Combination of carbon nanotube reinforced hollow fiber membrane microextraction with gas chromatography-mass spectrometry for extraction and determination of some nitroaromatic explosives in environmental water Maryam Fayazi, a Masoud Ghanei-Motlagh * a and Mohammad Ali Taher b A novel method was demonstrated for the determination of seven nitroaromatic components in environmental water samples using a combination of carbon nanotube reinforced hollow fiber membrane microextraction with gas chromatography-mass spectrometry (GC-MS). With this methodology, functionalized multi-walled carbon nanotubes (MWCNTs) immobilized into the pore structure of a polymeric membrane were evaluated for the extraction and preconcentration of these nitroaromatic explosives. This was accomplished by circulating–flowing an aqueous dispersion of the MWCNTs through a polypropylene hollow fiber placed into an ultrasonic bath using an HPLC pump. Under ultrasonic agitation, MWCNTs were forced into and trapped within the pore structure in both sides of the polypropylene fiber. The membrane extraction used in this research is a three-phase supported liquid membrane consisting of an aqueous (donor phase), organic solvents/nano sorbent (membrane) and organic (acceptor phase) system operated in the direct immersion sampling mode. In order to obtain high efficiency of this novel technique, the main parameters were optimized. Under the optimum conditions, the method presents good level of repeatabilities (RSDs less than 5.7%). Calculated calibration curves gave good levels of linearity with correlation coefficient values of between 0.9937 and 0.9968. Limit of detections (LODs) ranged from 0.03 ng mL 1 (for 2,6-dinitrotoluene) to 0.94 ng mL 1 (for 2-amino-4,6-dinitrotoluene). The proposed method was subsequently used successfully for the determination of all the analytes at trace levels in samples obtained from environmental waters. 1 Introduction The detection of high-energy explosives is a very important topic from a security point of view as such explosives are used by both terrorists and the military. 1 These compounds are generally recalcitrant to biological treatment and constitute a source of pollution due to both their toxic and their mutagenic effects on humans, sh, algae and microorganisms. 2–5 These compounds have been included in the US Environmental Protection Agency (EPA) list of priority pollutants. 6,7 This has generated tremendous demand for innovative analytical tools capable of detecting these compounds. Real samples are usually complicated matrices and these compounds are present at low concentrations, therefore, extraction is oen recommended before detection. Conventional liquid–liquid extraction (LLE) has been the main method for enrichment of nitroaromatic compounds from aqueous solutions. 7 However, LLE methods are time-consuming, tedious, and utilize large amounts of high purity organic solvents, which are potentially toxic and expensive. Miniaturized LLE, or liquid phase micro- extraction (LPME), was introduced in 1996, and involves the use of a droplet of organic solvent hanging at the end of a micro-syringe needle. 8–10 LPME can be classied as two-and three-phase categories. In two-phase LPME, the target analytes are extracted from the aqueous sample matrix into the organic receiving phase. 