离子液体高温顶空液相微萃取测定环境水样中的氯苯胺2005.pdf

Journal of Chromatography A,1072(2005)36Ionic liquid for high temperature headspace liquid-phase microextractionof chlorinated anilines in environmental water samplesJin-feng Peng,Jing-fu Liu,Gui-bin Jiang,Chao Tai,Min-jia HuangKey Laboratory of Environmental Chemistry and Ecotoxicology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,P.O.Box 2871,Beijing 100085,ChinaAvailable online 8 December 2004AbstractBased on the non-volatility of room temperature ionic liquids(IL),1-butyl-3-methylimidazolium hexafluorophosphate(C4MIMPF6)ILwasemployedasanadvantageousextractionsolventforhightemperatureheadspaceliquid-phasemicroextraction(LPME)ofchloroanilinesinenvironmentalwatersamples.Athightemperatureof90C,4-chloroaniline,2-chloroaniline,3,4-dichloroaniline,and2,4-dichloroanilinewereextracted into a 10?l drop of C4MIMPF6 suspended on the needle of a high-performance liquid chromatography(HPLC)microsyringeheld at the headspace of the samples.Then,the IL was injected directly into the HPLC system for determination.Parameters related toLPME were optimized,and high selectivity and low detection limits of the four chlorinated anilines were obtained because the extraction wasperformed at high temperature in headspace mode and the very high affinity between IL and chlorinated anilines.The proposed procedurewas applied for the analysis of the real samples including tap water,river water and wastewater samples from a petrochemical plant and aprintworks,andonly3,4-dichloroanilinewasdetectedintheprintworkswastewaterat88.2?gl1level.Therecoveriesforthefourchlorinatedanilines in the four samples were all in the range of 81.999.6%at 25?gl1spiked level.2004 Elsevier B.V.All rights reserved.Keywords:Headspace liquid-phase microextraction;High temperature;Ionic liquid;Chlorinated anilines;Wastewater1.IntroductionChlorinated anilines were widely used in a variety of in-dustries 13 and are often found in wastewater dischargedfrom these plants.As these substances are suspected can-cerogenous and highly toxic to aquatic organisms or humanbeings 45,most of them have been included in list of pri-ority pollutants by the US Environmental Protection Agency(EPA).High-performance liquid chromatography(HPLC)ismost frequently used for the determination of chlorinatedanilines 68,and sample pretreatment is usually required.Current sample pretreatment methods for wastewater sam-ples involve solid-phase extraction(SPE)9,solid-phasemicroextraction(SPME)10,liquidliquidextraction(LLE)11,and supported liquid membrane extraction(SLM)12.A derivatization step,however,was usually required in SPECorresponding author.E-mail address:(G.-b.Jiang).and SPME because of the strong polarity and high solubilityof the analytes.In our previous study 1314,ionic liquids(IL)wereused for liquid-phase microextraction(LPME)of some or-ganic pollutants.The main advantages of IL for LPME werethe applicability of long-term headspace extraction due tothe non-volatility of IL,and the compatibility with HPLCdue to the non-harmfulness of IL to HPLC column.Inthis present study,1-butyl-3-methylimidazolium hexafluo-rophosphate(C4MIMPF6)IL was demonstrated to be asuitable extraction solvent for high temperature headspaceLPME of chlorinated anilines in environmental watersamples.2.Experimental2.1.Reagents and chemicalsHPLC-grade acetonitrile was purchased from Dikma(Dikma,China).Standard stock solutions(1000mgl1)of0021-9673/$see front matter 2004 Elsevier B.V.All rights reserved.doi:10.1016/j.chroma.2004.11.0604J.-f.Peng et al./J.Chromatogr.A 1072(2005)364-chloroaniline(4-CA),3,4-dichloroaniline(3,4-DCA),and2,4-dichloroaniline(2,4-DCA)(Acros Organics,Belgium),aswellas2-chloroaniline(2-CA)(TokyokaseiKogyo,Japan)were prepared by dissolving 0.025g of the compounds in25ml acetonitrile.The solutions were stored in brown glassbottles and kept at 4C.Fresh working solutions(10mgl1)wereprepareddailybyappropriatedilutionofthestocksolu-tions.Reagents for synthesis of C4MIMPF6 including 1-methylimidazole(99%),1-chlorobutane(99%)and hexaflu-orophosphoric acid(60m%solution in water)were obtainedfrom Acros Organics.The synthesis and physicochemicalproperties of C4MIMPF6 IL were described in our previ-ous study 13.All of the other chemicals and solvents wereof analytical reagent grade and ultrapure water(EASY-pureLF)was used throughout.2.2.Extraction procedureThe extraction procedure is the same as that describedin our previous study 13,except that a 10?l IL drop wasused as extractant and 50ml flask was adopted for holding20ml of sample solution,and the flask with sample solutionwas placed in recycling hot water to control the