AnalyticalTechniquesin EnvironmentalResearch1stEditionReginaDuarte (Editor)
https://ebookmass.com/product/multidimensional-analyticaltechniques-in-environmental-research-1st-edition-reginaduarte-editor/
Instant digital products (PDF, ePub, MOBI) ready for you
Download now and discover formats that fit your needs...
Smartphone-Based Detection Devices: Emerging Trends in Analytical Techniques 1st Edition Chaudhery Mustansar Hussain (Editor)
https://ebookmass.com/product/smartphone-based-detection-devicesemerging-trends-in-analytical-techniques-1st-edition-chaudherymustansar-hussain-editor/ ebookmass.com
Tools, Techniques and Protocols for Monitoring Environmental Contaminants 1st Edition Satinder Kaur Brar (Editor)
https://ebookmass.com/product/tools-techniques-and-protocols-formonitoring-environmental-contaminants-1st-edition-satinder-kaur-brareditor/
ebookmass.com
Guide to Research Techniques in Neuroscience 3nd Edition Matt Carter
https://ebookmass.com/product/guide-to-research-techniques-inneuroscience-3nd-edition-matt-carter/
ebookmass.com
Advanced Biosensors for Health Care Applications Inamuddin https://ebookmass.com/product/advanced-biosensors-for-health-careapplications-inamuddin/
ebookmass.com
Philosophy in Ovid, Ovid as Philosopher Gareth D. Williams (Editor)
https://ebookmass.com/product/philosophy-in-ovid-ovid-as-philosophergareth-d-williams-editor/
ebookmass.com
Mais Esperto que o Diabo Napoleon Hill [Hill
https://ebookmass.com/product/mais-esperto-que-o-diabo-napoleon-hillhill/
ebookmass.com
Trouble déficit de l'attention-hyperactivité chez l'enfant et l'adulte: Guide d'une approche contemporaine du TDAH
1st Edition Thomas E. Brown
https://ebookmass.com/product/trouble-deficit-de-lattentionhyperactivite-chez-lenfant-et-ladulte-guide-dune-approchecontemporaine-du-tdah-1st-edition-thomas-e-brown/ ebookmass.com
Recent Trends and Best Practices in Industry 4.0 (River Publishers Series in Mathematical, Statistical and Computational Modelling for Engineering) 1st Edition
Abhinav Sharma (Editor)
https://ebookmass.com/product/recent-trends-and-best-practices-inindustry-4-0-river-publishers-series-in-mathematical-statistical-andcomputational-modelling-for-engineering-1st-edition-abhinav-sharmaeditor/ ebookmass.com
Biological Science, Third Canadian Edition, 3rd edition
Scott Freeman Kim Quillin Lizabeth Allison Michael Black
Greg Podgorski Emily Taylor Jeff Carmichael Michael Harrington Joan C. Sharp
https://ebookmass.com/product/biological-science-third-canadianedition-3rd-edition-scott-freeman-kim-quillin-lizabeth-allisonmichael-black-greg-podgorski-emily-taylor-jeff-carmichael-michaelharrington-joan-c-sharp/ ebookmass.com
Big Brother Naija and Popular Culture in Nigeria: A Critique of the Country's Cultural and Economic Diplomacy
1st ed. 2023 Edition Christopher Isike https://ebookmass.com/product/big-brother-naija-and-popular-culturein-nigeria-a-critique-of-the-countrys-cultural-and-economicdiplomacy-1st-ed-2023-edition-christopher-isike/ ebookmass.com
MultidimensionalAnalytical TechniquesinEnvironmental Research Multidimensional AnalyticalTechniques inEnvironmental Research Editedby ReginaM.B.O.Duarte
ArmandoC.Duarte
Elsevier
Radarweg29,POBox211,1000AEAmsterdam,Netherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates
©2020ElsevierInc.Allrightsreserved.
Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans,electronic ormechanical,includingphotocopying,recording,oranyinformationstorageandretrievalsystem,without permissioninwritingfromthepublisher.Detailsonhowtoseekpermission,furtherinformationabout thePublisher’spermissionspoliciesandourarrangementswithorganizationssuchastheCopyright ClearanceCenterandtheCopyrightLicensingAgency,canbefoundatourwebsite: www.elsevier.com/ permissions.
Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythe Publisher(otherthanasmaybenotedherein).
Notices
Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperiencebroaden ourunderstanding,changesinresearchmethods,professionalpractices,ormedicaltreatmentmay becomenecessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluating andusinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuch informationormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers,including partiesforwhomtheyhaveaprofessionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assume anyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability,negligence orotherwise,orfromanyuseoroperationofanymethods,products,instructions,orideascontained inthematerialherein.
LibraryofCongressCataloging-in-PublicationData
AcatalogrecordforthisbookisavailablefromtheLibraryofCongress
BritishLibraryCataloguing-in-PublicationData
AcataloguerecordforthisbookisavailablefromtheBritishLibrary
ISBN:978-0-12-818896-5
ForinformationonallElsevierpublicationsvisitour websiteat https://www.elsevier.com/books-and-journals
Publisher:SusanDennis
AcquisitionsEditor:KathrynEriylmaz
EditorialProjectManager:ReddingMorse
ProductionProjectManager:R.VijayBharath CoverDesigner:ChristianJ.Bilbow
TypesetbySPiGlobal,India
Contributors AntoineS.Almeida DepartmentofChemistry&CESAM,UniversityofAveiro, Aveiro,Portugal
PedroF.Branda ˜ o DepartmentofChemistry&CESAM,UniversityofAveiro, Aveiro,Portugal
Marie-CecileChalbot NewYorkCityCollegeofTechnology,BiologicalSciences Department,Brooklyn,NY,UnitedStates
XiChen AnhuiProvinceKeyLaboratoryofFarmlandEcologicalConservationand PollutionPrevention,SchoolofResourcesandEnvironment,AnhuiAgricultural University,Hefei,China
WenyingChu DepartmentofChemistryandBiochemistry,OldDominion University,Norfolk,VA,UnitedStates
ArmandoC.Duarte DepartmentofChemistry&CESAM,UniversityofAveiro, Aveiro,Portugal
ReginaM.B.O.Duarte DepartmentofChemistry&CESAM,UniversityofAveiro, Aveiro,Portugal
HongjianGao AnhuiProvinceKeyLaboratoryofFarmlandEcologicalConservation andPollutionPrevention,SchoolofResourcesandEnvironment,AnhuiAgricultural University,Hefei,China
JeffreyA.Hawkes UppsalaUniversity,Uppsala,Sweden
DeanHesterberg DepartmentofCropandSoilSciences,NorthCarolinaState University,Raleigh,NC,UnitedStates
IliasKavouras CUNYGraduateSchoolofPublicHealth&HealthPolicy, DepartmentofEnvironmental,OccupationalandGeospatialHealthSciences,New York,NY,UnitedStates
WilliamKew EnvironmentalMolecularSciencesLaboratory,PacificNorthwest NationalLaboratory,Richland,WA,UnitedStates
JingdongMao DepartmentofChemistryandBiochemistry,OldDominion University,Norfolk,VA,UnitedStates
Ca ´ tiaMartins DepartmentofChemistry&QOPNA/LAQV-REQUIMTE,University ofAveiro,Aveiro,Portugal
MauroMecozzi LaboratoryofChemometricsandEnvironmentalApplications, ISPRA,Rome,Italy
JenniferMejia DepartmentofChemistryandBiochemistry,OldDominion University,Norfolk,VA,UnitedStates
CarinaPedrosaCosta DepartmentofChemistry&QOPNA/LAQV-REQUIMTE, UniversityofAveiro,Aveiro,Portugal
Sı´lviaM.Rocha DepartmentofChemistry&QOPNA/LAQV-REQUIMTE, UniversityofAveiro,Aveiro,Portugal
YingxinShang NortheastInstituteofGeographyandAgroecology,Chinese AcademyofSciences,Changchun;UniversityofChineseAcademyofSciences, Beijing,China
AakritiSharma DepartmentofCropandSoilSciences,NorthCarolinaState University,Raleigh,NC,UnitedStates
KaishanSong NortheastInstituteofGeographyandAgroecology,ChineseAcademy ofSciences,Changchun,China
SophiaViar 2505TiswoodCourt,Chesapeake,VA,UnitedStates
ZhidanWen NortheastInstituteofGeographyandAgroecology,ChineseAcademy ofSciences,Changchun,China
YingZhao NortheastInstituteofGeographyandAgroecology,ChineseAcademy ofSciences,Changchun,China
Multidimensionalanalytical techniquesinenvironmental research:Evolutionofconcepts ReginaM.B.O.Duarte,ArmandoC.Duarte DepartmentofChemistry&CESAM,UniversityofAveiro,Aveiro,Portugal
Challengesinenvironmentalresearch 1 Nowadays,mostoftheenvironmentalchallengesareassociatedwiththeincreased releaseofpollutantsintotheair,water,andsoil,modificationsontheglobalcycling ofnutrientsandcontaminants,andclimatechangeissues.Theadvancementsmade thusfarinenvironmentalresearchhaveoriginatedeitherfromtheneedtounderstand theabovementionedissuesortoseeksolutionsandregulations.Eitherway,moststudiesfocusonunderstandingtheinteractionswithinandamongatmospheric,terrestrial, aquatic,andlivingcompartmentsofecosystems.Thisis,however,anextremelychallengingtask,mainlyduetothevariabilityofthoseecosystemsandthehighdegreeof heterogeneity,bothintermsofcompositionandconcentration,ofthesamplesand analytesofinteresttakenfromthedifferentenvironmentalcompartments.Thiscomplexityrepresentsatrueanalyticalchallenge.Itis,therefore,notsurprisingthatthe developmentofnewanalyticalstrategiestounravelsuchcomplexmatriceshasoccupiedacentralroleintheeffortofresearchers.