11,12 Three-phase LPME or liquid–liquid–liquid microextraction (LLLME) is performed in a hollow ber or droplet based mode. 13–15 In three-phase hollow ber micro- extraction (HF-LLLME), the extracting phase (aqueous acceptor solution) which is placed in the lumen of the ber is mechanically protected inside the hollow ber and is separated from the sample by the supported liquid membrane (SLM) containing an organic solvent. Recently, Ghambarian et al. introduced a novel HF-LLLME method based on using two immiscible organic solvents. Here, an organic solvent a Department of Chemistry, Kerman Branch, Islamic Azad University, Kerman, Iran. E-mail: [email protected]; Fax: +98-341-3210051; Tel: +98-341-3210043 b Department of Chemistry, Faculty of Sciences, Shahid Bahonar University, Kerman, Iran Cite this: Anal. Methods, 2013, 5, 1474 Received 23rd June 2012 Accepted 9th January 2013 DOI: 10.1039/c3ay25644h www.rsc.org/methods 1474 | Anal. Methods, 2013, 5, 1474–1480 This journal is ª The Royal Society of Chemistry 2013 Analytical Methods PAPER Published on 14 January 2013. Downloaded by Old Dominion University on 03/09/2013 20:22:33. View Article Online View Journal | View Issue
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AnalyticalMethods
PAPER
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aDepartment of Chemistry, Kerman Branch
E-mail: [email protected]; Fax:bDepartment of Chemistry, Faculty of Scien
Iran
Cite this: Anal. Methods, 2013, 5, 1474
Received 23rd June 2012Accepted 9th January 2013
DOI: 10.1039/c3ay25644h
www.rsc.org/methods
1474 | Anal. Methods, 2013, 5, 1474
Combination of carbon nanotube reinforced hollowfiber membrane microextraction with gaschromatography-mass spectrometry for extraction anddetermination of some nitroaromatic explosives inenvironmental water
Maryam Fayazi,a Masoud Ghanei-Motlagh*a and Mohammad Ali Taherb
A novel method was demonstrated for the determination of seven nitroaromatic components in
environmental water samples using a combination of carbon nanotube reinforced hollow fiber
membrane microextraction with gas chromatography-mass spectrometry (GC-MS). With this
methodology, functionalized multi-walled carbon nanotubes (MWCNTs) immobilized into the pore
structure of a polymeric membrane were evaluated for the extraction and preconcentration of these
nitroaromatic explosives. This was accomplished by circulating–flowing an aqueous dispersion of the
MWCNTs through a polypropylene hollow fiber placed into an ultrasonic bath using an HPLC pump.
Under ultrasonic agitation, MWCNTs were forced into and trapped within the pore structure in both
sides of the polypropylene fiber. The membrane extraction used in this research is a three-phase
supported liquid membrane consisting of an aqueous (donor phase), organic solvents/nano sorbent
(membrane) and organic (acceptor phase) system operated in the direct immersion sampling mode. In
order to obtain high efficiency of this novel technique, the main parameters were optimized. Under the
optimum conditions, the method presents good level of repeatabilities (RSDs less than 5.7%). Calculated
calibration curves gave good levels of linearity with correlation coefficient values of between 0.9937
and 0.9968. Limit of detections (LODs) ranged from 0.03 ng mL�1 (for 2,6-dinitrotoluene) to 0.94 ng
mL�1 (for 2-amino-4,6-dinitrotoluene). The proposed method was subsequently used successfully for the
determination of all the analytes at trace levels in samples obtained from environmental waters.
1 Introduction
The detection of high-energy explosives is a very importanttopic from a security point of view as such explosives are usedby both terrorists and the military.1 These compounds aregenerally recalcitrant to biological treatment and constitute asource of pollution due to both their toxic and their mutageniceffects on humans, sh, algae and microorganisms.2–5 Thesecompounds have been included in the US EnvironmentalProtection Agency (EPA) list of priority pollutants.6,7 This hasgenerated tremendous demand for innovative analytical toolscapable of detecting these compounds. Real samples areusually complicated matrices and these compounds arepresent at low concentrations, therefore, extraction is oenrecommended before detection. Conventional liquid–liquid
, Islamic Azad University, Kerman, Iran.
