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

Contents lists available at ScienceDirect

Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma

Ultrasound-assisted solid phase extraction of nitro- and chloro-(phenols) using magnetic iron oxide nanoparticles and Aliquat 336 ionic liquid Hooshang Parham ∗ , Sedighe Saeed Chemistry Department, Faculty of Sciences, Shahid Chamran University, 6135714168 Ahvaz, Iran

a r t i c l e

i n f o

Article history: Received 23 December 2013 Received in revised form 2 February 2014 Accepted 3 February 2014 Available online 8 February 2014 Keywords: Ultrasound-assisted Nitrophenols Chlorophenols Magnetic iron oxide nanoparticles Aliquat 336

a b s t r a c t A novel and sensitive ultrasound-assisted solid phase extraction (UASPE) method for pre-concentration and determination of ultra-trace amounts of nitrophenols and chlorophenols in water samples was demonstrated. Four hazardous phenolic compounds in water samples were extracted and monitored by high performance liquid chromatography. The results demonstrated that in the presence of Aliquat 336 (ALQ), magnetic iron oxide nanoparticles (MIONPs) were quite efficient in the adsorption and preconcentration of traces of analytes. MIONPs were synthesized and characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The important parameters influencing the extraction efficiency were studied and optimized. The separation and pre-concentration steps were fast and completed in 10 min. Acetonitrile was used for the desorption of target analytes. Under optimum adsorption conditions, a linear range between 0.015 and 100 ␮g L−1 (R2 ≥ 0.997), and limits of detections (LODs) ranging from 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 analytical method 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 in various water samples. The results showed that the proposed method is a rapid, convenient and feasible technique for the determination of nitrophenols and chlorophenols in aqueous samples. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Phenols are common by products of large-scale production and the use of man-made organics such as phenolic resins, drugs, dyes, antioxidants, paper pulp and pesticides that cause ecologically undesirable effects. Repeated or prolonged exposure to phenolic compounds or their vapors may cause headache, nausea, dizziness, difficulty in swallowing, diarrhea, vomiting, shock, convulsions, or death. Phenols can affect the central nervous system, liver, and kidneys [1–3]. These compounds are harmful to organisms at low concentrations and many of them have been classified as hazardous pollutants [4]. Most phenols exhibit different toxicities, and some chlorophenols and nitrophenols are even known to possess carcinogenic and immunosuppressive properties. Due to their potential harm to human health, phenol derivatives and

∗ Corresponding author. Tel.: +98 611 3360018/+98 611 3738015; fax: +98 611 3337009. E-mail address: [email protected] (H. Parham). http://dx.doi.org/10.1016/j.chroma.2014.02.012 0021-9673/© 2014 Elsevier B.V. All rights reserved.

related compounds are considered as priority pollutants. As a consequence, both the US Environmental Protection Agency (EPA) and the European Union (EU) have included some phenols in their lists of priority pollutants. The maximum amount of phenols in wastewater allowed by the European Community is lower than 1 mg L−1 [5,6]. The European Union sets a maximum concentration of 0.5 ␮g L−1 for total phenols and 0.1 ␮g L−1 for their individual concentration in drinking water [7,8]. The major sources of phenol pollution in aquatic environment are wastewaters from paint, pesticide, coal conversion, polymeric resin, gasoline, rubber proofing, steel, petroleum and petrochemical industries [9,10]. New SPE techniques based on the use of magnetic or magnetizable adsorbents called magnetic solid-phase extraction (MSPE) have been used for the separation and pre-concentration of an analyte from large volumes of water solution by using a permanent external magnet [11–15]. Generally, most of the dissolved environmental pollutants are nonmagnetic, and thus do not respond to the magnetic field. The surface modification of magnetic nanoparticles is a challenge for different applications and can be accomplished by the physical/chemical adsorption of organic compounds using

