Evaluation of capacitively coupled microwave plasma atomic emission spectrometer for the determination of lead in whole blood

170 Pages·1994·5 MB·English

by  Wensing, Michael Wallace, 1967-

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