extractiontemperature.The hot water was provided by a thermo bathsystem(TB-85 Thermo Bath,Shimadzu,Japan)setting atexpected temperature.2.3.HPLC determinationThe LC-VP liquid chromatographic instrument(Shi-madzu,Japan)consists of an SCL-10Avp system controller,two LC-10ATvp pumps,and an SPD-M10Avp detector set-ting at 240nm.Samples were injected with a 7725i manualinjection valve with a 20?l loop(Rheodyne,USA).Detec-tionwasachievedbythetechniqueofphotodiodearraydetec-tion.Data acquisition and process were accomplished witha Class-VP Workstation(Shimadzu,Japan).The analyticalcolumn was a 250mm4.6mm i.d.C18column(InertsilODS-P,GL Sciences Inc.,Japan,5?m particles).The mo-bile phase was a mixture of acetonitrilewater(50:50,v/v)delivered at a flow rate of 1.0mlmin1.2.4.Sample collectionTap water samples were collected from water tap in ourlaboratory,riverwatersampleswerecollectedfromtheHaiheRiver(Tianjin,China),and the wastewater samples werekindly supplied by a petrochemical plant and a printworks.Thesesampleswereallstoredatthetemperatureof4Caftercollection.3.Results and discussionIn this study,parameters related to liquid-phase microex-traction were optimized by utilizing the univariant methodfor simplifying the optimization procedure.3.1.Effect of salt additionThe optimization of salt concentration was conductedby keep using 10?l of IL extractants for extraction 30minat 60C,while adding varied amounts of sodium chloride(NaCl)in 10ml of phosphate buffer solution(pH 12.0)spikedwith0.2?gml1ofchlorinatedanilines.Experimentsdemonstrated that for the four chlorinated anilines the ex-traction efficiency increased with the NaCl concentration upto 20%and followed by decreasing with further increas-ing of NaCl concentration.This result is in agreement withthose reported in reference 8.This phenomenon can beexplained by the two simultaneously occurring processes:the salting out effect,and the electrostatic interactions be-tween polar molecules and salt ions in sample solution.At the beginning,the former process plays the predomi-nant role,but salt molecules begin to interact with analytemolecules when salt concentration increased further,whichdirectly leads to the decrease of the respond.Therefore,20%NaCl was adopted as the final addition in the followingstudies.3.2.Effect of temperatureUsually,increasing temperature improves the evapora-tion of target compounds from the sample matrix to theheadspace.In this experiment,we also investigated the ef-fect of temperature(from 50 to 90C)on the extraction ef-ficiency.Fig.1 shows that temperature has significant ef-fect on the extraction.With the increasing of the tempera-ture,the extraction efficiency improved sharply as expected.Therefore,an extraction temperature of 90C was consid-ered as the optimum temperature in the following experi-ments.Fig.1.Effectoftemperatureonthepeakareaofchlorinatedanilines.Buffersolutions(pH 12.0,10ml)containing 20%NaCl(w/v)and spiked with0.2?gml1ofchlorinatedanilineswereextractedwith10?lC4MIMPF6for 30min at different temperature.(?)3,4-DCA;(?)4-CA;(?)2,4-DCA;(?)2-CA.J.-f.Peng et al./J.Chromatogr.A 1072(2005)3653.3.Effect of sample pHForaweakorganicbaseandacid,theextractionefficiencydepends on the sample pH.The sample solutions were oftenadjusted to appropriate alkalinity prior to extraction,so thatthe chlorinated anilines were de-ionized and their solubilityin the sample solution reduced and extractability increased.Experimentsdemonstratedthattheextractionefficienciesim-proved significantly with the increasing of pH up to 10 andthenincreasedveryslowlywithfurtherincreasingofpH.Thisis because the pKavalues of 4-CA,2-CA,3,4-DCA and 2,4-DCA were 4.15,2.65,2.00,2.96,respectively 12,15,andthe non-ionic chlorinated anilines predominate largely overthe protonated ionic ones at pH10.Based on this investiga-tion,a samle pH value of over 10 is thus recommended andpH 12 was adopted in the following studies.3.4.Effect of sample volume and extraction timeDuring the headspace extraction process,sample volumecan influence the magnitude of the headspace and thus mightinfluence the extraction efficiency.For the optimization ofsample volume,different volume of phosphate buffer so-lution(containing 20%NaCl,w/v;pH 12.0)spiked with0.2?gml1ofchlorinatedanilineswereextractedfor30minat 90C.Experiments showed that the largest analytical re-sponse was obtained at 20ml of sample for all the studiedchlorinatedanilines.Furtherincreasingofsamplevolumere-Fig.2.Typical chromatograms of the four chlorinated anilines standard,wastewater sample and sample spiked with standard.