Ionic liquid-derived nano-fibrillated mesoporous carbon based on solid-phase microextraction fiber for the analysis of volatile organic compounds from aqueous solutions

Article abstract of DOI:10.1039/c5nj00451a

A novel nano-fibrillated mesoporous carbon (IFMC) solid phase microextraction (SPME) fiber was successfully prepared via the carbonization of the ionic liquid in the presence of SBA-15 as a structure-transducing agent. It was found that our new SPME fiber is an excellent adsorbent for the extraction of some volatile organic compounds (VOCs) from aqueous samples in combination with gas chromatography-mass spectrometry (GC-MS). Important extraction conditions (extraction temperature, ionic strength, stirring rate, pH and extraction time) and desorption conditions (desorption temperature and time) were systematically investigated and optimized. The developed method offers the advantages of being simple to use, with shorter analysis times, lower cost of equipment, thermal stability of fiber and high relative recovery in comparison to the conventional methods of analysis.

Full text of DOI:10.1039/c5nj00451a

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Ionic Liquid Derived Nano-Fibrillated Mesoporous Carbon based on solid-
phase microextraction fiber for analysis of volatile organic compounds from
aqueous solutions
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Mir Mahdi Abolghasemi1,*, Babak Karimi2, Vahid Yousefi1, Hesam Behzadnia2, Hossein
Barzegar2, Marzieh Piryaei3
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1Department of Chemistry, Faculty of Science, Maragheh University, Maragheh, Iran
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2Department of Chemistry Institute for Advanced Studies in Basic Sciences (IASBS) 45137-6731
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(Iran)
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3Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences,
Tabriz, Iran
 Corresponding author:
M. M. Abolghasemi
Department of Chemistry, Faculty of Science, Maragheh University, Maragheh, Iran
Tel: +98 4212276060 Fax: +98 4212276060
E-mail address: mehdiabolghasemi@gmail.com
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Abstract
A novel nano-fibrillated mesoporous carbon (IFMC) solid phase microextraction (SPME) fiber
was successfully prepared via carbonization of the ionic liquid in the presence of SBA-15 as a
structure-transducing agent. It was found that our new SPME fiber is an excellent adsorbent for
the extraction some volatile organic compounds (VOCs) from aqueous samples in combination
with gas chromatography-mass spectrometry (GC-MS). Important extraction conditions
(extraction temperature, ionic strength, stirring rate, pH and extraction time) and desorption
conditions (desorption temperature and time) were systematically investigated and optimized. 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.
Keywords: Volatile organic compounds, Nano-fibrillated mesoporous carbon, Ionic liquid, Solid-
phase microextraction, Gas chromatography-mass spectrometry.
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1. Introduction:
Solid-phase microextraction (SPME) has undergone a surge in popularity within the field of
analytical chemistry in the past decades since its introduction. Solid phase microextraction, first
introduced by Pawliszyn and co-workers, can be regarded as a combination of sampling, pre-
concentration, matrix removal, and sample introduction techniques. Nowadays, SPME is among
the most recommended techniques, employed for the extraction and pre-concentration of volatile
and semi-volatile compounds at trace levels in the different matrixes. This technique has important
advantages over conventional extraction techniques due to its ease of use, portable and solvent-
free [1-7]. Although, SPME has demonstrated extraordinary versatility in sampling capabilities,
the technique continues to experience a tremendous growth in innovation. Presently, increasing
efforts have been directed toward the developing of novel sorbent material in order to expand the
applicability of SPME for a wider range of analytes and matrices. For instance, porous materials
and their derivatives were used as novel-coating materials for SPME with excellent performance
[6-8].
Porous carbon materials are important in many areas of modern science and technology, including
water and air purification, gas separation, catalysis, chromatography, and energy storage [9-12].
