ASTM_D_7757_-_12.pdf

Designation:D775712Standard Test Method forSilicon in Gasoline and Related Products by MonochromaticWavelength Dispersive X-ray Fluorescence Spectrometry1This standard is issued under the fixed designation D7757;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of totalsilicon by monochromatic,wavelength-dispersive X-ray fluo-rescence(MWDXRF)spectrometry in naphthas,gasoline,RFG,ethanol and ethanol-fuel blends,and toluene at concen-trations of 3 to 100 mg/kg.The precision of this test methodwas determined by an interlaboratory study using representa-tive samples of the liquids described in 1.1 and 1.2.The pooledlimit of quantitation(PLOQ)was estimated to be 3 mg/kg.NOTE1Volatile samples such as high-vapor-pressure gasolines orlight hydrocarbons might not meet the stated precision because of theevaporation of light components during the analysis.NOTE2Aromatic compounds such as toluene are under the jurisdic-tion of Committee D16 on Aromatic Hydrocarbons and Related Chemi-cals.However,toluene can be a contributor to silicon contamination ingasoline(see 4.4),thus its inclusion in this test method.1.2 Gasoline samples containing ethanol and other oxygen-ates may be analyzed with this test method provided the matrixof the calibration standards is either matched to the samplematrices or the matrix correction described in Annex A1 isapplied to the results.The conditions for matrix matching andmatrix correction are provided Section 5,Interferences.1.3 Samples with silicon concentrations above 100 mg/kgcan be analyzed after dilution with appropriate solvent.Theprecision and bias of silicon determinations on diluted sampleshave not been determined and may not be the same as shownfor neat samples(Section 16).1.4 Afundamental assumption in this test method is that thestandard and sample matrices are well matched,or that thematrix differences are accounted for(see 13.5).Matrix mis-match can be caused by C/H ratio differences between samplesand standards or by the presence of other interfering heteroa-toms;observe the cautions and recommendations in Section 5.1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD4806 Specification for Denatured Fuel Ethanol for Blend-ing with Gasolines for Use as Automotive Spark-IgnitionEngine FuelD5798 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition EnginesD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6300 Practice for Determination of Precision and BiasData for Use in Test Methods for Petroleum Products andLubricants3.Summary of Test Method3.1 A monochromatic X-ray beam with a wavelength suit-able to excite the K-shell electrons of silicon is focused onto atest specimen contained in a sample cell(see Fig.1).Thefluorescent K radiation at 0.713 nm(7.13)emitted bysilicon is collected by a fixed monochromator(analyzer).Theintensity(counts per second)of the silicon X-rays is measuredusing a suitable detector and converted to the concentration ofsilicon(mg/kg)in a test specimen using a calibration equation.4.Significance and Use4.1 This test method provides rapid and precise measure-ment of total silicon in naphthas,gasoline,RFG,ethanol and1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved Jan.15,2012.Published March 2012.DOI:10.1520/D7757-12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 ethanol-fuel blends,and toluene with minimum sample prepa-ration.Typical analysis time is 5 to 10 min per sample.4.2 ExcitationbymonochromaticX-raysreducesbackground,simplifies matrix correction,and increases thesignal/background ratio compared to polychromatic excitationused in conventional WDXRF techniques.3