1、Designation: D 6334 98 (Reapproved 2003)e1An American National StandardStandard Test Method forSulfur in Gasoline by Wavelength Dispersive X-RayFluorescence1This standard is issued under the fixed designation D 6334; the number immediately following the designation indicates the year oforiginal adop
2、tion 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.e1NOTEWarning notes were editorially moved into the standard text in August 2003.1.
3、 Scope1.1 This test method covers the quantitative determinationof total sulfur in gasoline and gasoline-oxygenate blends. ThePooled Limit of Quantitation (PLOQ) was determined to be 15mg/kg. Therefore, the practical range for this test method isfrom 15 to 940 mg/kg.NOTE 1This concentration range is
4、 based on that used in theinterlaboratory round robin, which shows that the range of sulfur in theround robin samples was from 1.5 to 940 mg/kg; however, below 15mg/kg, the reproducibility approaches 100 % of the concentration.1.2 This standard does not purport to address all of thesafety concerns,
5、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 limitation prior to use.1.3 The values stated in SI units are to be regarded as thestandard. The preferred units
6、are mg/kg sulfur.2. Referenced Documents2.1 ASTM Standards:D 2622 Test Method for Sulfur in Petroleum Products byWavelength Dispersive X-Ray Fluorescence Spectrom-etry2D 3210 Test Method for Comparing Colors of Films fromWater-Emulsion Floor Polishes3D 4045 Test Method for Sulfur in Petroleum Produc
7、ts byHydrogenolysis and Rateometric Colorimetry4D 4057 Practice for Manual Sampling of Petroleum andPetroleum Products4D 4177 Practice for the Automatic Sampling of Petroleumand Petroleum Products4D 4294 Test Method for Sulfur in Petroleum Products byEnergy-Dispersive X-Ray Fluorescence Spectroscopy
8、4D 5453 Test Method for the Determination of Total Sulfurin Light Hydrocarbons, Motor Fuels and Oils by Ultravio-let Fluorescence5D 5842 Practice for Sampling and Handling of Fuels forVolatility Measurement5D 5854 Practice for Mixing and Handling of LiquidSamples of Petroleum and Petroleum Products5
9、3. Summary of Test Method3.1 The sample is placed in the X-ray beam, and theintensity of the sulfur Ka line at 5.373 is measured. Theintensity of a corrected background, measured at a recom-mended wavelength of 5.190 , or if a rhodium tube is used,5.437 , is subtracted from this intensity. The resul
10、tant netcounting rate is then compared to a previously preparedcalibration curve or equation to obtain the concentration ofsulfur in mg/kg. (WarningExposure to excessive quantitiesof X radiation is injurious to health. Therefore, it is imperativethat the operator avoid exposing any part of his or he
11、r person,not only to primary X-rays, but also to secondary or scatteredradiation that might be present. The X-ray spectrometer shouldbe operated in accordance with the regulations of recommen-dations governing the use of ionizing radiation.)4. Significance and Use4.1 Knowledge of the presence of sul
12、fur in petroleumproducts, especially fuels, helps predict performance charac-teristics, potential corrosion problems, and vehicle emissionlevels. In addition, some regulatory agencies mandate reducedlevels of sulfur in reformulated type gasolines.5. Interferences5.1 Fuels with compositions that vary
13、 from those specifiedin 9.1 may be analyzed with standards made from basematerials that are of similar composition to minimize matrixeffects.5.1.1 Fuels containing oxygenates may be analyzed usingstandards prepared with similar amounts of the same oxygenateadded to the standard dilution matrix. Howe
14、ver, round robin1This 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 10, 2003. Published August 2003. Originallyapproved in 1962. Last previous e
15、dition approved in 1998 as D 633498.2Annual Book of ASTM Standards, Vol 05.01.3Annual Book of ASTM Standards, Vol 15.04.4Annual Book of ASTM Standards, Vol 05.02.5Annual Book of ASTM Standards, Vol 05.03.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2
