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CHEMICAL OXYGEN DEMAND Method 410.2 (Titrimetric, Low Level) STORET NO. 00335 1 Scope and ApplicatIOn l I T h e scope of thIS modIficatIOn of the ChemICal Oxygen Demand (COD) test IS the same as for the hIgh level test It IS apphcable to the analySIS of surface waters, domestIc and Industnal wastes wIth low demand charactenstlcs 12 ThIS method (low level) IS apphcable f01 samples havIng a COD In the range of 5-50 mg/1COD 2 Summary of Method 21 Orgamc and OXIdIzable Inorgamc substances In an aqueous sample are OXIdIzed by potaSSIUm dIchromate solutIOn In 50 percent (by volume) sulfunc aCId In solutIOn The excess d1chromate IS tItrated WIth standard ferrous ammomum sulfate USIng orthophenanthroline ferrous complex (ferroIn) as an IndIcator 3 Sampling and PreservatIOn 31 CollectthesamplesInglassbottles,IfpossIble UseofplasticcontaInersISpermISSIbleIfIt IS known that no orgamc contamInants are present In the contaIners 32 BIOlogICally actIve samples should be tested as soon as possIble Samples contaInIng settleable matenal should be well mIXed, preferably homogemzed, to permIt removal of representative ahquots 33 Samples should be preserved WIth sulfunc aCId to a pH < 2 and maIntaIned at 4°C untIl analysIs 4 Interferences 41 Traces of orgamc matenal eIther from the glassware or atmosphere may cause a gross, pOSItIve error 4 1 1 Extreme care should be exerCIsed to aVOId InclUSIOn of orgamc matenah. In the dIstIlled water used for reagent preparatIOn or sample dIlutIOn 4 1 2 Glassware used In the test should be condItioned by runmng blank procedures to elImInate traces oforgamc matenal 42 VolatIle matenals may be lost when the sample temperature nses dunng the sulfunc aCId addItIOn step 43 Chlondes are quantItatIvely OXIdIzed by dIchromate and represent a pOSItive Interference Mercunc sulfate IS added to the dIgestIOn flask to complex the chlondes, thereby effectIvely elImInatIng the Interference on all but bnne and estuanne samples 5 Apparatus 5 1 Reflux apparatus Glassware should conSIst of a 500 ml Erlenmeyer flask or a 300 ml round bottom flask made of heat-resIstant glass connected to a 12 Inch AllIhn condenser Issued 1971 Edltonal reVISIOn 1974 and 1978 410 2-1PDF Image | Methods for Chemical Analysis of Water and Wastes
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