+98-341-3210051; Tel: +98-341-3210043
ces, Shahid Bahonar University, Kerman,
–1480
extraction (LLE) has been the main method for enrichment ofnitroaromatic compounds from aqueous solutions.7 However,LLE methods are time-consuming, tedious, and utilize largeamounts of high purity organic solvents, which are potentiallytoxic and expensive. Miniaturized LLE, or liquid phase micro-extraction (LPME), was introduced in 1996, and involves theuse of a droplet of organic solvent hanging at the end of amicro-syringe needle.8–10 LPME can be classied as two-andthree-phase categories. In two-phase LPME, the target analytesare extracted from the aqueous sample matrix into the organicreceiving phase.11,12 Three-phase LPME or liquid–liquid–liquidmicroextraction (LLLME) is performed in a hollow ber ordroplet based mode.13–15 In three-phase hollow ber micro-extraction (HF-LLLME), the extracting phase (aqueous acceptorsolution) which is placed in the lumen of the ber ismechanically protected inside the hollow ber and is separatedfrom the sample by the supported liquid membrane (SLM)containing an organic solvent. Recently, Ghambarian et al.introduced a novel HF-LLLME method based on using twoimmiscible organic solvents. Here, an organic solvent
This journal is ª The Royal Society of Chemistry 2013
(n-dodecane) is immobilized in the pores of the HF, providinga SLM, and another organic solvent (acetonitrile) is lled in itslumen. This methodology is compatible with most analyticalinstruments such as gas chromatography (GC), high perfor-mance liquid chromatography (HPLC), capillary electropho-resis (CE) and electrothermal atomic absorption spectrometry(ET-AAS).16
Carbon nanotubes (CNTs) are a new type of carbon materialrst found in 1991 by Iijima.17 They can be described as agraphite sheet rolled up into a nanoscale tube [single-wallCNTs (SWCNTs)] or with additional graphite tubes [multi-walled CNTs (MWCNTs)]. Because of their unique geometricalstructure, they exhibit excellent mechanical and thermalproperties. For example, the highly developed hydrophobicsurface of CNTs shows strong sorption properties towardsvarious compounds compared with a planar carbon surface.18
Recent studies have demonstrated that self-assembled nano-tubes are highly effective as high-resolution GC stationaryphases.19–21 CNTs have also been used as pseudostationary andstationary phases in CE and liquid chromatography respec-tively as well as in solid phase extraction.22–24 They are greatcandidates for ultratrace accumulation of analyte, especiallythose with a p electron structure, i.e., aromatic compounds,which are expected to adhere to the sp2 structure of graphenesheets via p–p interactions. Prior to this, Hylton et al.demonstrated that functionalized carbon nanotubes can bereadily immobilized into the pore structure of a polymericmembrane, thereby dramatically improving its performance inanalytical scale membrane extraction, and used it for tolueneand naphthalene extraction.25 In 2010, Es'haghi et al. usedcarbon nanotube reinforced hollow bers for the determina-tion of caffeic acid in medicinal plants samples. The authorscalculated some thermodynamics for the membrane–soluteinteractions for the nanotube immobilized membrane. Theidea is therefore to have a membrane based on CNTs that actsas an analyte trap, resulting in higher selectivity and enrich-ment because the MWCNTs act as solid sorbents do in solidphase microextraction (SPME) bers. In this study, we haveused MWCNTs immobilized hollow ber solid–liquid phasemicroextraction (HF-SLPME) to preconcentrate some nitro-aromatic explosives from aqueous samples obtained fromenvironmental sources. The technique could provide bothpreconcentration and sample clean-up capability in a singlestep and had good performance in terms of accuracy, linearity,repeatability and limits of detection (LODs).
2 Experimental2.1 Reagents and apparatus
Analytical grade n-dodecane and acetonitrile were purchasedfrom Merck Company (Darmstadt, Germany). 2,4,6-trinitrotol-uene (TNT), 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene(2,6-DNT), 1,3,5-trinitrobenzene (TNB), 4-amino-2,6-dini-trotoluene (4-ADNT) and 2-amino-4,6-dinitrotoluene (2-ADNT),1,3-dinitrobenzene (DNB) were purchased from Sigma-Aldrich.MWCNTs with 95% purity (10–20 nm diameter) and 1 mmlength were obtained from NanoLab (Brighton, MA, USA).
