EPA METHOD 7198 Chromium, Hexavalent (Differential Pulse Polarography)

《EPA METHOD 7198 Chromium, Hexavalent (Differential Pulse Polarography)》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、METHOD7198CHROMIUM,HEXAVALENT(DIFFERENTIALPULSEPOLAROGRAPHY)1.0SCOPEANDAPPLICATION1.1Thismethodisusedtodeterminetheconcentrationofhexavalentchromium[Cr(VI)]innaturalandwastewatersandinEPextracts.1.2Themethodcanquantitatechromiuminconcentrationsofupto1.0mg/Lto5.0mg/L,dependingonthemer

2、curydropsize.Higherconcentrationscanbedeterminedbydilution.1.3ThelowerlimitofdetectionforCr(VI)is10ug/Lfortheinstrumentalconditionsgiveninthismethod.Thelimitofdetectioncouldbeeasilyloweredbychangingtheseconditions.2.0SUMMARYOFMETHOD2.1Method7198measuresthepeakcurrentproducedfromthere

3、ductionofCr(VI)toCr(III)atadroppingmercuryelectrodeduringadifferentialpulsevoltageramp.2.2Themethoddescribedhereinuses0.125MNH4OH-0.125MNH4Clasthesupportingelectrolyte.Inthiselectrolyte,Cr(VI)reductionresultsinpeakcurrentoccurringatthepeakpotential(Ep)of-0.250Vvs.Ag/AgCl.2.3Alternati

4、vesupportingelectrolytes,suchasthosegiveninTable1,maybeused.2.4ThetechniqueofstandardadditionsmustbeusedtoquantitatetheCr(VI)content.3.0INTERFERENCES3.1CopperionatconcentrationshigherthantheCr(VI)concentrationisapotentialinterferenceduetopeakoverlapwhenusingthe0.125Mammoniacalelectro

5、lyte.Increasingtheammoniacalelectrolyteconcentrationto0.5Mshiftsthecopperpeakcathodically(Ep=-0.4V),eliminatingtheinterferenceatacopper-to-chromiumratioof10:1(Figure1).3.2Reductantssuchasferrousiron,sulfite,andsulfidewillreduceCr(VI)toCr(III);thusitisimperativetoanalyzethesamplesasso

6、onaspossible.4.0APPARATUSANDMATERIALS4.1Polarographicinstrumentation:Capableofperformingdifferentialpulseanalyses,includingrecorderorplotter.71981CD-ROMRevision0DateSeptember198671982CD-ROMRevision0DateSeptember1986TABLE1.POLAROGRAPHYOFHEXAVALENTCHROMIUMSupportingelectrolytePeakpoten

7、tial(vs.SCE)1MNaOH-0.851MPyridine,1MNaOH-1.481MNH4OH,1MNH4Cl-0.360.1MNH4OH,0.1M(NH4)2Tartrate-0.2440.2MKCl,0.3MTriethanolamine,pH9-0.281MNa2SO4-0.230.1MNH4OH,0.1MNH4Cl-0.2571983CD-ROMRevision0DateSeptember19864.2Droppingmercuryelectrodeassembly:Capableofperformingdifferentialpulseana

8、lyses.4.3Cou