Thedramaticdevelopmentduringthepastdecadeinadiversesuiteofanalytical tools,usingasecondorthirddimensionormultiscalehyphenatedmethods(i.e.,separativeanddetectionmethods),havecontributedtoadvancesinenvironmental research.Theseadvancesincludesignificantimprovementsin(i)analyticalsensitivity andaccuracyforthetargeted,semitargeted,anduntargetedscreeningofcomplex organicmatrices(e.g.,high-resolutionmassspectrometry,HR-MS [1–6]);(ii)the useand/orcombinationofspectroscopic[e.g.,one-andtwo-dimensional(2D) liquid-andsolid-statenuclearmagneticresonance(NMR)spectroscopy [7–12], andexcitation-emissionmatrix(EEM)fluorescencespectroscopy [13–16]],HR-MS [17–20],andchromatographicseparation(e.g.,Ref. [21])toacquirecompositional, geographic,andtimeevolutioninformationoncomplexorganicstructuresandinteractions;(iii)developmentofpowerfulcomprehensivemultidimensionalchromatographictoolsfortheresolutionofcomplexorganicmatrices(e.g.,Refs. [22–30]); (iv)useofsynchrotronradiation-basedmethodstoelucidatethespeciationandspatial arrangementoftoxicelementsandnutrientsincomplexenvironmentalmatrices(e.g., Refs. [31–36]);and(v)developmentofmore“user-friendly”dataprocessingand treatmentsoftwaretodealwiththecomplexityofmultidimensionaldatagathered
2 MultidimensionalAnalyticalTechniquesinEnvironmentalResearch
fromtheenvironmentalsamplesinordertogleanthedesiredinformation(e.g.,Refs. [37,38]),tonameafewofthemany.Thecomplementarityandtechnological advancesofthesemultidimensionalanalyticaltoolshavebeenkeytoallowawider rangeofcomplexenvironmentalmatricestobeanalyzed,enablingtheacquisitionof innovativedataandtransformativeadvancesinenvironmentalresearch.
Thischapteraimstointroducethereadertotheunderlyingconceptsthathave driventhedevelopmentanduseofsophisticatedmultidimensionalandmultiscale hyphenatedmethodsforunravelingcomplexorganicmixturesfromdifferentenvironmentalmatrices.Thefocusisonsecond-andthird-dimensionalspectroscopic, spectrometry,andchromatographicmethods,andhowthesestate-of-the-artmultidimensionalanalyticalstrategiesarebeingusedforthetargetedanduntargeted profilingofsuchcomplexorganicmixtures.Thisisnotacomprehensivereviewon theuseoftheseanalyticalmethodologiesbutinsteadabroadoverviewandan introductiontothesubsequentchapters,wherethemostpopularmultidimensional analyticaltechniquesusedinenvironmentalbiogeochemistryresearcharecarefully addressed.
Copingwithenvironmentalorganicmatricescomplexity Inrecentyears,therehasbeenanincreasingconcernforenvironmentalmonitoringand developmentofnewanalyticalproceduresfordealingwiththehugenumberofanalytes andtacklingthegreatcomplexityofenvironmentalsamples.Thesecomplexorganic mixturesexhibitadiversityofconstituentswithdifferentmolecularsizes,structures, andchemicalproperties,whichmakestheiranalysisoneoftheenduringchallenges inanalyticalchemistry.Forexample,whilesolvingthechemicalstructureofhigh molecularsizeanalytes,suchasproteinsorothernaturalpolymers,requiresexploring therelativelywell-organizedcompositionoftheirsmallermolecularsubunits (i.e.,monomers),theanalysisofsmallermoleculesinamixtureisrathermoredifficult. Inthelattersituation,theanalystfacesabroadchemicalandstructuraldiversity,which requiresdifferenttypesofanalysesifaimingatthefullstructuralidentificationofeach organiccompound[i.e.,elementalcomposition,spatialstructure(i.e.,itsisomers), and/orspatialconfiguration].Nevertheless,notallenvironmentalproblemsrequire thefullidentificationofallorganiccompoundspresentinasample. Fig.1.1 illustrates howdifferentlevelsofcompositionalinformationcanbedistinguished,depending onthepurposeofinvestigation:(i)functionalgroupanalysis,whichcopeswith thehighestlevelofmoleculardiversity(numberoforganiccompounds, n 1000)at theexpensesofchemicalresolution,istypicallyemployedwheninterestedinunderstandingspecificpropertiesofcomplexorganicassemblies(e.g.,structuralaverage information [7,8,10,12],chemicalprocesses [9,39],opticalproperties [13,40], andfine-scalespatialarrangementoforganiccarbonforms [31,34,35]);(ii)resolve thechemicalcompositionofcomplexorganicmixturesintodifferentorganic componentsormolecularstructures(10 n 100)isusuallychosentounraveling themolecularcodes [11,21,41–45],theorganicprecursors [20,46,47],andreactivity [1,48,49] ofthesehighlycomplexmixtures;(iii)targetanalysisofmolecularorganic
Fig.1.1 Levelsoforganiccompositionalidentificationintheanalysisofcomplexmixtures fromdiverseenvironmentalmatrices,highlightingthequantificationattainedbydifferent advancedanalyticaltechniques(n:numberoforganiccompoundsidentifiedand/ormeasured).
markers(n 10)istypicallyusedtoaccuratelyquantitateand/ormonitoringknown formationprocessesorsourcesofthetargetcompoundsindifferentenvironmental matrices [23,24,28,29,50–54];and(iv)correspondingtothehighestlevelofchemical resolution,theidentificationofuptothreespecificorganiccompounds(n 2–3)when studying,forexample,unknownformationprocessesorsourcesoforganicparticlesin theatmosphere(Ref. [55] andreferencestherein)oridentifyingemergingorganic pollutantsinindustrialwastewater [56] orfreshwater [57].
Inenvironmentalresearch,theaimoftheanalysisandthechoiceofafitforpurpose analyticalmethodologyarestronglyinterconnectedandshouldbethoroughly assessedbeforehand.Identifyingspecificorganiccompounds(knownorunknown) inacomplexenvironmentalsample(i.e., n 10in Fig.1.1,suchastheidentification andquantificationoforganicpollutantsinawatersample)isdifferentfromaglobal characterizationofthewholeenvironmentalsample[i.e., n 1000in Fig.1.1,suchas thecharacterizationofnaturalorganicmatter(NOM)].Regardlessofusingatargeted oruntargetedanalyticalapproach,akeyobjectiveofanalyticalchemistryhasbeenthe continuousimprovementanddevelopmentofanalyticalmethodologiescapableof reducingacomplexproblemintomanageabledatasets.Astheenvironmentalproblemscontinuetogrowevermorechallenging,thelevelofcompositionalidentification hasevolvedtowardtheintegrationofdifferentanalyticaldimensionstoreachtheresolutionnecessaryforthedetectionandidentificationofabroaderrangeofmolecular structures.Thefollowingsectionsintendtohighlightthosemultidimensionalanalyticalapproachesthatcanenticetheresearcherstocopewiththecomplexityofenvironmentalsamplesand,thus,discoveryetunknownnewmolecules.
Multidimensionalnuclearmagneticresonance(NMR) spectroscopyinenvironmentalresearch NMRspectroscopyhasunquestionablemeritsinthestructureelucidationoforganic structuresincomplexmixtures.Thehighreproducibility,aswellasthenondestructive andnoninvasivecharacteristicsofNMRspectroscopyarekeyadvantagesforemploying thistechniqueinenvironmentalresearch.NMRcanbeappliedforin-depthstudiesof mostenvironmentalmatrices,includingliquid,gels,andsolidsamples,orevenforthe elucidationoforganicstructurespresentinallphasesinunalteredenvironmental samples [58].ThisfeatureofNMRreliesonthedifferenttechniquesavailable,thus makingNMRspectroscopyapivotalanalyticaltooltounravelthecomplexityofthe countlessmolecularstructurestypicallyfoundinvariousenvironmentalsamples (Fig.1.2).TheNMRtechniquesavailableincludesolution-stateNMR,solid-state NMR,gel-phaseNMR,andcomprehensivemultiphase(CMP)NMRspectroscopy. Foramorein-depthdiscussionofallthesetechniques,experimentalprotocols,and applicationsintheanalysisofenvironmentalcomplexmatrices,thereaderisencouragedtorefertothereviewworksofSimpsonetal. [7,59],Maoetal. [8],andDuarte andDuarte [10],aswellasto Chapters2 and 3.Here,itisintendedtohighlightthe advantageofusingtheseNMRtechniques,particularly2DNMR,toacquireawealth ofinformationonthemolecularbonds,structures,andinteractionswithinthecomplex organicfractionpresentinwater,soils,sediments,andairparticles.