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

four major methods: organic vapor condensation, polymer coating, surfactant adsorption and direct silanation [16]. Removal of hazardous compounds from industrial effluents and also monitoring their concentrations are growing needs at the present time. Aliquat 336 (tricaprylmethylammonium chloride) is a water insoluble quaternary ammonium salt made by the methylation of mixed tri octyl/decyl amine, which is capable of forming oil soluble salts of anionic species at acidic or slightly alkaline pH. Aliquat 336 is composed of a large organic cation associated with chloride ion, [R3 NCH3 ]+ Cl− and exists as a stable cation–anion pair over a wide range of pH. Because the ammonium structure has a permanent positive charge, it can form salts with anions over a wider pH range than primary, secondary or tertiary amines. For this reason, Aliquat 336 finds application in environments ranging from acidic to slightly alkaline pH. In spite of several studies on the solid phase extraction of phenolic compounds with Cethyltrimethylammonium chloride (CTAB) [17,18], no procedure has been reported for the systematic solid phase extraction and separation of such compounds using Aliquat 336. Ultrasonic (US) radiation has been proven to be a very useful tool in intensifying the mass transfer process of the target analytes to the surface of an adsorbent [19,20]. This leads to an increment in the extraction efficiency of the pre-concentration technique in a short time. The effects of US are primarily related with the cavitation phenomenon, which involves the implosion of bubbles formed in the liquid medium during US application. The enhanced adsorption rate by sonication may be attributed to the extreme conditions generated during the violent collapse of the cavitation bubbles. When the bubble is collapsing near the solid surface, symmetric cavitation is hindered and the collapse occurs asymmetrically. The asymmetric collapse of bubbles in a heterogeneous system produces micro-jets with high velocity. Additionally, symmetric and asymmetric collapses generate shockwaves, which cause extremely turbulent flow at the liquid–solid interface, increasing the rate of mass transfer near the solid surface. An important effect of US is the dispersion of aggregated nanoparticles which produces more surfaces and increases more active sites. The mentioned factors results in an increment in the mass-transfer of the analytes onto the adsorbent surface [19–22]. Several diverse methods were applied for the determination of nitrophenols and chlorophenols in environmental samples. These include ultraviolet spectrophotometry (UV) [23,24], chemiluminescence [25–27], high performance liquid chromatography (HPLC) [12,28–34], gas chromatography [35,36] and electrochemical methods [5,37,38]. Some of these techniques suffer from interferences and matrices. On the other hand, the low level of these constituents makes their determination a difficult task. It is well known that the analysis of polar compounds such as nitrophenols and chlorophenols is a challenge due to the strong interactions of these compounds with water molecules in aqueous solutions. Establishing simple, fast, low-cost, sensitive, and selective analytical methods for the extraction and determination of pollutants in the environment is one of the main areas of research in environmental chemistry [11–16,32–38]. In this work, we developed a facile method to synthesize Aliquat 336 coated magnetic iron oxide nanoparticles (ALQ@MIONPs) for the adsorption of phenols. The ALQ@MIONPs demonstrated high potential ability for solid phase extraction (SPE) and preconcentration of phenolic compounds from environmental water samples with high efficiencies. Hence, 2,4,6-trinitrophenol (picric acid, PIC), paranitrophenol (PNP), 2-chlorophenol (2-CP) and 2,4dichlorophenol (2,4-DCP) were selected as the model analytes. Ultra-trace amounts of 2,4,6-trinitrophenol (picric acid, PIC), paranitrophenol (PNP), 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) were determined in water samples. The target analytes

35

(PIC, PNP, 2-CP and 2,4-DCP) were successfully evaluated by HPLC analysis. 2. Experimental 2.1. Chemicals and reagents All chemicals and reagents were of analytical grade. Acetone (99.5%, w/w), acetonitrile (HPLC grade), water (HPLC grade), 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), ammonia solution (25% w/w), FeCl3 (96% w/w), FeCl2 ·4H2 O (99.9% w/w), and Aliquat 336 were purchased from Merck (Darmstadt, Germany) and used without further purification. The stock standard solutions of the analytes were prepared in water–acetonitrile (70:30) solution mixture at a concentration of 100 mg L−1 and stored at 4 ◦ C, protected from light. The standard working solutions were prepared daily by appropriate dilution of the stock standard solutions with water–acetonitrile (70:30) solution to the required concentrations. ALQ stock solution (2% v/v, equivalent to 1760 mg L−1 ) was prepared 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 a Knauer HPLC system (Germany) consisting of a K-1001 pump and a k-2501 UV detector. Two KQ-100DE ultrasonic cleaner were purchased from Kunshan Ultrasonic Instrument Co., Ltd. (Kunshan, China). The frequency and output power of the ultrasonic cleaner were 21 kHz for both and 30, 60 W for the first and 45 W for the second, respectively. A pH-meter (827 pH lab, Metrohm1, Herisau, Switzerland) was also used for pH adjustment. Transmission electron microscopy (906E, LEO, Germany) and scanning electron microscopy (SEM) (XL-30 electron microscope, Philips, Eindhoven, The Netherlands) were used to study the morphology of the magnetic nano-particles. Structural analysis of the MIONPs was done using an X-ray diffractometer (XRD, Brucker D8 Discover, Germany). Infrared spectra were obtained using a Fourier Transform-Infrared Spectrometer (FT-IR spectrum 100, Perkin Elmer, Australia) to identify the functional groups and chemical 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 mixture of chloride salts of ferrous and ferric ions (molar ratio 1:2) in an ammonium hydroxide solution at 80 ◦ C under vigorous stirring and a N2 atmosphere was prepared based on our previous work [39]. In order to stabilize the nanoparticles they were stored in ultra-pure water. 2.4. Preparation of ALQ modified magnetic iron oxide nanoparticles A separate experiment was carried out to ensure the coating of MIONPs by ALQ ionic liquid. A 2 mL portion of MIONPs solution mixture (equivalent to 40 mg of dried MIONPs) and also 2 mL of 2% 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 resultant ALQ@MIONPs were collected by a magnet (10 cm × 5 cm × 4 cm, 1.2 T) and washed with deionized water several times to remove the unreacted materials, and dried at 40 ◦ C under nitrogen gas for

36

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

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

2.5. Extraction and determination procedure Fifty milliliters of the aqueous sample solution, spiked at the given concentrations of the target analytes (PIC, PNP, 2-CP and 2,4-DCP), were transferred into a beaker, and the sample pH was adjusted to 8 with a 0.01 M NaOH solution. Afterwards, 2 mL of MIONPs solution mixture (equivalent to 40 mg of dried MIONPs) and 2 mL of 2% ALQ in EtOH were added to the solution and then sonicated (21 kHz, 60 W) for 10 min. Then, the adsorbent was isolated from the suspension with the magnet. After decanting the supernatant solution, the adsorbed analytes were eluted with 0.5 mL acetonitrile after 6 min of contact time without stirring. Finally, the eluate was separated from the suspension with the magnet and 20 ␮L of it was injected into the HPLC instrument for analysis.

