ag(I) solution (10mL,5.0mgmL�1, pH 5.5), Thiourea (5mL, pH 5.5).


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In acidic media, dithizone produces a complex form asM2L, but in basic pH values a

secondary complex of the form M2L is produced [47]. This proves that at pH range of

above of 6.0, DTZ produces a more stable complex of the form M2L than its competitorthiourea and in other theory. Recoveries less than 100%, at basic solutions, could be

explained due to the formation of silver hydroxide. Furthermore, DTZ and/or SDS could

be washed out at these pH values, which consequently decrease the capacity of the

adsorbent. Therefore, pH 5.5 was selected as the optimum pH value for the eluent

solution.

3.7 Effect of sample volume

In order to carry out solid phase extraction procedure on water samples leading to high

enrichment factor, the sample volume need to be optimized. In this case the effect ofsample volume on the adsorption of silver ions on DTZ/SDS-ACMNPs was investigated.

By using different feed volumes of water samples ranging between 50–1000mL, each of

which containing fixed amounts of DTZ/SDS-ACMNPs (0.1 g) and silver ions (5.0 mg), themaximum sample volume with high recovery percentage for the process was determined.

The recoveries of silver ions were quantitative (496%) up to 500mL of sample volume.By applying 500mL sample volume under optimum conditions and as stated previously,

desorbing of silver ions with 5mL of thiourea solution (0.4mol L�1) and pH adjusting to

5.5 with phosphate buffer (0.1mol L�1) (the final volume of desorbed solution is 5mL as

mentioned in Section 2.5), the preconcentration factor of 100 was obtained.

3.8 Effect of co-existing ions

The optimal experimental conditions described above were used to study whether other

co-existing ions that could act as interferents during the preconcentration/separation and

analyte determination steps of the two-step method. The recovery of 5.0mgmL�1 of silverions was investigated in binary mixtures containing silver ion and one of the foreign ions.

The following excess of ions did not interfere the reaction (i.e., caused a relative error of

less than 5%): more than a 200-fold amount of Naþ, Ca2þ and Mg2þ; a 100-fold amount

of Mn2þ, Ni2þ, Zn2þ, Cu2þ, Fe2þ, Co2þ, Cd2þ, Kþ, Cr3þ, Fe3þ, Bi3þ and Pd2þ; a 50-foldamount of NHþ4 , NO�3 and CH3COO–, a 25-fold amount of SO2�

4 , PO3�4 , C2O

2�4 , Hg2þ

and a 20-fold amount of I–, F–, Cl– and Br–. The results showed that most of the

investigated ions do not interfere in the adsorption–desorption and determination of traces

of silver ion in water samples.

3.9 Sorbent regeneration study

Regeneration is one of the key factors for evaluating the performance of the sorbents.

In this work, it was found that the ACMNPs can be reused up to three times without

loss of analytical performance. This reusable number is suitable because 4.0 g ofACMNPs could be prepared in one batch and only 0.1 g of ACMNPs was used for

one extraction operation.


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3.10 Analytical performance and method validation

In order to show the validation of the proposed method, under the optimal experimentalconditions, the analytical features of the method such as limit of detection (LOD), linearrange of the calibration curve and precision were examined. The LOD of the proposedmethod based on three times the standard deviation of the blank (3Sb), was 0.52 ngmL�1

for silver ion (n¼ 10). The linear range of calibration curve for Ag(I) was2.0–5000.0 ngmL�1 with a correlation coefficient of 0.9991. The regression equation forthe line was A¼ 0.1667 CAgþ (3� 10�3) (n¼ 5), where CAg is the concentration of Ag(I)in ngmL�1 and A is the absorbance. The relative standard deviation (RSD) for 10replicate measurements of 5.0mgmL�1 of silver ion was 3.4%.

3.11 Analytical applications

In order to check the applicability of the proposed method it was applied to theseperation/preconcentration and determination of silver in spiked water and wastewatersamples. The results are tabulated in Table 1. According to these data, the added silverions can be quantitatively recovered from the water samples by the proposed procedure.These results demonstrate the applicability of the procedure for silver determinationin water samples.

