1、Designation: D7212 07D7212 13Standard 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 D7212; the number immediately following the designation indicates the
2、 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. Scope*1.1 This test method specifies an energy-dispersive X-
3、ray fluorescence (EDXRF) method for the determination of the totalsulfur content of automotive fuels with a concentration range from 7 mg/kg to 50 mg/kg.1.1.1 The pooled limit of quantitation of this test method as obtained by statistical analysis of interlaboratory test results is 7mg/kg sulfur.1.2
4、 The values stated in SI units are to be regarded as the standard. The preferred concentration units are mg/kg sulfur.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropria
5、te safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4045 Test Method for Sulfur in Petroleum Products by Hydrogenolysis and Rateometric ColorimetryD4057 Practice for Manual Sampling of Petroleum and Petroleu
6、m ProductsD4177 Practice for Automatic Sampling of Petroleum and Petroleum ProductsD6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-ment System PerformanceD6300 Practice for Determination of Precision and Bias Data for Use in Te
7、st Methods for Petroleum Products and LubricantsD6792 Practice for Quality System in Petroleum Products and Lubricants Testing LaboratoriesD7343 Practice for Optimization, Sample Handling, Calibration, and Validation of X-ray Fluorescence Spectrometry Methodsfor Elemental Analysis of Petroleum Produ
8、cts and LubricantsE29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 low background proportional counter, nan X-ray proportional counter that can suppress the noise generated whenin
9、cident X rays are absorbed near the wall with resulting incomplete charge collection.3.1.1.1 DiscussionAn electrode shield close to the wall detects incomplete charge collection and associated electronic detection circuitry rejects thoseevents. In comparison to conventional proportional counters, th
10、is gives lower spectral background and a lower limit of detection.1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricants and is the direct responsibility of Subcommittee D02.03 onElemental Analysis.Current edition approved May 1, 2007June 15, 2013. Pu
11、blished June 2007August 2013. Originally approved in 2006. Last previous edition approved in 20062007 asD7212D7212 07.06. DOI: 10.1520/D7212-07.10.1520/D7212-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of
12、 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 user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technicall
13、y possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this stand
14、ardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 The sample is placed in the beam emitted from an X-ray source with titanium target and primary filtration so that excitationis by essentially monochromati
15、c radiation of 4.51 keV and virtually no background at 2.3 keV. A low background proportionalcounter measures the intensity of the fluorescent sulfur K series intensity and argon K series intensity (from residual air) and theaccumulated counts are compared with counts from previously prepared calibr
16、ation standards to obtain the sulfur concentrationin mg/kg. If chlorine is expected to be present in some samples then other regions of the spectrum must be measured to providecompensation for spectral overlap. One group of calibration standards is required to span the concentration range from 0 to
17、150mg/kg sulfur.NOTE 1Operation of analyzers using X-ray tubes is to be conducted in accordance with the manufacturers safety instructions and federal, state, andlocal regulations governing the use of ionizing radiation.4.2 Practice D7343 should be consulted regarding standard operating protocols in
18、 XRF analysis.5. Significance and Use5.1 This test method determines total sulfur in automotive fuels with a typical analysis time around 10 min per sample.5.2 The quality of automotive fuel is related to the amount of sulfur present. Knowledge of sulfur level is necessary forprocessing purposes.5.3
19、 Sulfur level in automotive fuels affects performance characteristics and air quality. Federal, state, and local agencies regulatethe level of sulfur in fuel delivered at the pump.5.4 This test method can be referenced in specification documents to determine if the material meets the desired sulfur
20、content.5.5 If this test method is applied to petroleum matrices with significantly different composition to those used in theinterlaboratory precision study, then the caution and recommendations in Section 6 should be observed when interpreting theresults.6. Interferences6.1 Spectral interferences
21、result when some sample component element or elements emit X rays that the detector cannot resolvefrom sulfur X-ray emission. Overlapping peak lines are the result of this. This overlapping effect may be by lead alkyls, silicon,phosphorus, calcium, potassium, and halides if their aggregate concentra
22、tion is more than 10 mg/kg. The most likely interferenceis chlorine that has been found in biodiesel derived from recycled waste vegetable oil.6.2 The presence of oxygenates or water may alter the sensitivity for sulfur.6.3 Follow the manufacturers operating guide to compensate for the interferences
23、.7. Apparatus7.1 Energy-dispersive X-ray Fluorescence AnalyzerAny energy dispersive X-ray fluorescence analyzer may be used if itsdesign incorporates, as a minimum the following features:37.1.1 Source of X-ray Excitation, X-ray source with titanium target and primary filtration so that excitation is
24、 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 10eV or less, covering the energy range from 0 to 10 keV.7.1.4 Signal Conditioning and Data Handling Electronic
25、s, that include the functions of X-ray intensity counting, a minimumof four energy regions (to correct for background X rays and spectral overlap), spectral overlap corrections, and conversions ofsulfur X-ray intensity into sulfur concentration.7.1.5 Display or Printer, that reads out in mg/kg sulfu
26、r.7.1.6 Removable Sample Cell, providing a sample depth of at least 4 mm and equipped with a replaceable X-ray transparentplastic film window.7.1.7 Helium Purged Optical Path, to maximize sensitivity and minimize spectral overlap from argon in air. The helium shallbe at least 99.9 % purity.8. Reagen
27、ts and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such3 The sole source of supply of the ap