2.6. HPLC analysis A Nucleodur (100-5 C18, 250 mm × 4 mm) column and a 20 ␮L injection loop were used. Pure acetonitrile and water (containing 0.01% phosphoric acid, pH 3) mixture was used as the mobile phase via a gradient elution program. The gradient elution program was as follows: started at 40% acetonitrile and maintained for 3 min with a flow rate of 1.3 mL min−1 ; switched to 80% acetonitrile from 3 min to 5 min with a flow rate of 1.5 mL min−1 ; and finally, decreased to 40% acetonitrile after 5 min and kept constant for 10 min with a flow rate of 1.3 mL min−1 . The temperature of the column oven was kept constant at 25 ◦ C. Under these conditions, chromatographic retention times for PNP, 2-CP, 2,4-DCP and PIC were 4.1, 4.9, 6.6 and 8.9 min, respectively. The detection wavelengths were set at 280 nm for 7.5 min to detect PNP, 2-CP and 2,4-DCP, and then switched to 370 nm for the detection of PIC.

3. Results and discussion The adsorption mechanism of nitrophenols and chlorophenols onto the ALQ@MIONPs surface may be based on the electrostatic attraction between the cationic head of the surfactant and phenolate anions [12,13,15,17,18,37]. The transfer of the adsorbate from the solution to the surface of the adsorbent is controlled by either boundary layer diffusion (external mass transfer) or intraparticle diffusion (mass transfer through the pores), or by both. In general, the adsorption dynamics consists of three consecutive steps: Diffusion of adsorbate molecules from the bulk solution to the external surface of the adsorbent; from the external surface and into the pores of the adsorbent; and finally adsorption of the adsorbate on the active sites on the internal surface of the pores. The last step is usually very rapid in comparison to the first two steps. Hamdaoui and Naffrechoux [19] show that the values of the intraparticle diffusion coefficient obtained in the presence of ultrasound are greater than those obtained in the absence of ultrasound. Hydrodynamic effects induced by ultrasound promote a significant increase in mass transfer across the boundary layer. These behaviors increased with increasing ultrasonic power. Moreover, the cavitation event produced by sonication also gives rise to acoustic micro-streaming or formation of miniature eddies that enhance the mass and heat transfer at the interfacial films surrounding nearby adsorbent particles and within the pores. As a result, ultrasound energy could produce not only high-speed micro-jets but also highpressure shock waves and acoustic vortex micro-streaming.

3.1. Characterization of adsorbent The shape and size of the synthesized particles were observed by TEM and SEM. The TEM images of MIONPs (Fig. 1A) and ALQ@MIONPs (Fig. 1B) particles show that an obvious layer of ALQ is coated on the surface of MIONPs. The coated ALQ layer is clearly seen due to the different electron densities of the magnetic nanoparticles core (with dark color) and ALQ coating (with light color) in TEM micrographs. It can be seen that the synthesized MIONPs and ALQ-MIONPs (Fig. 1C and D) were nearly spherical in shape with an average diameter of about 40–60 nm and 50–70 nm, respectively. Scanning electron microscopy (SEM) was used to observe the surface physical morphology and to determine the size of MIONPs and ALQ@MIONPs. Fig. 1E and F show the structure of MIONPs before and after the modification process. The XRD spectrum of naked MIONPs is compared with ALQ capped particles, the XRD pattern of these nanoparticles agrees well with that of the pure nanoparticles (as shown in Fig. 2a); the result shows that the reflection peaks can be seen in an XRD pattern at 30.1, 35.5, 43.2, 53.5, 57.0 and 62.7. These peaks correspond to the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) planes. The XRD pattern of the MIONPs exactly matched the JCPDS reference no. 19–629. The X-ray diffraction pattern of ALQ@MIONPs is shown in Fig. 2b. It can be seen that the intensities of the peaks are decreased due to caption of MIONPs by ALQ. FT-IR studies was used to identify functional groups and the chemical 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 of MIONPs shows absorption bands at 570–640 cm−1 which are usually attributed to the Fe–O stretches (a) [41]. The spectrum of ALQ@MIONPs shows the characteristic peaks of both ALQ (–CH3 and–CH2 –stretching bands, (b)) and MIONPs (absorption bands at 570–640 cm−1 ) which confirms the adsorption of ALQ on MIONPs as adsorbent. The peaks at 1650–1450 cm−1 are assigned to the aromatic C=C stretching of PIC (c). FT-IR spectrum of PIC indicates the characteristic N=O peaks at 1538 and 1347 cm−1 (d). The pattern of the out-of-plane C–H bending bands in the region of 900–675 cm−1 and the –O–H stretch at 3100–3200 cm−1 (e) are characteristic of this aromatic compound [42]. The broad adsorption band at 3400–3700 cm−1 (f) is related to moisture adsorbed by PIC-ALQ@MIONPs. 3.2. Effect of pH The pH of water samples is an important parameter that affects the SPE of nitrophenols and chlorophenols because PIC is a relatively 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 values of phenols, changing the sample pH will cause deprotonation of phenolic groups and the functional groups on the adsorbent surface. In the present study, the pH effect was examined by varying pH 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 diluted solutions of 0.1 M HCl or 0.1 M NaOH. Then, 1 mL 2% ALQ solution was added to the test sample and the mixture sonicated for 7 min. ALQ@MIONPs were separated and eluted with 1 mL acetonitrile for 3 min contact time. As shown in Fig. 4, the ALQ@MIONPs exhibited no obvious adsorption for target analytes when pH was lower than 6. With increases in pH, the sorption amount increased dramatically before reaching a maximum at pH 8. This can be attributed to the fact that the surface of ALQ@MIONPs was positively charged when ALQ+ was attached to the surface of MIONPs. Low adsorption efficiency at low pHs could be related to the protonation of phenolate 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