Solution-stateNMRspectroscopyinenvironmentalresearch Solution-stateNMRisideallysuitedtoacquirecomprehensivemolecularinformationof complexorganicmatricesthatarenaturallysoluble,suchasthedissolvedorganic matter(DOM)fromice [60] andwater [20,61],butalsotheorganicmatterisolated fromsoils [7] andairparticles [11,62–64].Undoubtedly,solution-stateone-dimensional (1D) 1HNMRtechniquehasaprimepositionasatoolforrapidscreeningand determinationofthegeneralstructuralpropertiesofsuchcomplexorganicmixtures. Althoughprovidingarelativelybroad1DprofileofDOM,onecanstillwithdraw excellentcompositionalinformationonthesample,includingnear-quantitative dataonthedifferent 1HfunctionalgroupswithC-Hbonds,aslongasthespectraarecarefullyacquired,processed,andinterpreted.Thesesemiquantitativeapproacheshavebeen used,forexample,toassessthemoleculardivergencewithinDOMfromdifferent wetlands [61] ortoshedlightonthedominantsourcesofatmosphericorganicaerosols atdifferentlocations(i.e.,sourceapportionment) [65].Thewell-knowndownsideof solution-state1D 1HNMRofcomplexorganicmatricesisthataccuratequalitative andquantitativestructuralassessmentishamperedbythehighdegreeofoverlap characterizingthesespectra.Threemainreasonscanexplainthisspectraloverlap: (1)theresonancesaredispersedoveralimited 1Hchemicalshiftrange (δH 0–10ppm),(2)thepresenceoforganiccompoundswithresemblingstructural features,forwhichthecorresponding 1HNMRspectraareverysimilar,and(3)the presenceofahighnumberofcompoundsresonatinginthesamelimitedspectralregion.
Fig1.2 Seefigurelegendsonnextpage
Oneappealingsolutiontoovercomethespectraloverlappingissueistorelyon solution-statemultidimensionalNMRspectroscopy.Themultidimensionalapproach hasthehighadvantageofofferingamuchbetterdiscriminationofresonances than1DNMRasthepeaksarespreadalongasecondorthirddimension(1Hor 13C frequencies),thusenhancingthereliabilityofNMRassignmentsandallowthe identificationofmolecularfragments,viahomonuclear(1H-1H)andheteronuclear (1H-13C)connectivityinformation [7,66].Undoubtedly,themostimportantmultidimensionalsolution-stateNMRexperimentsappliedintoenvironmentalresearch arethe2DNMRtechniques,including(a) 1H-1HhomonuclearCOSYandTOCSY, whichprovideconnectivityinformationbetweenprotonsthataredirectlyattachedto adjacentcarbons(COSY),orregardingagivenprotonthatisinteractingwithother protonsofthesamestructurewhicharewithinthespinsystem(unbrokenchainof couplings)oftheatom(TOCSY);(b) 1H-13CHSQC,whichdetectsH-Ccouplings overonebondandprovideschemicalshiftdataforbothatomsinaC-Hunit; and(c) 1H-13CHMBC,whichprovidesdirectevidenceaboutthebondingofH-C fragmentsovertwo-andthree-bondrange(i.e.,H-C-C orH-C-C-C) [67].The combinationof 1H-1Hhomonuclear(COSYand/orTOCSY)with 1H-13Cheteronuclear (HSQCandHMBC)connectivityinformationisapowerfulapproachforassignmentof signals,allowingahigherspectralresolutionand,therefore,greaterdetailontheC-H backboneofthesubstructurespresentincomplexorganicmatricessuchasthoseof NOM [7,11,20,61–63,65,68].Recently,anisotope-filtered nDNMR methodology—acombinationofisotopictaggingand nDNMR—wasdevelopedto characterizephenolicmoietiesofhumicmolecules [69].Theprinciplewasillustrated
Fig.1.2 Solution-state,solid-state,andcomprehensivemultiphaseNMRspectroscopy employedinthestructuralcharacterizationofdifferentenvironmentalmatrices. Reprinted(adapted)withpermissionfromJ.T.V.Matos,R.M.B.O.Duarte,S.P.Lopes, A.M.S.Silva,A.C.Duarte,Persistenceofurbanorganicaerosolscomposition:decodingtheir structuralcomplexityandseasonalvariability,Environ.Pollut.231(2017)281–90, https://doi. org/10.1016/j.envpol.2017.08.022 (Copyright(2017),withpermissionfromElsevier),R.M.B.O. Duarte,S.M.S.C.Freire,A.C.Duarte,Investigatingthewater-solubleorganicfunctionalityof urbanaerosolsusingtwo-dimensionalcorrelationofsolid-state13CNMRandFTIRspectraldata, Atmos.Environ.116(2015)245–52, https://doi.org/10.1016/j.atmosenv.2015.06.043 (Copyright (2015),withpermissionfromElsevier),X.Cao,G.R.Aiken,R.G.M.Spencer,K.Butler,J. Mao,K.Schmidt-Rohr,NovelinsightsfromNMRspectroscopyintoseasonalchangesinthe compositionofdissolvedorganicmatterexportedtotheBeringSeabytheYukonRiver, Geochim.Cosmochim.Acta181(2016)72–88. https://doi.org/10.1016/j.gca.2016.02.029 (Copyright(2016),withpermissionfromElsevier),D.Courtier-Murias,H.Farooq,H. Masoom,A.Botana,R.Soong,J.G.Longstaffe,etal.,ComprehensivemultiphaseNMR spectroscopy:basicexperimentalapproachestodifferentiatephasesinheterogeneoussamples,J. Magn.Reson.217(2012)61–76, https://doi.org/10.1016/j.jmr.2012.02.009 (Copyright(2012), withpermissionfromElsevier),andM.TabatabaeiAnaraki,R.DuttaMajumdar,N.Wagner,R. Soong,V.Kovacevic,E.J.Reiner,etal.,Developmentandapplicationofalow-volumeflow systemforsolution-stateinVivoNMR,Anal.Chem.90(2018)7912–21, https://doi.org/10.1021/ acs.analchem.8b00370 (Copyright(2018)AmericanChemicalSociety).
usinga4D 13CH3O-filteredNMRexperiment,whichcorrelateschemicalshiftsoffour nuclei—thearomaticCHatoms ortho tomethoxygroupsandthoseof 13CH3Oatoms. Theinformationgatheredonthemultiplechemicalshiftsandcouplingconstantshave ledtotheidentificationofthemajorsubstitutionpatternsofninephenolicaromaticmoietiesofapeatsoilfulvicacid [69],andtheprospectofapplyingothertagscontaining NMR-activenuclei(e.g.,suchas 15Nand 31P).
Regardlessofthesolution-statemultidimensionalNMRexperimentemployedin thestructuralcharacterizationofcomplexorganicmixtures,itisadvantageousto extract/isolate/preconcentratetheorganiccomponentfromtheoriginalenvironmental matrix,particularlywhendealingwithwater,soil,orsedimentsamples.Theoutcome ofthepreprocessingsampleprocedureistwofold:(1)itdecreasestheheterogeneityof thesample,byenrichingtheisolatedfractionsinthoseorganicspeciesthatare targetedbythephysicochemicalmechanismsgoverningtheirextraction,and(2) removestheparamagneticspeciesthatinterferewithNMRsignalacquisition,thus enhancingboththesensitivityandresolutionofthespectra.Analternativewayof improvingNMRdetectionofuniquemolecularstructureswithincomplexorganic mixtures,suchasthoseofnaturalorganicmatter,isthroughthechromatographic separationofthesematricesintosimplifiedfractionspriortoofflineNMRdetection. AsshownbyWoodsetal. [21,45],improveddiscretestructuralassignmentswithin DOMarereadilyattainableusingmultidimensional[1D,2D,andthree-dimensional (3D)]NMRforthecharacterizationofsimplifiedchromatographicDOMfractions. MultidimensionalNMRdataprovidedarangeofconnectivityandchemicalshift informationthatisnotapparentfromtheunfractionatedDOMmaterial [21,45] Ithasbeenalsoshownthatsolution-statemultidimensionalNMRcanbeusedto characterizecomplexenvironmentalsampleswithlimited[e.g.,water-solubleorganic matter(WSOM)fromatmosphericaerosols [62]]orevenwithnopreconcentration procedure(e.g.,DOMfromice [60],aswellasrivers,lakes,andtheocean [70–72]).Theapplicationofimprovedwatersuppressiontechniqueshasallowed theacquisitionofmeaningfulNMRspectraandthesubsequentcharacterization oftheorganicmatteratitsnaturalabundanceinalmostunalteredenvironmentalsamples.Althoughprovidingcompositionalinformationontheorganicconstituentswithoutpretreatment,thesestructuraldataareacquiredattheexpensesoflongtimesof analysis,whichusuallypreventstheapplicationofthisprocedureonaroutinebasis.
Solid-stateNMRspectroscopyinenvironmentalresearch Solid-stateNMRistraditionallyperformedondriedsamples(100–500mgofsample massisrequired)andalsowidelyemployedtoinvestigatethestructureofNOMfrom diverseenvironmentalmatrices.Inthisregard,thereaderisencouragedtorefertothe reviewworksofMaoetal. [8],Cook [73],andDuarteetal. [10] ontheapplicationof solid-stateNMRspectroscopytoNOMstudiesfromwater,soils,andatmospheric particulateorganicmatter.Inasimilarwaytosolution-stateNMR,high-quality solid-stateNMRdataofenvironmentalsamplescanbeobtainedifconcentrating theorganicmatterbyremovingtheparamagneticspeciesfromthecomplexmatrix, typicallybyusingasolid-phaseextractionprocedure.
