Analytica Chimica Acta 804 (2013) 280–286

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Periodic mesoporous organosilica with ionic liquid framework as a novel fiber coating for headspace solid-phase microextraction of polycyclic aromatic hydrocarbons Mir Mahdi Abolghasemi a,∗ , Babak Karimi b , Vahid Yousefi a a b

Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), 45137-6731, Iran

h i g h l i g h t s

g r a p h i c a l

a b s t r a c t

• The Periodic mesoporous organosilica based on alkylimidazolium ionic liquid (PMO-IL) material was used for fabrication of the SPME fiber. • The fiber was evaluated for the extraction of polycyclic aromatic hydrocarbons. • Different parameters affecting the extraction efficiency were optimized. • The SPME fiber was applied in polluted river water and water samples.

a r t i c l e

i n f o

Article history: Received 29 May 2013 Received in revised form 8 October 2013 Accepted 11 October 2013 Available online 21 October 2013 Keywords: Polycyclic aromatic hydrocarbons Periodic mesoporous organosilica Ionic liquid Solid phase microextraction Gas chromatography–mass spectrometry

a b s t r a c t Periodic mesoporous organosilica based on alkylimidazolium ionic liquid (PMO-IL) was prepared and used as a highly porous fiber coating material for solid-phase microextraction (SPME). The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. The fiber was evaluated for the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography–mass spectrometry (GC–MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, stirring rate, and desorption temperature and time. In optimum conditions, the repeatability for one fiber (n = 3), expressed as relative standard deviation (R.S.D.%), was between 4.3% and 9.7% for the test compounds. The detection limits for the studied compounds were between 4 and 9 pg mL−1 . The developed method offers the advantage of being simple to use, with shorter analysis time, lower cost of equipment, thermal stability of fiber and high relative recovery in comparison to conventional methods of analysis. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Over the past few decades, ordered mesoporous silica-based inorganic materials such as MCM-41 [1], LUS-1 [2,3], and SBA15 [4] prepared via supramolecular assembly have attracted intense interest due to their potential use in a wide range of

∗ Corresponding author. Tel.: +98 4212276060; fax: +98 4212276060. E-mail addresses: [email protected], [email protected] (M.M. Abolghasemi). 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.10.022

applications. Ordered mesoporous materials that have uniform pores and high specific areas are received great attention from researchers because of their potential applications including catalysts, separation, adsorbents for organic molecules, biomolecules, controlled drug release and guest–host chemical supporters [5–13]. After the first reports, introducing the ordered mesoporous silicas at the beginning of the 1990s, the synthesis of advanced mesoporous materials has undergone an explosive growth and the research area broadened toward more specific applications. One of these research areas is the development of hybrid materials [14,15]; in this case, an organic functionality is combined with the stability

