EPA METHOD 7474 Mercury in Sediment and Tissue

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1、METHOD7474MERCURYINSEDIMENTANDTISSUESAMPLESBYATOMICFLUORESCENCESPECTROMETRY1.0SCOPEANDAPPLICATION1.1Thisproceduremeasurestotalmercuryinsedimentandtissuesamples.1.2Therangeofthismethodisfromapproximately1partperbilliontothepartpermillionrange.Analysisoftheentirerangecannotbeaccomp

2、lishedatonce,butratherdifferentportionsofthisrangecanbeanalyzeddependingupontheinstrumentgainsettings.1.3Thismethodshouldonlybeusedbyanalystsexperiencedwiththeanalysisoftraceelementsatverylowconcentrationswhenanalyzingsamplesintheppbrange.2.0SUMMARYOFTHEMETHOD2.1Arepresentativepo

3、rtionofsampleisdigestedinamicrowaveunit(avariationofMethod3052)usingnitricandhydrochloricacidsinaclosedfluorocarboncontainer.Thesampleisdigestedunderpressuretoaidinthedissolutionoforganiccompoundscontainingmercury.2.2Analiquotofthedigestedsampleisdilutedandsubjectedtocolddigestio

4、nwithanacid/bromate/bromidemixture.2.3Stannouschlorideisaddedtothedigestedsampleasareducingagenttoproduce0Hg.Thereducedmercuryisseparatedfromthesample/reagentmixtureasavaporthatiscarriedtothefluorescencedetectorbyastreamofhighpurityargon.3.0DEFINITIONSRefertoChapterOneandChapterT

5、hreeforalistingofapplicabledefinitions.4.0INTERFERENCES4.1Method3052willovercometheproblemsassociatedwithincompletedigestion.IncompletedigestionmayleadtotheincompletesolubilizationofsparinglysolubleHgcompounds.4.2Highpurityargon(99.999%)mustbeusedasthecarriergas.Nitrogenwillreduc

6、ethesensitivitybyafactoreight-fold,whiletheuseofairwillreducethesensitivitythirty-fold.4.3Thepresenceofwatervaporinthefluorescencedetectormayproducescatteringeffects,positiveinterferencesanddegradationoftheanalyticalsignal.Theuseofadryertubeisrequiredtoremoveanywatervaporfromthef

7、lowbeforereachingthedetector.4.4Contaminationisalwaysapotentialproblemintraceelementdeterminations.SeeChapterThreeforcleanlaboratoryprocedures.5.0SAFETY5.1RefertoChapterThreeforadiscussiononsafetyrelatedreferencesandissues.CD-ROM7474-1Revision0January19985.2Manymercurycompoundsar

8、ehighlytoxicifswallowed,inhaled,orabsorb