1、Designation: D 7212 07An American National StandardStandard Test Method forLow Sulfur in Automotive Fuels by Energy-Dispersive X-rayFluorescence Spectrometry Using a Low-BackgroundProportional Counter1This standard is issued under the fixed designation D 7212; the number immediately following the de
2、signation 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method specifies
3、 an energy-dispersive X-rayfluorescence (EDXRF) method for the determination of thetotal sulfur content of automotive fuels with a concentrationrange from 7 mg/kg to 50 mg/kg.1.1.1 The pooled limit of quantitation of this test method asobtained by statistical analysis of interlaboratory test results
4、 is7 mg/kg sulfur.1.2 The values stated in SI units are to be regarded as thestandard. The preferred concentration units are mg/kg sulfur.1.3 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
5、establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 4045 Test Method for Sulfur in Petroleum Products byHydrogenolysis and Rateometric ColorimetryD 4057 Practice for Manual Sampling of
6、 Petroleum andPetroleum ProductsD 4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformanceD 6300 Practice for Determination of Precision and BiasData for Use in Tes
7、t Methods for Petroleum Products andLubricantsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with Specifications3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 low background proportional counter, nan X-rayproportional counter that can suppress
8、the noise generatedwhen incident X rays are absorbed near the wall with resultingincomplete charge collection.3.1.1.1 DiscussionAn electrode shield close to the walldetects incomplete charge collection and associated electronicdetection circuitry rejects those events. In comparison toconventional pr
9、oportional counters, this gives lower spectralbackground and a lower limit of detection.4. Summary of Test Method4.1 The sample is placed in the beam emitted from an X-raysource with titanium target and primary filtration so thatexcitation is by essentially monochromatic radiation of4.51 keV and vir
10、tually no background at 2.3 keV. A lowbackground proportional counter measures the intensity of thefluorescent sulfur K series intensity and argon K series inten-sity (from residual air) and the accumulated counts are com-pared with counts from previously prepared calibration stan-dards to obtain th
11、e sulfur concentration in mg/kg. If chlorine isexpected to be present in some samples then other regions ofthe spectrum must be measured to provide compensation forspectral overlap. One group of calibration standards is requiredto span the concentration range from 0 to 150 mg/kg sulfur.NOTE 1Operati
12、on of analyzers using X-ray tubes is to be conductedin accordance with the manufacturers safety instructions and federal,state, and local regulations governing the use of ionizing radiation.5. Significance and Use5.1 This test method determines total sulfur in automotivefuels with a typical analysis
13、 time around 10 min per sample.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 2006. Las
14、t previous edition approved in 2006 as D 721206.2For 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.1*A Summary o
15、f Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 The quality of automotive fuel is related to the amountof sulfur present. Knowledge of sulfur level is necessary forprocessing p
16、urposes.5.3 Sulfur level in automotive fuels affects performancecharacteristics and air quality. Federal, state, and local agenciesregulate the level of sulfur in fuel delivered at the pump.5.4 This test method can be referenced in specificationdocuments to determine if the material meets the desire
17、d sulfurcontent.5.5 If this test method is applied to petroleum matrices withsignificantly different composition to those used in the inter-laboratory precision study, then the caution and recommenda-tions in Section 6 should be observed when interpreting theresults.6. Interferences6.1 Spectral inte
18、rferences result when some sample compo-nent element or elements emit X rays that the detector cannotresolve from sulfur X-ray emission. Overlapping peak lines arethe result of this. This overlapping effect may be by lead alkyls,silicon, phosphorus, calcium, potassium, and halides if theiraggregate
19、concentration is more than 10 mg/kg. The mostlikely interference is chlorine that has been found in biodieselderived from recycled waste vegetable oil.6.2 The presence of oxygenates or water may alter thesensitivity for sulfur.6.3 Follow the manufacturers operating guide to compen-sate for the inter