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of an inorganic matrix. In order to introduce an active functionality at the mesopore surface, different organosilane precursors are used as silica source for the synthesis of organically modified hybrid mesoporous materials [16,17]. Among these organic–inorganic hybrid materials, the periodic mesoporous organosilicas (PMOs) have attracted increasing interests because of their potential utility in different frontier areas. Potential use of PMOs depends critically on macroscopic morphologies and on the loading of accessible organic groups into the framework. This gives rise to very interesting properties, including high adsorption affinity for organic compounds, high surface area, narrow pore size distribution and adjustable pore diameter. Room temperature ionic liquids (ILs) are a group of organic salts consisting of a combination of organic cations and various anions that are liquids at room temperature. They have various advantages over traditional organic solvents, such as low vapor pressure, high stability, large viscosity, adjustable miscibility and polarity, good extractability for different organic and inorganic compounds [18,19]. Moreover, owing to their low volatility, flammability and toxicity, ILs have been proposed as an alternative to organic solvent, as green solvents for extraction. Some utilizations have been also demonstrated for various analytical purposes, such as the stationary phase for gas chromatography [20–22] or liquid chromatography [23], matrix-assisted laser desorption/ionization mass spectroscopy (MALDI-MS) [24–26], the mobile phase modifier in HPLC [27] and for liquid phase microextraction [18,19,28] and hybrid liquid–solid phase microextraction [29]. Solid phase microextraction (SPME), first introduced by Pawliszyn et al. more than a decade ago, can be regarded as a combination of sampling, preconcentration, matrix removal, and sample introduction techniques. Due to its simple, solventless and flexible properties, SPME has become an attractive alternative to some of conventional sampling techniques and has gained a widespread acceptance in many areas such as environmental, food, pharmaceutical, clinical and forensic [30]. SPME suffers from some drawbacks: its fiber is fragile and has limited lifetime and desorption temperature, and also sample carry over is another problem. Among the different developments for coating of SPME fibers, Wang et al. established a suitable method using sol–gel technology to overcome other important drawbacks of conventional SPME coatings such as: operating temperature problems, instability and swelling in organic solvents [31]. From solid phase microxtraction point of view, the fiber coating and the material of coating is very important. Many researchers have focused on developing new fibers and coatings by using new preparation methods or new materials. For new preparation methods, electrochemical procedures [32], immobilized resin [33], molecular imprinted [34] and sol–gel technology [35] have been developed. Previous studies [36,37] showed that ILs could be used as an alternative solvent for solvent extraction and liquid phase microextraction, showing comparable or even better extraction efficiency than conventionally used solvents. Recently, ILs have also been combined with SPME technique. Due to their relative high viscosity and thermal stability, the ILs can be coated on the surface of fused silica capillary tubing in place of regular SPME fiber. Jiang and co-workers [29] demonstrated that [C8 mim][PF6 ] can be physically absorbed on the surface of fused silica tubing and used as SPME fiber. Pang et al. [38] developed a new approach for constructing the IL-based SPME fiber through chemical binding for extraction of polycyclic aromatic hydrocarbons from water samples. Preparation this coating requires a lot of steps and expensive materials. However, despite the remarkable utility of ionic liquids, these systems often require large amounts of relatively expensive ionic liquids, which may hinder their widespread practical implementation. Furthermore, depending on the relatively high viscosity of the ionic liquids, the bulk ionic liquid may suffer from slow diffusion, causing the main part of the reaction to proceed in a small

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fraction of ILs called the “diffusion layer”. Therefore, from both economical and technical points of view, the productivity of the reaction based on bulk ILs is hampered since a large part of IL is not contributing in the over-all process. To address these inherent limitations, immobilized ionic liquids offer many advantages over homogeneous IL systems, such as easy handling and recyclability [37]. Although, these approaches decrease the amount of IL utilized in a typical process relative to homogeneous systems; leaching of IL from the heterogeneous support is commonplace. This problem can be partly impeded by using a variety of chemically bounded ionic liquids [39]. However, because the extraction efficiency is dependent on the quantity of IL-coated on the SPME fiber, this efficiency is still limited by the relatively low absorption force, and so the IL layer on the fiber was thin. Very recently one of us has designed a novel periodic mesoporous organosilica comprising ionic liquid (PMO-IL) for application as support on immobilizing and stabilizing metal nanoparticles in some of important chemical transformations [40–42]. An important and unique aspect of the PMO materials is that the ionic liquids are located in the channel wall, thus allowing higher organic loading without significant channel blockage. The present work focuses on the development of PMO-IL nanocomposite as novel coating for SPME fiber. Here, it is believed the integrating of PMO and IL providing new organic–inorganic hybrid materials that can open novel branch toward to expanding solid phase microextraction technique. For this purpose, polycyclic aromatic hydrocarbons (PAHs) were tested as model compounds in aqueous matrices at a trace level. The factors that influenced on the extraction efficiency of PAHs including sample temperature, stirring rate, extraction time and ionic strength were investigated and optimized. Finally, the proposed method was successfully applied to the analysis of trace PAHs in environmental samples. 2. Experimental 2.1. Chemicals and reagents Poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) (EO20–PO70–EO20 or Pluronic P123) as surfactant and tetramethoxyorthosilicate (TMOS) were purchased from Aldrich. Imidazole and 3-chloropropyl-trimethoxysilan, naphthalene, 1-methyl-naphthalene, anthracene, fluorene, biphenyl, acenaphthene, acenaphthylene, fluoranthene, pyrene and all chemical solvents were obtained from the Fluka or Merck companies. The stock solution of PAHs was prepared in methanol: dichloromethane (50:50, v/v) mixed the solvent at a concentration of 1 mg mL−1 . The working solutions of above compounds were prepared by diluting the stock solution with methanol and dichloromethane, and more diluted working solutions were prepared daily by diluting these solutions with deionized water. All solvents used in this study were of analytical reagent grade. Blank analyses were performed regularly to ensure that no PAHs were present in laboratory reagents, atmosphere, or fibers. 2.2. Apparatus A Hewlett-Packard HP 6890 series GC equipped with a split/splitless injector and a HP 5973 mass-selective detector system were used for the determination. The MS was operated in the EI mode (70 eV). Helium (99.999%) was employed as a carrier gas, and its flow-rate was adjusted to 1.1 mL min−1 . The separation of PAHs was performed on a 30 m × 0.25 mm HP-5 MS column with 0.25 ␮m film thickness. The column was held at 50 ◦ C for 3 min and increased to 180 ◦ C at a rate of 15 ◦ C min−1 and then raised to 260 ◦ C at 20 ◦ C min−1 and kept at this temperature for 5 min. The injector temperature was set