This widespread use of porous carbons results from their remarkable properties, such as high
specific surface areas, large pore volumes, versatile structural properties, chemical inertness, and
good chemical and mechanical stability. Porous carbons are usually obtained via carbonization of
precursors of natural or synthetic origin, followed by activation [13, 14].
Among all reported porous carbon materials, the most attractive members are the ordered
mesoporous carbons (OMC) which are synthesized by nanocasting with ordered mesoporous silica
as a hard substrate. Ryoo et al.[15-17] were first to report the synthesizing ordered mesoporous
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carbons (denoted as CMK-x) using the various types of ordered nanoporous silica templates and
sucrose as the carbon precursor which exhibits porous structures consisting of two disconnected
interwoven three-dimensional pore systems. The nanostructure, electronic properties, and surface
functionalities of mesoporous carbons are highly dependent on the carbon source and synthetic
conditions [18]. Carbon materials containing heteroatoms were found to have improved physical
and chemical properties [18–23]. Recently, Karimi and coworker have reported on a new protocol
for the synthesis of nitrogen-doped mesoporous carbons using ionic liquids as the carbon source.
They have shown that the ionic liquid derived nano-fibrillated mesoporous carbon (IFMC)
displays excellent electrochemical [24-26] and chemical properties and can be used as a support
for immobilization and stabilization palladium nanoparticles in the aerobic oxidation of a wide
range of alcohols in water at low temperature. There has been no report, however, on the
application of IFMC as a sorbent in the extraction methods. consequently, it seems that there is
still much room for the discovery of new application of porous carbon materials for separation and
analytical methods. In this regard, the present work focused on the development of new application
of IFMC as a novel coating for SPME fiber. Here, it is predicted that IFMC can open a novel
branch toward to expanding solid-phase microextraction technique. In this context, some volatile
organic compounds (VOCs) were tested as model compounds in aqueous matrices at a trace level.
The factors that influence the extraction efficiency of VOCs 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 VOCs in environmental samples.
2. Experimental
2.1. Chemicals and Reagents
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Poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol)
(EO20PO70EO20, Pluronic P123) as surfactant and tetraethyl orthosilicate (TEOS) were purchased
from Aldrich. 1-Methylimidazole, 2-phenylethyl bromide, sulfuric acid (95–98%), hydrochloric
acid (37%) and solvents were obtained from Merck Company and used without purification.
Phenol, 2, 4-dichlorophenol, 2, 6-dichlorophenol, 2, 4, 6-trichlorophenol, 3- and 4-nitroaniline, 3-
and 4-nitrophenol, naphthalene, anthracene, fluorene, biphenyl, acenaphthene, fluoranthene,
pyrene and all chemical solvents were obtained from the Fluka or Merck companies. The stock
solution from each compound was prepared with methanol and stored in a refrigerator. Working
solutions were prepared by diluting the stock solutions with methanol, and more diluted working
solutions were prepared daily by diluting these solutions with deionized water. Blank analyses
were performed regularly to ensure that no VOCs were present in laboratory reagents, atmosphere,
or fibers.
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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 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 VOCs was performed on a 30 m×0.25mm HP-5 MS column with 0.25µm
film thickness.
The column was held at 50 ºC for 3 min and increased to 180 ºC at a rate of 15 ºC min−1 and then
raised to 260 ºC at 20 ºC min−1 and kept at this temperature for 5 min. The injector temperature
was set at 250 ºC, 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 ºC, respectively.
Compounds were identified using the Wiley 7N (Wiley, New York, NY, USA) Mass Spectral
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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. GC–MS was tuned before each analysis with HP Chem-Station Standard
Spectra AutoTune routine with perfluorotributylamine (PFTBA). The morphology of the IFMC
was analyzed by using a Leo series 1430 VP 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-µm film thickness) were
purchased from Supelco (Bellefonte, PA, USA). The fiber was conditioned in the injection port of
a GC for 1 h.
