EPA METHOD 7199 Determination of Hexavalent Chromium

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1、METHOD7199DETERMINATIONOFHEXAVALENTCHROMIUMINDRINKINGWATER,GROUNDWATERANDINDUSTRIALWASTEWATEREFFLUENTSBYIONCHROMATOGRAPHY1.0SCOPEANDAPPLICATION1.1Thismethodprovidesproceduresforthedeterminationofhexavalentchromiumindrinkingwater,groundwater,andindustrialwastewat

2、ereffluents.1.2ThemethoddetectionlimitsfortheabovematricesarelistedinTable1.TheMDLobtainedbyanindividuallaboratoryforaspecificmatrixmaydifferfromthoselisteddependingonthenatureofthesampleandtheinstrumentationused.1.3Samplescontaininghighlevelsofanionicspeciessuc

3、hassulfateandchloridemaycausecolumnoverload.SamplescontaininghighlevelsoforganicsorsulfidescauserapidreductionofsolubleCr(VI)toCr(III).Samplesmustbestoredat4ECandanalyzedwithintwenty-fourhoursofcollection.1.4Thismethodshouldbeusedbyanalystsexperiencedintheuseofi

4、onchromatographyandintheinterpretationofionchromatograms.2.0SUMMARYOFMETHOD2.1Anaqueoussampleisfilteredthrougha0.45µmfilterandthefiltrateisadjustedtoapHof9to9.5withabuffersolution.Ameasuredvolumeofthesample(50-250µL)isintroducedintotheionchromatograph.Aguardcolu

5、mnremovesorganicsfromthesamplebeforetheCr(VI)2-asCrO4isseparatedonananionexchangeseparatorcolumn.Post-columnderivatizationoftheCr(VI)withdiphenylcarbazideisfollowedbydetectionofthecoloredcomplexat530nm.3.0INTERFERENCES3.1Interferenceswhichaffecttheaccuratedeterm

6、inationofCr(VI)maycomefromseveralsources.3.1.1Contamination-AtraceamountofCrissometimesfoundinreagentgradesalts.SinceaconcentratedbuffersolutionisusedinthismethodtoadjustthepHofsamples,reagentblanksshouldbeanalyzedtoassessforpotentialCr(VI)contamination.Contamin

7、ationcanalsocomefromimproperlycleanedglasswareorcontactorcausticoracidicreagentsofsampleswithstainlesssteelorpigmentedmaterial.3.1.2ReductionofCr(VI)toCr(III)canoccurinthepresenceofreducingspecies2-inanacidicmedium.However,atapHof6.5orgreater,CrO4whichislessreac

8、tivethan-theHCrO4,isthepredominantspecies.3.1.3Overloadingoftheanalyticalcolumncapacitywithhighconcentrationsofanionicspecies,especiallychlorideandsulfate,willcauseal