EPA METHOD 7470A Mercury in Liquid Waste (Manual Cold-Vapor Technique)

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1、METHOD7470AMERCURYINLIQUIDWASTE(MANUALCOLD-VAPORTECHNIQUE)1.0SCOPEANDAPPLICATION1.1Method7470isacold-vaporatomicabsorptionprocedureapprovedfordeterminingtheconcentrationofmercuryinmobility-procedureextracts,aqueouswastes,andgroundwaters.(Method7470canalsobeusedforanalyzin

2、gcertainsolidandsludge-typewastes;however,Method7471isusuallythemethodofchoiceforthesewastetypes.)Allsamplesmustbesubjectedtoanappropriatedissolutionsteppriortoanalysis.2.0SUMMARYOFMETHOD2.1Priortoanalysis,theliquidsamplesmustbepreparedaccordingtotheprocedurediscussedinth

3、ismethod.2.2Method7470,acold-vaporatomicabsorptiontechnique,isbasedontheabsorptionofradiationat253.7-nmbymercuryvapor.Themercuryisreducedtotheelementalstateandaeratedfromsolutioninaclosedsystem.Themercuryvaporpassesthroughacellpositionedinthelightpathofanatomicabsorptions

4、pectrophotometer.Absorbance(peakheight)ismeasuredasafunctionofmercuryconcentration.2.3Thetypicaldetectionlimitforthismethodis0.0002mg/L.3.0INTERFERENCES3.1Potassiumpermanganateisaddedtoeliminatepossibleinterferencefromsulfide.Concentrationsashighas20mg/Lofsulfideassodiums

5、ulfidedonotinterferewiththerecoveryofaddedinorganicmercuryfromreagentwater.3.2Copperhasalsobeenreportedtointerfere;however,copperconcen-trationsashighas10mg/Lhadnoeffectonrecoveryofmercuryfromspikedsamples.3.3Seawaters,brines,andindustrialeffluentshighinchloridesrequiread

6、ditionalpermanganate(asmuchas25mL)because,duringtheoxidationstep,chloridesareconvertedtofreechlorine,whichalsoabsorbsradiationof253.7nm.Caremustthereforebetakentoensurethatfreechlorineisabsentbeforethemercuryisreducedandsweptintothecell.Thismaybeaccomplishedbyusinganexces

7、sofhydroxylaminesulfatereagent(25mL).Inaddition,thedeadairspaceintheBODbottlemustbepurgedbeforeaddingstannoussulfate.Bothinorganicandorganicmercuryspikeshavebeenquantitativelyrecoveredfromseawaterbyusingthistechnique.3.4Certainvolatileorganicmaterialsthatabsorbatthiswavel

8、engthmayalsocauseinterference.Apreliminaryrunwithoutreagentsshoulddetermineifthistypeofinterfere