2.3. The Synthesis of 1-methyl-3-phenethyl- 1H-imidazolium hydrogen sulfate ionic liquid
(MPIHS)
In a typical synthesis, a solution of dry toluene (50 mL), freshly distilled 1-methylimidazole (73.1
mmol) and 2-bromo-1-phenylethane (80.3 mmol) was refluxed for 24 h under an argon
atmosphere. The resulting two-phase reaction mixture was then allowed to cool at room
temperature. The separated ionic liquid (IL) layer was washed with dry toluene and dry Et2O and
dried under vacuum. The anion-exchange reaction was carried out in dry CH2Cl2 containing 1
mmol 1, 3-dialkylimidazolium bromide and 1 mmol of H2SO4. The solution was refluxed for 48 h
until any hydrogen chloride by-product was removed. After evaporation of the solvent under
vacuum, 1-methyl-3-phenethyl-1H-imidazolium hydrogen sulfate (MPIHS) was isolated [24].
2.4. Synthesis of SBA-15
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Highly ordered mesoporous SBA-15 was synthesized using a procedure reported by Zhao and co-
workers [27]. SBA-15 is a hexagonally ordered silica material with uniform tubular channels
varying from 5 to 30 nm [27]. It has outstanding properties, such as highly ordered pore
structures, large surface areas (up to 1000 m2g−1), huge pore volume, high thermal stability
and ability of functionalization by incorporation of organic groups. Increasing attention has
been paid to SBA-15 supported nanocomposites because of their possible applications in
catalysis, optical devices, electrochemical sensors and separation techniques [28–31]. In a
typical synthesis, 3.2g of triblock, EO20PO70EO20 (PluronicP123, Mwav = 5800) as a template, was
dissolved through stirring in 125 mL of 2M HCl, at ambient temperature (25–30◦C) for 1 h. Finally,
6.8g of silica source (TEOS) was added to the homogeneous solution under stirring to form a gel
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at 25 C for 24 h, and this was allowed to stand for crystallization under static hydrothermal
conditions at 100 ºC for 48 h in a Teflon Parr reactor. The crystallized product was filtered off,
washed with warm deionized water, dried at 80 ºC, and finally calcined at 600 °C in the air for 6
h to remove the template.
2.5. Preparation of IFMC (Ionic Liquid derived Nano Fibrillated Mesoporous Carbon):
Ionic Liquid derived Nano Fibrillated Mesoporous Carbon was synthesized according to a
previous reported procedure by Karimi et. al. [24,25]. Briefly, a dry acetonitrile solution of IL (1
mL of 1-methyl-3-phenethyl-1H-imidazolium hydrogen sulfate (MPIHS) in 25 mL of CH3CN)
was added drop wise to a suspension of SBA-15 in CH3CN. After drying under reduced pressure
the resultant powder was impregnated with an aqueous solution of sulfuric acid (4 g H2O, 0.14 g
H2SO4) and placed at 100 °C in a vacuum drying oven. After 6 h, the oven temperature was
increased to 160 °C and maintained for 6 h until a dark brown powder was obtained. MPIHS (0.4
mL) was incorporated again into mesoporous silica matrix by the same procedure. The SBA-15
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composite was then kept under an argon flow at 900 °C for 3 h to carbonize the IL. In order to
remove the silica template, the black powder was stirred in a solution of 2 M sodium hydroxide at
50°C for 24 h. The filtered nanoporous carbon was washed several times with deionized water and
ethanol, and vacuum dried to give IFMC as a fine black powder. The Schematic representation of
the synthesis of IFMC is shown in Fig. 1.
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Fig.1. Schematic representation of the synthesis of IFMC.
2.6. Preparation of the SPME fiber
A piece of stainless steel wire with a 200-µm diameter was twice cleaned with methanol in an
ultrasonic bath for 20 min and dried at 70 ºC. One centimeter of the wire was limed with epoxy
glue and the IFMC nanocomposite was immobilized onto the wire. The coated wire was heated to
50 ºC 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 270 ºC for 2 h in a helium environment.
