汞记忆效应消除.docx

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ThemeasurementofmercuryinaqueoussolutionsbyICP-AESisadverselyaffectedbythememoryeffectwhereinmercuryaccumulateswithinthesampleintroductionsystemandisslowlyreleasedovertimetogive
・・・pT・・・p・
(II)complexants:thioureaandgold(III)(II)inaqueoussolutionsbyICP-AESunderroutineoperatingconditionsthatcanbeappliedtoothermetalionsbyadding1mgofgold(III)chlorideper3mgofmercury(II)tothosesolutions.
Introduction
Thetoxicityofmercuryatverylowlevelshasledtoitsstringentcontrolwitha
maximumcontaminantlevelof2“g/LbeingsetbytheUSEnvironmentalProtection
Agency[1].Thishasledtothedevelopmentoftechniquesforaccuratemonitoringofmercurylevels[2]viacoldvaporatomicabsorptionspectrometry[3,4],plasmaatomicemissionspectrometry[5],atomicfluorescencespectrometry[6,7],inductivelycoupledplasma(ICP)opticalemissionspectrometry[8]andICP-massspectrometry[9-11].Despitemethodswithgoodsensitivityandselectivity,fewcandirectlymeasureHg(II)inaqueoussolutionsunderroutineoperatingconditionsascanbedonewithotherions[12].Mercuryaccumulatesininstrumentsirrespectiveofitsinitialthereisagradualincreaseofthemercurysignalstrengthwithtime,anon-linearcalibration,andalongwash-outtime[13].Mercurycontaminationoftheinstrumentsmaybeattributedtoitsadsorptiononthetransfertubing,spraychamberandnebulizer[14].
MercuryinsolutionexistsasanequilibriumofHg(0),Hg(I),andHg(II).
SinceonlyHg(0)isvolatile,onemethodofeliminatingthememoryeffectentailscompletereductionofthemercurytoHg(0)withthereducingagentsstannouschlorideandsodiumborohydride[15].[16][17].Thegenerationofmercuryvapordoes,however,requireadditionalequipmentforitsgenerationandmeasurement.
AnalternativetechniqueinvolvesthestabilizationofmercuryinsolutionasHg(II).Gold(III)chlorideandpotassiumdichromatearetypicalstabilizingagentsthatgivecompleteconversiontoHg(II)thusobviatingvolatilization[18].ThetechniquehasbeenappliedtothemeasurementofmercuryviaICP-massspectrometry(MS)[19].TheadditionofchelantsthatbindHg(II)-100,ammoniaandEDTAallowsfortheaccuratemeasurementofmercuryinaqueoussolutionsbyICP-MS[20].Theuseof2-mercaptoethanolreducesthememoryeffecttothepointthatICP-[21].
Techniqueshavebeendevelopedtoallowtheuseofcoldvaporcoupledatomicabsorptionspectrometry(CVAAS)[22]andICP-[23].WhileICPisthusanexcellenttechniqueformercurydetermination,itsextensiontothemorecommonlyavailableICP-atomicemissionspectroscopy(AES)remainsproblematicduetothememoryeffect[24].Itisreasonabletoexpectthatmercury-stabilizingagentsaddedtosolutionswouldeliminatethememoryeffectinICP-AESastheyhavewithICP-%L-cysteinesolutioncontainingHg(II),butonlyat
averylowlevel(1yg/L),obviatesthememoryeffectinICP-AES[25].Wenowreportarapidandaccuratemethodforthedeterminationoftotalmercuryinaqueoussolutionsatthemg/LlevelusingICP-AESthroughacomparativestudyofgold(III)chloride,triethylamine,ethylenediaminetetraaceticacid(EDTA),disodiumethylenediaminetetraacetate(Na2EDTA)andthiourea.
Experimentalsection
Reagents
Mercurysolutionsarepreparedbydilutinga1000mg/Lmercury(II)%(III)solutionsarepreparedfroma1000mg/,ethylenediaminetetraaceticacid(EDTA),disodiumEDTA(Na2EDTA),andthiourea(analyticalgrade).
Instrumentation
ASpectroflameM120E(SpectroanalyticalInstruments)inductivelycoupledatomicemissionspectrometer(ICP-AES)-(alsoappropriatefortheanalysisofothertransitionmetalions).

