Atomic fluorescence spectroscopic methods for ultratrace elemental analysis using a high-repetition rate tunable dye laser and furnace sample atomization PDF
Preview Atomic fluorescence spectroscopic methods for ultratrace elemental analysis using a high-repetition rate tunable dye laser and furnace sample atomization
ATOMICFLUORESCENCESPECTROSCOPICMETHODSFORULTRATRACE ELEMENTALANALYSISUSINGAHIGH-REPETITIONRATETUNABLEDYE LASERANDFURNACESAMPLEATOMIZATION By RICARDOQ.AUCELIO ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1999 ACKNOWLEDGMENTS Iwouldfirstliketothankmyresearchadvisor,Dr.JamesD.Winefordner,for acceptingmeinhisgroupandforallhisguidanceandsupportthroughthepastfour years. IthasbeenatruelearningexperienceJimhasallowedmetoworkwithfreedom andallowedmetointeractwithpostdoctoralresearchersfromseveralpartsoftheworld anddifferentculturesandwithfellowgraduatecolleagues. Dr.BenjaminSmith(Ben) wasalsoafundamentalsupport,providingmeimportantsuggestionsandbackground. Manyfriendlypeopleparticipateddirectlyinthisworkandinotherprojectsin whichIhadtheopportunitytobeinvolved. IamgratefultoDr.NicoloOmeneto,Dr. EugeneWagner,Dr.EdisonBecerra,Dr.DavidPowell,Dr.IgorGomushkin,Dr.Scott Baker,Dr.BrianCastle,MelodyBi,MarkVilloria,ValeriaRubinandCelesteJohnson. I wouldliketoextendtheseacknowledgmentstoallotherpastandpresentmembersofthe group,speciallyDr.AndreaCroslyn,Dr.LeslieKing,Dr.RobinRussel,KrisIngenieri, MikeShepard,andGretchenPotts. IalsoextendthanksJeanneKarably,ToddProx, SteveMilles,andthepeoplefromtheUniversityofFloridaAnalyticalInstrumentation. Iamespeciallygratefultomyfamilyfortheirsupport. AndreiaGerkdeserves particularandspecialgratitude. InherIfoundtheloveandemotionalstrengththatI needed. n I am immensely thankful to Coordenacao de Aperfeicoamento de Pessoal de NivelSuperior(CAPES,Brasil)forthefinancialsupportthatallowedmetoobtainthe degree. FinancialsupportforthisworkwasprovidedbytheUnitedStatesDepartmentof Energy (DOE) and the EngineeringResearch Center(ERC) forParticle Science and TechnologyattheUniversityofFlorida. TABLEOFCONTENTS page ACKNOWLEDGMENTS i ABSTRACT vii CHAPTERS INTRODUCTION 1 1 NeedforUltratraceAnalysis 1 Laser-excitedAtomicFluorescence 2 IntentofDissertation 7 2 LASER-EXCITEDFLUORESCENCESPECTROMETRY 10 Introduction 10 FluorescenceExcitation-DetectionSchemes 12 GeneralFluorescenceFluxEquations 14 Laser-excitedAtomicFluorescence 16 OpticalSaturation 20 FluorescenceAnalyticalCurves 22 EfficiencyofDetection 24 SourcesofNoiseinLEAFS 27 ConcomitantScatter 27 StrayLight 28 BlackbodyEmission 29 MolecularFluorescence 30 Non-analyteAtomicFluorescence 30 OtherInterferencesandNoiseSources 30 3 SAMPLEATOMIZATION 31 Introduction 31 ElectrothermalAtomization 34 AtomizationMechanisms 39 iv MinimizationofInterferencesinElectrothermalAtomization 41 OptimalTemperatureProgram 42 StabilizedTemperaturePlatformFurnace 42 ChemicalModification .... 