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Journal of Chromatography A, 1336 (2014) 34–42

Contents lists available at ScienceDirect

Journal of Chromatography A

jo ur nal ho me pag e: www.elsev ier .com/ locate /chroma

ltrasound-assisted solid phase extraction of nitro- andhloro-(phenols) using magnetic iron oxide nanoparticlesnd Aliquat 336 ionic liquid

ooshang Parham ∗, Sedighe Saeedhemistry Department, Faculty of Sciences, Shahid Chamran University, 6135714168 Ahvaz, Iran

r t i c l e i n f o

rticle history:eceived 23 December 2013eceived in revised form 2 February 2014ccepted 3 February 2014vailable online 8 February 2014

eywords:ltrasound-assisteditrophenolshlorophenolsagnetic iron oxide nanoparticles

liquat 336

a b s t r a c t

A novel and sensitive ultrasound-assisted solid phase extraction (UASPE) method for pre-concentrationand determination of ultra-trace amounts of nitrophenols and chlorophenols in water samples wasdemonstrated. Four hazardous phenolic compounds in water samples were extracted and monitoredby high performance liquid chromatography. The results demonstrated that in the presence of Aliquat336 (ALQ), magnetic iron oxide nanoparticles (MIONPs) were quite efficient in the adsorption and pre-concentration of traces of analytes. MIONPs were synthesized and characterized by transmission electronmicroscopy (TEM) and X-ray diffraction (XRD). The important parameters influencing the extraction effi-ciency were studied and optimized. The separation and pre-concentration steps were fast and completedin 10 min. Acetonitrile was used for the desorption of target analytes. Under optimum adsorption condi-tions, a linear range between 0.015 and 100 �g L−1 (R2 ≥ 0.997), and limits of detections (LODs) rangingfrom 0.005 to 0.041 �g L−1 were obtained. Enrichment factors in the range of 76–195 were achieved and

relative standard deviations (%RSDs) were less than 10.0 (n = 3) for the target analytes. The analyticalmethod was successfully applied for environmental water samples such as tap water and river water.The recoveries varied within the range of 70–119% confirming the good performance of the method invarious water samples. The results showed that the proposed method is a rapid, convenient and feasibletechnique for the determination of nitrophenols and chlorophenols in aqueous samples.

. Introduction

Phenols are common by products of large-scale production andhe use of man-made organics such as phenolic resins, drugs, dyes,ntioxidants, paper pulp and pesticides that cause ecologicallyndesirable effects. Repeated or prolonged exposure to phenolicompounds or their vapors may cause headache, nausea, dizziness,ifficulty in swallowing, diarrhea, vomiting, shock, convulsions,r death. Phenols can affect the central nervous system, liver,nd kidneys [1–3]. These compounds are harmful to organismst low concentrations and many of them have been classifieds hazardous pollutants [4]. Most phenols exhibit different toxi-

ities, and some chlorophenols and nitrophenols are even knowno possess carcinogenic and immunosuppressive properties. Dueo their potential harm to human health, phenol derivatives and

∗ Corresponding author. Tel.: +98 611 3360018/+98 611 3738015;ax: +98 611 3337009.

E-mail address: hoparham@yahoo.com (H. Parham).

ttp://dx.doi.org/10.1016/j.chroma.2014.02.012021-9673/© 2014 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. All rights reserved.

related compounds are considered as priority pollutants. As a con-sequence, both the US Environmental Protection Agency (EPA) andthe European Union (EU) have included some phenols in theirlists of priority pollutants. The maximum amount of phenols inwastewater allowed by the European Community is lower than1 mg L−1 [5,6]. The European Union sets a maximum concentrationof 0.5 �g L−1 for total phenols and 0.1 �g L−1 for their individualconcentration in drinking water [7,8]. The major sources of phenolpollution in aquatic environment are wastewaters from paint, pes-ticide, coal conversion, polymeric resin, gasoline, rubber proofing,steel, petroleum and petrochemical industries [9,10].

New SPE techniques based on the use of magnetic or magne-tizable adsorbents called magnetic solid-phase extraction (MSPE)have been used for the separation and pre-concentration of an ana-lyte from large volumes of water solution by using a permanentexternal magnet [11–15]. Generally, most of the dissolved environ-mental pollutants are nonmagnetic, and thus do not respond to the

magnetic field. The surface modification of magnetic nanoparticlesis a challenge for different applications and can be accomplishedby the physical/chemical adsorption of organic compounds using

dx.doi.org/10.1016/j.chroma.2014.02.012http://www.sciencedirect.com/science/journal/00219673http://www.elsevier.com/locate/chromahttp://crossmark.crossref.org/dialog/?doi=10.1016/j.chroma.2014.02.012&domain=pdfmailto:hoparham@yahoo.comdx.doi.org/10.1016/j.chroma.2014.02.012

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our major methods: organic vapor condensation, polymer coating,urfactant adsorption and direct silanation [16]. Removal of haz-rdous compounds from industrial effluents and also monitoringheir concentrations are growing needs at the present time.