13Cisthemostcommonlydetectednucleusinsolid-stateNMRofenvironmental samples.Duetothelownaturalabundanceand,therefore,lowsensitivityof 13Cdetection,cross-polarization(CP)incombinationwithmagicanglespinning(MAS)is oftenusedtoenhancethe 13Csignal.DuringCP,themagnetizationispassedfrom protontocarbonforenhancingthesignal;however,thisfeatureisalsothemaindrawbackofCP-MAS,sinceitdoesnotdetectnonprotonatedcarbons(e.g.,carbonatoms ofcarboxylicgroups,orcarbonfromfusedaromaticrings)ormobilesegmentswith weakH–Cdipolarcouplings [74].Toachieveaquantitativeassessmentofallcarbon functionalgroupspresentinasample,directpolarization(DP)combinedwithMAS shouldbeperformed [75].However,theacquisitionofasolid-state 13CDP-MAS NMRspectrumismoretime-consumingthanthatofaCP-MASspectrum.Recently, anewmethodhasbeendevelopedthatyieldsquantitativesolid-stateMAS 13CNMR spectraoforganicmaterialswithgoodsignal-to-noiseratios.Themultiplecrosspolarization(multiCP)techniquedevelopedbyJohnsonandSchmidt-Rohr [74] providesquantitativeinformationaboutallcarbonatoms,typicallyreducingthemeasuringtimebymorethanafactorof50comparedtoquantitative 13CDP/MAS [74]. Thesolid-statemultiCP 13CNMRtechniqueaidbytheapplicationofsuitably designedradiofrequencypulsesequencesallowstargetingsubspectraofspecific typesoffunctionalgroups,suchassp3-hybridizedonly,nonprotonatedcarbons (e.g.,aromaticC-C,andanomericO-C-OandanomericO-C(R,R0 )-Ogroups),mobile CH3 groups,OCH3,immobileCHn-only(i.e.,CH2 andCH),CH2-only,andCH-only carbonsinNOMfromvariousorigins [48,75,76].Thecombinationofdifferent spectral-editingtechniques,whichhavebeendescribedindetailbyMaoetal. [8], couldallowtheidentificationofatleast27differentfunctionalgroupsin 13C NMRspectraofcomplexNOM,incontrasttolessthan10typicallydistinguished intheliteraturebasedonsimple,routine 13CCP-MASNMRspectroscopy.Additional advantagesofthesolid-state13CNMRapproachhasbeenrecentlyreviewedbyDuarte etal. [10],andinclude(1)thedistinctivefeatureofbeinganondestructivetechnique, leavingthesampleavailableforothercomplementarychemicalanalyses;(2)itfacilitatesamuchhighersampleconcentrationthansolution-stateNMR,enhancingsignalsandsavinginstrumenttime;(3)thetechniquedoesnothavesomeofthe problemsreportedforsolution-stateNMRanalysesofNOM,includingsolventeffects onthechemicalshiftsofthesample,potentialmaskingofcertainsamplechemical shiftsduetosolventsignals,andlimitedsolubilityoftheorganicmaterialinthe selectedsolvent;(4)thedetectionofnonprotonatedcarbonsusingsolid-state 13C NMRisstraightforward;and(5)themacromolecularstructuresand/orcolloidswithin NOMslowthetumblingofthesemolecules,leadingto T2 valuesthataretooshortto allowmanyofthepulsesequencesofsolutionNMRtobesuccessfullyused [8,73]. NOMapplicationsofnucleiotherthan 13Chavebeenalsoreportedforsolid-state NMR,includingboth 15Nand 31Pnuclei.AsrecentlyreviewedbyMaoandcoworkers [8], 15NCP-MAShasbeentheprimarysolid-stateNMRtechniqueusedforstudying organicnitrogenformsinNOMfromsoil,water,sediments,coal,andkerogen. However,acquiringameaningful 15NCP-MASNMRspectraofsuchcomplexNOM matricesisratherdifficult.Analternativesolid-stateNMRtechnique, 13C{14N}
saturationpulse-induceddipolarexchangewithrecoupling(SPIDER),hasbeensuccessfullyemployedtoinvestigatethechemicalnatureofnitrogeninNOMbydetecting 13C bondedtonitrogen [8,77,78] 31PsolidsNMRhavebeenreportedformarineDOM [79] andbulksoils [80],beingsuccessfullyusedfortheidentificationofdifferentphosphorus formsandfortheevaluationoftheirdynamicsinthestudiedsamples.
Solid-state2D 1H-13Cheteronuclearcorrelation(HETCOR)NMRispossibleand hasprovedextremelyusefulforassessingthrough-space 1H-13Ccorrelationsand, therefore,acquirevaluableinformationonthestructureofthesurroundingsofcarbon functionalgroups [8,48,75,78].This2Dsolid-stateNMRtechniqueallowstheidentificationofconnectivitiesorproximitiesofdifferentfunctionalgroups(e.g.,aromatic andalkyl),beingparticularlyusefulfortheidentificationofthenearestprotonsfor nonprotonatedcarbons,suchasCOO/NC ]O [75] orquaternarycarbons [48]
ComprehensivemultiphaseandinvivoNMRforanalysis ofnaturalsamples Comprehensivemultiphase(CMP)NMR,whichintegratesthecapabilitiesofsolutionstate,solid-state,andgel-stateNMRintoasingleapproach,allowstodetectand differentiateallliquids,solutions,andgelsinunalteredsamplesintheirnaturalstate. Gel-phaseNMR,alsoreferredtoashigh-resolutionmagicanglespinning(HR-MAS) NMR,involvesthestudyofsamplesthatare“swellable”and/orinthegelphase [7]. Thesamplesconstituentsareanalyzedafterbeingswolleninapenetratingsolvent (e.g.,DMSO-d6)ortheycanbeanalyzedintheirundriednaturalstatewith wateractingasthenatural“solvent” [7].Forexample,theHR-MAShashugepotential fortheanalysisofsoil,plantmaterials,atmosphericparticles,andsmallorganismsin theirswollensate [59].Insoil,forexample,HR-MASprovidesinformationonthe structuresandassociationsoforganiccomponentsatthesolid-waterinterface [81].Combinedwithsolution-andsolid-stateNMRtechniques,aswellasediting-basedexperimentsasinCMP-NMR,itcanprovideamultidimensionaldetailedinsightintothe organizationofsoilcomponentsandhowthedomainsandassociationschangewith pHandsolvent [12],usingsamplesthatareintheirunalteredstate.Thisapproachhas beenalsoappliedtoexamineoil-contaminatedsoil [82],tostudythemolecularinteractionsandfateduringcontaminantsequestrationinurbansoil [9],aswellasforinvivo2D 1H-13CHSQCidentificationofmetabolitesin 13Cenrichedlivingorganisms [59,83–86], andexaminationofplantsstructureandfunctionintheirnativestate [87]
High-resolutionmassspectrometryinenvironmental research High-resolutionmassspectrometry(HR-MS)(addressedin Chapter4)isanothersignificantanalyticaladvanceandholdsgreatpromiseinstudiesofcomplexmaterials,such asNOMfromaqueous [1,2,20,61,77,88–90],soils [6,91,92],extraterrestrialorganic matter [19],andorganicmatterinatmosphericaerosols [18,47,93] andrainwater [94] samples.ThemostsignificantadvantageofHR-MStechniquesintheanalysisof
complexmixturesistheirabilitytoprovidehighpeakcapacityandhighmeasurement throughputnecessarytoassignaccuratemolecularweightsand,thus,molecularformulastotheindividualcomponents,withouttheneedforpriorseparation.Asdiscussedby MayandMcLean [44],multidimensionalseparationsbasedonHR-MStechniques exhibitpeakcapacitiesapproaching100,000orgreaterandarecapableofveryhigh peakproductionratesrangingfrom100,000peakspersecondforOrbitrapMS [FouriertransformMS(FTMS)]toover100millionpeakspersecondfortime-of-flight (TOF)MS.Electrosprayionization(ESI)combinedwithFouriertransformioncyclotron resonance(FT-ICR)-MShasbecomeaprevailingmethodtoassignmolecularformulas tothousandsofmoleculesinasinglecomplexorganicmatrix [89].ESIisa“soft”ionizationtechniquethattransfersionsfromsolutiontothegasphasewithminimal fragmentationbeforetheyaresubjectedtoMSanalysis [89].Whiletheapplication ofthisapproachisfairlystraightforwardforwater-solubleNOMfractions,itisof limitedutilityforpoorlysolublematerials,suchassoilorganicmatterunlessone canextractthisorganiccomponentwithlittleornochemicalalteration [6].
AtypicalFT-ICRmassspectrumofcomplexorganicmixtures,suchasthoseof NOM,containsthousandsofindividualpeaks,eachrepresentingauniquemolecular mass,signalmagnitude,andaspecificmolecularformula [89].OncesuchHRmass spectraareobtained,twoimportantissuesneedtobeaddressed:(1)separatenoisefrom analytepeaksinordertoavoidassigningfalsemolecularformulas [90] and(2)find adequatewaystovisualizeandreducetheacquiredcomplexmultidimensionaldata sets [89].IntegratingadditionalseparationdimensionswithFT-ICR-MSprovides additionalcompositionalinformation,butitaddstothecomplexityofanalyzinglarge datasetsproducedbythehyphenatedHR-MSmethod [95].
