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StudyofthepHinfluenceontheopticalpropertiesofdissolvedorganicmatterusingfluorescenceexcitation–emissionmatrixandparallelfactoranalysisMingquanYana,n,QiangweiFub,DechaoLib,GunfaGaob,DongshengWangcaDepartmentofEnvironmentalEngineering,PekingUniversity,TheKeyLaboratoryofWaterandSedimentSciences,MinistryofEducation,Beijing100871,ChinabCollegeofEnvironmentalSciencesandEngineering,Chang’anUniversity,Xi’an,Shanxi,710064,ChinacStateKeyLaboratoryofEnvironmentalAquaticChemistry,ResearchCenterforEco-EnvironmentalSciences,CAS,POB2871,Beijing100085,ChinaarticleinfoArticlehistory:Received7November2012Receivedinrevisedform31January2013Accepted28February2013Availableonline30March2013Keywords:FluorescencePARAFACpHDissolvedorganicmatterabstractThisstudyinvestigatedtheopticalpropertiesofdissolvedorganicmatter(DOM)usingthefluorescenceexcitation–emissionmatrix(EEM)methodcombinedwithparallelfactor(PARAFAC)analysis.TheexaminedDOMsamplesincludedSuwanneeRiverfulvicacid(SRFA)andNordicReservoirnaturalorganicmatter(NRNOM).TheopticalpropertiesoftheDOMweredeterminedfromthebehaviorofindividualgroupsofDOMfluorophoresrespondingtodifferentionizationstates.ThePARAFACexaminationrevealedthatthereweresixindependentEEMcomponentsintheSRFAthatbehaveddifferentlyintermsofpHinfluenceontheirfluorescenceintensity.ThedominantEEMpeaklocations(λex/λem)ofthesecomponentswere(230,330)nm/420nm(Component1),(250,350)nm/450nm(Component2),(240,340)nm/460nm(Component3),(220,280)nm/380nm(Component4),(270,400)nm/490nm(Component5),and(280,340)nm/540nm(Component6).However,onlyfourEEMcomponentswereobservedintheNRNOM,whicharesimilartoComponents1,2,3and4intheSRFA.ItcanbespeculatedthatComponents1,2,3and6canbecategorizedastraditionalterrestrialhumic-likechromophores,whiletheyarecomposedofdifferentfractionsofcarboxylic-likeandphenolic-likechromophores;Component4canbecategorizedasprotein-likefluorophoresprimarilycomposedofcarboxylic-likechromophores,andComponent5canbecategorizedasamicrobialhumic-likecomponentthatisoverwhelminglycomposedofphenolic-likefluorophores.TheresultsdemonstratedthatPARAFACanalysisisapromisingapproachforcharacterizingthefinefunctionsinDOM.&2013ElsevierB.V.Allrightsreserved.1.IntroductionDissolvedorganicmatter(DOM)isubiquitousinnaturalwatersandisderivedfromplantorterrestrial(allochthonous)andalgal(autochthonous)sources.DOMisaheterogeneousmixtureofvariousmolecularweightaromaticandaliphaticorganiccom-poundsthatcontainoxygen,nitrogen,andsulfurfunctionalgroups(e.g.,carboxyl,phenol,enol,alcohol,carbonyl,amine,andthiol)[1,2].ThepropertiesofDOMstronglyaffectitsreactivityinbothnaturalandengineeredaquaticsystems[1,3–7].Fluorescencespectroscopyisasimple,sensitive,andnondes-tructiveanalyticaltechniquethathasthepotentialtoprovideinvaluableinformationaboutthemolecularstructure,functional-ities,andconformationandintramolecularandintermolecularinteractionsofDOMwithprotonandmetalions[1,8,9].Earlystudiesusedsingleexcitationandemissionwavelengths,whicharetypicalofhumic-likefluorophores[8,10–16].Fluorescenceexcitation–emissionmatrix(EEM)spectroscopycanmeasureemissionspectraacrossarangeofexcitationwavelengthsandprovideanoverallviewofallthefeaturesthatexistwithinaselectedspectralrange.ThistechniquehassatisfactorilybeenusedtocharacterizeDOMinnaturalenvironments.AlthoughtheEEMspectroscopicapproachhasagreaterdensityofspectralinforma-tionthanthetraditionalfluorescenceapproaches,itcandemon-stratethatquenching(orenhancement)offluorescenceintensitybyprotonandmetalionsisquantitativelydissimilarindifferentregionsofthefluorescencelandscape[2,17–21].TheEEMland-scapehasbeentypicallycharacterizedbynotingthelocationsofoneormorepeaksthatcorrespondtothemaximumfluorescenceintensities(“peakpicking”)[22–24].Duetothebroadnatureandthelackoffinestructureoftheorganicmatterfluorescencespectra,thevisual“peakpicking”processissubjectiveinnatureandmayleadtoerroneousconclusionsbecausepeakscommonlyreflectmorethanoneunderlyingfluorophore.Analternative,multiwaymethods,suchasparallelfactor(PARAFAC)analysisoftheEEMsamplepool,canbeusedtoresolvemixturesContentslistsavailableatSciVerseScienceDirectjournalhomepage:://dx.doi.org/10.1016/j.jlumin.2013.02.052nCorrespondingauthor.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail],[e-mail](M.Yan).JournalofLuminescence142(2013)103–109offluorescentcompoundsintotheirindividualconstituentsbyrelyingonthevisualidentificationofpeaksandtheratiosoffluorescenceindifferentregionsofthespectrum,therebyreducingtheinterferenceproblemandallowingamoreaccuratequantifica-tion[25–27].Therefore,EEMincombinationwithPARAFAChasbeenusedtoinvestigatetheoxidationandmetalcomplexationprocessesofDOM[28–31].BecausethefunctionalityofDOM,suchascarboxylic,phenolic,alcoholic,enolichydroxyl,carbonylandnitrogen-,S-andP-containingfunctionalgroups,isverysensitivetopH,andthehydrolysisprocessofthefunctionalitiesmayaffecttheirfluores-cenceintensity[23].Inthispaper,theopticalproperties