Aliquat 336 (tricaprylmethylammonium chloride) is a waternsoluble quaternary ammonium salt made by the methylation of

ixed tri octyl/decyl amine, which is capable of forming oil solu-le salts of anionic species at acidic or slightly alkaline pH. Aliquat36 is composed of a large organic cation associated with chloride

on, [R3NCH3]+Cl− and exists as a stable cation–anion pair over aide range of pH. Because the ammonium structure has a perma-ent positive charge, it can form salts with anions over a widerH range than primary, secondary or tertiary amines. For this rea-on, Aliquat 336 finds application in environments ranging fromcidic to slightly alkaline pH. In spite of several studies on the solidhase extraction of phenolic compounds with Cethyltrimethylam-onium chloride (CTAB) [17,18], no procedure has been reported

or the systematic solid phase extraction and separation of suchompounds using Aliquat 336.

Ultrasonic (US) radiation has been proven to be a very useful tooln intensifying the mass transfer process of the target analytes tohe surface of an adsorbent [19,20]. This leads to an increment in thextraction efficiency of the pre-concentration technique in a shortime. The effects of US are primarily related with the cavitationhenomenon, which involves the implosion of bubbles formed inhe liquid medium during US application. The enhanced adsorptionate by sonication may be attributed to the extreme conditions gen-rated during the violent collapse of the cavitation bubbles. Whenhe bubble is collapsing near the solid surface, symmetric cavitations hindered and the collapse occurs asymmetrically. The asym-

etric collapse of bubbles in a heterogeneous system producesicro-jets with high velocity. Additionally, symmetric and asym-etric collapses generate shockwaves, which cause extremely

urbulent flow at the liquid–solid interface, increasing the rate ofass transfer near the solid surface. An important effect of US is

he dispersion of aggregated nanoparticles which produces moreurfaces and increases more active sites. The mentioned factorsesults in an increment in the mass-transfer of the analytes ontohe adsorbent surface [19–22].

Several diverse methods were applied for the determinationf nitrophenols and chlorophenols in environmental samples.hese include ultraviolet spectrophotometry (UV) [23,24], chemi-uminescence [25–27], high performance liquid chromatographyHPLC) [12,28–34], gas chromatography [35,36] and electro-hemical methods [5,37,38]. Some of these techniques sufferrom interferences and matrices. On the other hand, the lowevel of these constituents makes their determination a difficultask.

It is well known that the analysis of polar compounds such asitrophenols and chlorophenols is a challenge due to the strong

nteractions of these compounds with water molecules in aqueousolutions. Establishing simple, fast, low-cost, sensitive, and selec-ive analytical methods for the extraction and determination ofollutants in the environment is one of the main areas of research

n environmental chemistry [11–16,32–38].In this work, we developed a facile method to synthesize Ali-

uat 336 coated magnetic iron oxide nanoparticles (ALQ@MIONPs)or the adsorption of phenols. The ALQ@MIONPs demonstratedigh potential ability for solid phase extraction (SPE) and pre-oncentration of phenolic compounds from environmental wateramples with high efficiencies. Hence, 2,4,6-trinitrophenol (picriccid, PIC), paranitrophenol (PNP), 2-chlorophenol (2-CP) and 2,4-

ichlorophenol (2,4-DCP) were selected as the model analytes.ltra-trace amounts of 2,4,6-trinitrophenol (picric acid, PIC), paran-

trophenol (PNP), 2-chlorophenol (2-CP) and 2,4-dichlorophenol2,4-DCP) were determined in water samples. The target analytes

ogr. A 1336 (2014) 34–42 35

(PIC, PNP, 2-CP and 2,4-DCP) were successfully evaluated by HPLCanalysis.

2. Experimental

2.1. Chemicals and reagents

All chemicals and reagents were of analytical grade. Ace-tone (99.5%, w/w), acetonitrile (HPLC grade), water (HPLCgrade), 2,4,6-trinitrophenol (picric acid, PIC), paranitrophenol(PNP), 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP),hydrochloric acid (37% w/w), methanol (99.9% w/w), ammoniasolution (25% w/w), FeCl3 (96% w/w), FeCl2·4H2O (99.9% w/w), andAliquat 336 were purchased from Merck (Darmstadt, Germany) andused without further purification. The stock standard solutions ofthe analytes were prepared in water–acetonitrile (70:30) solutionmixture at a concentration of 100 mg L−1 and stored at 4 ◦C, pro-tected from light. The standard working solutions were prepareddaily by appropriate dilution of the stock standard solutions withwater–acetonitrile (70:30) solution to the required concentrations.ALQ stock solution (2% v/v, equivalent to 1760 mg L−1) was pre-pared in pure EtOH. Tap water was collected from our laboratory.River water samples were gathered from the Karron River at Ahvaz,Iran.

2.2. Apparatus

Chromatographic measurements were carried out using aKnauer HPLC system (Germany) consisting of a K-1001 pump anda k-2501 UV detector. Two KQ-100DE ultrasonic cleaner werepurchased from Kunshan Ultrasonic Instrument Co., Ltd. (Kun-shan, China). The frequency and output power of the ultrasoniccleaner were 21 kHz for both and 30, 60 W for the first and 45 Wfor the second, respectively. A pH-meter (827 pH lab, Metrohm1,Herisau, Switzerland) was also used for pH adjustment. Trans-mission electron microscopy (906E, LEO, Germany) and scanningelectron microscopy (SEM) (XL-30 electron microscope, Philips,Eindhoven, The Netherlands) were used to study the morphol-ogy of the magnetic nano-particles. Structural analysis of theMIONPs was done using an X-ray diffractometer (XRD, BruckerD8 Discover, Germany). Infrared spectra were obtained using aFourier Transform-Infrared Spectrometer (FT-IR spectrum 100,Perkin Elmer, Australia) to identify the functional groups and chem-ical bonding of the adsorbent, modifier and target analytes.

