1、Designation: D7757 12D7757 17Standard 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 oforigina
2、l 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. Scope Scope*1.1 This test method covers the determination of total silicon
3、by monochromatic, wavelength-dispersive X-ray fluorescence(MWDXRF) spectrometry in naphthas, gasoline, RFG, gasoline-ethanol blends, reformulated gasoline (RFG), ethanol andethanol-fuel blends, and toluene at concentrations of 33 mgkg to 100100 mg mg/kg. kg. The precision of this test method wasdete
4、rmined by an interlaboratory study using representative samples of the liquids described in 1.1 and 1.2. The pooled limit ofquantitation (PLOQ) was estimated to be 3 3 mgmg/kg.kg.NOTE 1Volatile samples such as high-vapor-pressure gasolines or light hydrocarbons might not meet the stated precision be
5、cause of the evaporationof light components during the analysis.NOTE 2Aromatic compounds such as toluene are under the jurisdiction of Committee D16 on Aromatic Hydrocarbons and Related Chemicals.However, toluene can be a contributor to silicon contamination in gasoline (see 4.4), thus its inclusion
6、 in this test method.1.2 Gasoline samples containing ethanol and other oxygenates may be analyzed with this test method provided the matrix ofthe calibration standards is either matched to the sample matrices or the matrix correction described in Annex A1 is applied to theresults. The conditions for
7、 matrix matching and matrix correction are provided Section 5, Interferences.1.3 Samples with silicon concentrations above 100100 mg mg/kg kg can be analyzed after dilution with appropriate solvent.The precision and bias of silicon determinations on diluted samples have not been determined and may n
8、ot be the same as shownfor neat samples (Section 16).1.4 A fundamental assumption in this test method is that the standard and sample matrices are well matched, or that the matrixdifferences are accounted for (see 13.5). Matrix mismatch can be caused by C/H ratio differences between samples and stan
9、dardsor by the presence of other interfering heteroatoms; observe the cautions and recommendations in Section 5.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.6 This standard does not purport to address all of the safet
10、y concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.7 This international standard was developed in accordance with internationall
11、y recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D4057 Practice f
12、or Manual Sampling of Petroleum and Petroleum ProductsD4177 Practice for Automatic Sampling of Petroleum and Petroleum ProductsD4806 Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use asAutomotive Spark-Ignition Engine FuelD5798 Specification for Ethanol Fuel Blends for Fle
13、xible-Fuel Automotive Spark-Ignition EnginesD6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-ment System Performance1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubri
14、cants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved Jan. 15, 2012July 1, 2017. Published March 2012July 2017. DOI:10.1520/D7757-12.Originally approved in 2012. Last previous edition approvedin 2012 as D7757 12. DOI:10.1520/D7757-17.2 For refere
15、ncedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the
16、 user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standar
17、d as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D6300 Practice for Determination of Precision and Bias D
18、ata for Use in Test Methods for Petroleum Products and LubricantsD7343 Practice for Optimization, Sample Handling, Calibration, and Validation of X-ray Fluorescence Spectrometry Methodsfor Elemental Analysis of Petroleum Products and Lubricants3. Summary of Test Method3.1 A monochromatic X-ray beam
19、with a wavelength suitable to excite the K-shell electrons of silicon is focused onto a testspecimen contained in a sample cell (see Fig. 1). The fluorescent K radiation at 0.713 nm (7.13 ) 0.713 nm (7.13 ) emittedby silicon is collected by a fixed monochromator (analyzer). The intensity (counts per
20、 second) of the silicon X-rays is measuredusing a suitable detector and converted to the concentration of silicon (mg/kg) in a test specimen using a calibration equation.4. Significance and Use4.1 This test method provides rapid and precise measurement of total silicon in naphthas, gasoline, gasolin
21、e-ethanol blends,RFG, ethanol and ethanol-fuel blends, and toluene with minimum sample preparation. Typical analysis time is 55 min to 10 min10 min per sample.4.2 Excitation by monochromatic X-rays reduces background, simplifies matrix correction, and increases the signal/backgroundratio compared to
