Designation:D7757−12StandardTestMethodforSiliconinGasolineandRelatedProductsbyMonochromaticWavelengthDispersiveX-rayFluorescenceSpectrometry1ThisstandardisissuedunderthefixeddesignationD7757;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thistestmethodcoversthedeterminationoftotalsiliconbymonochromatic,wavelength-dispersiveX-rayfluo-rescence(MWDXRF)spectrometryinnaphthas,gasoline,RFG,ethanolandethanol-fuelblends,andtolueneatconcen-trationsof3to100mg/kg.Theprecisionofthistestmethodwasdeterminedbyaninterlaboratorystudyusingrepresenta-tivesamplesoftheliquidsdescribedin1.1and1.2.Thepooledlimitofquantitation(PLOQ)wasestimatedtobe3mg/kg.NOTE1—Volatilesamplessuchashigh-vapor-pressuregasolinesorlighthydrocarbonsmightnotmeetthestatedprecisionbecauseoftheevaporationoflightcomponentsduringtheanalysis.NOTE2—Aromaticcompoundssuchastolueneareunderthejurisdic-tionofCommitteeD16onAromaticHydrocarbonsandRelatedChemi-cals.However,toluenecanbeacontributortosiliconcontaminationingasoline(see4.4),thusitsinclusioninthistestmethod.1.2Gasolinesamplescontainingethanolandotheroxygen-atesmaybeanalyzedwiththistestmethodprovidedthematrixofthecalibrationstandardsiseithermatchedtothesamplematricesorthematrixcorrectiondescribedinAnnexA1isappliedtotheresults.TheconditionsformatrixmatchingandmatrixcorrectionareprovidedSection5,Interferences.1.3Sampleswithsiliconconcentrationsabove100mg/kgcanbeanalyzedafterdilutionwithappropriatesolvent.Theprecisionandbiasofsilicondeterminationsondilutedsampleshavenotbeendeterminedandmaynotbethesameasshownforneatsamples(Section16).1.4Afundamentalassumptioninthistestmethodisthatthestandardandsamplematricesarewellmatched,orthatthematrixdifferencesareaccountedfor(see13.5).Matrixmis-matchcanbecausedbyC/Hratiodifferencesbetweensamplesandstandardsorby...