2.3. Preparation of magnetic iron oxide nanoparticles

MIONPs were synthesized by the co-precipitation of a mixtureof chloride salts of ferrous and ferric ions (molar ratio 1:2) in anammonium hydroxide solution at 80 ◦C under vigorous stirring anda N2 atmosphere was prepared based on our previous work [39]. Inorder to stabilize the nanoparticles they were stored in ultra-purewater.

2.4. Preparation of ALQ modified magnetic iron oxidenanoparticles

A separate experiment was carried out to ensure the coatingof MIONPs by ALQ ionic liquid. A 2 mL portion of MIONPs solutionmixture (equivalent to 40 mg of dried MIONPs) and also 2 mL of2% ALQ in EtOH were added to 50 mL deionized water at pH 8 and

then sonicated (21 kHz, 60 W) for 5 min. Subsequently, the resultantALQ@MIONPs were collected by a magnet (10 cm × 5 cm × 4 cm,1.2 T) and washed with deionized water several times to removethe unreacted materials, and dried at 40 ◦C under nitrogen gas for

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0 min. The TEM images and FT-IR spectra of MIONPs and ALQ-IONPs confirm the adsorption of ALQ on MIONPs.

.5. Extraction and determination procedure

Fifty milliliters of the aqueous sample solution, spiked at theiven concentrations of the target analytes (PIC, PNP, 2-CP and,4-DCP), were transferred into a beaker, and the sample pH wasdjusted to 8 with a 0.01 M NaOH solution. Afterwards, 2 mL ofIONPs solution mixture (equivalent to 40 mg of dried MIONPs)

nd 2 mL of 2% ALQ in EtOH were added to the solution andhen sonicated (21 kHz, 60 W) for 10 min. Then, the adsorbent wassolated from the suspension with the magnet. After decantinghe supernatant solution, the adsorbed analytes were eluted with.5 mL acetonitrile after 6 min of contact time without stirring.inally, the eluate was separated from the suspension with theagnet and 20 �L of it was injected into the HPLC instrument for

nalysis.

.6. HPLC analysis

A Nucleodur (100-5 C18, 250 mm × 4 mm) column and a 20 �Lnjection loop were used. Pure acetonitrile and water (contain-ng 0.01% phosphoric acid, pH 3) mixture was used as the mobilehase via a gradient elution program. The gradient elution pro-ram was as follows: started at 40% acetonitrile and maintainedor 3 min with a flow rate of 1.3 mL min−1; switched to 80% ace-onitrile from 3 min to 5 min with a flow rate of 1.5 mL min−1; andnally, decreased to 40% acetonitrile after 5 min and kept constant

or 10 min with a flow rate of 1.3 mL min−1. The temperature of theolumn oven was kept constant at 25 ◦C. Under these conditions,hromatographic retention times for PNP, 2-CP, 2,4-DCP and PICere 4.1, 4.9, 6.6 and 8.9 min, respectively. The detection wave-

engths were set at 280 nm for 7.5 min to detect PNP, 2-CP and,4-DCP, and then switched to 370 nm for the detection of PIC.

. Results and discussion

The adsorption mechanism of nitrophenols and chlorophenolsnto the ALQ@MIONPs surface may be based on the electrostaticttraction between the cationic head of the surfactant and pheno-ate anions [12,13,15,17,18,37]. The transfer of the adsorbate fromhe solution to the surface of the adsorbent is controlled by eitheroundary layer diffusion (external mass transfer) or intraparticleiffusion (mass transfer through the pores), or by both. In general,he adsorption dynamics consists of three consecutive steps: Diffu-ion of adsorbate molecules from the bulk solution to the externalurface of the adsorbent; from the external surface and into theores of the adsorbent; and finally adsorption of the adsorbate onhe active sites on the internal surface of the pores.

The last step is usually very rapid in comparison to the first twoteps. Hamdaoui and Naffrechoux [19] show that the values of thentraparticle diffusion coefficient obtained in the presence of ultra-ound are greater than those obtained in the absence of ultrasound.ydrodynamic effects induced by ultrasound promote a significant

ncrease in mass transfer across the boundary layer. These behav-ors increased with increasing ultrasonic power. Moreover, theavitation event produced by sonication also gives rise to acousticicro-streaming or formation of miniature eddies that enhance the

ass and heat transfer at the interfacial films surrounding nearby

dsorbent particles and within the pores. As a result, ultrasoundnergy could produce not only high-speed micro-jets but also high-ressure shock waves and acoustic vortex micro-streaming.

ogr. A 1336 (2014) 34–42

3.1. Characterization of adsorbent

The shape and size of the synthesized particles were observedby TEM and SEM. The TEM images of MIONPs (Fig. 1A) andALQ@MIONPs (Fig. 1B) particles show that an obvious layer ofALQ is coated on the surface of MIONPs. The coated ALQ layer isclearly seen due to the different electron densities of the mag-netic nanoparticles core (with dark color) and ALQ coating (withlight color) in TEM micrographs. It can be seen that the synthesizedMIONPs and ALQ-MIONPs (Fig. 1C and D) were nearly spherical inshape with an average diameter of about 40–60 nm and 50–70 nm,respectively. Scanning electron microscopy (SEM) was used toobserve the surface physical morphology and to determine the sizeof MIONPs and ALQ@MIONPs. Fig. 1E and F show the structure ofMIONPs before and after the modification process.