Fig. 1. The TEM images and average particle sizes of MIONPs (A and C) and ALQ@MIONPs (B and D). (E) and (F) Show the SEM of MIONPs and ALQ-MIONPs.

pH of the test solution up to 8, the abundance of phenolate forms of PIC, PNP, 2-CP and 2,4-DCP increases. Hence, the strong electrostatic attraction between the positive charged ALQ molecules and the negatively charged analytes is high enough to produce a great adsorption affinity for target analytes. Therefore, pH 8.0 was selected as optimum for further studies. Higher pHs decrease the extraction efficiency due to higher concentration of hydroxide ions which can compete with phenolate anions of the target analytes.

desorption of analytes from adsorbent surfaces due to the small volume of acetonitrile (0.5 mL) as the desorbing solvent. 3.4. Influence of ALQ 336 ionic liquid Primary tests showed that in the absence of ALQ, the adsorption of PIC, PNP, 2-CP and 2,4-DCP (50 mL, 30 ␮g L−1 of each analyte)

3.3. Effect of the adsorbent amount The amount of MIONPs adsorbent required for the quantitative removal of PIC, PNP, 2-CP and 2,4-DCP was optimized. The effect of different quantities of MIONPs ranging from 10 to 100 mg was investigated. Fifty milliliters of the aqueous sample solution of target analytes (30 ␮g L−1 of each analyte), were transferred into a series of beakers, and the sample pH was adjusted to 8. Different quantities of MIONPs and 1 mL of 2% ALQ in EtOH were added to each solution and then sonicated (21 kHz, 60 W) for 7 min. ALQ@MIONPs were separated and eluted with 1 mL acetonitrile for 3 min contact time. The results are shown in Fig. 5. Maximum adsorption was obtained when 40 mg of MIONPs was in contact with the sample solution of target analytes. For amounts more than 40 mg of adsorbent, recoveries decreased because of incomplete

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. 6. Influence of ALQ 336 ionic liquid on the extraction efficiency of target analytes. Extraction conditions: sample solution, 50 mL of 30 ␮g L−1 of the analytes at pH = 8; adsorbent amount, 40 mg of MIONPs; Sonication (21 kHz, 60 W) time, 7 min; eluent volume, 1 mL; desorption time, 3 min. Fig. 3. FT-IR spectra of MIONPs, ALQ, ALQ@MIONPs, PIC and PIC-ALQ@MIONPs.

added. Furthermore, the micelles caused the PIC, PNP, 2-CP and 2,4-DCP to redistribute into the solution again and adsorption efficiency decreased. Based on these results, 2 mL of 2% solution of ALQ (88 mg) in EtOH was adopted as the optimum amount of surfactant in further studies. 3.5. Effect of contact type and ultrasonic power

Fig. 4. The effect of solution pH on the adsorption efficiency of PNP, 2-CP, 2,4-DCP and PIC. Extraction conditions: sample solution, 50 mL of 30 ␮g L−1 of the analytes; adsorbent amount, 25 mg of MIONPs; 1 mL of 2% ALQ solution; sonication (21 kHz, 60 W) time, 7 min; eluent volume, 1 mL; desorption time, 3 min.

onto the surface of MIONNPs is very low. But, with increases in ALQ (2% v/v in EtOH, 1760 mg L−1 ), the sorption amount of target analytes increased remarkably. Fig. 6 depicts the peak area of adsorbed phenols as a function of the amount of ALQ added. The increase in sorption can be explained by the gradual formation of hydrophobic hemimicelles and also ion pair formation between ALQ+ and phenolate anions on the surface of MIONPs. Maximum sorption was obtained when the ALQ volume reached 2 mL (2% v/v, 88 mg) in 50 mL sample solution. The results clearly indicated that hydrophobic interactions played an important role in the adsorption process. The adsorption amount decreased when the amount of ALQ added exceeded 88 mg, after which the ALQ molecules began to form micelles in the bulk aqueous solution with more surfactant

