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1、METHOD7195CHROMIUM,HEXAVALENT(COPRECIPITATION)1.0SCOPEANDAPPLICATION1.1Method7195istobeusedtodeterminetheconcentrationofdissolvedhexavalentchromium[Cr(VI)]inExtractionProcedure(EP)toxicitycharacteristicextractsandgroundwaters.Thismethodmayalsobeapplicabletocertaindomesticandindustrialwastes,provid
2、edthatnointerferingsubstancesarepresent(seeParagraph3.1below).1.2Method7195maybeusedtoanalyzesamplescontainingmorethan5ugofCr(VI)perliter.Eitherflameorfurnaceatomicabsorptionspectroscopy(Methods7190and7191)canbeusedwithcoprecipitation.2.0SUMMARYOFMETHOD2.1Method7195isbasedontheseparationofCr(VI)fr
3、omsolutionbycoprecipitationofleadchromatewithleadsulfateinasolutionofaceticacid.Afterseparation,thesupernate[containingCr(III)]isdrawnoffandtheprecipitateiswashedtoremoveoccludedCr(III).TheCr(VI)isthenreducedandresolubilizedinnitricacidandquantifiedasCr(III)byeitherflameorfurnaceatomicabsorptionsp
4、ectroscopy(Methods7190and7191).3.0INTERFERENCES3.1Extractscontainingeithersulfateorchlorideinconcentrationsabove1,000mg/Lshouldbedilutedpriortoanalysis.4.0APPARATUSANDMATERIALS4.1Filteringflask:Heavywall,1-litercapacity.4.2Centrifugetubes:Heavyduty,conical,graduated,glass-stoppered,10-mLcapacity.4
5、.3Pasteurpipets:Borosilicateglass,6.8cm.4.4Centrifuge:Anycentrifugecapableofreaching2,000rpmandacceptingthecentrifugetubesdescribedinSection4.2maybeused.4.5pHmeter:Awidevarietyofinstrumentsarecommerciallyavailableandsuitableforthiswork.4.6Testtubemixer:Anymixercapableofimpartingathoroughvortexisac
6、ceptable.71951CD-ROMRevision0DateSeptember19865.0REAGENTS5.1ASTMTypeIIwater(ASTMD1193):Watershouldbemonitoredforimpurities.5.2Leadnitratesolution:Dissolve33.1gofleadnitrate,Pb(NO3)2(analyticalreagentgrade),inTypeIIwateranddiluteto100mL.5.3Ammoniumsulfatesolution:Dissolve2.7gofammoniumsulfate,(NH4)
7、2SO4(analyticalreagentgrade),inTypeIIwateranddiluteto100mL.5.4Calciumnitratesolution:Dissolve11.8gofcalciumnitrate,Ca(NO3)2@4H2O(analyticalreagentgrade),inTypeIIwateranddiluteto100mL(1mL=20mgCa).5.5Nitricacid:Con