The XRD spectrum of naked MIONPs is compared with ALQcapped particles, the XRD pattern of these nanoparticles agreeswell with that of the pure nanoparticles (as shown in Fig. 2a); theresult shows that the reflection peaks can be seen in an XRD patternat 30.1, 35.5, 43.2, 53.5, 57.0 and 62.7. These peaks correspond tothe (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) planes. The XRDpattern of the MIONPs exactly matched the JCPDS reference no.19–629. The X-ray diffraction pattern of ALQ@MIONPs is shown inFig. 2b. It can be seen that the intensities of the peaks are decreaseddue to caption of MIONPs by ALQ.

FT-IR studies was used to identify functional groups and thechemical bonding of those compounds attaching to MIONPs.FT-IR spectra (Fig. 3) show characteristic peaks of MIONPs,ALQ, ALQ@MIONPs, PIC and PIC-ALQ@MIONPs. The spectrum ofMIONPs shows absorption bands at 570–640 cm−1 which are usu-ally attributed to the Fe–O stretches (a) [41]. The spectrum ofALQ@MIONPs shows the characteristic peaks of both ALQ (–CH3and–CH2–stretching bands, (b)) and MIONPs (absorption bands at570–640 cm−1) which confirms the adsorption of ALQ on MIONPsas adsorbent. The peaks at 1650–1450 cm−1 are assigned to thearomatic C=C stretching of PIC (c). FT-IR spectrum of PIC indi-cates the characteristic N=O peaks at 1538 and 1347 cm−1 (d). Thepattern of the out-of-plane C–H bending bands in the region of900–675 cm−1 and the –O–H stretch at 3100–3200 cm−1 (e) arecharacteristic of this aromatic compound [42]. The broad adsorp-tion band at 3400–3700 cm−1 (f) is related to moisture adsorbed byPIC-ALQ@MIONPs.

3.2. Effect of pH

The pH of water samples is an important parameter that affectsthe SPE of nitrophenols and chlorophenols because PIC is a rela-tively strong acid (pKa = 0.38) and PNP, 2-CP and 2,4-DCP (pKa = 7.2,8.5 and 7.8, respectively) are weak acids. Based on the pKa valuesof phenols, changing the sample pH will cause deprotonation ofphenolic groups and the functional groups on the adsorbent sur-face. In the present study, the pH effect was examined by varyingpH between 4 and 10. The pH of the test solution (50 mL, 30 �g L−1

of each analyte) was adjusted to the desired value using dilutedsolutions of 0.1 M HCl or 0.1 M NaOH. Then, 1 mL 2% ALQ solutionwas added to the test sample and the mixture sonicated for 7 min.ALQ@MIONPs were separated and eluted with 1 mL acetonitrile for3 min contact time. As shown in Fig. 4, the ALQ@MIONPs exhibitedno obvious adsorption for target analytes when pH was lower than6. With increases in pH, the sorption amount increased dramati-cally before reaching a maximum at pH 8. This can be attributedto the fact that the surface of ALQ@MIONPs was positively charged

when ALQ+ was attached to the surface of MIONPs. Low adsorptionefficiency at low pHs could be related to the protonation of pheno-late anions leading to weak electrostatic attraction between ALQ+

(on the surface of MIONPs) and penalate anions. With increases in

H. Parham, S. Saeed / J. Chromatogr. A 1336 (2014) 34–42 37

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3.4. Influence of ALQ 336 ionic liquid

Primary tests showed that in the absence of ALQ, the adsorptionof PIC, PNP, 2-CP and 2,4-DCP (50 mL, 30 �g L−1 of each analyte)

Fig. 1. The TEM images and average particle sizes of MIONPs (A and C) and

H of the test solution up to 8, the abundance of phenolate formsf PIC, PNP, 2-CP and 2,4-DCP increases. Hence, the strong elec-rostatic attraction between the positive charged ALQ moleculesnd the negatively charged analytes is high enough to produce

great adsorption affinity for target analytes. Therefore, pH 8.0as selected as optimum for further studies. Higher pHs decrease

he extraction efficiency due to higher concentration of hydrox-de ions which can compete with phenolate anions of the targetnalytes.

.3. Effect of the adsorbent amount

The amount of MIONPs adsorbent required for the quantita-ive removal of PIC, PNP, 2-CP and 2,4-DCP was optimized. Theffect of different quantities of MIONPs ranging from 10 to 100 mgas investigated. Fifty milliliters of the aqueous sample solution of

arget analytes (30 �g L−1 of each analyte), were transferred into series of beakers, and the sample pH was adjusted to 8. Dif-erent quantities of MIONPs and 1 mL of 2% ALQ in EtOH weredded to each solution and then sonicated (21 kHz, 60 W) for 7 min.LQ@MIONPs were separated and eluted with 1 mL acetonitrile

or 3 min contact time. The results are shown in Fig. 5. Maximumdsorption was obtained when 40 mg of MIONPs was in contactith the sample solution of target analytes. For amounts more than

0 mg of adsorbent, recoveries decreased because of incomplete

MIONPs (B and D). (E) and (F) Show the SEM of MIONPs and ALQ-MIONPs.

desorption of analytes from adsorbent surfaces due to the smallvolume of acetonitrile (0.5 mL) as the desorbing solvent.

