Evaluation of capacitively coupled microwave plasma atomic emission spectrometer for the determination of lead in whole blood PDF
Preview Evaluation of capacitively coupled microwave plasma atomic emission spectrometer for the determination of lead in whole blood
EVALUATIONOFACAPACITIVELYCOUPLEDMICROWAVEPLASMA ATOMICEMISSIONSPECTROMETERFORTHEDETERMINATIONOFLEAD INWHOLEBLOOD By MICHAELWALLACEWENSING ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1994 ACKNOWLEDGEMENTS Firstandforemost,mythanksgotowardmyparentswhoalwayssupportedme andneverrestrictedmeinwhateverIdid. Fortheirfriendshipandsupport, IwouldliketothankCheriMorgan, Cheryl Davis,DennisHueber,TyeBarber,WesHoy,andSophiaDixon. Professionally,Imustthankmyhighschoolchemistryteacher.Dr.MacElroy, whoinitiallyencouragedmetopursuechemistryandgavememyfirst"C". Drs.Harold BellandJimWolfeprovidedmewithascholarshipatVirginiaTech,keptupwithmy progress, and taught mehow tobeindependentatalarge university. In addition. Dr.I.C. Chu was kind enough toprovidethree months ofindustrial experience at DuPont. Finally,myprofessionalexperiencewasroundedoutbyDr.BenSmithand Dr.JimWinefordnerwhocontributedsubstantiallytomyknowledgeofmolecularand atomicspectroscopy. 11 TABLEOFCONTENTS ACKNOWLEDGEMENTS « ACRONYMKEY vi ABSTRACT TCHHEAPDTEETRER1MINATIONOFLEADINWHOLEBLOOD 1 Introduction 1 LeadSources 1 LeadToxicity 2 ReferenceRange 4 CurrentNeedsfortheDeterminationofPbinBlood 5 PotentialScreeningMethods 5 AtomicAbsorptionApproaches 8 Delves Cup Flame Atomic Absorption Spectrometry (FAAS) 8 Electrothermal Atomization - Atomic Absorption Spectrometry(ETA-AAS) 9 AnodicStrippingVoltammetry(ASV) 9 EmissionMethods 11 DCArc 11 DirectCurrentPlasma(DCP) 12 InductivelyCoupledPlasma(ICP) 12 Conclusions 13 CHAPTER2 PLASMAEXCITATIONSOURCESINATOMICEMISSIONSPECTROSCOPY 14 Introduction 14 GeneralPlasmaParameters 14 PlasmaExcitationSources 16 InductivelyCoupledPlasma(ICP) 16 DirectCurrentPlasma(DCP) 17 MicrowaveInducedPlasma(MIP) 18 CapacitivelyCoupledMicrowavePlasma(CMP) 19 iii MicrosamplingintoaPlasma 20 LiquidPlugTechniques 20 ElectrothermalVaporizationTechniques 21 DirectInsertionTechniques 22 FlowInjectionAnalysis 23 Conclusions 24 CHAPTER3 CAPACITIVELYCOUPLEDMICROWAVEPLASMAINSTRUMENTATION 26 Introduction 26 Magnetrons 26 Waveguides 27 InstrumentationUsedinThisWork 34 DeterminationoftheOptimumLengthandPositionoftheElectrode ... 46 Experimental 46 Results 46 Conclusions 50 CHAPTER4 THEDETERMINATIONOFLEADINAQUEOUSSAMPLESUSING DSI-CMP-AES 51 GeneralIntroduction 51 SelectionofWavelength 51 SelectionofElectrodeMaterial 60 EvaluationoftheHePurgeTime 63 FlowRateOptimization 73 79 PowerOptimization 79 CalibrationCurve 79 Conclusions 88 CHAPTER5 THEDETERMINATIONOFLEADINWHOLEBLOODBYDSI-CMP-AES . 93 CharacterizationofWholeBloodat405nm 93 CharacterizationofthePlasmaAshingStepusingAqueousSamples .... 106 RadialandAxialProfiles 109 OptimizationoftheAshingTime 115 PercentRecoveryStudy 118 DeterminationofAccuracy 125 Conclusions 146 CHAPTER6 CONCLUSIONSANDFUTUREWORK 148 SummaryofResults 148 IV FutureWork 148 NickelCups 148 MatrixModifiers 149 FeedbackRegulationoftheAshingStep 150 OtherThermalAshingTechniques 150 RedesignofthePlasmaTorch 150 REFERENCES 152 BIOGRAPHICALSKETCH 160 V ACRONYMKEY Theacronymsthatwereusedinthisdissertationaredefinedbelow. Someofthe acronymsusedinthisdissertationarecomposedofcombinationsofsimpleacronyms which havebeenjoinedbyahyphen, Only thesimpleacronymshavebeen shown below. Acronvm Definition AAS Atomicabsorptionspectrometry. ACorac Alternatingcurrent. AES Atomicemissionspectrometry. ALA Aminolevulinicacid. ALAD Aminolevulinicaciddehydrase. ASV Anodicstrippingvoltammetry. CDC U.S.CentersforDiseaseControl(Atlanta). CMP