4. Conclusions

The new sorbent DTZ/SDS-ACMNPs can be successfully applied for separation andpreconcentration of silver in water samples. Comparative data from some papers on solidphase extraction of trace Ag are summarized in Table 2. The analytical performance is notsignificantly different to those achieved by other methods described in the literatures.This solid phase extractant has the following advantages: preparation of the sorbent is

Table 1. Recoveries results of real water samples spiked with silver ion and wastewater samples.

Sample

Ag(I) (ngmL�1)a

Recovery (%)Added Found

Wastewater (Copper factory, Sarchashmeh, Rafsanjan) 0 11.4 (�0.5) –5 16.2 (�0.6) 9610 21.1 (�0.3) 97

Tap water (Sirjan) 0 BLRb –5 4.9 (�0.1) 9810 10.1 (�0.2) 101

River water (Hajiabad, Bandar Abbas) 0 BLR –5 5.1 (�0.3) 10210 10.1 (�0.4) 101

Spring water (Koran, Sirjan) 0 BLR –5 4.8 (�0.4) 9610 9.9 (�0.3) 99

aMean� standard deviation (n¼ 5).bBelow of linear range.


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Table

2.

Comparisonoftheproposedmethodwithother

reported

SPE

methodsforseparation/preconcentrationofsilver(I)ion.

System

Analysis

method

Sorbent

Sorbent

capacity

(mgg�1)

Sample

volume

(mL)

Enrichment

factor

RSD

(%)

Linear

range

(ngmL�1)

LOD

(ngmL�1)

Reference

SPE

GFAAS

Modifiedoctadecylsilica

mem

branedisks

0.220b

100

400

2.6

–0.008

[33]

C-SPEa

Colorimetry

Modifiedpolystyrene–divinylbenzenedisk

––

830

–5–1000

4.0

[34]

SPE

FAAS

Modifiedaluminausing2-m

ercaptobenzothiazole

–200

100

1.59

––

[35]

SPE

FAAS

Modifiedsilica

gel

using2,4,6-trimorpholino-

1,3,5-triazin

0.384

5130

3.03

––

[36]

SPE

FAAS

Modifiednaphthaleneusingdithizone

0.029

50

10

0.9,4.4

10–1000

3.9

[37]

SPE

FAAS

Amberlite

XAD-16

12.4

100

200

3.1

–0.11

[38]

SPE

FAAS

Modifiedoctadecylsilica

mem

branedisks

1.07c

500

360

––

0.006

[39]

SPE

FAAS

Modifiedalumina

–25

100

0.01–0.502

––

[40]

SPE

FAAS

Modifiedsilica

gel

using5-(4-

dim

ethylaminobenzylidene)-rhodanine

0.420

1100

220

1.5

–0.02

[41]

C-SPE

Colorimetry

Mem

braneim

pregnatedwith(5-[4-(dim

ethylamino)

benzylidene]rhodanine)

––

––

0–1000

100

[42]

MSPE

FAAS

Modifiedalumina-coatedmagnetitenanoparticles

9.7

10

100

3.4

2–5000

0.52

Thiswork

aC-SPEisthecolorimetricsolid-phase

extraction.

bThemaxim

um

capacity

ofthediskwasdetermined

tobe220�4mg

ofAg(I)onthedisk.

cThemaxim

um

capacity

ofthediskwasdetermined

tobe1070�12mg

ofAg(I)onthedisk.


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simple, rapid and low cost. Furthermore, it avoids the time-consuming column passing(about 1 h in conventional SPE method) and filtration operation, and no clean-up stepswere required. The sorption capacities are also better or comparable with the othermethods. The accuracy of the results was verified by analyzing the spike real samples.The good precision and high tolerance to interferences from matrix ions are other

advantages of this method.

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solid phase extraction of trace amounts of silver (i) using dithizone-immobilized alumina-coated...

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