Extraction and pre-concentration efficiency can be affected by the type of hydrodynamic mixing of adsorbates and adsorbent particles. Different mixing methods such as static, shaking, stirring and sonication were examined with 50 mL sample solutions (30 ␮g L−1 of each analyte, pH 8) containing 2 mL of 2% solution of ALQ and 40 mg of MIONPs. The conditions of different contact methods between adsorbent particles 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 produced the best extraction efficiency. Acoustic streaming with hydrodynamic phenomenon due to cavitation is responsible for the perfect mixing of the reactor content. In order to determine the effect of sonication energy on extraction efficiency, different ultrasound powers were examined. Ultrasonic wave frequency of 21 kHz was used for sonication experiments at three different ultrasonic powers (30, 45 and 60 W). The temperature was maintained constant and equal to 25 ◦ C. The adsorption increased with increasing acoustic power of ultrasound (Fig. 7B), because with high power more cavitation events occur and more molecules are adsorbed. Higher ultrasound powers decreased the extraction efficiency dramatically by destroying the MIONPs and a brown color suspension was produced. 3.6. Effect of contact time

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

The effect of sonication (21 kHz, 60 W) time on the adsorption efficiency of the target analytes was examined. The results are shown in Fig. 8. As illustrated, the extraction efficiencies of the PIC, PNP, 2-CP and 2,4-DCP increase continuously by increasing the time from 2 to10 min, and decrease with further increase in time. Indeed, because of the very high surface area to volume ratios in nanosorbents and their short diffusion routes which lead to a highly

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

39

was also examined. The acidity of acetonitrile eluent was increased by nitric acid solutions (0.001 to 0.1 M) and several tests were explored. The results revealed that as the acidity of elution solvent increases, desorption efficiency decreases. This may be due to the solubility of ALQ@MIONPs in acidic solutions. Hence, the best desorption of target analytes is attained by using pure acetonitrile which was finally chosen as the elution solvent in subsequent experiments. The effect of contact time on the desorption of target analytes was also studied. The results revealed that there is an increase in the extraction efficiency for desorption times up to 4 min. Longer contact times (>4 min) cause a slight decrease in desorption efficiency due to re-adsorption of analytes on the surface of ALQ@MIONPs. So, the time of 4 min was applied for desorption of analytes in subsequent experiments. 3.8. Effect of ionic strength

Fig. 7. Effects of (A) contact type and (B) ultrasonic power on the extraction efficiency of target analytes. Extraction conditions: sample solution, 50 mL of 30 ␮g L−1 of the analytes at pH = 8; adsorbent amount, 40 mg of MIONPs; 2 mL of 2% ALQ solution; Sonication (21 kHz, 60 W) time, 7 min; eluent volume, 1 mL; desorption time, 3 min.

rapid adsorption process, equilibrium between the sample solution and the adsorbent surface can be reached in a shorter contact time in comparison with other SPE sorbents. Based on these results, the contact time of 10 min was selected as the optimum value for sensitivity enhancement. 3.7. Eluting conditions Desorption of PIC, PNP, 2-CP and 2,4-DCP from the ALQ@MIONPs was studied using different organic solvents like acetonitrile, methanol and ethanol via static contact between ALQ@MIONPs and elution solvent for 3 min. Quantitative recoveries (above 80%) of target analytes were obtained using 2 mL acetonitrile. Under this optimized desorption condition, no carryover was observed in the next analysis. The volume of eluent was also optimized and the highest extraction efficiency was obtained with 0.5 mL of acetonitrile. The effect of eluent acidity on the desorption of target analytes

The effect of ionic strength on adsorption and pre-concentration processes was examined using different concentrations of KNO3 as electrolyte. Results show that the adsorption and extraction efficiencies of PIC, PNP, 2-CP and 2,4-DCP were increased by increasing the KNO3 concentration up to 0.001 M of KNO3 which may be due to salting out effect. But, peak areas of target analytes decreased in more concentrated (up to 0.01 M) solutions due to the saturation of active adsorbent sites by co-existing ions. This implied that electrostatic attraction plays a significant role in the adsorption/desorption steps under these test conditions. 3.9. Effect of co-existing species The optimum experimental conditions which have been described were used to study the interfering effect of some ions and organic compounds on the separation, pre-concentration and determination processes of PIC, PNP, 2-CP and 2,4-DCP (50 mL, 30 ␮g L−1 for each analyte). To this end, separation and determination of target analytes were performed in the presence of co-existing interfering substances. The maximum acceptable error was ±5% change in HPLC peak area of target analytes. The obtained results show that most of the investigated ions did not interfere during separation, pre-concentration, and determination. The cations Fe2+ , Fe3+ , Ca2+ and Mg2+ , Cl− , NO3 − , K+ , Na+ , Br− , I− , F− , PO4 3− , CO3 2− , SO4 2− , NH4 + and acetate ions do not interfere at concentration 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 times higher ratios than analytes. 3.10. Breakthrough volume The effect of sample volume on adsorption and preconcentration processes was investigated using a series of solutions with fixed amounts of PIC, PNP, 2-CP and 2,4-DCP (1.5 ␮g for each analyte) at different volumes. Results in Fig. 9 show that initial sample volume had no effect on the recovery rate up to 100 mL and recoveries ≥92% were obtained for sample volumes up to 100 mL. 3.11. Reusability studies