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Table 1 Some analytical data obtained for microextraction of PAHs using the PMO-IL. Compound

Target ion (m/z)

Naphthalene m-Naphthalene Biphenyl Acenaphthene Fluorene Anthracene Fluoranthene Pyrene

128 142 154 153 166 178 202 202

a b c

Confirmation ions (m/z) 129,127 115,139 139,155 154,152 165,167 179,177 203,101 203,101

DLRa (ng mL−1 ) 0.05–10 0.05–10 0.05–10 0.05–10 0.01–10 0.01–10 0.01–10 0.01–10

Regression coefficient

LODb (pg mL−1 )

Repeatability R.S.D.%c (5 ng mL−1 )

Reproducibility R.S.D.% (5 ng mL−1 )

0.983 0.986 0.988 0. 989 0.996 0.995 0.995 0.998

8 9 8 8.1 4.2 4 5 4

8.2 9.7 5.6 6.3 4.3 4.6 5.2 6.3

17.1 16.6 16.5 17.3 14.4 15.6 17.2 13.1

Dynamic linear range. Limit of detection calculated as three times the baseline noise. Relative standard deviation.

at 250 ◦ C, and all injections were carried out on the splitless mode for 2 min. The GC–MS interface, ion source and quadrupole temperatures were set at 280, 230 and 150 ◦ C, respectively. Compounds were identified using the Wiley 7N (Wiley, New York, NY, USA) Mass Spectral Library. The MS mode was set on selected ion monitoring (SIM) considering characteristic ions for each compound. A scan range from 50 to 550 m/z was used. Ions were selected after injection of concentrated solution of compounds and recording the total ion chromatogram. The highest abundant ion was selected as the quantitative ion; two other ions were used for confirmation of individual analytes (Table 1). GC–MS was tuned before each analysis with HP Chem-Station Standard Spectra AutoTune routine with perfluorotributylamine (PFTBA). The morphology of the PMO-IL was observed by using a Seron AIS-2100 scanning electron microscope (SEM). A homemade SPME device was used for holding and the injection of the proposed fiber into the GC–MS injection port. The commercial SPME device and PDMS fiber (100-␮m film thickness) were purchased from Supelco (Bellefonte, PA, USA). The fiber was conditioned in the injection port of a GC for 1 h.

first washed thoroughly with toluene (5× 50 mL) and then super dry CH2 Cl2 was added to precipitation of NaCl. The supernatant dichloromethane solution was transferred in another well-dried flask. A yellow viscous ionic liquid was obtained after removal of the solvent and drying under vacuum. To prepare the PMO-IL, 1.67 g Pluronic P123 and 8.8 g KCl were added to a solution of distilled water (10.5 g) and HCl (2 M, 46.14 g) with stirring at 40 ◦ C. After clear a homogeneous solution, a pre-prepared mixture of ionic liquid (0.86 g) and tetramethoxysilane (2.74 g), in absolute methanol, was rapidly added and stirred at the same temperature for 24 h. The resulting mixture was then transmitted into a Teflon-lined autoclave and statically heated at 100 ◦ C for 72 h. The obtained solid material was filtered, washed completely with deionized water, and dried at room temperature. The extraction of surfactant was accomplished four times by a Soxhlet apparatus using 100 mL of ethanol and 3 mL of concentrated HCl (for each time) for 1 g of sample during 12 h. The final PMO material was denoted as PMO-IL (Fig. 1). 2.4. Preparation of the SPME fiber