Inordertoaddressthefirstissue,RiedelandDittmar [90] haverecentlyproposeda newdetectionlimitmethodfortheanalysisofNOMviaFT-ICR-MS,allowingto identifypeaksthatcanreliablybedistinguishedfromnoise.Asexplainedbythe authors,thismethodrequirestheanalysisofreplicateblanks,aprocedureusually implementedtocheckforimpuritiesorcontaminations.Thenoisepeaksfound intheblanksarethenusedtodefinethesignaluncertaintyofthenoise,andpeaks thatareindistinguishablefromthisnoisecanreadilyberemovedfromrealsamples, withsoftwarehelp [90].ThesecondissueinFT-ICR-MSstudiesofcomplexsamples isdatapresentationandexploitation.AspointedoutbyReemtsma [89,96], FT-ICR-MSdatasetsofcomplexorganicmatrices,suchasthoseofNOM,arenot onlylargebutalsomultidimensional,whereforonemoleculethenumberofseveral elementsisknown(C,H,Oasaminimum,butalsoofN,S,and/orP),togetherwithits molecularmass,signalintensity,andretentiontimeincasethatchromatographicseparationisemployed.The2DvanKrevelendiagram(Fig.1.3),whichplotstheH/C ratiosofthemoleculesagainsttherespectiveO/Cratios [89,96,97],isthemost widelyusedgraphicalrepresentationofFTICR-MSdata,producinganillustration ofdifferentcompoundclassesbasedonthemolecularformuladataofthemolecules withinthecomplexmatrix.The2DvanKrevelendiagramcanbefurtherexpandedtoa 3Drepresentation,byaddingionabundanceoranothermolarratio(N/C,S/C)asthe z-axis [97].AsexplainedbyReemtsma [89,96],thevanKrevelendiagramhasitsown disadvantagesbecauseitnormalizestothecarbonnumber,thusdiscardingalargeset ofinformation:differentmoleculesthatexhibitsimilarO/CandH/Cratiosplotatthe
Fig.1.3 SchematicrepresentationoftheVanKrevelendiagramofmajorcompoundclasses identifiedinDOMsamples.
AdaptedfromtheworksofR.L.Sleighter,P.G.Hatcher,Theapplicationofelectrospray ionizationcoupledtoultrahighresolutionmassspectroscopyforthemolecularcharacterisationof NOM,J.MassSpectrom.43(2008)854–64, https://doi.org/10.1002/jms,andA.Nebbioso,A. Piccolo,Molecularcharacterizationofdissolvedorganicmatter(DOM):acriticalreview,Anal. Bioanal.Chem.405(2013)109–24, https://doi.org/10.1007/s00216-012-6363-2.
samepointinthediagram,thuslosinganymass-dependentinformation.Reemtsma [96] suggestedanalternativegraphicalrepresentation,byplottingthenumberof carbonsineachformulavsitsnominalmass(CvsM),wherethemoleculesare classifiedintodifferentcategoriesbasedontheirsumofcarbonandoxygenatoms. However,thisCvsMapproachhasnotbeenemployedasmuchasthevanKrevelen diagramintheFTICR-MSanalysisofcomplexorganicmatrices.
AlthoughFT-ICR-MShasbeenprovedtobehighlysuitableforresolvingthousands ofmolecularformulaswithinacomplexorganicmixture,itsuseincombinationwith othertechniques,forexample,2DNMRspectroscopy(e.g., 1H-1HCOSYandTOCSY and 1H-13CHSQC)offersunsurpassedmolecularresolutionallowinganin-depth descriptionofmolecularskeletonandfunctionalgroupsofthestudiedsamples [19, 20,61,92,98].Forexample,Hertkornetal. [61] usedthismultidimensional FT-ICR-MSand2DNMRapproachtodescribeandcomparethecompositionalfeatures ofDOMinsubtropicalwetlandsfromdifferentregionsaroundtheglobe[Everglades (USA),Pantanal(Brazil),andtheOkavangoDelta(Botswana)],whichareunderthe influenceofdifferentorganicmattersourcesandfloodingevents.Withthisnewmultidimensionalanalyticalwindow,theauthorsconcludedthatwetlandDOMsamples sharevariousmolecularfeatures;however,eachDOMsamplewasuniqueinitscomposition,reflectingspecificenvironmentaldriversand/orspecificbiogeochemicalprocesses [61].Astheneedtogetadeeperinsightintothemoleculardiversityofunknown complexenvironmentalmatricesincreases,thecombineduseofmultidimensional HR-MSandNMRtoolsrepresentsamajorsteptowardanimprovedunderstanding oftheenvironmentalimportanceofsuchcomplexmixtures.
Two-dimensionalcorrelationspectroscopy inenvironmentalresearch 2Dcorrelationspectroscopy(Chapter5)isaversatilechemometrictechniqueintroduced byIsaoNoda(e.g.,Refs. [99–102] referencestherein),whichhasstartedtobecomepopularinenvironmentalresearchinthelast10years.The2Dcorrelationspectroscopyhas beenmostlyusedtoresolveandbetterassignoverlappedpeakstypicallyshowninconventional1DNMRandFouriertransforminfrared(FTIR)spectraofcomplexorganic mixturesfromwater [17,42,103,104],sediments [105],atmosphericparticles [43],and biofilms [106].In2Dcorrelationspectroscopy,thesampleunderspectroscopicstudyis subjectedtoanexternalperturbation(e.g.,temperature,pH,orsalinity),whichinduces systematicvariationsinthespectralsignalintensity.Theobtainedsetofspectra observedasafunctionoftheperturbationvariableisthentransformedintoasetof 2Dcorrelationspectrabyaformofcrosscorrelations,whichdefinestructuralrelationships [99] (anexampleofsuch2Dcorrelationspectraisshown Fig.1.4;inthiscasefor WSOMinatmosphericparticles [43]).Forexample,Abdullaetal. [42,103] appliedthe
Fig.1.4 ExampleofasynchronousmapgeneratedfromCP-MAS 13CNMRspectraof atmosphericaerosolWSOMsamplescollectedduringdifferentseasons,wherethetopandthe rightsidearetheaverage 13CNMRspectra.Redandbluerepresentpositiveandnegative correlations,respectively.
Reprinted(adapted)withpermissionfromR.M.B.O.Duarte,S.M.S.C.Freire,A.C.Duarte, Investigatingthewater-solubleorganicfunctionalityofurbanaerosolsusingtwo-dimensional correlationofsolid-state13CNMRandFTIRspectraldata,Atmos.Environ.116(2015)245–52, https://doi.org/10.1016/j.atmosenv.2015.06.043 (Copyright(2015),withpermissionfromElsevier).
2Dcorrelationtechniqueonasetof 13CNMR, 1HNMR,andFouriertransforminfrared (FTIR)spectraofhighmolecular-weightDOMsamplesisolatedalongasalinitytransect.Bycombininginsightsfromthesespectralprobes,eithercorrelatingthesameor differentspectroscopicprobes(asinhetero-spectral2Dcorrelations)alongthesameperturbation(salinity),theauthorsconcludedthattheDOMsamplesconsistsofthreemajor components[i.e.,heteropolysaccharides(HPS),carboxyl-richalicyclicmolecules (CRAM),andamide/aminosugars]thathavedifferentbiogeochemicalreactivities [42].The2Dcorrelationmapsinvolving 1HNMRspectrafurtherrevealedthemajor compoundclasseswithineachcomponent—forexample,itwassuggestedthatHPS encompassthreemajorcompoundclasses(N-acetylaminosugars,6-deoxysugars, andsulfatedpolysaccharidecompounds),whereasCRAMconsistsofatleasttwocompoundclasses(lignin-likeandcarboxylicfunctionalgroupsofaliphaticnature) [103]
Anotherexampleofcouplingbetween 13CNMRandFTIRprobesthrough2DcorrelationanalysishasbeenusedtogleannewstructuralinformationonWSOMfromfine urbanairparticlescollectedduringdifferentseasons,withthemedianofairtemperature withineachseasonastheperturbationvariablethatpromptstheobservedspectralfeatures [43] (Fig.1.4).ItwasconcludedthattheWSOMsamplesconsistsofatleasttwo classesofcompounds:oneisrichinbothcarboxylicandhydroxylfunctionalgroupsand ithasanaliphaticcharacter,andtheotherentailslignin-derivedstructures [43].
The2DcorrelationanalysishasbeenalsoperformedbetweenFT-ICR-MSand 13C NMRspectraofDOMsamplesfromasalinitytransect [88].Thegenerated2Dcorrelationmapdistributedthemassspectralpeaksbasedontheircorrelationwithspecificcarbonfunctionalgroups(namely,HPSandlignin/CRAM-likecomponents) detectedinthe 13CNMRspectra.AsstatedbyAbdullaetal. [88],thistypeof hetero-spectral2Dcorrelationanalysishasthepotentialtoexpandouranalyticalwindowtowardadeeperunderstandingofcomplexorganicmixturescontainingthousandsofcomponents,thusallowingtogleanin-depthknowledgeonthemolecular structuralfeaturesanddynamicsofsuchcomplexmixtures.Regardlessoftheselected spectroscopicprobe,itisclearthatthestructuralinformationobtainedbymeansof2D correlationanalysiscanbehardlyretrievedbyusingasinglespectroscopic techniquealone.