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

To evaluate the ability of adsorbent to be regenerated and reused, several (adsorption/desorption) regeneration cycles were run for the adsorbent. After each extraction process, the adsorbent was rinsed with 1 mL of eluent (acetonitrile) two times and then used in subsequent extractions. It was found that the recoveries of

40

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

and 50 ␮g L−1 solutions (n = 6) of PIC, PNP, 2-CP and 2,4-D and it was found that RSD values were in the range of 4.0–9.8% for 1 ␮g L−1 and 2.0–4.8% for 50 ␮g L−1 . Enrichment factors were obtained by comparing the peak area of the target analytes after pre-concentration with the peak areas of analytes for calibration curves without preconcentration. The interday precision was measured in five days with 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 relative standard deviations (RSDs) of 3.7–7.1%. The interday RSDs were in 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 the 70–130% recoveries range criterion [43]. Fig. 9. The effect of sample volume on adsorption and pre-concentration of fixed amounts of PIC, PNP, 2-CP and 2,4-DCP (1.5 ␮g for each analyte) at different volumes.

the target analytes are not diminished even after three successive extraction processes, suggesting the good reusability of the sorbent. 3.12. Analytical characteristics In order to estimate the efficiency and feasibility of the proposed method for its application to the analysis of environmental samples, the analytical characteristics of the proposed method were determined in terms of linearity, precision (expressed as the relative standard deviation), limit of detection and enrichment factor, The obtained results are summarized in Table 1. Calibration curves were obtained in the concentration range of 0.015–100 ␮g L−1 (n = 12) for PIC and PNP, and also 0.075–100 ␮g L−1 (n = 10) for 2-CP and 2,4-DCP after pre-concentration with ALQ@MIONPs and desorption with 0.5 mL acetonitrile. The repeatability of the method in terms of relative standard deviation (%RSD) was evaluated for 1

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 raw water from the Karon river were tested and spiked. A simple cleanup step was carried out as follows: 50 mL of water samples were filtered through a Watman 42 filter paper and recommended procedure was applied. No chromatographic signal of target analytes in the pretreated sample solution was observed. Standard addition method was applied to estimate the reliability of the proposed method. In this regard, different amounts of PIC, PNP, 2-CP and 2,4-DCP were added to the tap water and raw river water samples and the described procedure was undertaken; the analytical results are summarized in Table 2. The proposed method indicated satisfactory recoveries for PIC, PNP, 2-CP and 2,4-DCP adsorption and determination in real samples. This revealed that the proposed method is applicable for target analytes sensing for direct analysis of PIC, PNP, 2-CP and 2,4-DCP in surface water samples. Evaluations indicated satisfactory recoveries and high sensitivity that

Table 1 Analytical parameters of the proposed method. Analyte

LDRa (␮g L−1 )

LODb (␮g L−1 )

%RSD

Correlation coefficient (r2 )

Enrichment factor

PNP 2-CP 2,4-DCP PIC

0.015–100 0.075–100 0.075–100 0.015–100

0.012 0.041 0.031 0.005

3.6–4.5 6.1–10 5.9–9.6 1.3–5.8

0.9963 0.9931 0.9857 0.9938

93 70 89 195

a b

Linear dynamic range. Limit of detection.

Table 2 Results from determination of target analytes (n = 3) by the proposed method in different real water samples. Compound

River water Added (ng mL−1 )

Tap water Found (ng mL−1 ) *

%Recovery

PNP

0.00 1.00 7.00 50.00

ND 0.85 ± 0.01 8.37 ± 0.09 39.66 ± 0.17

– 85 ± 2 119 ± 5 79 ± 4

2-CP

0.00 1.00 7.00 50.00

ND* 0.82 ± 0.01 6.25 ± 0.14 37.84 ± 0.16

– 83 ± 3 89 ± 5 75 ± 3

2,4-DCP

0.00 1.00 7.00 50.00

ND* 0.77 ± 0.01 5.50 ± 0.18 39.44 ± 0.21

– 77 ± 2 79 ± 4 79 ± 4

PIC

0.00 1.00 7.00 50.00

ND* 0.71 ± 0.01 6.50 ± 0.19 37.53 ± 0.07

– 71 ± 3 93 ± 5 75 ± 3

*

Not detected.

Added (ng mL−1 ) 0.00 0.35 1.00 7.00 50.00 0.00 0.35 1.00 7.00 50.00 0.00 0.35 1.00 7.00 50.00 0.00 0.35 1.00 7.00 50.00

Found (ng mL−1 ) *

ND 0.32 ± 0.02 1.11 ± 0.04 8.40 ± 0.11 44.77 ± 0.21 ND* 0.36 ± 0.01 0.87 ± 0.01 6.97 ± 0.25 45.40 ± 0.68 ND* 0.33 ± 0.01 0.88 ± 0.03 5.91 ± 0.47 42.06 ± 0.27 ND* 0.30 ± 0.01 0.87 ± 0.02 5.70 ± 0.08 43.98 ± 0.42

%Recovery – 91 ± 2 109 ± 2 120 ± 6 90 ± 4 – 102 ± 2 87 ± 4 99 ± 5 90 ± 2 – 94 ± 4 88 ± 3 84 ± 3 84 ± 4 – 85 ± 3 87 ± 3 81 ± 2 88 ± 4

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

41

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

FI-CL FI-CL FI-CL CNTs-SBSEd HF-LPMEe HPLC–MS/MSf SPE-HPLC IP-SAMEg SPE–HPLC SBSE-GC–MSh USAEME-SFOi MSPE-GC–MSj UASPEk a b c d e f g h i j k

LDRa (␮g L−1 )

LODb (␮g L−1 )

%RSD

Ref.