20、ferences.7. Apparatus7.1 Energy-dispersive X-ray Fluorescence AnalyzerAnyenergy dispersive X-ray fluorescence analyzer may be used ifits design incorporates, as a minimum the following features:37.1.1 Source of X-ray Excitation, X-ray source with titaniumtarget and primary filtration so that excitat
21、ion is by essentiallymonochromatic radiation of 4.51 keV.7.1.2 Low Background Proportional Counter (see 3.1.1),with sensitivity at 2.3 keV.47.1.3 Multi-channel Analyzer, with a channel width of 10eVor less, covering the energy range from 0 to 10 keV.7.1.4 Signal Conditioning and Data Handling Electr
22、onics,that include the functions of X-ray intensity counting, aminimum of four energy regions (to correct for background Xrays and spectral overlap), spectral overlap corrections, andconversions of sulfur X-ray intensity into sulfur concentration.7.1.5 Display or Printer, that reads out in mg/kg sul
23、fur.7.1.6 Removable Sample Cell, providing a sample depth ofat least 4 mm and equipped with a replaceable X-ray transpar-ent plastic film window.7.1.7 Helium Purged Optical Path, to maximize sensitivityand minimize spectral overlap from argon in air. The heliumshall be at least 99.9 % purity.8. Reag
24、ents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.5Other g
25、rades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Di-n Butyl Sulfide (DBS), a high purity standard withcertified analysis for sulfur content. Use the certified sulfurcontent when
26、calculating the exact concentrations of thecalibration standards. (WarningDi-n-butyl sulfide is flam-mable and toxic).8.3 Mineral Oil, White (MOW), with sulfur content less than0.2 mg/kg as certified by a suitable analytical method, like TestMethod D 4045.8.4 X-ray Transparent Film, any film that re
27、sists attack bythe sample, is free of sulfur and other interfering elements (see6.1), and is sufficiently X-ray transparent may be used.NOTE 2Polycarbonate with thickness of 5 or 6 m most closelymatches these requirements and eight of nine participants in the interlabo-ratory study6used one of these
28、 films, while the other laboratory used 3 mpolyester.8.4.1 Samples of high aromatic content may dissolve poly-carbonate film and polypropylene has a tendency to absorbsome hydrocarbons and may stretch during a long measure-ment time.NOTE 3One laboratory has shown that polycarbonate resists a mix-tur
29、e of 25 mass % isooctane and 75 mass % toluene for 80 min.8.4.2 In these cases high purity polyester is acceptable, butoverall, polycarbonate offers the best combination of spectralpurity and resistance to stretching. Other materials may be usedfor X-ray windows, provided that they do not contain an
30、yelemental impurities and match the listed films for X-raytransmission.8.5 Sample Cells, resistant to sample attack and meet thegeometry requirements of spectrometer.8.6 Calibration Check Samples, portions of one or moreautomotive fuel standards of known sulfur content and not usedin the generation
31、of the calibration line. The check samplesshall be used to determine the accuracy of the initial calibration(see 11.3).8.7 Quality Control (QC) Samples, preferably portions ofone or more automotive fuel materials that are stable andrepresentative of the samples of interest.3The sole source of supply
32、 of the apparatus known to the committee at this timeis the Twin-X ULS from Oxford Instruments Analytical, Halifax Road, HighWycombe, Bucks, HP12 3SE, England. If you are aware of alternative suppliers,please provide this information to ASTM International Headquarters. Your com-ments will receive ca
33、reful consideration at a meeting of the responsible technicalcommittee,1which you may attend.4The low background proportional counter is covered by a pending patent.Interested parties are invited to submit information regarding the identification of analternative(s) to this patent-pending item toAST
34、M International Headquarters. Yourcomments will receive careful consideration at a meeting of the responsibletechnical committee,1which you may attend.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington DC. For suggestions on testing of reagents not lis
35、tedby the American Chemical Society, see Annual Standards for Laboratory , BDHLtd., Poole Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S Pharmacopeial Convention, Inc. (USPC), Rockville, MD.6Supporting data have been filed at ASTM International Headquarters and maybe obt