2.3. The synthesis of ionic liquid based periodic mesoporous organosilica (PMO-IL) PMO-IL was synthesized according to a previous reported procedure by our research group [40]. In a typical synthesis, sodium imidazolide (3.002 g, 30 mmol) and 3-chloropropyltrimethoxysilane (6.082 g, 30 mmol) were added in a well dried flask containing super dry THF (100 mL) and stirred at 65 ◦ C for 24 h under an argon atmosphere. After cooling the reaction mixture to room temperature, the solvent was removed under reduced pressure and the obtained oil was transferred to another flask containing 30 mmol of 3-chloropropyl-trimethoxysilane in absolute toluene (100 mL) and refluxed for 48 h in the absence of light. After cooling of solution to room temperature, the reaction mixture was

A piece of stainless steel wire with a 200-␮m diameter was twice cleaned with methanol in an ultrasonic bath for 20 min and dried at 70 ◦ C. One centimeter of the wire was limed with epoxy glue and the PMO-IL nanocomposite was immobilized onto the wire. The coated wire was heated to 50 ◦ C for 48 h in an oven, gently scrubbed to remove non-bonded particles and assembled to the SPME holder device. Finally, prepared SPME fiber was inserted into the GC injection port to be cleaned and conditioned at 260 ◦ C for 2 h in a helium environment. Fig. 2 shows the SEM image of a fabricated SPME fiber with a stainless steel core. The thickness of the uniform coating layer was calculated from the difference between the coated and uncoated stainless steel wire and come out to be about 20 ␮m.

Fig. 1. Schematic representation of the synthesis of PMO-IL.

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Fig. 2. SEM image of a fabricated SPME fiber.

2.5. The headspace solid phase microextraction (HS-SPME) procedure SPME was performed with the prepared PMO-IL fiber, mounted in its SPME device. During the headspace extraction, the aqueous samples were continuously stirred with a magnetic stir bar. The extraction temperature was controlled using a thermostated water bath. Thermal desorption of retained compounds on fiber was carried out at 260 ◦ C while the split valve of injector on the GC kept closed at different periods. In all experiments, 10 mL of double distilled water or wastewater was spiked with PAHs standards in a 20 mL vial and placed on a magnetic stirrer. After reaching the extraction time, the SPME probe containing analytes from the sample, was withdrawn from the vial and inserted into the GC injection port for thermal desorption. 2.6. Water and waste water samples Water samples were collected (on April 2013) from Maragheh, Iran (polluted part of the Sofi river (at Moalem bridge) and Alaviyan dam near the Maragheh city. The samples were stored at 4 ◦ C before the analysis. 3. Results and discussion The periodic mesoporous organosilicas exhibit unique properties coating in the following point: (1) high surface area can increase the solute extraction (2) the existence of organic groups in the mesoporous framework can increase the adsorption (3) the covalently bonded organic groups make the material stable under different analysis medium (4) versatile types of organic group could be incorporated in the material [41]. Therefore, to prove and increase the surface area and the sorption properties of PMO as a coating material for SPME fibers we used IL to fabricate PMO-IL as organic and inorganic hybrid materials. The samples were investigated by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), the 29 Si and 13 C cross-polarization magic angle spinning (CP/MAS) NMR, N2 adsorption/desorption analyses, Transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA) measurements in our previous work [40]. The thermal gravimetric analysis (TGA) of PMO-IL was recorded, and the results confirmed the previous report [40]. Thermal gravimetric analysis of PMO-IL was conducted to prove the thermal stability of the mesoporous framework. Results showed two zones in the TGA curves: (1) weight loss up to 100 ◦ C that refers to the removal of physically adsorbed water and alcoholic solvents