4–400 2–400 0.6–10 1–1000 0.45–75 0.01–3.0 5–200 0.2–75 0.75–100 25–1750 2.5–1000 50–3000 0.015–100

0.63 0.4 0.1 0.14–1.76 0.14–0.29 0.01–1.0 0.1–0.2 0.1 0.3–0.4 0.3–1.4 0.6–3.2 31–77 0.005–0.041

2.99 2.3 2.7 4.7–11.1 2.1–6.0 2.7–4.6 1.1–5.5 3.4 2.8–4.9 4.7 6–10 4.86–11.2 1.3–10

[25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] Present work

Linear dynamic range. Limit of detection. Flow-injection chemiluminescence. Carbonnanotubes coated stir bar sorptive extraction. Hollow fiber based liquid phase microextraction. High performance liquid chromatography–tandem mass spectrometry. Ion pair based surfactant assisted microextraction. Stir bar sorptive extraction gas chromatography and mass spectrometry. Ultrasound-assisted emulsification microextraction method based on solidification of a floating organic droplet. Magnetic solid phase extraction gas chromatography and mass spectrometry. Ultrasound-assisted solid phase extraction.

Fig. 10. HPLC chromatograms of tap water sample after UASPE: (A) non-spiked, (B) 200 ␮g L−1 spiked with the target analytes without pre-concentration process, and (C) after desorption of pre-concentrated target analytes (20 ␮g L−1 spiked).

ensure the matrix of raw water sample does not interfere with the pre-concentration and determination of ultra trace amounts of target analytes. Fig. 10 illustrates the typical chromatograms of the extracted PIC, PNP, 2-CP and 2,4-DCP from tap water samples before and after spiking with target analytes. The potential of this UASPE method is illustrated by comparison between chromatograms of target analytes without pre-concentration (200 ␮g L−1 spiked) and after desorption of pre-concentrated target analytes by 0.5 mL acetonitrile (20 ␮g L−1 spiked). 4. Conclusion In this study, a novel SPE method based on ALQ@MIONPs mixed hemimicelles was developed for the pre-concentration of four phenolic compounds (PIC, PNP, 2-CP and 2,4-DCP) as the model analytes. The ALQ@MIONPs were successfully applied

in the extraction and detection of trace amounts of phenolic compounds from real water samples, which showed that these nanoparticle adsorbents have great application potential in the adsorption and pre-concentration of phenolic compounds from environmental water systems. The use of ALQ 336 ionic liquid assisted MIONPs endued the SPE method with high extraction capacity and pre-concentration factors. The magnetic separation greatly improved the separation rate while avoiding the timeconsuming column washing of adsorbent particles. The use of auxiliary ultrasound energy increased the adsorption efficiency of target analytes in comparison to conventional contact methods. The strong hydrophobic interactions between the mixed hemimicelles and PIC, PNP, 2-CP and 2,4-DCP made this new developed SPE method capable of high extraction efficiency and capacity. The adsorbed analytes were easily desorbed with acetonitrile and no carryover was observed in the next analysis. Many other methods have been reported to detect phenolic compounds from water sample [5,12,23–38]. The established SPE method proved to be highly effective for concentrating traces of target analytes in water prior to HPLC analysis. The proposed method showed much better LODs, good RSD, high enrichment factor, recovery rates and precision in comparison to a variety of other methods reported in related literature [5,12,23–38] for the determination of related compounds (Table 3). The results revealed that the ALQ@ MIONPs mixed hemimicelles UASPE method for the determination of trace amounts of nitrophenols and chlorophenols in water sample was highly efficient, simple, rapid and sensitive. Acknowledgment The authors wish to thank Shahid Chamran University Research Council and Environment Protection Agency (EPA) of Khosestan Province, Iran, for the financial support for this work (Grant 1392). References [1] G. Favaro, D. De Leo, P. Pastore, F. Magno, A. Ballardin, J. Chromatogr. A 1177 (2008) 36. [2] C.J. Liao, C.P. Chen, M.K. Wang, P.N. Chiang, C.W. Pai, Environ. Toxicol. 21 (2006) 71. [3] F.E.O. Suliman, S.S. Al-Kindi, S.M.Z. Al-Kindy, H.A.J. Al-Lawati, J. Chromatogr. A 1101 (2006) 179. [4] B.H. Hameed, A.A. Rahman, J. Hazard. Mater. 160 (2008) 576. [5] X.H. Zhou, L.H. Liu, X. Bai, H.C. Shi, Sens. Actuators, B 181 (2013) 661.