CapacitivelyCoupledMicrowavePlasma. DCordc Directcurrent. DCP Directcurrentplasma. DSI Directsampleinsertion. ETA Electrothermalatomization. ETV Electrothermalvaporization. FAAS Flameatomicabsorptionspectrometry. FIA Flowinjectionanalysis. VI FWHM Fullwidthathalfmaximum. ICP Inductivelycoupledplasma. ID Isotopedilution. LC Liquidchromatography. MIP Microwaveinducedplasma. MS Massspectrometry. NAA Neutronactivationanalysis. NHANES National health and nutrition examination survey. ppb Partsperbillion. ppm Partspermillion. ppth Partsperthousand. QCM Qualitycontrolmaterial. RSD Relativestandarddeviation. SFC Supercriticalfluidchromatography. TE Transverseelectric. TM Transversemagnetic. TTL Transistor-transistorlogic. Vll AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy EVALUATIONOFACAPACITIVELYCOUPLEDMICROWAVEPLASMA ATOMICEMISSIONSPECTROMETERFORTHEDETERMINATIONOFLEAD INWHOLEBLOOD By MichaelWallaceWensing August1994 Chairperson: JamesD.Winefordner MajorDepartment: Chemistry Thedeterminationofleadinwholebloodhasbecomeofparamountimportance astheCentersforDiseaseControlinAtlantahasrecently(1991)loweredthe"levelof concern" for lead inblood to 10 ^g/dL. This action invalidated the mostpopular screeningtechniquethatwaspreviouslyused,theindirectdeterminationofleadinblood byhematofluorometryoferythrocyteprotoporphyrin, whichcannotdetermineleadat levelsbelow25tigldX. Thisworkevaluatedtheuseofacapacitivelycoupledmicrowaveplasmaatomic emissionspectrometerforthedeterminationofleadinwholeblood(CMP-AES). This CMP-AESincorporatedatungstenwireelectrodewhichwasusedbothtosupportthe plasmaandtoholdthesample. Thesamplewasdepositedontheelectrodeanddriedat lowmicrowavepowers. Followingthis,alow-powerheliumplasmawasignitedand viii allowedtoashthe sample. Finally, thepowerwas increased which resultedinthe atomizationand excitation oflead. The resulting lead emission was detected as a transientsignalusingamonochromatorandaphotodiodearraydetector. Suchadevice improvesuponotheratomicemissiondevicesas100%ofthesamplewastransferredinto theplasma. Detectionlimitsaslowas0.6ppb(3pgPb)weredeterminedforaqueous sampleswithaprecisionbetterthan10%. Detectionlimitsaslowas4ppb(20pgPb) wereobtainedforleadinwholebloodwithaprecisionof16%atconcentrationsaslow as 80ppb. These detectionlimitsrival thoseofelectrothermal vaporizationatomic absorption spectrometry, and are better than those obtained by inductively coupled plasmaatomicemissionspectrometry. IX ‘ CHAPTER1 THEDETERMINATIONOFLEADINWHOLEBLOOD Introduction Leadisabundantintheenvironment,originatingmostlyfromindustrialsources. It is not essential for the human body and has no beneficial role.* At high concentrations, itistoxic. Adultsarelesssusceptibletotheeffectsofleadpoisoning thanchildren. Leadpoisoningissilentassymptomsofleadpoisoningarenotreadily discemable. Although a massive effort had been launched by the U.S. and other countriesoftheworldtoreduceleadexposure^,ithasrecentlybeenrealizedthatlead is toxic at lower concentrations than was previously thought.* Therefore, further reductiontoleadexposureisnecessary. Bloodscreeningmethodsareusedtodetermineanindividualsexposuretolead. Consideringthatthelevelofconcernforleadinbloodhasbeenlowered*,moresensitive methodsneedtobedeveloped. Potentialnewscreeningmethodsareunderevaluation.^ Thegoaloftheresearchinthisdissertationwastoevaluateonepotentialmethodforthe evaluationofleadinblood. LeadSources Industrialsourcesarethemajorsourceofleadexposure,andtheatmosphereis themajorrouteofcontamination. Anthropogenicactivitiestransfer700timesmorelead intotheenvironmentthannaturalcauses."* Thetotalemissionofleadintothe 1
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