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Diluted aqueous solutions were prepared by adding theacetonitrile stock solution to water puried by a Milli-Q waterpurication system from Millipore (Bedford, MA, USA). A 25 mLsyringe model 702 NR from Hamilton (Bonaduz, Switzerland)was employed to introduce the acceptor phase solution intothe lumen of the hollow ber. Q3/2 Accurel polypropylenehollow ber membrane (with a pore size of 0.2 mm, an ID of600 mm and a wall thickness of 200 mm) was obtained fromMembrana (Wuppertal, Germany). An ultrasonic instrumentmodel UP400S (Made of Germany) was used to disperseMWCNTs in deionized water and to prepare the MWCNTsimmobilized membrane.
2.2 GC-MS analysis
Analysis of analyte was performed using an Agilent (Wilming-ton, DE, USA) 7890C series, Agilent 5975C gas chromatograph-mass spectrometer. The split/splitless injector was operated at200 �C with the split closed for 1 min. Helium (purity $
99.999%) was used as a carrier gas at a ow rate of 2.0 mLmin�1. The analysis was carried out on an HP-5MS fused-silicacapillary column (10 m � 0.25 mm � 0.25 mm lm thickness)with the following oven temperature programme: the initialoven temperature was 60 �C (held for 6min), increased to 130 �Cat a rate of 5 �C min�1 and then to 250 �C at 20 �C min�1. Themass spectrometer was operated with an EI source in the scanmode. The ionization mode was electron impact (70 eV). Theinterface temperature was maintained at 260 �C and thedetector voltage was at 1.40 kV. Data was acquired in the full-scan detection mode from 45 to 300 amu at a rate of 0.5 scansper s and the solvent delay was set to 3 min.
2.3 Preparation of MWCNTs immobilized membrane
To eliminate metal oxide impurities within the nanotubes,MWCNTs were reuxed in the presence of 2.0 M HNO3 for15 h, then washed with deionized water and dried at roomtemperature. The presence of functional groups in the func-tionalized MWCNTs improves the adhesion to the membranematerial.26 0.010 g of the puried MWCNTs was dispersed in10.0 mL deionized water by using ultrasonic agitation to obtaina relatively stable suspension. 100 mL of the above suspensionwas dispersed in 10 mL deionized water in a glass containerwith two connectors on both sides. Then a 8 cm long poly-propylene hollow ber membrane was settled using conven-tional medical syringe needles into 10 mL of aqueousdispersion of the MWCNTs, and the dispersion was circulatedinto the lumen, in an ultrasonic bath, at a ow rate of 200 mLs�1 using an HPLC pump. Under ultrasonic agitation,MWCNTs were forced into and trapped within the porestructure of the polypropylene in both sides of the ber. Thisallowed us to achieve immobilization while keeping theMWCNTs surface fully accessible to adsorption/desorption. Itwas found that the incorporation was quite rugged, and themembrane did not lose the CNTs in spite of several washeswith water and solvent. A new immobilized membrane wasmade for each extraction to eliminate carryover effects. Fig. 1
Fig. 1 Schematic diagram of the preparation of nanotube immobilizedmembrane.
Fig. 2 Diagram of extraction platform.
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shows the schematic diagram of the preparation of the nano-tube immobilized membrane.
Fig. 3 Photographs of (a) original fiber with aqueous dispersion of the MWNTsprior ultrasonic agitation. (b) MWNTs immobilized membrane with aqueousdispersion of the MWNTs after ultrasonic agitation.