44 4 EXPERIMENTAL 46 Instrumentation 46 ExcitationSource 48 SampleAtomizer 55 Detection-signalprocessing-acquisitionSystem 55 WavelengthTunning 58 CleaningofGlassware 58 Procedures 58 AnalyteSolutions 58 OtherSolutions 59 Samples 59 Pre-conditioningoftheGraphite 61 MicrowaveDigestion 61 Theory 62 Instrumentation 65 Procedures 68 5 LASER-EXCITEDFLUORESCENCEOFGe,In,ANDPtINA GRAPHITEFURNACE 72 Briefoverviewoftheimportanceandcurrentmethodstodetermine ultratraceconcentrationsofGe,InandPt 72 ResultsandDiscussion 77 ChoiceoftheLaserRepetitionRate 77 OpticalSaturationConditions 78 ImagingConsiderations 81 ChoiceoftheFluorescenceAnalyticalSchemes 85 AtomizationTechniquesandFurnaceParameters 86 LimitingNoises 100 InfluenceofAcidsandBases 100 ChemicalModificationStudies 105 InfluenceofSaltsandPotentialInterferents 112 AnalyticalFiguresofMerit 114 SampleAnalysis 120 Conclusion 138 v 6 FILTERFURNACELASER-EXCITEDATOMICFLUORESCENCE SPECTROMETRYFORTHEDETERMINATIONOFLEADIN WHOLEBLOOD 140 Introduction 140 FilterFurnaceAtomization 142 ResultsandDiscussion 143 PermeabilityoftheFilterandFluorescenceTimeProfile 146 ComparisonofAtomizationTechniquesforBloodAnalysis 148 InfluenceoftheAmountofBloodintheRecoveryand Reproducibility 154 Conclusion 157 7 DETERMINATIONOFTHULIUMBYLEAFSINARHENIUM- LINEDTUBEATOMIZER 160 UltratraceDeterminationofThulium 160 MetallicAtomizers 162 Introduction 162 AtomizationMechanisms 164 IntentoftheChapter 165 ResultsandDiscussion 165 AnalyticalSchemeandLaserRepetitionRate 165 AtomizationandFurnaceParameters:AComparativeStudy BetweenDifferentTubeAtomizer 166 SampleAnalysis 185 Conclusion 187 8 FINALCOMMENTS 190 APPENDIX 193 LISTOFACRONYMS 193 REFERENCES 195 BIOGRAPHICALSKETCH 207 VI AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy ATOMICFLUORESCENCESPECTROSCOPICMETHODSFORULTRATRACE ELEMENTALANALYSISUSINGAHIGHREPETITIONRATETUNABLEDYE LASERANDFURNACESAMPLEATOMIZATION By RicardoQ.Aucelio July1999 Chairman:JamesD.Winefordner MajorDepartment:Chemistry The goal of this work was to develop ultrasensitive methods based on Electrothermalatomizationlaser-excitedatomicfluorescence(ETA-LEAFS)todetermine Ge,In,Pb,PtandTmincomplexsamplessuchasbiologicalandenvironmental. The ultimate goal was to achieve high sensitivity and high selectivity with little sample manipulationandsimplesamplecalibrationprocedures. For In, Ge, and Pt sensitive determination methods (femtogram limits of detection)usingastandardgraphitefurnacetechniqueweredeveloped. Highsensitivity wasachievedbytheproperchoiceofexperimentalparametersandinstrumentaldesign. Ahigh repetitionrate coppervaporpumped dye laserwas employedto probe more efficientlythetransientatompopulationgeneratedintheatomizer. Tubeatomizerswith frontilluminationdetectionschemewasemployedtoincreasethenumberoffluorescent vii atomsdetected,improvethedynamiclinearrangeanddecreaseinterferencesfromthe surrounding atmosphere. Experimental parameters were optimized to maximize the signaltonoiseratio. Specialcareconcerningimagingandsampleatomizationconditions wastakentominimizethenoiselevelreachingthedetectionsystem.Improvementsinthe sampleatomizationefficiencyandminimizationofinterferenceswereachievedbythe choice ofthebest atomizationtechnique, graphite material, use ofmatrix modifiers. Efforts are made to improve sensitivity and minimizing interferences by choosing betweenwallandplatformtechniques,andoptimizingfurnaceparameterstoeliminate samplematrixcomponents. ForPb, aporous graphite filterwas used to develop a filter furnace LEAFS