Designation:D6238−98(Reapproved2011)StandardTestMethodforTotalOxygenDemandinWater1ThisstandardisissuedunderthefixeddesignationD6238;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thistestmethodcoversthedeterminationoftotaloxygendemandintherangefrom100to100000mg/L,inwaterandwastewaterincludingbrackishwatersandbrines(see6.5).Largerconcentrations,orsampleswithhighsuspendedsolids,orboth,maybedeterminedbysuitabledilutionofthesample.1.1.1Sincetheanalysisisbasedonthechangeinoxygenreadingofthecarriergascomparedtothatwhenasampleisintroduced(see4.1),themeasurementrangeisafunctionoftheamountofoxygeninthecarriergas.Thehigherthedesiredconcentrationrange,themoreoxygenrequiredinthecarriergas.Underrecommendedconditions,thecarriergasconcen-trationshouldbebetweentwotofourtimesthemaximumdesiredoxygendemand.1.1.2Thelowermeasurementrangeislimitedbythestabilityofthebaselineoxygendetectoroutput.Thissignalisafunctionofthepermeationsystemtemperature,carriergasflowrate,oxygendetectortemperature,andreferencesensorvoltage.Combined,thesevariableslimittheminimumrecom-mendedrangeto2to100mg/L.1.1.3Theuppermeasurementrangeislimitedbythemaximumoxygenconcentrationinthecarriergas(100%).Withtherecommendedconditionsofcarriergasconcentrationbeingtwotofourtimesthemaximumoxygendemand,thislimitsthemaximumpossibleoxygendemandtobetween250000to500000mg/L.However,asapracticalapplicationtowateranalysis,thistestmethodwillconsideramaximumrangeof100000mg/L.1.2Thistestmethodisapplicabletoalloxygen-demandingsubstancesundertheconditionsofthetestcontainedinthesamplethatcanbeinjectedintothereactionzone.Theinjectoropeninglimitsthemaximumsizeofparticlesthatcanbeinjected.Ifoxygen-demandingsubstancesthatarewater-insolubleliquidsorsolidsarepresent,apreliminarytreatmentmaybedesired.Thesepretreatmentmethods...