(A)standard(25?gl1);(B)wastewatersamplefromprintworks;(C)wasterwatersamplespikedwithchlorinatedanilinesstandard(75.0?gl1);(D)blank;(E)standard(1.0?gl1).Peaksidentified as:(1)4-CA;(2)2-CA;(3)3,4-DCA;(4)2,4-DCA.6J.-f.Peng et al./J.Chromatogr.A 1072(2005)36sulted in the decreasing of peak area,which can be explainedby the two successive processes occurred in the extractionproceeding.At the beginning,the percentage headspace de-creases with the increase of sample volume,which acceler-ates the diffusion of the analytes into the IL drop until satu-ration.If sample volume further increased,however,the an-alytes will take more time to transfer from the liquid to theheadspace,thus the response begins to decrease.Therefore,20ml was chosen as the optimal sample volume.The optimization of extraction time was conducted at theabove-optimized conditions.Experiments showed that thehighest peak areas of the analytes were obtained at 30minof extraction time,and further increasing of extraction timeresulted in decreasing of peak areas.The probable reason isthat,with the increasing of extraction time at the given hightemperature,more water vapor will present in the headspaceand the amount of analytes in IL drop decreased due to thedistribution of anlytes between the IL and the water vaporphase.Anotherpossibilityissomechlorinatedanilinesmightdegraded at such a high extraction temperature(90C).Ac-cording to this investigation,30min was chosen in the fol-lowing study.3.5.Analytical performance and applicationEach analyte exhibited good linearity with correlationcoefficient r20.999 in the studied range(5100?gl1for 2-CA and 3,4-DCA,1150?gl1for 4-CA,and2.5100?gl1for 2,4-DCA).The repeatability was studiedby five replicate experiments.This proposed procedure pos-sessed good repeatability with relative standard deviations(R.S.D.s)in the range of 57%.This is because IL is a verystable and non-volatile compound and there is no losing ofextractant during headspace extraction.The limits of detec-tion(LODs),estimated based on signal-to-noise ratio of 3(S/N=3),were in the range of 0.51.0?gl1.The excel-lent characteristics of IL contributed a great to these verylow LODs.At first,the involatile IL permits the headspaceextraction at a high temperature of 90C to make the fourchlorinated anilines with high boiling point(232C for 4-CA,208.8C for 2-CA,272C for 3,4-DCA and 245C for2,4-DCA 15)diffuse into the headspace and thus be ex-tracted more efficiently.In addition,the very high affinitybetween IL and chlorinated anilines 16 benefitted the trapof chlorinated anilines in IL.The applicability of the proposed method was evalu-ated by analysis of real environmental samples includingtap water,river water,and wastewater from a petrochem-ical plant and a printworks,respectively.The four chlori-nated anilines were under their detection limits except that88.25.8?gl1(n=3)of 3,4-DCA was detected in wastewater from printworks.The spiking recoveries of standard at25?gl1level(75?gl1for 3,4-DCA as it was detected at88.25.8?gl1levelinwastewaterfromprintworks)wereintherangeof81.999.6%.Thetypicalchromatogramswereshown in Fig.2.4.ConclusionsA novel procedure,high temperature headspace liquid-phase microextraction based on ionic liquid,was proposedforthedeterminationofchlorinatedanilinesinenvironmentalwater samples.The main advantages of the proposed proce-dureweretheapplicabilityoflong-termheadspaceextractionat high temperature(90C)due to the non-volatility of IL,and the high efficient trap of chlorinated anilines in IL dueto the very high affinity between IL and chlorinated anilines.Therefore,the proposed method possessed high sensitivity(LODs=0.51.0?gl1)and low influence of sample matrix(with recoveries of 81.999.6%).On the other hand,the pro-posedmethodisrapidandeasytoconductasILiscompatiblewith HPLC column and thus IL with extracted analytes canbe injected into the HPLC system for determination.AcknowledgementsThis work was jointly supported by the National NaturalScience Foundation of China(20377045,20477052)and theNational Key Project for Basic Research(2002CB412308).References1 L.M.Games,R.A.Hltes,Anal.Chem.49(1977)1433.2 N.Boon,J.Goris,P.De Vos,W.Verstraete,E.M.Top,Appl.Environ.Microbiol.67(2001)1107.3 M.Ucan,A.G urten,A.Ayar,Colloids Surf.A:Physicochem.Eng.Aspects 219(2003)193.4 M.A.Valentovic,T.Yahia,J.G.Ball,S.K.Hong,P.I.Brown,G.O.Rankin,Toxicology 124(1997)125.5 Conciseinternationalchemicalassessmentdocument48:Chloroanaline(4-),World Health Organization,Geneva,2003.6 J.Jen,C.Chang,T.C.Yang,J.Chromatogr.A 930(2001)119.7 R.M.Riggin,T.F.Cole,S.Billets,Anal.Chem.55(1983)1862.8 L.Zhao,L.Zhu,H.K.Lee,J.Chromatogr.A 963(2002)239.9 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