22、 polychromatic excitation used in conventional WDXRF techniques.34.3 Silicone oil defoamer can be added to coker feedstocks to minimize foaming in the coker. Residual silicon in the cokernaphtha can adversely affect downstream catalytic processing of the naphtha. This test method provides a means to
23、 determine thesilicon content of the naphtha.4.4 Silicon contamination of gasoline, gasoline-ethanol blends, denatured ethanol, and their blends has led to fouled vehiclecomponents (for example, spark plugs, exhaust oxygen sensors, catalytic converters) requiring parts replacement and repairs.Finish
24、ed gasoline gasoline, gasoline-ethanol blends, and ethanol-fuel blends can come into contact with silicon a number of ways.Waste hydrocarbon solvents such as toluene can be added to gasoline. Such solvents can contain soluble silicon compounds.Silicon-based antifoam agents can be used in ethanol pla
25、nts, which then pass silicon on to the finished ethanol-fuel blend. This testmethod can be used to determine if gasoline gasoline, gasoline-ethanol blends, and ethanol-fuel blends meet specifications withrespect to silicon content of the fuel, and for resolution of customer problems.4.5 Some silicon
26、 compounds covered by this test method are significantly more volatile than the silicon compounds typicallyused for the preparation of the calibration standards. Volatile compounds (for example, hexamethyldisiloxane with a boiling pointof 101C), which typically have boiling points below 170C can giv
27、e higher silicon sensitivities than the standard.may not meetthe stated precision from this test method because of selective loss of light materials during the analysis.5. Interferences5.1 Differences between the elemental composition of test samples and the calibration standards can result in biase
28、d silicondeterminations. For fuels within the scope of this test method, the only important elements contributing to bias resulting fromdifferences in the matrices of calibrants and test samples are hydrogen, carbon, and oxygen. A matrix-correction factor (C) may3 Bertin, E. P., Principles and Pract
29、ices of X-ray Spectrometric Analysis, Plenum Press, New York, 1975, pp. 115-118.118.FIG. 1 Schematic of the MWDXRF AnalyzerD7757 172be used to correct this bias; the calculation is described in AnnexA1. For general analytical purposes, the matrices of test samplesand the calibrants are considered to
30、 be matched when the calculated correction factor C is within 0.95 to 1.05. No matrix correctionis required within this range. A matrix correction is required when the value of C is outside the range of 0.95 to 1.05. For mosttesting, matrix correction can be avoided with a proper choice of calibrant
31、s. For example, Fig. 2 and the calculation in Annex A1show that a calibrant with 87.5 87.5 % by mass % carbon and 12.5 12.5 % by mass % hydrogen can cover non-oxygen containingsamples with C/H ratios from 5.0 to 11.0, which corresponds to a correction factor range of 0.95 to 1.05.5.2 Fuels containin
32、g large quantities of ethanol, such as ethanol fuel ethanol,blends, denatured fuel ethanol, and gasoline-ethanol blends (see Specifications D4806 and D5798), can have a high oxygen content leading to significant absorption of siliconK radiation and low silicon results. Such fuels may be analyzed usi
33、ng this test method provided either that correction factors (seeTable 1 and Figs. 3 and 4Table 2) are applied to the results or by using calibration standards that are matrix matched to the testsample. For gasoline samples with oxygenates, up to 3.1 3.1 % by mass % oxygen can be tolerated for test s
34、amples with the sameC/H ratio as the calibrants.5.2.1 For test samples with high oxygenate content, such as fuel ethanol, denatured fuel ethanol,ethanol and gasoline-ethanolethanol fuel blends (see Specifications D4806 and D5798), ethanol based ethanol-based calibrants may be used provided thecorrec
35、tion factors as described in 5.1 are applied to the results. Table 1 and Figs. 3 and 4Table 2 show the correction factor thatshould be applied to the measurement results of the gasoline-gasoline gasoline-ethanol and ethanol fuel blends if they are measuredusing either an isooctane or ethanol calibra
36、tion curve.NOTE 3Alcohol based calibration standards may be preferred for test samples containing a high oxygenate content.5.3 To minimize any bias in the results, use calibration standards prepared from silicon-free base materials of the same or similarelemental composition as the test samples.5.3.
