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AnalyticaChimicaActa706(2011)261–267ContentslistsavailableatSciVerseScienceDirectAnalyticaChimicaActajournalhomepage:fluenceofacidificationontheopticalpropertiesandmolecularcompositionofdissolvedorganicmatterMalakM.Tfailya,DavidC.Podgorskia,JaneE.Corbettb,JeffreyP.Chantonb,WilliamT.Coopera,∗aDepartmentofChemistry&Biochemistry,FloridaStateUniversity,Tallahassee,FL32306-4390,USAbDepartmentofOceanography,FloridaStateUniversity,Tallahassee,FL32306-4320,USAarticleinfoArticlehistory:Received26May2011Receivedinrevisedform22August2011Accepted24August2011Availableonline31August2011Keywords:Dissolvedorganicmatter(DOM)SamplepreservationOpticalpropertiesMolecularcompositionUltrahighresolutionmassspectrometryofDOMUV–visspectroscopyExcitation–emissionmatrixfluorescencespectroscopyabstractAcidificationisacommonmethodforpreservingdissolvedorganicmatter(DOM)innaturalwatersam-plesuntilsophisticatedlaboratoryanalysescanbeperformed.However,littleisknownabouttheeffectsofthispracticeonthecompositionandopticalpropertiesofDOM.Inthisstudy,theeffectsofacidificationonDOMinporewatersamplescollectedfromtheRLIVbogsystemoftheGlacialLakeAgassizPeatlandsinnorthernMinnesotawerecharacterized.MolecularcompositionwasdeterminedbyultrahighresolutionmassspectrometryandopticalpropertiesbyUVabsorptionandthree-dimensionalfluorescencespec-troscopy.Excitation–emissionmatrixfluorescencespectroscopyresultsindicatethatthefluorescencepropertiesofthepeatlandporewaterDOMweresensitivetopHandthattheobservedchangeswerefluorophoredependent.UltrahighresolutionFouriertransformioncyclotronresonancemassspectrom-etryrevealedtheappearanceofnewlyformed,oxygen-richcompoundsuponacidification.Theextenttowhichtheseoxygen-richcompoundswereformedwasalsodependentonthecompositionoftheDOM.©2011ElsevierB.V.Allrightsreserved.1.IntroductionDissolvedorganicmatter(DOM)isdefinedoperationallyastheportionoforganicmatterthatwillpassthroughafilterranginginporesizebetween0.1and1m.Chromophoricdissolvedorganicmatter(CDOM)istheopticallyactivecomponentthatcontrolstheopticalpropertiesofmostnaturalwatersystems[1,2].DOMorig-inatesfromavarietyofsources,includingdecomposednonlivingplantmaterialsintroducedintothehydrologicalsystemvialeach-ingorrunofffromland.ThisDOMisinfluencedbytheland-use,geologyandhydrologyofitsorigin.DOMisalsoproducedinsituthroughthedecayofphytoplanktondetritus.Thecontributionofeachsourcedependsonboththelocationandtheenvironmentalconditionsofthewaterbody[3].DOMplaysanimportantroleinaffectingmetalspeciationandsolubilityoforganicpollutants,alteringpH,andabsorbingradiantlightfromthewatercolumn.Itcanalsoactasafoodsupplementsupportinggrowthofmicroorganisms[4,5].DOMisthoughttoplayanimportantroleasanintermediateinrespiration,withCO2andCH4theendproducts.Chantonetal.[6]reportedthatanaerobicrespirationwithinthepeatcolumntodepthsof3misfueledby∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](W.T.Cooper).DOMderivedinpartfromsurfaceproductionratherthanfromthedecompositionofpeatataparticularhorizon.DOMcomprisesapolydisperseandhighlycomplexmixtureofmoleculeswhosecharacterizationremainsademandingchallengeinmodernanalyticalchemistry.Despitemajoradvancesinanalyti-caltechniquesoverthepastyears,nosingleanalyticaltechniqueiscapableofentirelycharacterizingthechemicalstructureandcom-positionofbulkDOM[7].Thecombinationofseveralanalyticalmethodsisthereforerequiredtoconstructamorecompletepicturefromthepiecesofinformationeachapproachcanprovide.SincethechemicalcompositionandtheopticalpropertiesofDOMareinterrelated,opticaltechniquessuchasabsorptionandfluorescencespectroscopyhavebeensuccessfullyutilizedtoelucidatethechemicalcompositionofbulkDOM[7,8].Opticalspec-troscopyofDOMcharacterizesCDOM.CDOMabsorbsvisibleandUVlight.Byusingabsorptionspectralslopeandabsorptionratios,themolecularsizeandthearomaticityofCDOMcanbeestimated.CDOMalsohasintrinsicfluorescencepropertieswhenexcitedbyradiationintheUVandblueregionofthespectrum[3].Thesepropertiesdifferasafunctionofsourcematerialandlightexpo-sure[9,10].OneofthemostpopularfluorescencetechniquesforcharacterizingCDOMisExcitationEmissionMatrixfluorescencespectroscopy(EEM)whichinvolvesthecollectionofmultipleemis-sionspectrascannedoverawiderangeofexcitationwavelengthsanddepictedinasingle3Dmapofopticalspace.EEMSspectracan0003-2670/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.aca.2011.08.037262M.M.Tfailyetal./AnalyticaChimicaActa706(2011)261–267beinterpretedtoidentifythecomponentsofCDOMbasedonthepositionsofexcitation/emissionmaxima[3].AbsorptionandfluorescencemeasurementsofDOMaresensi-tivetothechangesintheenvironmentalconditionsofasample.Theseincludechangesintemperature,pH,quenchingbychelat-ingwithmetalionsandinteractionswithsolventandothersolutemolecules.Asacidificationandfreezingarecommonlyusedproto-colsforstoringDOMforlateranalysis,itisimportanttoinvestigatewhethertheyhaveanyeffectonDOMcompositionandopticalproperties[3,11,12].Fellmanetal.[13]evaluatedfreezingasapreservationtech-niqueforanalyzingDOMinsu