methodallowingthedeterminationofthiselementbysimplecalibrationcurvemethodin wholebloodwithminimumsamplemanipulation. Agraphitetubelinedwithrheniumfoilwasemployedforthedeterminationof Tm.Theperformanceoftherheniumlinedtubewascomparedwithpyrolyticgraphite, W graphitetubescoatedwithcarbideformingelements,andgraphitetubeslinedwith and Ta foils. Abetterperformance interms ofsensitivity, reproducibility and long term stabilitywasachieved. viii CHAPTER 1 INTRODUCTION NeedforUltratraceElementalAnalysis Atomic spectrometry holds a central role in the monitoring ofbiological and environmentalsamplesaswellasinthecharacterizationoftechnologicallyinteresting highpuritymaterials. Theimpactoftraceelementsintheenvironmentandconsequently onman’shealthhasresultedinboththedevelopmentofanalyticalinstrumentationand techniqueswhicharesensitive,selective,accurate,reliableandthatareapplicabletoreal samples.1,2,3 Thenecessityofthedeterminationofultratracelevelsofelementsinthese samplesoftenrequireshighlysensitivestateofthearttechniquescapableoflimitsof detectionbetween0.1pgto0.1fgorevenlower.4 Inmanycases,especiallyinbiological monitoring,thechallengeisevengreatersinceverylimitedsamplesizesareavailable.5 Formostoftheelementspresentintraceamountsandcertainlyforthosepresent inultratraceamounts,verylittleisknownabouttheirexactbiologicalbehavior. The effectsofasubstanceinthehumanbodydependonitsrelativeconcentration. This meansthatatoxicelementcancertainlybeessentialatlowconcentrations;therefore,the analystmustnotonlymonitorthehigherconcentrationsatwhichacertainelementsare toxic, but also learnto determine the often low concentration levels at which these elements are essential.6 In biological systems, there is a growing interest in the 1 2 distributionofelementalcomponentsintissuesandevensinglecellsandmembranes. Thedeterminationofanelementattheconcentrationof1 ngg'1 inanindividualcell weighing1|ug,forexamplewouldrequireanabsolutelimitof1fg.5 Globalecologicalproblemshaveresultedinanincreasingawarenessandinterest intheanalysisofenvironmentalsamples. Concentrationsnogreaterthanpartperbillion or lower are ofconcern in all phases ofthe environment: air, water, soil and the biosphere,andincludeindigenousmetalsaswellasthosederivedfromanthropogenic activities. Highlysensitivetechniquesareespeciallynecessarytoestablish ‘baseline’ levelsofmanyelementsandtoattempttoreconstructthepastnaturaldistributionoftoxic pollutantsonaglobalscale.7 Inmaterialsciences,thereisagreatdemandforhighlysensitivetechniquessince propertiesofultrahighpuritymetals,highperformanceceramicsandmicroelectronic componentscanbeexpectedtobeaffectedbyforeignatomsorimpurityconcentrations oftheorderof10'12%.5 Laser-excitedAtomicFluorescence Laser-basedtechniquesare,inmanyoccasions,theonlychoiceforanalysisand areespeciallyindicatedintwosituations. First,formicroanalysis,wheretheabsolute detectionlimitofatechniqueistheimportantparameterratherthantheconcentration detectionlimit. Thisisasuitabledomainforlaser-basedtechniquesduetotheabilityto detectatomswithahighsensitivityinasmallvolumeduringashorttime.Second,when thesensitivity,selectivity,andfreedomfrommatrixinterferencesneedstobeenhanced.
The list of books you might like