28、paratus known to the committee at this time is the Twin-X ULS from Oxford Instruments Analytical, Halifax Road, High Wycombe,Bucks, HP12 3SE, England. If you are aware of alternative suppliers, please provide this information toASTM International Headquarters.Your comments will receive carefulconsid
29、eration at a meeting of the responsible technical committee,1 which you may attend.4 The 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 to ASTM Inter
30、national Headquarters. Your comments will receive careful consideration at a meeting of the responsible technicalcommittee,1 which you may attend.D7212 132specifications are available.5 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permi
31、t its use without lessening the accuracy of the determination.8.2 Di-n Butyl Sulfide (DBS), a high purity standard with certified analysis for sulfur content. Use the certified sulfur contentwhen calculating the exact concentrations of the calibration standards. (WarningDi-n-butyl sulfide is flammab
32、le and toxic).8.3 Mineral Oil, White (MOW), with sulfur content less than 0.2 mg/kg as certified by a suitable analytical method, like TestMethod D4045.8.4 X-ray Transparent Film, any film that resists attack by the sample, is free of sulfur and other interfering elements (see 6.1),and is sufficient
33、ly X-ray transparent may be used.NOTE 2Polycarbonate with thickness of 5 or 6 m most closely matches these requirements and eight of nine participants in the interlaboratory study6used one of these films, while the other laboratory used 3 m polyester.8.4.1 Samples of high aromatic content may dissol
34、ve polycarbonate film and polypropylene has a tendency to absorb somehydrocarbons and may stretch during a long measurement time.NOTE 3One laboratory has shown that polycarbonate resists a mixture of 25 mass % isooctane and 75 mass % toluene for 80 min.8.4.2 In these cases high purity polyester is a
35、cceptable, but overall, polycarbonate offers the best combination of spectral purityand resistance to stretching. Other materials may be used for X-ray windows, provided that they do not contain any elementalimpurities and match the listed films for X-ray transmission.8.5 Sample Cells, resistant to
36、sample attack and meet the geometry requirements of spectrometer.8.6 Calibration Check Samples, portions of one or more automotive fuel standards of known sulfur content and not used in thegeneration of the calibration line. The check samples shall be used to determine the accuracy of the initial ca
37、libration (see 11.3).8.7 Quality Control (QC) Samples, preferably portions of one or more automotive fuel materials that are stable andrepresentative of the samples of interest.9. Sampling9.1 A sample shall be taken in accordance with the instructions in Practice D4057 or D4177, where appropriate. D
38、o not shakesamples, thus avoiding entrained air.Analyze samples immediately after pouring into a sample cell and allowing the escape of theair bubbles caused by mixing.9.2 For the measurement of low sulfur contents disposable cells are recommended. Preparation of sample cells must be donewith care a
39、nd by following any advice from the supplier.Afreshly prepared sample cell including film is required prior to analyzingthe samples. Avoid touching the inside of the sample cell or portion of the window film in the cell or in the instrument windowthat is exposed to X rays. Oil from fingerprints affe
40、cts the reading when analyzing for low level of sulfur. Ensure that the film isnot scratched, especially by the tear-off bar as it is withdrawn from the container. Wrinkles in the film will affect the intensity ofsulfur X rays transmitted. Therefore, it is essential that the film be taut and clean t
41、o ensure reliable results. Film may becomeelectrostatically charged during handling so it is important that the cell window does not attract any dust, fiber, and hair. Theanalyzer will need recalibration if the type or thickness of the window film is changed.9.3 If the instrument has a replaceable s
42、econdary/safety window, it must be changed for every sample to ensure there is nocross-contamination. When changing it, follow the precautions given in 9.2.9.4 Impurities that may affect the measurement of low levels of sulfur have been found in polyester films. All films may varyin thickness from r
43、oll to roll. Therefore, the calibration shall be verified after starting each new roll of film.9.5 Where laboratories use more than one XRF spectrometer or analyze different types of sample, a variety of cell windowmaterials may be used. Always ensure that the correct film is clearly distinguished.1
44、0. Preparation of Apparatus10.1 Set up the apparatus in accordance with the manufacturers instructions. Whenever possible, the instrument should remainenergized to maintain optimum stability.10.2 When changing the helium gas cylinder or after a system has been idle for a day or more ensure that the
45、helium pipes arepurged of air by performing a dummy measurement.11. Calibration and Standardization11.1 Preparation of Calibration Standards:5 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington DC. For suggestions on testing of reagents not listed by t
46、heAmerican Chemical Society, see Annual Standards for Laboratory , BDH Ltd., Poole Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.SPharmacopeial Convention, Inc. (USPC), Rockville, MD.6 Supporting data have been filed at ASTM International Headquarters and may be obtained
47、 by requesting Research Report RR:D02-1587.D7212 13311.1.1 Preparation of Stock Calibration StandardAccurately weigh the nominal quantity of white mineral oil to the nearest0.1 mg, as shown in Table 1, into a suitable narrow-necked container, then accurately weigh in the nominal quantity of di-n-but
48、ylsulfide. Mix thoroughly (a PTFE-coated magnetic stirrer is advisable) at room temperature. Calculate the concentration of sulfurin the stock standard to 1 mg/kg using the following equation:SStock5DBS3SDBS/DBS1MO!# 310000 (1)where:SStock = mg/kg of sulfur in the stock standard,DBS = actual mass of
49、 DBS, g,SDBS = the mass % of sulfur in DBS, typically 21.91 %, andMO = actual mass of white mineral oil, g.11.1.2 Preparation of Calibration StandardsAccurately weigh the nominal quantity of white mineral oil to the nearest 0.1 mg,as shown in Table 2, into a suitable narrow-necked container, then accurately weigh in the nominal quantity of stock standard. Mixthoroughly (a PTFE-coated magnetic stirrer is advisable) at room temperature. Calculate the concentration of sulfur in the eachstandard to 0.1 mg/kg using the following equation:SStd5STK3SStock/STK1MO! (2)