Fig. 2. The XRD spectrum of (a) naked MIONPs and (b) ALQ capped MIONPs.

38 H. Parham, S. Saeed / J. Chromatogr. A 1336 (2014) 34–42

Fig. 3. FT-IR spectra of MIONPs, ALQ, ALQ@MIONPs, PIC and PIC-ALQ@MIONPs.

Fig. 4. The effect of solution pH on the adsorption efficiency of PNP, 2-CP, 2,4-DCPaa6

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Fig. 6. Influence of ALQ 336 ionic liquid on the extraction efficiency of target ana-

nd PIC. Extraction conditions: sample solution, 50 mL of 30 �g L−1 of the analytes;dsorbent amount, 25 mg of MIONPs; 1 mL of 2% ALQ solution; sonication (21 kHz,0 W) time, 7 min; eluent volume, 1 mL; desorption time, 3 min.

nto the surface of MIONNPs is very low. But, with increases inLQ (2% v/v in EtOH, 1760 mg L−1), the sorption amount of tar-et analytes increased remarkably. Fig. 6 depicts the peak area ofdsorbed phenols as a function of the amount of ALQ added. Thencrease in sorption can be explained by the gradual formation ofydrophobic hemimicelles and also ion pair formation betweenLQ+ and phenolate anions on the surface of MIONPs. Maximumorption was obtained when the ALQ volume reached 2 mL (2% v/v,8 mg) in 50 mL sample solution. The results clearly indicated that

ydrophobic interactions played an important role in the adsorp-ion process. The adsorption amount decreased when the amountf ALQ added exceeded 88 mg, after which the ALQ molecules begano form micelles in the bulk aqueous solution with more surfactant

ig. 5. Effect of the adsorbent amount on the extraction efficiency of PNP, 2-CP,,4-DCP and PIC. Extraction conditions: sample solution, 50 mL of 30 �g L−1 of thenalytes at pH = 8; 1 mL of 2% ALQ solution; Sonication (21 kHz, 60 W) time, 7 min;luent volume, 1 mL; desorption time, 3 min.

lytes. Extraction conditions: sample solution, 50 mL of 30 �g L−1 of the analytes atpH = 8; adsorbent amount, 40 mg of MIONPs; Sonication (21 kHz, 60 W) time, 7 min;eluent volume, 1 mL; desorption time, 3 min.

added. Furthermore, the micelles caused the PIC, PNP, 2-CP and2,4-DCP to redistribute into the solution again and adsorption effi-ciency decreased. Based on these results, 2 mL of 2% solution of ALQ(88 mg) in EtOH was adopted as the optimum amount of surfactantin further studies.

3.5. Effect of contact type and ultrasonic power

Extraction and pre-concentration efficiency can be affected bythe type of hydrodynamic mixing of adsorbates and adsorbent par-ticles. Different mixing methods such as static, shaking, stirring andsonication were examined with 50 mL sample solutions (30 �g L−1

of each analyte, pH 8) containing 2 mL of 2% solution of ALQ and40 mg of MIONPs.

The conditions of different contact methods between adsorbentparticles and target analytes sample were as follow:

• Static method: contact with no hydrodynamic force for 10 min.• Shaking method: shaking at 60 rpm for 10 min.• Stirring method: stirring with a magnetic stirrer at a speed of

400 rpm (10 min).• Sonication method: the mixture was sonicated (21 kHz, 60 W) for

7 min.

Results given in Fig. 7A indicate that ultrasound waves producedthe best extraction efficiency. Acoustic streaming with hydro-dynamic phenomenon due to cavitation is responsible for theperfect mixing of the reactor content.

In order to determine the effect of sonication energy onextraction efficiency, different ultrasound powers were examined.Ultrasonic wave frequency of 21 kHz was used for sonication exper-iments at three different ultrasonic powers (30, 45 and 60 W).The temperature was maintained constant and equal to 25 ◦C. Theadsorption increased with increasing acoustic power of ultrasound(Fig. 7B), because with high power more cavitation events occur andmore molecules are adsorbed. Higher ultrasound powers decreasedthe extraction efficiency dramatically by destroying the MIONPsand a brown color suspension was produced.

3.6. Effect of contact time

The effect of sonication (21 kHz, 60 W) time on the adsorptionefficiency of the target analytes was examined. The results areshown in Fig. 8. As illustrated, the extraction efficiencies of the

PIC, PNP, 2-CP and 2,4-DCP increase continuously by increasing thetime from 2 to10 min, and decrease with further increase in time.Indeed, because of the very high surface area to volume ratios innanosorbents and their short diffusion routes which lead to a highly

H. Parham, S. Saeed / J. Chromat

Fig. 7. Effects of (A) contact type and (B) ultrasonic power on the extraction effi-ciency of target analytes. Extraction conditions: sample solution, 50 mL of 30 �g L−1

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f the analytes at pH = 8; adsorbent amount, 40 mg of MIONPs; 2 mL of 2% ALQ solu-ion; Sonication (21 kHz, 60 W) time, 7 min; eluent volume, 1 mL; desorption time,

min.

apid adsorption process, equilibrium between the sample solu-ion and the adsorbent surface can be reached in a shorter contactime in comparison with other SPE sorbents. Based on these results,he contact time of 10 min was selected as the optimum value forensitivity enhancement.