37、1 When diluting samples, use a diluent with an elemental composition the same or similar to the base material used forpreparing the calibration standards.5.3.2 A base material for gasoline may be simulated by mixing 2,2,4-trimethylpentane (isooctane) and toluene in a ratio thatapproximates the expec
38、ted aromatic content of the samples to be analyzed.6. Apparatus6.1 Monochromatic Wavelength Dispersive X-ray Fluorescence (MWDXRF) Spectrometer4, equipped for X-ray detection at0.713 nm (7.13 ). 0.713 nm (7.13 ). Any spectrometer of this type may be used if it includes the following features, and th
39、eprecision and bias of test results are in accordance with the values described in Section 16.4 The sole source of supply of the apparatus known to the committee at this time is XOS, Inc., 15 Tech Valley Drive, Suite 1, East Greenbush, NY 12061. If you are awareof alternative suppliers, please provi
40、de this information toASTM International Headquarters.Your comments will receive careful consideration at a meeting of the responsibletechnical committee,1 which you may attend.FIG. 2 Matrix Correction for a Test Sample versus C/H and Total Oxygen Content Using Chromium K for the Excitation BeamD775
41、7 1736.1.1 X-ray Source, capable of producing X-rays to excite silicon. X-ray tubes with a power 20W20 W capable of producingRh L, Pd L, Ag L, Ti K, Sc K, andor Cr K radiation are recommended for this purpose.6.1.2 Incident-beam Monochromator, capable of focusing with an effective collection solid a
42、ngle greater than 0.05 sr 0.05 sr andselecting a single wavelength of characteristic X-rays from the source onto the specimen. A monochromatic beam is consideredto be monochromatic when it has an energy bandwidth (Full Width Half Maximum) less than 61.5%61.5 % relative to theselected energy and cont
43、aining more than 98%98 % flux of the spectrum of the excitation beam which is incident on the sample.6.1.3 Optical Path, designed to minimize the absorption along the path of the excitation and fluorescent beams using a heliumor vacuum atmosphere.6.1.4 Fixed-Channel Monochromator, suitable for dispe
44、rsing silicon K X-ray photons with an effective collection solid anglegreater than 0.3 sr. 0.3 sr.6.1.5 Detector, designed for efficient detection of silicon K X-ray photons.6.1.6 Single-Channel Analyzer, an energy discriminator to monitor only silicon radiation.6.1.7 Removable Sample Cell, compatib
45、le with the sample and the geometry of the MWDXRF spectrometer. A disposable cellis recommended.6.1.8 X-Ray Transparent Film, for containing and supporting the test specimen in the sample cell (see 6.1.7) while providinga low-absorption window for X-rays to pass to and from the sample. Use an X-ray
46、transparent film resistant to chemical attack.attack that does not contain a listed silicon impurity. Follow manufacturers recommendations for appropriate film types.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is i
47、ntended that allreagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where suchspecifications are available.5 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without
48、 lessening the accuracy of the determination.5 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed bythe American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole
49、, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.TABLE 1 Correction Factors for Gasoline-Ethanol and Ethanol Fuel Blends Measured on an Isooctane Calibration CurveNOTE 1Determine the correction factor in the table below by finding the known ethanol content of the test specimen (for example, 15 % by mass)as the sum of the value in the first column and the value in the first row (for example, 15 = 10+5). The intersection of these two values is the correctionfactor (for ex
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