36、ained by requesting Research Report RR: D02-1587.D72120729. Sampling9.1 A sample shall be taken in accordance with the instruc-tions in Practice D 4057 or D 4177, where appropriate. Do notshake samples, thus avoiding entrained air. Analyze samplesimmediately after pouring into a sample cell and allo
37、wing theescape of the air bubbles caused by mixing.9.2 For the measurement of low sulfur contents disposablecells are recommended. Preparation of sample cells must bedone with care and by following any advice from the supplier.A freshly prepared sample cell including film is required priorto analyzi
38、ng the samples. Avoid touching the inside of thesample cell or portion of the window film in the cell or in theinstrument window that is exposed to X rays. Oil fromfingerprints affects the reading when analyzing for low level ofsulfur. Ensure that the film is not scratched, especially by thetear-off
39、 bar as it is withdrawn from the container. Wrinkles inthe film will affect the intensity of sulfur X rays transmitted.Therefore, it is essential that the film be taut and clean toensure reliable results. Film may become electrostaticallycharged during handling so it is important that the cell windo
40、wdoes not attract any dust, fiber, and hair. The analyzer will needrecalibration if the type or thickness of the window film ischanged.9.3 If the instrument has a replaceable secondary/safetywindow, it must be changed for every sample to ensure there isno cross-contamination. When changing it, follo
41、w the precau-tions given in 9.2.9.4 Impurities that may affect the measurement of lowlevels of sulfur have been found in polyester films. All filmsmay vary in thickness from roll to roll. Therefore, the calibra-tion shall be verified after starting each new roll of film.9.5 Where laboratories use mo
42、re than one XRF spectrom-eter or analyze different types of sample, a variety of cellwindow materials may be used. Always ensure that the correctfilm is clearly distinguished.10. Preparation of Apparatus10.1 Set up the apparatus in accordance with the manufac-turers instructions. Whenever possible,
43、the instrument shouldremain energized to maintain optimum stability.10.2 When changing the helium gas cylinder or after asystem has been idle for a day or more ensure that the heliumpipes are purged of air by performing a dummy measurement.11. Calibration and Standardization11.1 Preparation of Calib
44、ration Standards:11.1.1 Preparation of Stock Calibration StandardAccurately weigh the nominal quantity of white mineral oil tothe nearest 0.1 mg, as shown in Table 1, into a suitablenarrow-necked container, then accurately weigh in the nominalquantity of di-n-butyl sulfide. Mix thoroughly (a PTFE-co
45、atedmagnetic stirrer is advisable) at room temperature. Calculatethe concentration of sulfur in the stock standard to 1 mg/kgusing the following equation:SStock5 DBS 3 SDBS/ DBS 1 MO!# 3 10 000 (1)where:SStock= mg/kg of sulfur in the stock standard,DBS = actual mass of DBS, g,SDBS= the mass % of sul
46、fur in DBS, typically 21.91 %,andMO = actual mass of white mineral oil, g.11.1.2 Preparation of Calibration StandardsAccuratelyweigh the nominal quantity of white mineral oil to the nearest0.1 mg, as shown in Table 2, into a suitable narrow-neckedcontainer, then accurately weigh in the nominal quant
47、ity ofstock standard. Mix thoroughly (a PTFE-coated magneticstirrer is advisable) at room temperature. Calculate the concen-tration of sulfur in the each standard to 0.1 mg/kg using thefollowing equation:SStd5 STK 3 SStock/ STK 1 MO! (2)where:SStd= mg/kg of sulfur in the calibration standard, andSTK
48、 = actual mass of stock standard, g.11.2 Storage of Standards and Calibration CheckSamplesStore all standards and check samples in glassbottles in a cool, dark place until required. The glass bottlesshall be either dark or wrapped in opaque material and closedwith glass stoppers, inert plastic lined
49、 screw caps, or otherequally inert, impermeable enclosures. As soon as any sedi-ment or change of concentration is observed, discard thestandard.11.3 Instrument CalibrationCalibrate the instrument fol-lowing the manufacturers instructions. Typically, the calibra-tion procedure involves setting up the instrument for recordingof fluorescent sulfur K series intensity, argon K series intensity,and two intensities to determine spectral overlap from chlorine.In effect, sulfur is measured simultaneously with three differentregions of interest, which are the normal setting