2.4 HF-SLPME procedure
A 20 mL portion of aqueous sample solution was transferredinto a 25 mL glass vial containing a 10 mm � 4 mm magneticstirring bar then the vial was placed on a magnetic stirrermodel ZMS 74 from ZAG Chimi Chemical Company (Tehran,Iran). A 25 mL HPLC syringe needle and a conventional medicalsyringe needle were inserted through the silicon septum; theformer served to introduce the acceptor solution intothe hollow ber prior to extraction and to collect this solutionaer extraction while the latter needle was utilized for supportof the hollow ber. The ends of the needles were connected tothe two ends of an 8 cm piece of HF. Also, a 10 mL GCsyringe was used to inject the samples into the GC-MS injec-tion port. The bers were immersed into the extracting organicsolvent (n-dodecane) for several seconds to impregnate thepores of the ber with extracting solvent. Aer solventimpregnation, the solvent in the lumen of the ber wasremoved using an air blow from a 5 mL syringe, and a 25 mLportion of acetonitrile was withdrawn into the microsyringeand the needle tip was inserted into one end of the HF. Theother end of the HF was connected to the needle of theconventional medical syringe to support the ber. At the end ofthe extraction time, the hollow ber was removed from thesample solution, and the acceptor phase was withdrawn intothe syringe. Finally, 1 mL of the acceptor phase was injectedinto the GC-MS for analysis. In initial experiments, thevolumes of donor phase and acceptor phase solutions were15 mL and 25 mL, respectively. Also to obtain suitable signalsin the optimization experiment, a relatively high concentrationof aqueous solution of each target analyte (50 ng mL�1) wasused. The donor phase was stirred at a rate of 700 rpm for aperiod of 20 min. A diagram of the extraction platform ispresented in Fig. 2.
1476 | Anal. Methods, 2013, 5, 1474–1480
3 Results and discussion
The presence of the MWCNTs in the porous polypropylenemembrane was investigated by scanning electron microscopy(SEM). SEM analysis also revealed homogenously distributedcoatings on the entire surface of the ber. Fig. 3 shows thephotograph of the original ber, MWCNTs immobilizedmembrane with aqueous dispersion of the MWCNTs (prior andaer ultrasonic agitation). The presence of the MWCNTs led tothe formation of a dark color on the surface of the ber.
The presence of CNTs will have a strong inuence on themicroextraction mechanism. The hexagonal arrays of sp2-likecarbon atoms in the tubular graphene sheets on the surfaces ofCNTs provide a favorable morphological structure for adsorbingaromatic compounds. The highly developed surface of
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MWCNTs exhibits strong sorption properties towards analy-tes.27 The strong binding is attributed to p–p interaction andhydrogen bond interactions existing between the analytes andthe polar functional groups such as –COOH and –OH on thesurface of oxidized MWCNTs. All these factors led to an overallenhancement in solute transport. Also, incorporation of carbonnanotubes in the membrane quite dramatically changes themechanism of analyte transport. In HF-LLLME with a plainhollow ber the target analytes are extracted from the aqueoussample into the SLM based on diffusion, in which extraction ispromoted by high partition coefficients, and then, easily backextracted into the organic acceptor phase by the concentrationgradient between both the organic solvents.
This phenomenon is still encountered in the case of theMWCNTs immobilized hollow ber. However, the introductionof the MWCNTs provides an additional way for solute transport.The analytes from the aqueous sample diffuses through theporous polypropylene membrane on the MWCNTs, which weretrapped within the pore structure in the polypropylene ber.The analytes were trapped in a sorbent (MWCNTs) trap and SLMsimultaneously. Then the analytes were desorbed into the smallvolume of organic acceptor phase that was owing on the insideof the membrane and were thus enriched. In general, themechanism of analyte transfer in MWCNTs immobilized hollowber involves both liquid and solid phase extractions. In otherwords, we have two extractants, the solvent and the MWCNTs.The overall effect is to increase the effective partition coefficienton the membrane, and lead to higher permeability of the ana-lytes.25 In the present work, we studied the effectiveness ofMWCNTs mediated membrane extraction by two analyticalapproaches: (1) LLLME based on two immiscible organicsolvents and (2) SLPME based on two immiscible organicsolvents. The operations of LLLME and SLPME are similar, theonly difference being the mechanism of solute transport. Inboth cases, a few microlitres of an extractant were injected intothe lumen of the hollow ber. During extraction, the solutionwas stirred. Aer extraction, the acceptor solution was removedfrom the lumen and analyzed using analytical instruments.
