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1、METHOD9210APOTENTIOMETRICDETERMINATIONOFNITRATEINAQUEOUSSAMPLESWITHANION-SELECTIVEELECTRODESW-846isnotintendedtobeananalyticaltrainingmanual.Therefore,methodproceduresarewrittenbasedontheassumptionthattheywillbeperformedbyanalystswhoareformallytrainedinatleastthebasicprinc
2、iplesofchemicalanalysisandintheuseofthesubjecttechnology.Inaddition,SW-846methods,withtheexceptionofrequiredmethodusefortheanalysisofmethod-definedparameters,areintendedtobeguidancemethodswhichcontaingeneralinformationonhowtoperformananalyticalprocedureortechniquewhichalab
3、oratorycanuseasabasicstartingpointforgeneratingitsowndetailedStandardOperatingProcedure(SOP),eitherforitsowngeneraluseorforaspecificprojectapplication.Theperformancedataincludedinthismethodareforguidancepurposesonly,andarenotintendedtobeandmustnotbeusedasabsoluteQCacceptan
4、cecriteriaforpurposesoflaboratoryaccreditation.1.0SCOPEANDAPPLICATION1.1Thismethodmaybeusedformeasuringsolubilizednitrateindrinkingwater,naturalsurfacewater,groundwater,domesticandindustrialwastewater,soilextracts(ASTMStandardsD4646,D5233orD3987)andaqueousextractsofotherso
5、lids.NOTE:Thismethodisfortheanalysisofthesimple(non-complexed)nitrateionratherthanthetotalnitrate,becausetheanalysisusingtheion-selectiveelectrodeisnotprecededbyadistillationstep.1.2Alinearcalibration(±20%RSD)canbeobtainedovertherangeof5.0to200(mg/L).Resultslessthan5.0mg/L
6、willbebiasedhighwhileresultsgreaterthan200mg/Lwillbebiasedlow.1.3Ion-selectiveelectrodes(ISEs)mustbeusedcarefully,andresultsmustbeinterpretedcautiously,sinceanISEmaybeaffectedbynumerousanalyticalinterferenceswhichmayeitherincreaseordecreasetheapparentanalyteconcentration,o
7、rwhichmaydamagetheISE.Effectsofmostinterferencescanbeminimizedoreliminatedbyaddingappropriatechemicalreagentstothesample(seeSec.4.1).Obtainingthemostaccurateresults,therefore,requiressomeknowledgeofthesamplecomposition.NOTE:ISEmanufacturersusuallyincludealistofinterference
8、sintheinstructionmanualaccompanyinganISE,alongwithrecommendedmethodsforminimizingorelimin