.7. Eluting conditions

Desorption of PIC, PNP, 2-CP and 2,4-DCP from the ALQ@MIONPsas studied using different organic solvents like acetonitrile,ethanol and ethanol via static contact between ALQ@MIONPs and

lution solvent for 3 min. Quantitative recoveries (above 80%) ofarget analytes were obtained using 2 mL acetonitrile. Under thisptimized desorption condition, no carryover was observed in the

ext analysis. The volume of eluent was also optimized and theighest extraction efficiency was obtained with 0.5 mL of acetoni-rile. The effect of eluent acidity on the desorption of target analytes

ig. 8. The effect of sonication (21 kHz, 60 W) time on the adsorption efficiency ofhe target analytes. Extraction conditions: sample solution, 50 mL of 30 �g L−1 of thenalytes at pH = 8; adsorbent amount, 40 mg of MIONPs; 2 mL of 2% ALQ solution;luent volume, 1 mL; desorption time, 3 min.

ogr. A 1336 (2014) 34–42 39

was also examined. The acidity of acetonitrile eluent was increasedby nitric acid solutions (0.001 to 0.1 M) and several tests wereexplored. The results revealed that as the acidity of elution sol-vent increases, desorption efficiency decreases. This may be dueto the solubility of ALQ@MIONPs in acidic solutions. Hence, thebest desorption of target analytes is attained by using pure acetoni-trile which was finally chosen as the elution solvent in subsequentexperiments.

The effect of contact time on the desorption of target analyteswas also studied. The results revealed that there is an increase in theextraction efficiency for desorption times up to 4 min. Longer con-tact times (>4 min) cause a slight decrease in desorption efficiencydue to re-adsorption of analytes on the surface of ALQ@MIONPs.So, the time of 4 min was applied for desorption of analytes insubsequent experiments.

3.8. Effect of ionic strength

The effect of ionic strength on adsorption and pre-concentrationprocesses was examined using different concentrations of KNO3 aselectrolyte. Results show that the adsorption and extraction effi-ciencies of PIC, PNP, 2-CP and 2,4-DCP were increased by increasingthe KNO3 concentration up to 0.001 M of KNO3 which may be dueto salting out effect. But, peak areas of target analytes decreasedin more concentrated (up to 0.01 M) solutions due to the satu-ration of active adsorbent sites by co-existing ions. This impliedthat electrostatic attraction plays a significant role in the adsorp-tion/desorption steps under these test conditions.

3.9. Effect of co-existing species

The optimum experimental conditions which have beendescribed were used to study the interfering effect of some ionsand organic compounds on the separation, pre-concentration anddetermination processes of PIC, PNP, 2-CP and 2,4-DCP (50 mL,30 �g L−1 for each analyte). To this end, separation and deter-mination of target analytes were performed in the presence ofco-existing interfering substances. The maximum acceptable errorwas ±5% change in HPLC peak area of target analytes. The obtainedresults show that most of the investigated ions did not inter-fere during separation, pre-concentration, and determination. Thecations Fe2+, Fe3+, Ca2+ and Mg2+, Cl−, NO3−, K+, Na+, Br−, I−, F−,PO43−, CO32−, SO42−, NH4+ and acetate ions do not interfere at con-centration ratios of 1000 with respect to PIC, PNP, 2-CP and 2,4-DCP.Organic compounds such as benzene, nitrobenzene, naphthalene,phenanthrene and anthracene do not interfere even at 100 timeshigher ratios than analytes.

3.10. Breakthrough volume

The effect of sample volume on adsorption and pre-concentration processes was investigated using a series of solutionswith fixed amounts of PIC, PNP, 2-CP and 2,4-DCP (1.5 �g for eachanalyte) at different volumes. Results in Fig. 9 show that initial sam-ple volume had no effect on the recovery rate up to 100 mL andrecoveries ≥92% were obtained for sample volumes up to 100 mL.

3.11. Reusability studies

To evaluate the ability of adsorbent to be regenerated and

reused, several (adsorption/desorption) regeneration cycles wererun for the adsorbent. After each extraction process, the adsorbentwas rinsed with 1 mL of eluent (acetonitrile) two times and thenused in subsequent extractions. It was found that the recoveries of

40 H. Parham, S. Saeed / J. Chromat

Fa

te

3

mtmsoof2tt

TA

TR

ig. 9. The effect of sample volume on adsorption and pre-concentration of fixedmounts of PIC, PNP, 2-CP and 2,4-DCP (1.5 �g for each analyte) at different volumes.

he target analytes are not diminished even after three successivextraction processes, suggesting the good reusability of the sorbent.