2.7. The headspace solid phase microextraction (HS-SPME) procedure
SPME was performed with the prepared IFMC fiber, mounted in its SPME device. During the
headspace extraction, the aqueous samples were continuously stirred with a magnetic stir bar. The
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extraction temperature was controlled using a thermostated water bath. Thermal desorption of
retained compounds on fiber was carried out at 270 °C while the split valve of injector on the GC
kept closed at different period of times. In all experiments, 5 mL of double distilled water or
wastewater was spiked with VOCs 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. Fig. 2
shows the comparison between SEM images of a fabricated IFMC and SBA-15 fiber with a
stainless steel core. The thickness of the uniform coating layer of IFMC fiber was calculated from
the difference between the coated and uncoated stainless steel wire and come out to be about 25
μm.
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Fig.2. SEM images of a fabricated SPME fibers (a) IFMC fiber (b) SBA-15 fiber.
2.8. Field samples
A sewage water and river water samples were collected for the study. The Aji river (Tabriz, Iran)
and the Chichi (Ahar, Iran) river water samples were collected from polluted parts of the rivers.
The sewage water sample was collected from the Aji river (at Polsangi bridge), Iran.
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3. Results and discussion
Owing their excellent chemical stability, large surface area, and versatile structural properties,
porous carbon materials have received wide applications in the different field. Among all reported
porous carbon materials, the most attractive members are the ordered mesoporous carbons which
are synthesized by nanocasting with ordered mesoporous silica as a hard substrate. The nano-
structure, electronic properties, and surface functionalities of mesoporous carbons are highly
dependent on the carbon source and synthetic conditions. Carbon materials containing heteroatoms
were found to have improved physical and chemical properties. Antonietti et al. and Dai et al.
independently proposed a new strategy for the synthesis of nitrogen-doped carbon materials from
nonvolatile, task specific, ionic liquids with either nitrile functionalized imidazolium cations or
cyanide-containing anions. Amongst the out-standing characteristics of these hybrid carbon
materials are their high stability against thermal decomposition and catalytic properties. In this
work, three kinds of laboratory-made fiber coatings (Activated Carbon, CMK-3 and IFMC) were
prepared and their extraction efficiency for phenolic compounds was comparatively studied.
Preliminary experiments show that IFMC exhibits the best extraction efficiency for the target
VOCs, followed by CMK-3 and Activated Carbon. The higher peak area of the IFMC SPME fiber
for the VOCs resulted from the combined effects of the large surface area and unique porous
structure, hydrophobic effect, and π-π stacking interaction between the analytes and the IFMC
materials. The π-π interaction between the surface of IFMC and the benzene ring of the analytes
should also contribute a lot to the hydrophobic– hydrophobic interaction between IFMC and the
analytes. Besides, hydrogen bonding between the nitrogen heteroatoms in the carboneous
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framework and the polar functional groups on the analytes also enhances the interaction between
the IFMC hybrid material bonded fiber and the studied polar compounds.
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3.1 Characterization of the Ionic Liquid derived Nano Fibrillated Mesoporous Carbon
Ionic liquid derived Fibrillated Mesoporous Carbon (IFMC) was characterized by X-ray
photoelectron spectroscopy (XPS), N2 adsorption–desorption analysis, and transmission electron
microscopy (TEM). N2-sorption analysis of IFMC exhibited a type IV isotherm with an H2
hysteresis loop, which is the characteristic of mesoporous materials. The Brunauer–Emmett–Teller
(BET) surface area and the pore volume were calculated to be 778 m2g-1 and 0.98 cm3g-1,
respectively. Unlike the OMC materials prepared via nanocasting, IFMC exhibited indistinct
capillary condensation steps in N2 sorption measurements, implying that mesostructure of the
material have broad pore size distributions (Fig. S1, in ESI). The SEM images of IFMC 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.
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Fig.3. The SEM images of IFMC material.
