EPA 9213 POTENTIOMETRIC DETERMINATION OF CYANIDE

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1、METHOD9213POTENTIOMETRICDETERMINATIONOFCYANIDEINAQUEOUSSAMPLESANDDISTILLATESWITHION-SELECTIVEELECTRODE1.0SCOPEANDAPPLICATION1.1Thismethodcanbeusedformeasuringfree(non-complexed)cyanideandhydrocyanicacidindrinkingwaters,naturalsurfacewaters,domesticandindustrialwastewaters,andinsoilextra

2、cts(ASTMmethodsD4646-87,D5233-92orD3987-85).ThemethodmayalsobeusedasthedeterminativestepfortotalcyanideindistillatefollowingthedistillationinMethod9010.1.2Themethoddetectionlimitis0.05mg/L.Cyanideconcentrationsfrom0.01to10mg/Lmaybemeasured.However,usingalinearcalibration,resultslessthan

3、0.05mg/Lmaybebiaseduptoapproximately120percenthigh.1.3ISEsmustbeusedcarefully,andresultsmustbeinterpretedcautiously,sinceanISEmaybeaffectedbynumerousanalyticalinterferenceswhichmayeitherincreaseordecreasetheapparentanalyteconcentration,orwhichmaydamagetheISE.Effectsofmostinterferencesca

4、nbeminimizedoreliminatedbyaddingappropriatechemicalreagentstothesample.Obtainingthemostaccurateresults,therefore,requiressomeknowledgeofthesamplecomposition.NOTE:ISEmanufacturersusuallyincludealistofinterferencesintheinstructionmanualaccompanyinganISE,alongwithrecommendedmethodsforminim

5、izingoreliminatingeffectsoftheseinterferences.1.4ThecyanideISEshouldnotbeusedinsolutionscontainingmorethan30mg/Loffreecyanide,becausesuchsolutionswilldissolvetheISEsensorsilvercompounds.2.0SUMMARYOFMETHOD2.1Cyanideisdeterminedpotentiometricallyusingacyanideion-selectiveelectrode(ISE)inc

6、onjunctionwithadouble-junctionreferenceelectrodeandapHmeterwithanexpandedmillivoltscaleoranISEmetercapableofbeingcalibrateddirectlyintermsofcyanideconcentration.2.2Standardsandsamplesaremixed100:1withanionicstrengthadjustmentsolution(ISA).Calibrationisperformedbyanalyzingaseriesofstanda

7、rdsandplottingmVvs.cyanideconcentrationonsemilogpaperorbycalibratingtheionmeterdirectlyintermsofcyanideconcentration.3.0INTERFERENCES3.1TransitionmetalcationsinterferebyformingverystablecomplexeswithcyanidewhicharenotmeasuredbythecyanideISE.Forexample,copper(II)ionsinterferewit