Fluorescencespectroscopyinthecharacterization ofenvironmentalsamples Excitation-emissionmatrix(EEM)fluorescencespectroscopyisahighsensitivityand nondestructive3Dtechnique,widelyusedtocompareanddiscernthedynamicsand transformationsofchromophoricdissolvedorwater-extractedorganicmatterin diverseenvironmentalmatrices(freshwater [1,16,107],estuaries [108,109],wetlands [61],soil [110],andatmosphericparticles [13,14,111]).OneadditionalexampleoftheuseofEEMfluorescencespectroscopyforthecharacterizationofDOMin anaquaticecosystemcanbefoundin Chapter6
TheacquisitionofanEEMfluorescencespectruminvolvesthecollectionof sequentialfluorescenceemission(Em)spectraatsuccessivelyincreasingexcitation
(Ex)wavelengths.TheEmspectraobtainedareconcatenatedtoproduceaplotin whichthefluorescenceintensityisdisplayedasafunctionofExandEmwavelengths. ThemainfluorescentgroupsinDOMstudiesthathavebeenidentifiedcorrespondto humic-like,protein-like(tyrosine-andtryptophan-like),andpigment-likesubstances [112,113].EEMfluorescencespectroscopycombinedwithparallelfactoranalysis (PARAFAC)modelinghasmadeitpossibletofurtherresolvethecomplex3D EEMspectraintoitsdominantfluorescentcomponentsandquantifyeachcomponent’scontributiontothetotalfluorescence.Inthisregard,thereaderisencouraged torefertothetutorialofMurphyetal. [114] inthepracticalapplicationofPARAFAC tofluorescencedatasets,usingaDOMfluorescencedataset.Forexample,Singhetal. [109] usedEEM-PARAFACtoexaminethecompositionaldistributionandchromophoricDOMvariabilityinanestuarinesystem.Fourcomponentswereidentifiedby thePARAFACmodel,withthePARAFACsamplescoresbeingusedtoexamine probablelinkagestowetlands,agriculturalsources,andotherwaterbodies.Hertkorn etal. [61] alsousedEEM-PARAFACtodiscriminatechromophoricDOMsamples fromthreesubtropicalwetlands[Everglades(USA),Pantanal(Brazil),andOkavango Delta(Botswana)].Inthiscasestudy,theauthorsreportedanalogiesintheDOMfluorescencepropertiesforthethreewetlandsinsuchawaythatthegeneratedEEMPARAFACmodelwasperfectlyapplicabletothethreewetlands.Whenappliedto investigatethefluorescencefeaturesofchromophoricWSOMinatmosphericaerosols fromdifferentenvironments(urban,forest,marine,andpristine),EEM-PARAFAC aidedintheclassificationandsourceidentificationofchromophoresinatmospheric organicaerosols [13,14,111].TheacquiredEEM-PARAFACdataisofutmost importancetoshedlightonthepivotalroleplayedbytheWSOMintheopticalpropertiesandphotochemicalreactivityofatmosphericorganicaerosols.
AnadditionalinterestingapplicationofEEM-PARAFACanalysiswasshownby Woodsetal. [21],combiningchromatographicseparation(bypolarity)withoffline solution-statemultidimensionalNMRintothecharacterizationofSuwanneeRiver DOMfractions.FindingssuggestedthatboththestructuralfeaturesfromNMRand EEM-PARAFACcomponentsvarywithpolarity [21].Themajorityofthefluorescencesignalsweredominantinthemosthydrophobicfractionswhichwerefound tobeenrichedinstructuresderivedfrombothcyclicandlinearterpenoids [21].The hydrophilicmaterial,ontheotherhand,washighlycorrelatedwithcarbohydrate-type structuresaswellashighcontributionsfromaminoacidfluorescence [21].Thiscombinedapplicationofmultidimensionalanalyticaltechniquessetthebasisfornewanalyticstrategiesaimingatthemolecular-levelidentificationandfurtherunderstanding oftheorigin,structure,fate,andchemicalreactivityofcomplexenvironmental matrices.
Comprehensivetwo-dimensionalchromatography inenvironmentalanalysis One-dimensionalgasandliquidchromatography(1D-GCand1D-LC,respectively) areundoubtedlysuccessfulanalyticalseparationtoolsinenvironmentalanalysis. When1Dchromatographicseparation,evenafteranoptimizationprocess,stillis
insufficienttoachieveagoodresolutionbetweenco-elutedcompounds,particularly whendealingwithcomplexenvironmentalsamples,itbecomesnecessarytoupgrade theanalyticalprocessbyaddingtwoormoredifferentseparationmechanismsinorder totakefulladvantageofcouplingadvanceddetectionsystems(e.g.,HR-MS).Inthis context,comprehensive2Dgasandliquidchromatography(GC GCandLC LC, respectively)havebecomeattractiveanalyticalapproaches,offeringincreasedpeak capacityandselectivityrelativetoconventional1D-GCand1D-LCseparations, respectively.BothGC GCandLC LCinvolvetheuseoftwoindependent separationmechanisms(i.e.,orthogonal),separatedbyaninterfacecalledmodulator, oftenreferredtoasthe“heart”ofGC GCorLC LC [27,115].Thismodulation interfacehasthefunctionoftransferringfractionsofthefirst-dimension(1D)effluent tothesecond-dimension(2D)column,whilepreservingtheintegrityof 1Dseparation. InbothGC GCandLC LC,thewholesampleissubjectedtomultidimensionaland independentseparationmechanisms,ensuringthattheseparationachievedinany previousdimensionismaintainedinthefollowingone.Inthismethodology,the obtainedchromatogrammustberepresentativeoftheentiresampleand,forthis reason,itisnecessarythatthewholesamplepassesthroughthedetectororatleast inapercentagethatguaranteesitsrepresentativeness [116].Multiplereviewshave discussedthetheoreticalandpracticalaspectsofGC GCandLC LC,including thefundamentalprinciples,instrumentalinnovations,parameteroptimization,and dataprocessingapproaches [26–28,30,37].Inthisregard,interestedreadersshould refertothesereviewworksforadditionalinformationontheaspectsofLC LC and/orGC GCmethoddevelopment.Thissectionsolelyaimstoprovideabrief flavorofthediversityofstudiesusingLC LCandGC GCinenvironmental analysisastheseareaddressedin Chapters7 and 8,respectively.
LC LChasbeenappliedinadiversityofareas,includingbiochemicalanalysis, pharmaceuticalanalysis,analysisofTraditionalChineseMedicines,andpolymer analysis.ReadersinterestedinoneoftheseLC LCapplicationsshouldrefer totherecentreviewworksofStollandCarr [26] andPiroketal. [27].Althoughthere isagreatpotentialtoapplyLC LCinenvironmentalresearch,thisareaisstillin itsearlystages.Thehugecomplexityofenvironmentalmatrices,infact,placesa greatdemandintermsofresolutionpower,challenginganalyststochoosethemost appropriatecolumnswithorthogonalselectivitiesforeachseparationdimension,as wellasaninformation-richdetector.Nonetheless,oneoftheattractivefeaturesfor applyingLC LCintheanalysisofcomplexenvironmentalsamplesisthatitadds additionalinformationonthesesamples(e.g.,polarity,size,andelectrophoretic mobility),whichenhancestheinterpretationoftheirphysicochemicalcomposition, especiallywhenhyphenatedwithMSdetection.Mostenvironmentalstudiesusing LC LCcoupledtohigh-resolutiondetectorshavefocusedeitherontheidentification andquantificationofasmallgroupofpolarcompounds(i.e.,targetedanalysis) [53,117–119] orinthenonselectivesearch(i.e.,untargetedanalysis)andcharacterizationofunknowncomponentsinasample [23–25,51].Bothanalyticalapproaches requireLC LCmethodoptimization(e.g.,couplingofhighlycomplementary(i.e., orthogonal)separationmodes,mobilephasescompositioninbothdimensionsand theircompatibility,flowrates,andtimeofanalysis),aswellasseparationofbackgroundinterferencesfromtheanalytesandaccuracyinthegeneratedLC LCdata.
Givenitsuniversalapplicability,theimportanceofLC LCisexpectedtogrowrapidlyinenvironmentalresearch.Infact,untargetedanalysesusingLC LCcoupledto MSdetectionisapowerfultoolwiththecapabilityofrevealingnewcompositional andyethiddenstructuraldetailsofcomplexenvironmentalsamples,thusavailing newpathwaysofinvestigation—andthisresearchfieldisonlyatitsbeginning.
TheastoundingseparationpowerofferedbyGC GChyphenatedtoeitheruniversalorselectivedetectors,enticestheresearcherstousethisapproachforthetargeted nonpolarcompoundanalysisinenvironmentalmatrices [28,30].UnlikeLC LC, onecanfindintheliteratureahugenumberofenvironmentalstudiesmorefocused onthechemicalinformationprovidedbyGC GCcoupledtoanH-MSdetector ratherthanontheperformanceandoptimizationofthewholemultidimensional analyticaltechnique.Recently,MuscaluandGo ´ recki [28] presentedasystematic reviewofthemostrecentapplicationsofGC GCcoupledwithHR-MSdetectors intheanalysisofpersistentorganicpollutantsinwater,wastewater,leachates,soil, sediments,sludge,andbiota.Thetargetedanalytesincludehydrocarbons,polycyclic aromatichydrocarbonsanditsderivatives,polychlorinatedbiphenylsandpesticides, benzothiazoles,benzotriazolesandbenzosulfonamides,nonylphenolsandtheirderivatives(e.g.,fromproductionofplasticsandsurfactants),steroids,syntheticmusks, personalcareproducts,andpharmaceuticals [28].Complexatmosphericorganic aerosolscontainingvolatileandsemivolatilecompoundshavebeenalsosuccessfully determinedwithGC GC-basedmethods [55].AshighlightedbyMuscaluand Go ´ recki [28],GC GCalsoallowstheseparationofmanyconstituentsofpreviously unresolvedcomplexmixturesofcontaminants.WhenhyphenatedwithaHR-MSor otherMSdetectors,thisGC GCapproachoffersunsurpassedresourcesforthe nonselectivesearchofadiversityoforganicpollutantgroupsthatmightbeenvironmentallyrelevantbutarenotroutinelyanalyzed.Forexample, Chapter8 highlights howGC GCcoupledwithHR-MSdetectionenablesabetterunderstandingof theimpactofenvironmentalexposuresonhumanhealth.Thischapterdiscusses howGC GC-HR-MSmethodsarebeingusedaskeyanalyticalresourcesforthe identificationandquantificationofawiderangeofanalytes(e.g.,persistentorganic pollutants,dibenzo-p-dioxins,andaromaticamines),sometimesfoundonlyintrace amounts,inbodyfluids(e.g.urine,blood,andbreath).