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remaining from the solvent extraction process, (2) the major weight loss between 350 ◦ C and 450 ◦ C due to thermal dissociation of the ionic liquid groups. This data clearly demonstrated the high thermal stability of nanostructured PMO-IL material. The physical and textural properties of PMO-IL organosilica material was evaluated by nitrogen-sorption experiments. The N2 adsorption–desorption isotherm of PMO-IL illustrated a type IV isotherm with a H1 hysteresis loop that is characteristic of SBA15-type materials with two-dimensional structure (Fig. 1). The nitrogen-sorption experiment also showed that the PMO-IL has a BET surface area of 671 m2 g−1 and a primary mesopore volume of 1.21 cm3 g−1 . The average pore diameter is also calculated from the adsorption branch of the isotherm to be 7.0 nm by using the BJH method (see Table 1S in the Supplementary material) [40]. Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.aca.2013.10.022. The FT-IR spectrum (see Fig. 1S in the Supplementary material) of the PMO-IL sample was also measured in order to confirm the presence and stability of ionic liquid moieties in the mesoporous framework. FT-IR of PMO-IL can be assigned to the absorption peaks as follows: 1090 and 925 cm−1 (for asymmetric and symmetric stretching vibration of Si O Si), 1620 cm−1 (C N stretching of immidazolium ring), 1558 cm−1 (C C stretching of immidazolium ring), 1442 cm−1 (C H deformation vibrations), and 700–790 cm−1 (for C Si stretching vibrations), respectively. These data strongly confirm the presence of ionic liquid moieties in the mesoporous network. Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.aca.2013.10.022. The SEM images of PMO-IL material also illustrate a uniform structure. As it is shown in Fig. 3, the nanocomposites have a homogeneous structure, which could significantly increase the available surface area for adsorption. 3.1. Optimization of the HS-SPME apparatus To evaluate the ability of PMO-IL for extracting aromatic compounds from water samples, a mixture of PAHs including naphthalene, 1-methyl naphthalene, biphenyl, anthracene, fluorene, acenaphthene, fluoranthene and pyrene was used. The extraction of these selected analytes from spiked water solutions was performed using the headspace SPME (HS-SPME) mode. The use of headspace is usually preferred as the extent of damage to the fiber caused by the sample matrix is quite limited. In addition, PAHs have sufficient vapor pressure to be analyzed by headspace mode. Effects of different parameters such as the extraction temperature, stirring rate, the ionic strength and extraction time on the amounts of extracted PAHs from water samples were investigated using PMOIL fiber. Before optimization of the extraction parameters, complete desorption of the collected analytes in the GC–MS injection port, and their proper separation over the column had been optimized. For this purpose, different injector temperatures and desorption times were tested. The upper temperature that can be used for desorption of the analytes from a fiber is limited by the thermal stability of its coating. A temperature of 260 ◦ C was found to be appropriate for the efficient desorption of analytes from the PMOIL fiber without damaging its coating. Desorption times from 1 to 5 min were investigated at optimum temperature (260 ◦ C); 2 min was selected for a complete desorption with no memory effect. 3.1.1. Temperature effect For HS-SPME, the sample temperature is a very important factor because it can affect the rate and equilibrium of extraction. The effect of temperature on the extraction of the PAHs compounds, present in 10 mL aqueous solution in the range of 30–80 ◦ C, was investigated. Fig. 4 presents the effect of sample temperature on the

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Fig. 5. Effect of the extraction time on the peak area of PAHs. Conditions: PAHs concentration: 5 ng mL−1 , extraction temperature: 65 ◦ C, stirring rate: 500 rpm, NaCl: 20%.

time. The adsorption time profiles were studied by monitoring the GC/MS peak area as a function of extraction time, while the fiber was exposed to standard solutions of the PAHs at a concentration of 5 ng mL−1 for a time ranging from 10 to 60 min. Fig. 5 shows that at constant temperature the extraction efficiency increases with extraction time and reaches a plateau when equilibrium is established. The equilibrium times for the PAHs increased with increasing molecular mass. Thus, an extraction time of 40 min was selected to shorten the analysis time.