3.1 Optimization of the SLPME
3.1.1 Selection of the supported liquid membrane. Solventselection is one of the main steps in solvent microextractiontechniques. For this critical stage, several factors have to betaken into consideration. First, the analytes in the samplesolution should have high partition coefficients in the organicsolvent in the pores of the hollow ber. In addition, the watersolubility should be as low as possible, and the solvent shouldhave a high boiling point to avoid evaporation during theexperiment. This solvent system should also be compatible witha polypropylene hollow ber. It should be immiscible withwater and the acceptor organic phase, because a thin lmshould be formed during the microextraction procedure. Andlast, the acceptor organic solvent should be compatible withGC-MS. Several kinds of supported liquid membrane, n-dodec-ane, n-nonane and n-undecane were selected to study theireffect on extraction efficiency. In this work, n-dodecane was
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selected as the SLM and acetonitrile as the acceptor organicsolvent. Acetonitrile has excellent chromatographic behavior,low solubility in n-dodecane and effectively remained duringthe extraction (no leakage to membrane phase and no solventloss due to evaporation).16
3.1.2 Inuence of the sample stirring speed. Stirring speedis one of the major factors that affects the extraction efficiency.Agitation of the sample is routinely applied to the mass transfercoefficient in aqueous solution and accelerates the extractionkinetics. Increasing the stirring rate can decrease the thicknessof the diffusion lm in the aqueous phase and improve therepeatability of the extraction method.28 In this work, the effectof stirring rate on the extraction of target explosives was inves-tigated by agitating 20.0 mL sample solution at different stirringrates (100, 300, 500, 700 and 900 rpm) using a magnetic stirrer.The experimental results showed that the extraction efficiencyincreased by increasing the stirring speed from 100 to 700 rpm.However, by extracting at higher rates, occasionally excessive airbubbles were generated that adhered to the surface of thehollow ber, making the experiments difficult to control, andthus leading to poor reproducibility. Therefore, 700 rpm wasdeemed to be the optimum stirring speed.
3.1.3 Inuence of ion strength. Addition of salt to thesample may have triple aspects on extraction. Firstly, thedissolution of NaCl in water might change the physical prop-erties of the Nernst diffusion lm and reduce the rate of diffu-sion of the target analytes into the extraction solvent. Secondly,the addition of salt could lead to an increase in the ionicstrength of the solution and then decrease the solubility of thetarget analytes in the aqueous phase and enhance their parti-tioning into the organic phase. Thirdly, the addition of saltcould also affect the phase ratio. The rst and the third factorswould lead to a decrease in the extraction efficiency, while thesecond one causes an increase. This result has also been seen byother authors.29 The effect of NaCl concentration (ranging from0% to 25%) on the extraction efficiency was investigated. Theresults showed that the extraction efficiency reached amaximum at 15% of sodium chloride and subsequentlydecreased with the salt concentration up to 25%. This may bedue to the increase in viscosity of the aqueous sample followingaddition of large amounts of NaCl, thereby impeding the mass-transfer process. Based on the results obtained, a 15% saltconcentration was used for all subsequent extractions.
3.1.4 Inuence of extraction time. In the three micro-extraction modes, extraction efficiency depends on the masstransfer of analytes from the sample solution to the extractants.30
In the proposed HF-SLPME method, the solute transfer in carbonnanotube reinforced hollow ber membrane involves both liquidand solid phase extractions. The presence of CNTs increased theeffective surface area, the overall partition coefficient, while theacceptor in contact with the CNTs readily desorbed the solutes.25
On the other hand, HF-SLPME is not an exhaustive extractionmethod and the analytes are partitioned between the donor andthe acceptor phases until the equilibrium is established. More-over, equilibrium exposure times are not necessary for analyticalmethods when extraction time, mixing rate, and sample volumesremain constant.31 Therefore, the extraction time was another
Fig. 4 The effect of extraction time on the extraction efficiency of the analytes.Stirring rate, 700 rpm; concentration of NaCl, 15% w/v; concentration of analytes50 ng mL�1.