.12. Analytical characteristics

In order to estimate the efficiency and feasibility of the proposedethod for its application to the analysis of environmental samples,

he analytical characteristics of the proposed method were deter-ined in terms of linearity, precision (expressed as the relative

tandard deviation), limit of detection and enrichment factor, Thebtained results are summarized in Table 1. Calibration curves werebtained in the concentration range of 0.015–100 �g L−1 (n = 12)

or PIC and PNP, and also 0.075–100 �g L−1 (n = 10) for 2-CP and,4-DCP after pre-concentration with ALQ@MIONPs and desorp-ion with 0.5 mL acetonitrile. The repeatability of the method inerms of relative standard deviation (%RSD) was evaluated for 1

able 1nalytical parameters of the proposed method.

Analyte LDRa (�g L−1) LODb (�g L−1) %RS

PNP 0.015–100 0.012 3.6–2-CP 0.075–100 0.041 6.1–2,4-DCP 0.075–100 0.031 5.9–PIC 0.015–100 0.005 1.3–

a Linear dynamic range.b Limit of detection.

able 2esults from determination of target analytes (n = 3) by the proposed method in different

Compound River water

Added (ng mL−1) Found (ng mL−1) %Rec

PNP 0.00 ND* – 1.00 0.85 ± 0.01 85 ±7.00 8.37 ± 0.09 119 ±

50.00 39.66 ± 0.17 79 ±

2-CP 0.00 ND* – 1.00 0.82 ± 0.01 83 ±7.00 6.25 ± 0.14 89 ±

50.00 37.84 ± 0.16 75 ±

2,4-DCP 0.00 ND* – 1.00 0.77 ± 0.01 77 ±7.00 5.50 ± 0.18 79 ±

50.00 39.44 ± 0.21 79 ±

PIC 0.00 ND* – 1.00 0.71 ± 0.01 71 ±7.00 6.50 ± 0.19 93 ±

50.00 37.53 ± 0.07 75 ±

* Not detected.

ogr. A 1336 (2014) 34–42

and 50 �g L−1 solutions (n = 6) of PIC, PNP, 2-CP and 2,4-D and it wasfound that RSD values were in the range of 4.0–9.8% for 1 �g L−1 and2.0–4.8% for 50 �g L−1. Enrichment factors were obtained by com-paring the peak area of the target analytes after pre-concentrationwith the peak areas of analytes for calibration curves without pre-concentration. The interday precision was measured in five dayswith three repetitions each day. The average recoveries for PIC, PNP,2-CP and 2,4-D were in the range of 80–109% with the intraday rela-tive standard deviations (RSDs) of 3.7–7.1%. The interday RSDs werein the range of 2.3–5.5%.The average desorption recoveries for PIC,PNP, 2-CP and 2,4-D were in the range of 71–120% that satisfy the70–130% recoveries range criterion [43].

3.13. Analysis of the raw river water

To determine the ability of the proposed method for PIC, PNP,2-CP and 2,4-DCP analysis in a real sample, tap water and rawwater from the Karon river were tested and spiked. A simple clean-up step was carried out as follows: 50 mL of water samples werefiltered through a Watman 42 filter paper and recommended pro-cedure was applied. No chromatographic signal of target analytesin the pretreated sample solution was observed. Standard addi-tion method was applied to estimate the reliability of the proposedmethod. In this regard, different amounts of PIC, PNP, 2-CP and2,4-DCP were added to the tap water and raw river water sam-ples and the described procedure was undertaken; the analyticalresults are summarized in Table 2. The proposed method indicatedsatisfactory recoveries for PIC, PNP, 2-CP and 2,4-DCP adsorption

and determination in real samples. This revealed that the proposedmethod is applicable for target analytes sensing for direct analysisof PIC, PNP, 2-CP and 2,4-DCP in surface water samples. Evalu-ations indicated satisfactory recoveries and high sensitivity that

D Correlation coefficient (r2) Enrichment factor

4.5 0.9963 9310 0.9931 709.6 0.9857 895.8 0.9938 195

real water samples.

Tap water

overy Added (ng mL−1) Found (ng mL−1) %Recovery

0.00 ND* – 2 0.35 0.32 ± 0.02 91 ± 2

5 1.00 1.11 ± 0.04 109 ± 2 4 7.00 8.40 ± 0.11 120 ± 6

50.00 44.77 ± 0.21 90 ± 40.00 ND* –

3 0.35 0.36 ± 0.01 102 ± 2 5 1.00 0.87 ± 0.01 87 ± 4 3 7.00 6.97 ± 0.25 99 ± 5

50.00 45.40 ± 0.68 90 ± 20.00 ND* –

2 0.35 0.33 ± 0.01 94 ± 4 4 1.00 0.88 ± 0.03 88 ± 3 4 7.00 5.91 ± 0.47 84 ± 3

50.00 42.06 ± 0.27 84 ± 40.00 ND* –

3 0.35 0.30 ± 0.01 85 ± 3 5 1.00 0.87 ± 0.02 87 ± 3 3 7.00 5.70 ± 0.08 81 ± 2

50.00 43.98 ± 0.42 88 ± 4

H. Parham, S. Saeed / J. Chromatogr. A 1336 (2014) 34–42 41

Table 3Comparison of the current method characteristics with those of the other published techniques for extraction and determination of some phenols.

Method LDRa (�g L−1) LODb (�g L−1) %RSD Ref.

