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1、METHOD8520CONTINUOUSMEASUREMENTOFFORMALDEHYDEINAMBIENTAIR1.0SCOPEANDAPPLICATION1.1Thismethodisapplicabletothecontinuousmeasurementofformaldehyde(CASNo.50-00-0)inambientair.Thismethodisforuseprimarilyfornonoccupationalexposuremonitoring.31.2Thismethodisapplicabletoconcentratio
2、nsofformaldehydefrom6to500μg/m.Detectionlimitsaredependentonsampleairflowrate,withamaximumratesetat1.0L/min.1.3Thismethodisrestrictedtousebyorunderthesupervisionoftrainedanalysts.Eachanalystmustdemonstratetheabilitytogenerateacceptableresultswiththismethod.2.0SUMMARYOFMETHOD2
3、.1Amodifiedportablecommercialanalyzerwhichconsistsofasmalldiaphragmpump,ananalyticalmodule,acolorimeterwithglassflowcells,aperistalticpumpandtubing,anda12voltrechargeablebatteryforoptionalDCpoweroperationisusedforthismethod(SeeFigure1).Anacidifiedpararosanilinescrubbersolutio
4、nispumpedthroughthereferencecellinthecolorimeterandisthendiluted1:1withaliquidflowstreamcontainingwater.Thedilutedsolutionthenpassesintoanairscrubbercoilwhereformaldehydeisquantitativelyabsorbedfromtheairsamplestream.Aftertheliquidandairareseparated,thesamplesolutionismixed1:
5、1withadiluteaqueousNa2SO3reagent.Aseriesoftimedelaycoilsallow16minutesforcolordevelopmentofthechromophore.ThecoloredproductiscontinuouslydetectedasitpassesthroughthesamplecellbyaUV-Visiblespectrophotometersetat550nmandisrecordedonastripchartrecorderoranautomateddataacquisitio
6、nsystem.3.0INTERFERENCES3.1Methodinterferencesmaybecausedbycontaminantsinreagents,glassware,andsampleprocessinghardware.3.1.1Glasswaremustbescrupulouslycleaned.Cleanallglasswareassoonaspossibleafterusebyrinsingwiththelastsolventused.Thisshouldbefollowedbydetergentwashingwithh
7、otwater,andrinseswithtapwaterandorganic-freereagentwater.Itshouldthenbedraineddry,andheatedinalaboratoryovenat130ECforseveralhoursbeforeuse.Solventrinsingmaybesubstitutedfortheovenheating.Afterdryingandcooling,glasswareshouldbestoredinacleanenvironment,coveredwithaluminumfoil
8、topreventanyaccumulationofdustorothercontaminants.3.1.2Allofthesemat