TEM images of IFMC clearly demonstrates that carbon materials comprising a well-ordered array
of carbon nanofibers (Fig. 4). This is somewhat surprising, because according to our methodology,
it seems that SBA-15 operated as a structural guide for the formation of nano-fibrillated carbon
rather than a mould, which is normally observed in nanocasted-based protocols. The fibrillar
structure is clearly visible at low magnification.
Fig.4. TEM images of IFMC.
X-Ray photoelectron spectroscopy (XPS) of IFMC presents signals located at 285, 403 and 535
eV, which were assigned to C, N and O, respectively (Fig. S2, in ESI).
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3.2. Optimization of the HS-SPME apparatus
To evaluate the ability ofIFMC for extracting aromatic compounds from water samples, a mixture
of VOCs including naphthalene, biphenyl, anthracene, fluorene, acenaphthene, fluoranthene,
pyrene, phenol, 2, 4-dichlorophenol, 2, 6-dichlorophenol, 2, 4, 6-trichlorophenol, 3- and 4-
nitroaniline and 3- and 4-nitrophenol 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.
Preliminary experiments indicated that the prepared fiber could successfully adsorb all the test
compounds. 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 were optimized.
For this purpose, different injection temperatures and desorption times were tested. The upper
temperature that can be used for desorption of a fiber is limited by the thermal stability of its
coating. Different desorption temperatures were tested and a temperature of 270 ◦C was found to
be most appropriate for efficient desorption of the analytes from the IFMC fiber without damaging
its coating. Desorption times from 1 to 3 min were investigated at this temperature and 3 min was
selected for a complete desorption with no carry over effect.
Different temperature programs were tested for an appropriate separation of the phenolic
compounds and the program mentioned in Section 2 was selected as optimum. Effects of different
parameters such as desorption temperatures, desorption times, extraction temperature, stirring rate,
the ionic strength, pH and extraction time on the amounts of extracted VOCs from water samples
were investigated using IFMC fiber.
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The variation of temperature during HS-SPME affects the extraction efficiency, the volatility of
the analytes, and desorption of the analytes from the matrix. Using high extraction temperature
increases the release of analytes from their matrix, whereas it can adversely decrease their partition
coefficients and subsequent extraction from head-space to the coating, due to the exothermic
nature of the adsorption. Hence, there is usually an optimum temperature for headspace sampling.
The effect of temperature on the extraction of the VOCs compounds, present in 5mL aqueous
solution in the range of 30–95 °C, was investigated. Fig.5 presents the effect of sample temperature
on the extraction ability of volatile compounds. As can be seen, the extraction ability increases,
with increasing temperature, up to 40 ºC, 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 ºC. When performing
experiment with aqueous sample at high temperatures, the possibility of leaking small amount of
water vapor into the needle rises. Expansion of water vapor would produce loss of analyte in the
septum purge line and could affect the proper quantitative measurements. Therefore, the higher
temperatures than 95°C were not tested for practical problems and the extraction temperature was
set at 80 °C in the subsequent experiments.
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Fig.5. (a) Influence of the extraction temperature on the peak area of VOCs (VOCs
concentration:10ngmL−1, extraction time: 45min, stirring rate: 500 rpm, NaCl:20%).
HS-SPME is an equilibrium-based technique, and there is a direct relationship between the amount
extracted and the extraction time. For HS-SPME extraction, the extraction time of an analyte is
dependent on its distribution constants: the headspace/aqueous sample distribution constant (Khs),
and the fiber coating/headspace distribution constant (Kfh). If the difference in the distribution
constant between the fiber coating and the headspace is large, the amounts of material extracted
increase and a longer time is required to reach equilibrium. 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 VOCs at a concentration of 10 ng mlL−1 for a time ranging
from 10 to 60 min. Fig.6 shows that at constant temperature the extraction efficiency increases
with extraction time and reaches a plateau when equilibrium is established. The equilibrium times
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for the VOCs increased with increasing molecular mass. Thus, an extraction time of 45 min was
selected to shorten the analysis time.