FI-CLc 4–400 0.63 2.99 [25]FI-CL 2–400 0.4 2.3 [26]FI-CL 0.6–10 0.1 2.7 [27]CNTs-SBSEd 1–1000 0.14–1.76 4.7–11.1 [28]HF-LPMEe 0.45–75 0.14–0.29 2.1–6.0 [29]HPLC–MS/MSf 0.01–3.0 0.01–1.0 2.7–4.6 [30]SPE-HPLC 5–200 0.1–0.2 1.1–5.5 [31]IP-SAMEg 0.2–75 0.1 3.4 [32]SPE–HPLC 0.75–100 0.3–0.4 2.8–4.9 [33]SBSE-GC–MSh 25–1750 0.3–1.4 4.7 [34]USAEME-SFOi 2.5–1000 0.6–3.2 6–10 [35]MSPE-GC–MSj 50–3000 31–77 4.86–11.2 [36]UASPEk 0.015–100 0.005–0.041 1.3–10 Present work

a Linear dynamic range.b Limit of detection.c Flow-injection chemiluminescence.d Carbonnanotubes coated stir bar sorptive extraction.e Hollow fiber based liquid phase microextraction.f High performance liquid chromatography–tandem mass spectrometry.g Ion pair based surfactant assisted microextraction.h Stir bar sorptive extraction gas chromatography and mass spectrometry.i Ultrasound-assisted emulsification microextraction method based on solidification oj Magnetic solid phase extraction gas chromatography and mass spectrometry.k Ultrasound-assisted solid phase extraction.

F2(

epgeamtat

4

mot

71.

ig. 10. HPLC chromatograms of tap water sample after UASPE: (A) non-spiked, (B)00 �g L−1 spiked with the target analytes without pre-concentration process, andC) after desorption of pre-concentrated target analytes (20 �g L−1 spiked).

nsure the matrix of raw water sample does not interfere with there-concentration and determination of ultra trace amounts of tar-et analytes. Fig. 10 illustrates the typical chromatograms of thextracted PIC, PNP, 2-CP and 2,4-DCP from tap water samples beforend after spiking with target analytes. The potential of this UASPEethod is illustrated by comparison between chromatograms of

arget analytes without pre-concentration (200 �g L−1 spiked) andfter desorption of pre-concentrated target analytes by 0.5 mL ace-onitrile (20 �g L−1 spiked).

. Conclusion

In this study, a novel SPE method based on ALQ@MIONPsixed hemimicelles was developed for the pre-concentration

f four phenolic compounds (PIC, PNP, 2-CP and 2,4-DCP) ashe model analytes. The ALQ@MIONPs were successfully applied

f a floating organic droplet.

in the extraction and detection of trace amounts of phenoliccompounds from real water samples, which showed that thesenanoparticle adsorbents have great application potential in theadsorption and pre-concentration of phenolic compounds fromenvironmental water systems. The use of ALQ 336 ionic liquidassisted MIONPs endued the SPE method with high extractioncapacity and pre-concentration factors. The magnetic separationgreatly improved the separation rate while avoiding the time-consuming column washing of adsorbent particles. The use ofauxiliary ultrasound energy increased the adsorption efficiency oftarget analytes in comparison to conventional contact methods.The strong hydrophobic interactions between the mixed hemim-icelles and PIC, PNP, 2-CP and 2,4-DCP made this new developedSPE method capable of high extraction efficiency and capacity. Theadsorbed analytes were easily desorbed with acetonitrile and nocarryover was observed in the next analysis. Many other meth-ods have been reported to detect phenolic compounds from watersample [5,12,23–38]. The established SPE method proved to behighly effective for concentrating traces of target analytes in waterprior to HPLC analysis. The proposed method showed much bet-ter LODs, good RSD, high enrichment factor, recovery rates andprecision in comparison to a variety of other methods reportedin related literature [5,12,23–38] for the determination of relatedcompounds (Table 3). The results revealed that the ALQ@ MIONPsmixed hemimicelles UASPE method for the determination of traceamounts of nitrophenols and chlorophenols in water sample washighly efficient, simple, rapid and sensitive.

Acknowledgment

The authors wish to thank Shahid Chamran University ResearchCouncil and Environment Protection Agency (EPA) of KhosestanProvince, Iran, for the financial support for this work (Grant 1392).

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Ultrasound-assisted solid phase extraction of nitro- and chloro-(phenols) using magnetic iron oxide nanoparticles and Aliq...1 Introduction2 Experimental2.1 Chemicals and reagents2.2 Apparatus2.3 Preparation of magnetic iron oxide nanoparticles2.4 Preparation of ALQ modified magnetic iron oxide nanoparticles2.5 Extraction and determination procedure2.6 HPLC analysis

3 Results and discussion3.1 Characterization of adsorbent3.2 Effect of pH3.3 Effect of the adsorbent amount3.4 Influence of ALQ 336 ionic liquid3.5 Effect of contact type and ultrasonic power3.6 Effect of contact time3.7 Eluting conditions3.8 Effect of ionic strength3.9 Effect of co-existing species3.10 Breakthrough volume3.11 Reusability studies3.12 Analytical characteristics3.13 Analysis of the raw river water

4 ConclusionAcknowledgmentReferences