Mercury(II)(II)/Lwerepreparedin50mLvolumetricflasksalsocontainingoneofthefollowing:Au(III),%triethylamine,EDTA(saturatedsolution),%Na2EDTA,%thiourea(followingreportsintheliteraturewithICP-MS,%TritonX-100wasaddedtotheamineandthioureasolutionsasawettingagent).(III),Na2EDTAandthioureasolutionswerepreparedbydilutionoftheir1%(),(II)(III)/Lwerepreparedbysuccessivedilutionof1000mg/LHg(II)andAu(III),nanopurewateracidifiedwith1%nitricacidwasusedtowashthesampleintroductionsystemandtheinstrumentallowedtostabilizefor15-,thesamplesolutionaspiratedintotheICP-AES,(1M)(III)/Lwereusedtorinsethesampleintroductionsystembetweensamplesfor1-2min.
Results
(II)-(II),,,spraychamberand/-more,:(II)solutionisused,amercurysignalwithintensityof166410cpsisstillobserved().ThissignificantmemoryeffectobviatestheroutineanalysisofHg(II)byICP-AESwithouttheadditionofmercury-stabilizingagents.
TEA,EDTA,Na2EDTA,thioureaandgold(III)chloridearecomparedtodeterminewhichcanmosteffectivelystabilizeHg(II)thuseliminatingthememoryeffectintheICP-()andhighbackgroundconcentrationscanaffectplasmatemperatureandnebulization,,%andtheAu(III);thesaturatedEDTAsolutionhadthesameAu(III),EDTA,Na2EDTA,thiourea,orgold(III)chlorideisaddedtothemercury
,-,
measurementwhile,withEDTAandNa2EDTA,%inthemaximummercurysignalintensitythoughtheinitialmercuryresponseisstillmuchgreaterthanthatoftheAu(III)-.
Whilecomplexantswithnitrogen-andsulfur-basedligandsareknowntoformstableHgcomplexes(.,immobilizedtertiaryaminesdisplayahighaffinityforHg(II)fromdilutesolutionsafteracontacttimeoflessthan30min[26]andsolublethioureacancomplexHg2+andCH3Hg+fromaqueoussolutions[27]),(Table2).Thoughthesituationimprovescomparedtotheresultswitha1hcontacttime,theincreaseinmercurysignalresponseremainsevidentwithTEA,EDTA,andNa2EDTA.(ThememoryeffectisevidentwithNa2EDTAevenaftera5-daycontacttime.)Thelengthycontacttime,however,clearlydiminishes,andmayeliminate,thememoryeffectwhenthioureaisusedasthecomplexant.
Table3showstheeffectofaddingvaryingamountsofAu(III).0mg/Leliminatesthememoryeffect:(III)(II).5%.Au(III)(II),gold(III)chlorideistheagentofchoiceforstabilizingthemercurysignal.
Alinearcalibrationcurvewasobtained(brN=-)(III)/LandincreasinglevelsofHg(II)(,,,,,).,chloride,|Jg/,contactingasolutioncontaining10mgHg(II)/Lwithcrosslinkedpolystyrenebeadsbearingimmobilizeddimethylamineligandsfor17hgaveICP-AESspectrathatwerenearlyidenticaltothebaselineofablanksolution,indicatingaHg(II)leveloflessthan10Jg/L.
InordertodeterminethelowerlimitoftheAu:Hgratio,sixsolutionsof10mgHg(II)/,,,,,(III)/L(Table4).Threemeasurementswererecordedforeachsolution;(III)/LwasusedtowashthesampleintroductionsystembetweenHg(II)-,followedbythesolutionswithlowergoldlevels,,(.,,,,)werethenpreparedagainforre-investigationandtostudytheeffectofAu(III),fromlefttoright;,,()andasteadyHg(II)(II)signaliftheintensitiesarereadinasequencefrommoreconcentratedtolessconcentratedAusolutions(Table4)orlessconcentratedtomoreconcentratedsolutions(Table5);thisisdiscussedinthefollowingsection.
Discussion
Theresultsclearlyindicatethattheadditionofalowlevelofgold(III)chloridetomercury-(III),thought