Fig. 3. The SEM images of PMO-IL material.

extraction ability of volatile compounds. As can be seen, the extraction ability increases, with increasing temperature, up to 40 ◦ C, due to the increasing distribution constant of analytes between the sample phase and headspace; However, for most of the compound a slight decrease in adsorption capacity was observed when temperature increased up to 80 ◦ C. This is most probably due to a decreased partition coefficient of analytes between headspace and fiber because adsorption is generally an exothermic process. On the basis of these experimental observations, the optimum sample temperature was chosen to be 65 ◦ C. 3.1.2. Extraction time HS-SPME is an equilibrium-based technique, and there is a direct relationship between the amount extracted and the extraction

3.1.3. Effect ionic strength The addition of salt often increased the ionic strength and thus increased the extraction efficiency due to the salting out effect. For this purpose, the influence of the NaCl concentration on the extraction efficiency was investigated by preparing solutions of PAHs in a range of 0–30% (w/v). The results indicated that the extraction efficiency increases with increasing concentration of NaCl, reaches a maximum in the presence of 10% NaCl and remains constant thereafter. The best results obtained for an aqueous sample containing 20% NaCl, which was three to seven times greater than that obtained for an aqueous sample with no added NaCl. Therefore, all further extractions were conducted with 20% NaCl added. 3.1.4. Stirring rate Agitation of the sample improve mass transfer in the aqueous phase and induces the convection in the headspace, and consequently, the between the aqueous phase and headspace can be achieved more rapidly. In other words, sample stirring reduces the time required to reach the equilibrium by enhancing the diffusion of the analytes toward the fiber, especially for higher molecular mass analytes. Extraction efficiency of the studied compounds was measured from 10 mL of the model sample solutions containing 20% (w/v) NaCl and 40 min extraction times at various stirring speeds. The results revealed that extraction efficiency reaches a maximum and remains constant above 500 rpm. 3.2. Quantitative evaluation and real sample analysis

Fig. 4. Influence of the extraction temperature on the peak area of PAHs. Conditions: PAH concentration: 5 ng mL−1 , extraction time: 40 min, stirring rate: 500 rpm, NaCl: 20%.

Figures of merit of the method including dynamic linear range (DLR), the correlation coefficient of the calibration graph, and relative standard deviation are listed in Table 1. Calibration curves were drawn using 10 spiking levels of PAHs in the concentration range of 0.005–10 ng mL−1 . For each level, three replicate extractions and determination were performed at optimal conditions. The values of the correlation coefficient obtained were between 0.983 and 0.998, showing an acceptable linearity in the dynamic ranges represented in Table 1.

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Table 2 Comparison of the developed method with other SPME fibers (HS-SPME-GC-MS with PDMS (100 ␮m) [44], PDMS/DVB (65 ␮m) [45], Polyacrilate (65 ␮m) [45], PDMS (7 ␮m) [46], and PPy-DS [47]. Compound

Naphthalene m-Naphtalene Biphenyl Acenaphthene Fluorene Anthracene Fluoranthene Pyrene a b

Current method

PDMS (100 ␮m)

PDMS/DVB (65 ␮m)

Polyacrilate (85 ␮m)

PDMS (7 ␮m)

PPy-DS

LODa

%RSDb

LOD

%RSD

LOD

%RSD

LOD

%RSD

LOD

%RSD

LOD

%RSD

8 9 8 8.1 4.2 4 5 4

8.2 9.7 5.6 6.3 4.3 4.6 5.2 4.3

20 – – 10 10 10 10 20

8.64 – – 9.02 10.7 8.52 4.31 10.9

16 – – 65 31 21 43 75

17.45 – – 10.62 8.16 13.62 17.30 18.25

13 – – 44 12 22 47 138

9.02 – – 8.12 9.30 7.97 5.68 9.33

12 – – 10 8 11 10 10

7.8 – – 9.8 9.3 8.8 9.4 9.7

160 – – 90 50 – 120 130

6.8 – – 2.9 2.6 – 4.8 6.9

Limit of detection calculated as three times the baseline noise (ng L−1 ). Relative standard deviation.