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Fig.6. Effect of the extraction time on the peak area of VOCs (VOCs concentration:
10 ngmL−1, extraction temperature: 80°C, stirring rate: 500 rpm, NaCl:20%)
In SPME, the pH of the sample can be adjusted to decrease the solubility of some analytes and to
provide better selectivity by increasing the extraction towards the headspace. This behavior altered
with the characteristics of each VOCs. For most compounds, extraction increased up to pH 4.5,
and then decreased or remained constant. Therefore, after a survey of the pH effect on the pH range
2–6, using 1 M acetate/acetic acid buffer solutions, by adding the appropriate hydrochloric acid or
sodium hydroxide solution to the aqueous phase the maximum efficiency is obtained at pH 4.5.
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Salt addition is another parameter that must be taken into account because the enhancement of
ionic strength of the matrix brings a decrease of the analyte solubility increasing, therefore, the
sensitivity of the analytical method. By decreasing the solubility of the analyte in water, the amount
of analyte was partitioned into the headspace and, finally, into the fiber coating it was increased.
For many of the organic analytes, their solubility in aqueous solution also decreases with
increasing ionic strength. For this purpose, the influence of the NaCl concentration on the
extraction efficiency was investigated by preparing solutions of VOCs 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.
Agitation of the sample improves mass transfer in the aqueous phase and induces the convection
in the headspace, and consequently, the equilibrium 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 towards the fiber, particularly for the
analytes with higher molecular weights. Extraction efficiency of the studied compounds was
measured from 10 ml of the model sample solutions containing 20% (W/V) NaCl and 45 min
extraction times at various stirring speeds. The results revealed that extraction efficiency reaches
a maximum and remains constant above 500 rpm.
3.3 Validation parameters and real sample analysis
Table 1 summarizes the figures of merit (including dynamic linear range, the correlation
coefficient of the calibration graph, and relative standard deviation) of the proposed HS-SPME
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method. The linear range was determined by extracting aqueous solutions of the mixture of VOCs
in the range of 0.01–200 ngmL-1. The values of the correlation coefficient obtained were between
0.993 and 0.998, showing an acceptable linearity in the dynamic ranges represented in Table 1. 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
Table1. These data show that repeatability of the method is good. Relatively high fiber-to-fiber
R.S.D. (≤14.2%) indicatethat, most likely, the coating volume varies significantly between fibers.
Consequently, the coating procedure needs to be improved to ensure the thickness is 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.
3.4. Comparison of the IFMC and commercial fiber
The efficiency of the IFMC fiber for the extraction of the volatile organic compounds in water
at trace levels were compared with a commercial solid coated based SPME fiber,
polydimethylsiloxane 100 µm, 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. The observed results showed that chromatographic
responses of the IFMC fiber 2.3–3.4 times higher than those obtained by using the PDMS
100 µm.
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Table 1. Some analytical data obtained for microextraction of VOCs using the IFMC in optimum
conditions (extraction temperature 80°C, stirring rate 500 rpm, pH 4.5, ionic strength 20% (w/v)
NaCl and extraction time 45 min).
