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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