Table 3 The results obtained for the analysis of the spiked water samples (5 ng mL−1 ) by the proposed method, under the optimized conditions. Sample

Sofi-river Alaviyan dam a

Added (ng mL−1 )

5 5

Founda (ngmL−1 ) Naphthalene

Methyl-naphthalene

Biphenyl

Anthracene

Fluorene

Acenaphthene

Fluoranthene

Pyrene

5.1(0.3) 5.3(0.6)

5.6(0.6) 5.1(0.5)

5.2(0.8) 5.4(0.8)

5.9(0.6) 5.3(0.7)

5.9(0.9) 5.2(0.7)

5.5(0.9) 5.1(0.3)

5.3(0.2) 5.5(0.6)

5.3(0.2) 5.6(0.8)

The figures within parentheses are standard deviations for three replicates.

In order to assess the repeatability (for one fiber) and reproducibility (fiber-to-fiber), we constructed five fibers under the same conditions and five repeated experiments were carried out using each fiber. The R.S.D. for each fiber and for fiber-to-fiber were calculated and are summarized in Table 1. These data show that repeatability of the method is good. Relatively high fiber-to-fiber R.S.D. (≤17.3%) indicate that, most likely, the coating volume varies significantly between fibers. Consequently, the coating procedure needs to be improved to ensure the thickness is more uniform and reproducible. On the other hand, the proposed SPME fiber is mechanically stable and there is no need to use different fibers in analysis. The extraction capabilities of the PMO-IL coating for sampling PAHs in water at trace levels were compared with a commercial solid coated based SPME fiber, polydimethylsiloxane 100 ␮m, under similar condition. Taking into account that the polydimethylsiloxane (PDMS) is the suggested coating for the adsorption of relatively non-polar and semi-volatile compounds like PAHs [43]. The observed results showed that chromatographic responses of the PMO-IL fiber 3–4 times higher than the results acquired by using the PDMS fiber. In comparison to other coating materials in literature data such as PPy-DS, polydimethyl-siloxane (PDMS) and polyacrylate (PA) [43–47] for extraction and determination of PAHs, the proposed fiber (PMO-IL) shows a suitable limit of detection (Table 2). The PMO-IL nanocomposites fibers were applied to the determination of PAHS compounds in polluted river water and water samples. Since the concentrations of most of the PAHs compounds in the real samples were lower than the detection limit of the method, the samples were spiked with the PAHs compounds. Table 3 shows the satisfactory results obtained for the real samples. 3.3. The lifetime of homemade SPME device The lifetime of the homemade SPME device was evaluated after more than 100 analyses, using a 5 ng spiked sample as the performance test sample. The extraction of fluorene was used to assess the prepared nanocomposite fiber durability after repeating the sampling/desorption cycles. As depicted in Fig. 6, the extracting capability of fluorene after 150 cycles remained almost unchanged. These results provide strong indication that the developed fiber has

Fig. 6. The durability of the prepared PMO-IL coating fiber examined to extract fluorene during 150 runs, experimental condition as follows: 5 ng mL−1 , extraction time: 40 min, extraction temperature: 65 ◦ C, stirring rate: 500 rpm, NaCl: 20%.

a rather high durability. So no significant variance was observed in the obtained results which indicate the stability of the mentioned device. 4. Conclusion In the research, a PMO-IL material was prepared and tested. The PMO-IL particles can be used as a novel SPME fiber. The PMO-IL SPME fiber was introduced and evaluated for the extraction of PAHs from water samples. The presented experimental results clearly demonstrate that PMO-IL fibers are suitable for HS-SPME of PAH analyses. The combination of HS-SPME using PMO-IL fiber with GC–MS under full scan acquisition mode can achieve low LODs (in comparison to other coating materials), and can be applied to determine PAHs in real samples. References [1] J.S. Beck, J.C. Vartuli, W.J. Roth, C.T. Kresge, M.E. Leonowicz, K.D. Schmitt, C.T.W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834. [2] P. Reinert, B. Garcia, C. Morin, A. Badiei, P. Perriat, O. Tillement, L. Bonneviot, Stud. Surf. Sci. Catal. 146 (2003) 133. [3] L. Bonneviot, M. Morin, A. Badiei, Patent WO 01/55031 A1, 2001.

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