Repeatability
Reproducibility
DLR a
LOD b
Regression
coefficient
Compound
R.S.D. c %,
(10ng ml−1)
6.8
R.S.D. %,
(10ng ml−1)
7.5
(ng ml−1)
(ng ml−1)
Phenol
10-200
1-200
0.998
0.997
0.996
0.993
0.994
0.994
0.995
0.996
0.997
0.995
0.997
0.998
0.997
0.997
0.998
0.995
0.998
0.996
0.09
0.05
2, 4-Dichlorophenol
2, 6-Dichlorophenol
2, 4, 6-Trichlorophenol
3- Aminophenol
4- Aminophenol
3-Nitrophenol
4- Nitrophenol
3-Nitroaniline
4- Nitroaniline
Naphthalene
2.9
10.1
8.4
1-200
0.04
7.3
0.1-200
20-200
15-500
15-500
15-500
15-500
15-500
0.2-100
0.2-100
0.1-100
0.01-100
0.01-100
0.01-100
0.01-100
0.01-100
0.01
6.3
11.0
12.9
9.1
0.51
5.9
0.31
8.8
0.23
4.9
8.6
0.41
5.2
7.5
0.55
4.9
9.2
0.43
5.6
14.2
12.1
11.2
9.9
0.01
6.9
Methyl Naphthalene
Biphenyl
0.02
5.4
0.01
8.2
Acenaphthene
Fluorene
0.002
0.0008
0.001
0.0006
0.0008
3.6
6.9
7.2
8.9
Anthracene
5.2
7.3
Fluoranthene
Pyrene
4.9
9.8
8.2
9.2
385
386
387
a Dynamic Linear Rang.
b Limit of detection calculated as three times the baseline noise.
c Relative Standard Deviation
388
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3.5. Application to field samples
Field water samples, collected from Aji and Chichi were analyzed by the proposed method. The
IFMC fiber was applied to determine VOCs in the described water samples. Since the
concentrations of most target compounds in the field samples were lower than the detection limit
of the method, recovery testing was carried out with spiking 10 ngmL−1 standard VOCs mixture to
5 mL of wastewater sample. Table 2 collects the satisfied results obtained for the field samples.
396
397
Table 2. The results obtained for the analysis of the spiked water samples (10 ngmL-1)by the proposed
method, under the optimized conditions.
398
399
400
401
Compound
Polsangi bridge
10.3(0.4)
10.3(0.3)
10.1(0.5)
10.2(0.4)
10.1(0.6)
10.1(0.7)
10.2(0.8)
10.1(0.5)
10.4(0.5)
10.2(0.6)
10.2(0.4)
10.3(0.6)
10.1(0.2)
10.3(0.4)
10.3(0.3)
10.4(0.2)
10.1(0.6)
10.2(0.1)
Chichih river
10.5(0.3)
10.2(0.5)
10.3(0.2)
10.2(0.2)
10.1(0.5)
10.3(0.5)
10.4(0.7)
10.1(0.4)
10.2(0.5)
10.3(0.9)
10.1(0.3)
10.2(0.3)
10.5(0.3)
10.2(0.3)
10.2(0.4)
10.2(0.2)
10.4(0.1)
10.1(0.2)
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
Phenol
2, 4-Dichlorophenol
2, 6-Dichlorophenol
2, 4, 6-Trichlorophenol
3- Aminophenol
4- Aminophenol
3-Nitrophenol
4- Nitrophenol
3-Nitroaniline
4- Nitroaniline
Naphthalene
Methyl Naphthalene
Biphenyl
Acenaphthene
Fluorene
Anthracene
Fluoranthene
Pyrene
427
429
figures
a The
within
428
parentheses are standard deviations for three replicates.
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3.6. The lifetime of homemade SPME device
The lifetime of the homemade SPME device was evaluated after more than 60 analyses, using a
10 ngmL−1 spiked sample as the performance test sample. The extraction of fluorene was used to
assess the prepared nano-composite fiber durability after repeating the sampling/desorption cycles.
Result show that the extracting capability of fluorene after 70 cycles remained almost unchanged.
These results provide strong indication that the developed fiber has 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 present study, a novel solid phase microextraction sorbent based on IFMC hybrid material
was fabricated. Prepared nanocomposites were successfully used in the process of pre-
concentration of volatile organic compounds in water samples. The enhanced sorbent capacity was
originated from the properties of the nanomaterials, including porous structure, large surface area,
and homogeneous morphology. The above nanostructure also had the advantage of the strong
interaction between analyte and sorbent, simplicity, high thermal stability, and more convenient
handling than the other traditional SPME fibers. Also good linearity and reasonable repeatability
were achieved.
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