42

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

[6] Commission of the European Communities, Would you Drink your Wastewater? A Water Brochure for Young People, Urban Water Directive 91/271/EC. [7] C.M. Santana, Z.S. Ferrera, M.E. Padron, J.J. Rodriguez, Molecules 14 (2009) 298. [8] States Environmental Protection Agency, Sampling and Analysis Procedure for Screening of Industrial Effluents for Priority Pollutants, United States Environmental Protection Agency (USEPA), Environment Monitoring and Support Laboratory, Cincinnati, OH, USA, 1977. [9] Md. Ahmaruzzaman, Adv. Colloid Interface Sci. 143 (2008) 48. [10] S. Lin, R. Juang, J. Environ. Manage. 90 (2009) 1336. [11] B. Zargar, H. Parham, A. Hatamie, Talanta 77 (2009) 1328. [12] H. Parham, B. Zargar, Z. Heidari, A. Hatamie, J. Iran. Chem. Soc. 8 (2011) S9. [13] B. Zargar, H. Parham, A. Hatamie, Chemosphere 76 (2009) 554. [14] J. Meng, J. Bu, C. Deng, X. Zhang, J. Chromatogr. A 1218 (2011) 1585. [15] Z. Li, D. Huang, C. Fu, B. Wei, W. Yu, C. Deng, X. Zhang, J. Chromatogr. A 1218 (2011) 6312. [16] M. Takafuji, S. Ide, H. Ihara, Z. Xu, Chem. Mater. 16 (2004) 1977. [17] H. Parham, B. Zargar, M. Rezazadeh, Mater. Sci. Eng., C 32 (2012) 2109. [18] J. Li, X. Zhao, Y. Shi, Y. Cai, S. Mou, G. Jiang, J. Chromatogr. A 1180 (2008) 24. [19] O. Hamdaoui, E. Naffrechoux, Ultrason. Sonochem. 16 (2009) 15. [20] R.-S. Juang, S.-H. Lin, C.-H. Cheng, Ultrason. Sonochem. 13 (2006) 251. [21] C. Bendicho, I. De La Calle, F. Pena, M. Costas, N. Cabaleiro, I. Lavilla, Trends Anal. Chem. 31 (2012) 50. [22] M.D. Luque de Castro, F. Priego-Capote, Talanta 72 (2007) 321. [23] I. Lavilla, S. Gil, M. Costas, C. Bendicho, Talanta 98 (2012) 197. [24] K. Takeda, M. Moriki, W. Oshiro, H. Sakugawa, Mar. Chem. 157 (2013) 208. [25] S. Xu, W. Liu, B. Hu, W. Cao, Z. Liu, J. Photochem. Photobiol., A 227 (2012) 32. [26] W. Liu, W. Cao, W. Liu, K. Du, P. Gong, Spectrochim. Acta, Part A 85 (2012) 283.

[27] Z. Wang, Y. Tang, H. Hu, L. Xing, G. Zhang, R. Gao, J. Lumin. 145 (2014) 818. [28] C. Hu, B. Chen, M. He, B. Hu, J. Chromatogr. A 1300 (2013) 165. ´ J.L. Pe´rez-Bernal, R. Fernandez-Torres, ´ [29] M. Villar-Navarro, M. Ramos-Payan, M. ´ M.Á. Bello-Lopez, Talanta 99 (2012) 55. Callejón-Mochon, [30] M. Noestheden, D. Noot, R. Hindle, J. Chromatogr. A 1263 (2012) 68. [31] A.H. El-Sheikh, A.M. Alzawahreh, J.A. Sweileh, Talanta 85 (2011) 1034. [32] M. Moradi, Y. Yamini, J. Kakehmam, A. Esrafili, M. Ghambarian, J. Chromatogr. A 1218 (2011) 3945. [33] E. Tahmasebi, Y. Yamini, S. Seidib, M. Rezazadeh, J. Chromatogr. A 1314 (2013) 15. [34] R.-J. Chung, M.-I. Leong, S.-D. Huang, J. Chromatogr. A 1246 (2012) 55. ˜ [35] J.I. Cacho, N. Campillo, P. Vinas, M. Hernández-Córdoba, Talanta 118 (2014) 30. [36] J. Meng, C. Shi, B. Wei, W. Yu, C. Deng, X. Zhang, J. Chromatogr. A 1218 (2011) 2841. [37] L. Fernandez, I. Ledezma, C. Borras, L.A. Martinez, H. Carrero, Sens. Actuators, B 182 (2013) 625. [38] E. C¸evik, M. Senel, A. Baykal, M.F. Abasiyanik, Sens. Actuators, B 173 (2012) 396. [39] J.H. Jang, H.B. Lim, Microchem. J. 94 (2010) 148. [41] Y.W. Jun, Y.M. Huh, J.S. Choi, J.H. Lee, H.T. Song, S. Kim, S. Yoon, K.S. Kim, J.S. Shin, J.S. Suh, J. Cheon, J. Am. Chem. Soc. 127 (2005) 5732. [42] R.L. Pecsok, L.D. Shields, T. Cairns, I.G. McWilliam, Modern Method of Chemical Analysis, second ed., John Wiley & Sons, New York, NY, 1976, pp. 165. [43] United States Environmental Protection Agency, Nitroaromatics and nitramins by high performance liquid chromatography, in: Method 8330A, Office of Solid Waste, United States Environmental Protection Agency (USEPA), Washington, DC, 1996.