Synchrotron-basedtechniquesasmultidimensional analyticaltools Theliteratureshowsthattwoimportantsynchrotron(Sr)-basedtechniques—Sr-FTIR andnear-edgeX-rayabsorptionfinestructure(NEXAFS)—canbeusedforelemental speciationaswellasanalysisofthebulkpropertiesandspatialdistributionofcarbon formsinenvironmentalsamples,particularlyinsoils [31,35,120,121].Animportant strengthoftheSr-basedtechniquesisthehighspatialresolutionatthefinescale, whichallowstodrawamultidimensionalmapofthechemicalenvironmentsof organiccarbon,minerals,metals,andmicrobialhabitatsindifferentenvironmental matrices [31,35,36,104,120,122,123].Theabilitytopotentiallydiscernorganic 16
carbonfunctionalgroupsandtheirpixel-scaleassociationswithotherelementsinthe formofmultidimensionalmapsandonscalesofnano-andmicrometerswithinany givensample,maysignificantlyenhancethecurrentunderstandingofthemechanisms responsiblefornutrientandcontaminantmobility,reactivity,bioavailability,andfate intheenvironment [35,120].Thereis,however,adownsideofsuchgrain-scalemultidimensionaldistributionoforganiccarbonandassociatedelements.Accordingto LehmannandSolomon [31],significantconstraintsareencounteredwheninformation onsinglemicro-ornanoscalelocationswithinasampleneedstobescaledtoprocesses observedatthemacroscale(e.g.,insoilorlandscapes).Additionalconcernsthatneed tobeconsideredandfurtheroptimizedwhenusingsynchrotron-basedtechniques includesamplepreparationprotocolsthatpreservethespatialassemblage,control ofradiationdamage,sectioningartifacts,andspectralquantification [31].Amajor obstacletothewidespreaduseofsynchrotron-basedtechniquesinenvironmental studiesisrelatedtothelimitednumberofanalyticalfacilitiesavailableandassociated expertisetoconductsuchresearch [121].Therefore,researchersmustbecautious abouttheenvironmentalproblemstheywanttoaddressbymeansofthesesophisticatedanalyticaltechniques.
Conclusions Exploringthechemicalcompositionofdifferentenvironmentalmatrices(air,soil, sediments,water,andlivingorganisms)andthebiogeochemicalprocessestaking placeinthosematrices,involvesmanyunknownsandasnearlymanychallenges. Thedifferentmultidimensionaltechniquesintroducedinthischapterandfurther exploredinthisbook,constituteagreatpromiseinenvironmentalresearch.Integratingmultidimensionalseparationandspectroscopicanalysesatmultiplescales,from smallsolublemoleculestomacromolecules,nanoparticlesorevenlargersizedsamplesisusefulfordecodinghighlyheterogeneousenvironmentalmedia(air,soil,sediments,water,livingorganisms,andbodyfluids)withahighdegreeofspecificity.
Notwithstandingthesophisticatedmultidimensionalanalyticaltechniquesthatare beingusedinenvironmentalresearch,twoadditionalmajorchallengesremain:(1) lackofknowledgeandanalyticalexpertisetodealwithsuchadvancedmultidimensionalapproaches,includingprocessingandinterpretationofthevoluminous andcomplexdatasets,and(2)thedevelopmentofexpertiseforsamplingandmonitoringhighlyheterogeneousenvironmentalmatrices(e.g.,airparticles,waters,soils, andsediments)inanextensiveandregularmanner.Withoutimprovementsinthese importantareas,theuseofmultidimensionalanalyticaltechniqueswillnotbenoteworthyinenvironmentalresearch.
Acknowledgments ThanksareduetoFCT/MCTESforthefinancialsupporttoCESAM(UID/AMB/50017/2019) andprojectAMBIEnCE(PTDC/CTA-AMB/28582/2017),throughnationalfunds(OE).FCT/ MCTESisalsoacknowledgedforanInvestigatorFCTContract(IF/00798/2015).
References [1]A.M.Kellerman,F.Guillemette,D.C.Podgorski,G.R.Aiken,K.D.Butler,R.G. M.Spencer,Unifyingconceptslinkingdissolvedorganicmattercompositiontopersistenceinaquaticecosystems,Environ.Sci.Technol.52(2018)2538–2548, https://doi. org/10.1021/acs.est.7b05513
[2]M.Zark,T.Dittmar,Universalmolecularstructuresinnaturaldissolvedorganicmatter, Nat.Commun.9(2018)1–8, https://doi.org/10.1038/s41467-018-05665-9.
[3]A.T.Lebedev,O.V.Polyakova,D.M.Mazur,V.B.Artaev,Thebenefitsofhighresolutionmassspectrometryinenvironmentalanalysis,Analyst138(2013)6946–6953, https://doi.org/10.1039/c3an01237a.
[4]J.Hollender,E.L.Schymanski,H.P.Singer,P.L.Ferguson,Nontargetscreeningwith highresolutionmassspectrometryintheenvironment:ReadytoGo?Environ.Sci. Technol.51(2017)11505–11512, https://doi.org/10.1021/acs.est.7b02184
[5]M.Krauss,H.Singer,J.Hollender,LC-highresolutionMSinenvironmentalanalysis: fromtargetscreeningtotheidentificationofunknowns,Anal.Bioanal.Chem. 397(2010)943–951, https://doi.org/10.1007/s00216-010-3608-9
[6]M.M.Tfaily,R.K.Chu,N.Tolic,K.M.Roscioli,C.R.Anderton,L.Pas ˇ a-Tolic,etal., Advancedsolventbasedmethodsformolecularcharacterizationofsoilorganicmatter byhigh-resolutionmassspectrometry,Anal.Chem.87(2015)5206–5215, https://doi. org/10.1021/acs.analchem.5b00116.
[7]A.J.Simpson,D.J.McNally,M.J.Simpson,NMRspectroscopyinenvironmental research:frommolecularinteractionstoglobalprocesses,Prog.Nucl.Magn.Reson. Spectrosc.58(2011)97–175, https://doi.org/10.1016/j.pnmrs.2010.09.001
[8]J.Mao,X.Cao,D.C.Olk,W.Chu,K.Schmidt-Rohr,Advancedsolid-stateNMRspectroscopyofnaturalorganicmatter,Prog.Nucl.Magn.Reson.Spectrosc.100(2017) 17–51, https://doi.org/10.1016/j.pnmrs.2016.11.003
[9]H.Masoom,D.Courtier-Murias,R.Soong,W.E.Maas,M.Fey,R.Kumar,etal.,From spilltosequestration:themolecularjourneyofcontaminationviacomprehensive multiphaseNMR,Environ.Sci.Technol.49(2015)13983–13991, https://doi.org/ 10.1021/acs.est.5b03251.
[10]R.M.B.O.Duarte,A.C.Duarte,NMRstudiesoforganicaerosols,in:G.A.Webb(Ed.), AnnualReportsonNMRSpectroscopy,92,AcademicPress,Oxford,2017,pp.83–135, https://doi.org/10.1016/bs.arnmr.2017.04.003.
[11]J.T.V.Matos,R.M.B.O.Duarte,S.P.Lopes,A.M.S.Silva,A.C.Duarte,Persistence ofurbanorganicaerosolscomposition:decodingtheirstructuralcomplexityand seasonalvariability,Environ.Pollut.231(2017)281–290, https://doi.org/10.1016/j. envpol.2017.08.022
[12]H.Masoom,D.Courtier-Murias,H.Farooq,R.Soong,B.P.Kelleher,C.Zhang,etal., Soilorganicmatterinitsnativestate:unravellingthemostcomplexbiomaterialonEarth, Environ.Sci.Technol.50(2016)1670–1680, https://doi.org/10.1021/acs.est.5b03410.
[13]J.T.V.Matos,S.M.S.C.Freire,R.M.B.O.Duarte,A.C.Duarte,Naturalorganicmatterin urbanaerosols:comparisonbetweenwaterandalkalinesolublecomponentsusing excitation–emissionmatrixfluorescencespectroscopyandmultiwaydataanalysis, Atmos.Environ.102(2015)1–10, https://doi.org/10.1016/j.atmosenv.2014.11.042.
[14]Q.Chen,Y.Miyazaki,K.Kawamura,K.Matsumoto,S.Coburn,R.Volkamer,etal.,Characterizationofchromophoricwater-solubleorganicmatterinurban,forest,andmarine aerosolsbyHR-ToF-AMSanalysisandexcitation–emissionmatrixspectroscopy,Environ. Sci.Technol.50(2016)10351–10360, https://doi.org/10.1021/acs.est.6b01643 18
[15]A ´ .Andrade-Eiroa,M.Canle,V.Cerda ´ ,Environmentalapplicationsofexcitationemissionspectrofluorimetry:anin-depthreviewII,Appl.Spectrosc.Rev.48(2013) 77–141, https://doi.org/10.1080/05704928.2012.692105.
