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1、METHOD7741ASELENIUM(ATOMICABSORPTION,GASEOUSHYDRIDE)1.0SCOPEANDAPPLICATION1.1Method7741isanatomicabsorptionprocedurethatisapprovedfordeterminingtheconcentrationofseleniuminwastes,mobility-procedureextracts,soils,andgroundwater,providedthatthesamplematrixdoesnotcontainhighconcentrationsofch
2、romium,copper,mercury,silver,cobalt,ormolybdenum.Allsamplesmustbesubjectedtoanappropriatedissolutionsteppriortoanalysis.Spikedsamplesandrelevantstandardreferencematerialsareemployedtodetermineapplicabilityofthemethodtoagivenwaste.IfinterferencesarepresenttheanalystshouldconsiderusingMethod
3、7740.2.0SUMMARYOFMETHOD2.1Samplesarepreparedaccordingtothenitric/sulfuricaciddigestionproceduredescribedinthismethod.Next,theseleniuminthedigestateisreducedtoSe(IV)withtinchloride.TheSe(IV)isthenconvertedtoavolatilehydridewithhydrogenproducedfromazinc/HClorsodiumborohydrate/HClreaction.2.2
4、Thevolatilehydrideissweptintoanargon-hydrogenflamelocatedintheopticalpathofanatomicabsorptionspectrophotometer;theresultingabsorbanceisproportionaltotheseleniumconcentration.2.3Thetypicaldetectionlimitforthismethodis0.002mg/L.3.0INTERFERENCES3.1Highconcentrationsofchromium,cobalt,copper,me
5、rcury,molybdenum,nickel,andsilvercancauseanalyticalinterferences.3.2Tracesofnitricacidleftfollowingthesamplework-upcanresultinanalyticalinterferences.NitricacidmustbedistilledoffthesamplebyheatingthesampleuntilfumesofSO3areobserved.3.3Elementalseleniumandmanyofitscompoundsarevolatile;there
6、fore,certainsamplesmaybesubjecttolossesofseleniumduringsamplepreparation.4.0APPARATUSANDMATERIALS4.1100-mLbeaker.4.2Electrichotplateorequivalent-Adjustableandcapableofomaintainingatemperatureof90-95C.4.3Acommerciallyavailablezincslurryhydridegeneratororageneratorconstructedfromthefollowing
7、material(seeFigure1):CD-ROM7741A-1Revision1September19944.3.1Medicinedropper:Fittedintoasize"0"rubberstoppercapableofdelivering1.5mL.4.3.2Reactionflask:50-mL,pear-shaped,withtwo14/20necks(ScientificGlass,JM-5835).4.3.3Gasinlet-outlettube:Constructedfromamicroc
