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1、METHOD7742SELENIUM(ATOMICABSORPTION,BOROHYDRIDEREDUCTION)1.0SCOPEANDAPPLICATION1.1Method7742isanatomicabsorptionprocedurefordetermining3μg/Lto750μg/Lconcentrationsofseleniuminwastes,mobilityprocedureextracts,soils,andgroundwater.Method7742isapprovedforsamplematricesthatcont
2、ainatotalofupto1000mg/Lconcentrationsofcobalt,copper,iron,mercury,andnickel.Asolidsamplecancontainupto10%byweightoftheinterferentsbeforeexceeding1000mg/Linadigestedsample.Allsamplesincludingaqueousmatricesmustbesubjectedtoanappropriatedissolutionsteppriortoanalysis.Spikedsa
3、mplesandrelevantstandardreferencematerialsareemployedtodeterminetheapplicabilityofthemethodtoagivenwaste.2.0SUMMARYOFMETHOD2.1SamplesarepreparedaccordingtothenitricaciddigestionproceduredescribedinMethod3010foraqueousandextractsamplesandthenitric/peroxide/hydrochloricaciddi
4、gestionproceduredescribedinMethod3050(furnaceAAoption)forsediments,soils,andsludges.Excessperoxideisremovedbyevaporatingsamplestonear-drynessattheendofthedigestionfollowedbydilutiontovolumeanddegassingthesamplesuponadditionofurea.Theseleniumisconvertedtothe+4oxidationstated
5、uringdigestioninHCl.Aftera1:10dilution,seleniumisthenconvertedtoitsvolatilehydrideusinghydrogenproducedfromthereactionoftheacidifiedsamplewithsodiumborohydrideinacontinuous-flowhydridegenerator.2.2Thevolatilehydridesaresweptinto,anddecomposein,aheatedquartzabsorptioncellloc
6、atedintheopticalpathofanatomicabsorptionspectrophotometer.Theresultingabsorptionofthelampradiationisproportionaltotheseleniumconcentration.2.3Thetypicaldetectionlimitforthismethodis3μg/L.3.0INTERFERENCES3.1Veryhigh(>1000mg/L)concentrationsofcobalt,copper,iron,mercury,and,ni
7、ckelcancauseanalyticalinterferencesthroughprecipitationasreducedmetalsandassociatedblockageoftransferlinesandfittings.3.2Tracesofperoxidesleftfollowingthesamplework-upcanresultinanalyticalinterferences.Peroxidesmustberemovedbyevaporatingeachsampletonear-drynessfollowedbyrea
8、ctingeachsamplewithureaandallowingsufficienttimefordegassingbeforeanalysis(seeSect