[16]S.A.Baghoth,S.K.Sharma,G.L.Amy,Trackingnaturalorganicmatter(NOM)inadrinkingwatertreatmentplantusingfluorescenceexcitation-emissionmatricesandPARAFAC, WaterRes.45(2011)797–809, https://doi.org/10.1016/j.watres.2010.09.005
[17]H.A.N.Abdulla,P.G.Hatcher,Dynamicsofdissolvedorganicmatter:aviewfromtwo dimensionalcorrelationspectroscopytechniques,J.Mol.Struct.1069(2014)313–317, https://doi.org/10.1016/j.molstruc.2014.03.038
[18]A.S.Willoughby,A.S.Wozniak,P.G.Hatcher,Detailedsource-specificmolecularcompositionofambientaerosolorganicmatterusingultrahighresolutionmassspectrometry and1HNMR,Atmosphere7(2016), https://doi.org/10.3390/atmos7060079.
[19]N.Hertkorn,M.Harir,P.Schmitt-Kopplin,NontargetanalysisofMurchisonsoluble organicmatterbyhigh-fieldNMRspectroscopyandFTICRmassspectrometry,Magn. Reson.Chem.53(2015)754–768, https://doi.org/10.1002/mrc.4249
[20]N.Hertkorn,M.Harir,B.P.Koch,B.Michalke,P.Schmitt-Kopplin,High-fieldNMR spectroscopyandFTICRmassspectrometry:powerfuldiscoverytoolsforthemolecular levelcharacterizationofmarinedissolvedorganicmatter,Biogeosciences10(2013) 1583–1624, https://doi.org/10.5194/bg-10-1583-2013
[21]G.C.Woods,M.J.Simpson,P.J.Koerner,A.Napoli,A.J.Simpson,HILIC-NMR:toward theidentificationofindividualmolecularcomponentsindissolvedorganicmatter,Environ.Sci.Technol.45(2011)3880–3886, https://doi.org/10.1021/es103425s.
[22]P.F.Brandao,A.C.Duarte,R.M.B.O.Duarte,Comprehensivemultidimensionalliquid chromatographyforadvancingenvironmentalandnaturalproductsresearch,TrAC TrendsAnal.Chem.116(2019)186–197, https://doi.org/10.1016/j.trac.2019.05.016.
[23]A.S.Paula,J.T.V.Matos,R.M.B.O.Duarte,A.C.Duarte,Twochemicallydistinctlightabsorbingpoolsofurbanorganicaerosols:acomprehensivemultidimensionalanalysisof trends,Chemosphere145(2016), https://doi.org/10.1016/j.chemosphere.2015.11.093
[24]J.T.V.Matos,S.M.S.C.Freire,R.M.B.O.Duarte,A.C.Duarte,Profilingwater-soluble organicmatterfromurbanaerosolsusingcomprehensivetwo-dimensionalliquid chromatography,AerosolSci.Technol.49(2015), https://doi.org/10.1080/02786826. 2015.1036394.
[25]T.A.Brown,B.A.Jackson,B.J.Bythell,A.C.Stenson,Benefitsofmultidimensional fractionationforthestudyandcharacterizationofnaturalorganicmatter, J.Chromatogr.A1470(2016)84–96, https://doi.org/10.1016/j.chroma.2016.10.005.
[26]D.R.Stoll,P.W.Carr,Two-dimensionalliquidchromatography:astateofthearttutorial, Anal.Chem.89(2017)519–531, https://doi.org/10.1021/acs.analchem.6b03506.
[27]B.W.J.Pirok,D.R.Stoll,P.J.Schoenmakers,Recentdevelopmentsintwo-dimensional liquidchromatography:fundamentalimprovementsforpracticalapplications,Anal. Chem.91(2019)240–263, https://doi.org/10.1021/acs.analchem.8b04841
[28]A.M.Muscalu,T.Go ´ recki,Comprehensivetwo-dimensionalgaschromatographyin environmentalanalysis,TrendsinAnal.Chem.106(2018)225–245, https://doi.org/ 10.1016/j.trac.2018.07.001.
[29]D.C.Hilton,R.S.Jones,A.Sj€ odin,Amethodforrapid,non-targetedscreeningforenvironmentalcontaminantsinhouseholddust,J.Chromatogr.A1217(2010)6851–6856, https://doi.org/10.1016/j.chroma.2010.08.039.
[30]J.V.Seeley,S.K.Seeley,Multidimensionalgaschromatography:fundamentaladvances andnewapplications,Anal.Chem.85(2013)557–578, https://doi.org/10.1021/ ac303195u.
[31]J.Lehmann,D.Solomon,Organiccarbonchemistryinsoilsobservedbysynchrotronbasedspectroscopy,in:B.Singh,M.Grafe(Eds.),DevelopmentsinSoilScience, vol.34,ElsevierMassonSAS,2010,pp.289–312, https://doi.org/10.1016/S01662481(10)34010-4
[32]D.Hesterberg,I.McNulty,J.Thieme,SpeciationofsoilphosphorusassessedbyXANES spectroscopyatdifferentspatialscales,J.Environ.Qual.46(2017)1190–1197, https:// doi.org/10.2134/jeq2016.11.0431
[33]S.Legros,P.Chaurand,J.Rose,A.Masion,V.Briois,J.H.Ferrasse,etal.,Investigation ofcopperspeciationinpigslurrybyamultitechniqueapproach,Environ.Sci.Technol. 44(2010)6926–6932, https://doi.org/10.1021/es101651w.
[34]S.Peth,C.Chenu,N.Leblond,A.Mordhorst,P.Garnier,N.Nunan,etal.,Localizationof soilorganicmatterinsoilaggregatesusingsynchrotron-basedX-raymicrotomography, SoilBiol.Biochem.78(2014)189–194, https://doi.org/10.1016/j.soilbio.2014.07.024.
[35]J.Lehmann,D.Solomon,J.Kinyangi,L.Dathe,S.Wirick,C.Jacobsen,Spatialcomplexityofsoilorganicmatterformsatnanometrescales,Nat.Geosci.1(2008)238–242, https://doi.org/10.1038/ngeo155
[36]P.M.Kopittke,P.Wang,E.Lombi,E.Donner,Synchrotron-basedX-rayapproachesfor examiningtoxictracemetal(loid)sinsoil-plantsystems,J.Environ.Qual.46(2017) 1175–1189, https://doi.org/10.2134/jeq2016.09.0361
[37]J.T.V.Matos,R.M.B.O.Duarte,A.C.Duarte,Trendsindataprocessingofcomprehensivetwo-dimensionalchromatography:stateoftheart,J.Chromatogr.BAnal.Technol. Biomed.LifeSci.910(2012), https://doi.org/10.1016/j.jchromb.2012.06.039.
[38]B.K.Lavine,J.Workman,Chemometrics,Anal.Chem.85(2013)705–714, https://doi. org/10.1021/ac303193j.
[39]M.Brege,M.Paglione,S.Gilardoni,S.Decesari,M.CristinaFacchini,L.R.Mazzoleni, Molecularinsightsonagingandaqueous-phaseprocessingfromambientbiomassburningemissions-influencedPoValleyfogandaerosol,Atmos.Chem.Phys.18(2018) 13197–13214, https://doi.org/10.5194/acp-18-13197-2018
[40]A.Vergnoux,R.DiRocco,M.Domeizel,M.Guiliano,P.Doumenq,F.Theraulaz, Effectsofforestfiresonwaterextractableorganicmatterandhumicsubstancesfrom Mediterraneansoils:UV–visandfluorescencespectroscopyapproaches,Geoderma 160(2011)434–443, https://doi.org/10.1016/j.geoderma.2010.10.014.
[41]Y.Li,M.Harir,M.Lucio,M.Gonsior,B.P.Koch,P.Schmitt-Kopplin,etal.,Comprehensivestructure-selectivecharacterizationofdissolvedorganicmatterbyreducing molecularcomplexityandincreasinganalyticaldimensions,WaterRes.106(2016) 477–487, https://doi.org/10.1016/j.watres.2016.10.034.
[42]H.A.N.Abdulla,E.C.Minor,P.G.Hatcher,Usingtwo-dimensionalcorrelationsof13C NMRandFTIRtoinvestigatechangesinthechemicalcompositionofdissolvedorganic matteralonganestuarinetransect,Environ.Sci.Technol.44(2010)8044–8049, https:// doi.org/10.1021/es100898x
[43]R.M.B.O.Duarte,S.M.S.C.Freire,A.C.Duarte,Investigatingthewater-solubleorganic functionalityofurbanaerosolsusingtwo-dimensionalcorrelationofsolid-state13C NMRandFTIRspectraldata,Atmos.Environ.116(2015)245–252, https://doi.org/ 10.1016/j.atmosenv.2015.06.043.
[44]J.C.May,J.A.McLean,Advancedmultidimensionalseparationsinmassspectrometry: navigatingthebigdatadeluge,Annu.Rev.Anal.Chem.9(2016)387–409, https://doi. org/10.1146/annurev-anchem-071015-041734.
[45] G.C.Woods,M.J.Simpson,A.J.Simpson,Oxidizedsterolsasasignificantcomponent ofdissolvedorganicmatter:evidencefrom2DHPLCincombinationwith2Dand3D
