对数转换光谱数据定量金属与DOC的络合

Quantifyingmetalionsbindingontodissolvedorganicmatterusinglog-transformedabsorbancespectraMingquanYana,*,DongshengWangb,GregoryV.Korshinc,MarcF.BenedettidaDepartmentofEnvironmentalEngineering,PekingUniversity,TheKeyLaboratoryofWaterandSedimentSciences,MinistryofEducation,Beijing100871,ChinabStateKeyLaboratoryofEnvironmentalAquaticChemistry,ResearchCenterforEco-EnvironmentalSciences,CAS,POB2871,Beijing100085,ChinacDepartmentofCivilandEnvironmentalEngineering,UniversityofWashington,Box352700,Seattle,WA98195-2700,UnitedStatesdUniv.ParisDiderot,SorbonneParisCite´,IPGP,UMR-CNRS7154,Paris,FrancearticleinfoArticlehistory:Received1November2012Receivedinrevisedform11February2013Accepted22February2013Availableonline6March2013Keywords:AluminumCadmiumComplexCopperLog-transformedabsorbanceNaturalorganicmatterNICA-DonnanmodelabstractThisstudyintroducestheconceptofconsistentexaminationofchangesoflog-transformedabsorbancespectraofdissolvedorganicmatter(DOM)atincrementallyincreasingconcentrationsofheavymetalcationssuchascopper,cadmium,andaluminumatenvironmentallyrelevantconcentrations.Theapproachisdesignedtohighlightcon-tributionsoflow-intensityabsorbancefeaturesthatappeartobeespeciallysensitivetoDOMreactions.Inaccordwiththisapproach,log-transformedabsorbancespectraoffractionsofDOMfromtheSuwanneeRiverwereacquiredatvaryingpHsandconcentra-tionsofcopper,cadmium,andaluminum.Theselog-transformedspectrawereprocessedusingthedifferentialapproachandusedtoexaminethenatureoftheobservedchangesofDOMabsorbanceandcorrelatethemwiththeextentofMe-DOMcomplexation.Twoalternativeparameters,namelythechangeofthespectralslopeintherangeofwave-lengths325e375nm(DSlope325e375)anddifferentiallogarithmofDOMabsorbanceat350nm(DLnA350)wereintroducedtoquantifyCu(II),Cd(II),andAl(III)bindingontoDOMs.DLnA350andDSlope325e375datasetswerecomparedwiththeamountofDOM-boundCu(II),Cd(II),andAl(III)estimatedbasedonNICA-Donnanmodelcalculations.ThisexaminationshowedthattheDLnA350andDSlope325e375acquiredatvariouspHvalues,metalionsconcentrations,andDOMtypeswerestronglyandunambiguouslycorrelatedwiththeconcentrationofDOM-boundmetalions.TheobtainedexperimentalresultsandtheirinterpretationindicatethattheintroducedDSlope325e375andDLnA35parametersarepre-dictiveofandcanbeusedtoquantifyinsitumetalionsinteractionswithDOMs.ThepresentedapproachcanbeusedtogainmoreinformationaboutDOM-metalinteractionsandforfurtheroptimizationofexistingformalmodelsofmetal-DOMcomplexation.ª2013ElsevierLtd.Allrightsreserved.1.IntroductionAbsorbanceandfluorescencespectroscopyhasbeenwidelyusedtoprobethechemistryandreactivityofdissolvedorganicmatter(DOM).Majorbenefitsofthesemethodsarethattheydonotrequiresamplepre-concentrationandyettheyprovideinformationaboutDOMinteractionswithmetalionsandothersolutioncomponentsinenvironmentally-*Correspondingauthor.Tel.:þ86106275591481;fax:þ861062756526.E-mailaddresses:[e-mail],[e-mail](M.Yan).Availableonlineat(2013)2603e26110043-1354/$eseefrontmatterª2013ElsevierLtd.Allrightsreserved.fluorescenceandabsor-bancespectroscopycanbeusedtoexaminechangesofDOMcausedbyprotonandmetalionsbinding,theutilityofabsorbancespectrainascertainingDOM-metalinteractionshasbeendeemedtobelimitedbecause,asopposedtofeature-richexcitation/emissionmatrixesofDOM(Baietal.,2008;daSilvaetal.,1998;Lusteretal.,1996;Ohnoetal.,2008;Park,2009;PullinandCabaniss,1995;RyanandWeber,1982;Seredynska-Sobeckaetal.,2011;Vieyraetal.,2009;Wuetal.,2011,2012),itsabsorbancespectraarefeatureless.Asaresult,theirinterpretationisfrequentlyreducedtousingonlyafewparameters(e.g.,absorbanceataparticularwavelength,typicallyat254andassociatedDOC-normalizedSUVA254,ra-tiosofabsorbancevaluesataprioriselectedwavelengths,widthoftheelectron-transferabsorbancebandDelta(ET))assurrogatesofNOMproperties,suchasDOCconcentration,DOMaromaticityandinsomecasesitsmolecularweight(Helmsetal.,2008;Heretal.,2008;Korshinetal.,1997;Yanetal.,2012).RecentresearchhasdemonstratedthatDOMabsorbancespectracanbeprocessedusingthedifferentialapproachtorevealthepresenceofinterpretablefeaturesassociatedwithdeprotonationofDOMmolecules(Dryeretal.,2008)andtheirinteractionswithoxidantshalogensandadsorbingsurfaces(Janotetal.,2010;Maureretal.,2010).AsimilarapproachcanbeappliedtoquantifytheengagementofDOMincomplexa-tionwithmetalcations.OurpreviousstudyshowedthatnumericdeconvolutionofthedifferentialspectraofstandardSuwanneeRiverfulvicacid(SRFA)generatedatvaryingpHsandcopperconcentrationsallowsdeterminingcontributionsofdiscreteGaussianbandsandestablishingcommonalitiesseeninthechangesofabsorbancecausedbydeprotonationofDOManditsinteractionswithcopper(II)ions(Yanetal.,2013).TheaboveinterpretationdoesnotaddresspotentiallypronouncedrelativechangesofDOMabsorbanceintherangeofwavelengths,typically320nmwhereDOMabsorbancedeclinesrapidly.TheabsorbanceofDOMisknowntodecreasenearlyexponentiallyasafunctionoftheobserva