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important parameter to be optimized. The prole of the extractiontime was studied by monitoring the variation of extraction effi-ciency for the target analytes with time under other optimizedconditions. Fig. 4 shows that relative peak areas increased rapidlywith increasing extraction time up to 30 min, and increased veryslowly aer that. It is not necessary for a routine analysis to reachcomplete equilibrium as long as the extraction time is keptconstant. Therefore, 30 min was chosen as the extraction timebased on the consideration of sensitivity and analysis speed.
Fig. 5 HF-SLPME-GC-MS chromatogram of river water sample under optimizedchromatographic conditions. Conditions: 25 ngmL�1 of the analytes: stirring rate,700 rpm; concentration of NaCl, 15% w/v; SLM, n-dodecane; extraction time, 30min; volume of acceptor phase 25.0 mL; volume of donor phase 20.0 mL.
3.2 Validation of the method
Table 1 summarizes the results of the method validation forTNT in HF-LLLME with a plain hollow ber and HF-SLPME witha MWCNTs immobilized membrane. Under the optimalconditions, a good linear relationship between the corre-sponding peak areas and the concentrations was obtained forall the analytes (R2 > 0.9937). The LODs were calculated as theconcentration of the analytes equal to three times the standarddeviation of the blank signal divided by the slope of the cali-bration curve. LODs in the range from 0.03 ng mL�1 (for 2,6-dinitrotoluene) to 0.9 ng mL�1 (for 2-amino-4,6-dinitrotoluene)were obtained. The precision of the method was evaluated bycarrying out ve independent measurements of the studiedcompounds at 50 ng mL�1. The results showed that the relativestandard deviations (RSDs) ranged from 4.3% to 5.7%.
Table 1 Performance of new three-phase HF-SLPME and three-phase HF-LPME
Three real environmental water samples including tap water,river water and ground water were studied using the developedmethod. Tap water was collected from Tehran (Iran), river andgroundwater was collected from Karun, a village near Tehran.No target compounds could be detected in the samples.Therefore, separate samples were spiked with two concentra-tions of all the analytes. Fig. 5 shows a typical chromatogramobtained for studied compounds aer HF-SLPME of a real riverwater sample. Three replicates were analyzed of each realsample and the analytical results are shown in Table 2. Theproposed method showed good reproducibility with standarddeviation values in the range of 3.4 to 5.2%. However,according to the F-test (95% condence level), there was nosignicant difference in the precision of the results obtainedfor spiked environmental water samples with those obtainedfor ultra-pure water spiked. The extraction efficiency of thepresented method was compared with other reported samplepretreatment techniques from the viewpoint of LOD, RSD andlinearity. Table 3 compares the gures of merit generated by
a Relative recovery percent. b Relative standard deviation.
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the proposed method with other methods applied for theextraction and determination of nitroaromatic explosives fromwater samples.32–35 The linearity range of the proposed methodshows a wider value and higher sensitivity in comparison withconventional HF-LLLME.
5 Conclusion
The aim of the present work was to develop an efficient methodfor the extraction, clean up and determination of trace amountsof seven nitroaromatic explosives in environmental watersamples. With the help of incorporating functionalized CNT in
Table 3 Comparison of the proposed method with other developed methods to d
Ref. Instrumenta
This work TNB, DNB, TNT, 2,4-DNT, 2,6-DNT, 4-ADNT, 2-ADNT
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a porous polypropylene matrix, concentration of these nitro-aromatic explosives could be determined and lower detectionlimits compared to those obtained with other methods could beachieved. The proposed method has advantages such as sensi-tivity, good precision, relatively short extraction time, andminimum organic solvent consumption. Conditions for theextraction and analysis of trace amounts of nitroaromaticcompounds in different aqueous samples such as extractiontime, organic solvent, stirring speed and ion strength volume ofthe donor phase were investigated. This procedure can besuccessfully used for the analysis of organic analytes in envi-ronmental water samples.
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