EPA METHOD 9031 Extractable Sulfides

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1、METHOD9031EXTRACTABLESULFIDES1.0SCOPEANDAPPLICATION1.1TheextractionproceduredescribedinthismethodisdesignedfortheextractionofsulfidesfrommatricesthatarenotdirectlyamenabletothedistillationprocedureMethod9030.Specifically,thismethodisdesignedfortheextractionofsolublesulfid

2、es.Thismethodisapplicabletooil,solid,multiphasic,andallothermatricesnotamenabletoanalysisbyMethod9030.Thismethodisnotapplicableforreactivesulfide.RefertoChapterSevenforthedeterminationofreactivesulfide.1.2Method9031issuitableformeasuringsulfideinsolidsamplesatconcentratio

3、nsabove1mg/kg.2.0SUMMARYOFMETHOD2.1Ifthesamplecontainssolidsthatwillinterferewithagitationandhomogenizationofthesamplemixture,orsomuchoilorgreaseastointerferewiththeformationofahomogeneousemulsioninthedistillationprocedure,thesamplemaybefilteredandthesolidsextractedwithwa

4、teratpH>9and<11.Theextractisthencombinedwiththefiltrateandanalyzedbythedistillationprocedure.Separationofsulfidefromthesamplematrixisaccomplishedbytheadditionofsulfuricacidtothesample.Thesampleisheatedto70ECandthehydrogensulfide(H2S)whichisformedisdistilledunderacidiccond

5、itionsandcarriedbyanitrogenstreamintozincacetategasscrubbingbottleswhereitisprecipitatedaszincsulfide.2.2Thesulfideinthezincsulfideprecipitateisoxidizedtosulfurwithaknownamountofexcessiodine.Thentheexcessiodineisdeterminedbytitrationwithastandardsolutionofphenylarsineoxid

6、e(PAO)orsodiumthiosulfateuntiltheblueiodinestarchcomplexdisappears.Theuseofstandardsulfidesolutionsisnotpossiblebecauseoftheirinstabilitytooxidativedegradation.ThereforequantitationisbasedonthePAOorsodiumthiosulfate.3.0INTERFERENCES3.1Sampleswithaqueouslayersmustbetakenwi

7、thaminimumofaerationtoavoidvolatilizationofsulfideorreactionwithoxygenwhichoxidizessulfidetosulfurcompoundsthatarenotdetected.3.2Sulfurcompoundssuchassulfiteandhydrosulfitedecomposeinacidandmayformsulfurdioxide.Thisgasmaybecarriedovertothezincacetategasscrubbingbottlesand

8、subsequentlyreactwiththeiodinesolutionyieldingfalsehighvalues.Theadditionofformaldehydeintothezi