16、959, United States.studies done by the Western States Petroleum Association haveshown no significant bias in determining sulfur in gasolineswith and without oxygenates at regulatory levels (0 to 2.7weight percent oxygen).5.1.2 Methanol fuels (M85 and M100) exhibit interferencesat this level of detec
17、tion (100 mg/kg). They can be analyzedusing a calibration curve produced by diluting the standards ina similar matrix of M85 or M100 or by Test Method D 2622.6. Apparatus6.1 Wavelength Dispersive X-Ray Fluorescence Spectrom-eter (WDXRF), equipped for soft ray detection in the 5.37 range. For optimum
18、 sensitivity to sulfur, equip the instrumentwith the following:6.1.1 Optical Path, of helium.6.1.2 Pulse-Height Analyzer, or other means of energydiscrimination.6.1.3 Detector, designed for the detection of long wave-length X-rays.6.1.4 Analyzing Crystal, suitable for the dispersion of sulfurKa X-ra
19、ys within the angular range of the spectrometeremployed. Pentaerythritol and germanium are the most popu-lar, although materials, such as EDDT, ADP, graphite, andquartz, may be used.6.1.5 X-Ray Tube, capable of exciting sulfur Karadiation.Tubes with anodes of rhodium, chromium, and scandium aremost
20、popular, although other anodes may be suitable.7. Reagents7.1 Di-n-Butyl Sulfide (MW 146.30), a high-purity gradestandard with a certified sulfur analysis.7.2 Thiophene MW 84.14), a high-purity (98+ %) gradestandard with a certified sulfur analysis.7.3 2-Methylthiophene MW 98.17), a high purity (98+
21、 %)grade standard with a standard sulfur analysis.7.4 2,2,4-Trimethylpentane,(isooctane), reagent grade,MW-114.23.7.5 Methylbenzene, (Toluene), reagent grade, MW-92.14.7.6 Drift Correction Monitor(s), (Optional), several differ-ent materials have been found to be suitable for use as driftcorrection
22、monitors. Examples of sulfur containing materialsthat meet these requirements are renewable liquid petroleummaterials, semipermanent solids, pressed powder pellets, metalalloys, or fused glass disks. Bracket the calibration range withconcentrations of monitor samples. The counting rate for eachmonit
23、or is determined during calibration (see 9.7) and again atthe time of analysis (see 10.1). These counting rates are used tocalculate a drift correction factor (see 11.1).7.7 Calibration Check Standards, one or more liquid petro-leum or product standards of known sulfur content (which donot represent
24、 one of the samples prepared in Section 9) areused to verify the accuracy of the calibration curve.7.8 Quality Control (QC) Sample, one or more stable liquidpetroleum or product samples, which are used to verify that themeasurement system is in control. Preferably the QC sample(s)should be represent
25、ative of the samples typically analyzed. Incases where volatility of the QC sample(s) may affect thesample integrity, precautions need to be taken to minimize oreliminate sample losses prior to analysis to ensure that a stableand representative sample can be taken and analyzed over theperiod of inte
26、nded use. It is permissible to use calibrationstandards for this purpose. Since standard samples are dis-carded after each determination, it is recommended that alower cost material be used for daily calibration checks.8. Sampling and Specimen Preparation8.1 Samples shall be taken in accordance with
27、 the instruc-tions in Practice D 4057, D 4177, D 5842, or D 5854, whereappropriate.8.2 Clean and dry reusable cells before use. Disposablesample cups are not to be reused. Window material usually is8 m polyester, 8 m polycarbonate, or 6 m polypropylenefilm. Renewal of the window of the sample cup is
28、 essential forthe measurement of each sample. Avoid touching the inside ofthe sample cup, the portion of the window film in the cup, orthe instrument window that is exposed to X-rays. Oil fromfingerprints can affect the reading when analyzing for lowlevels of sulfur. Wrinkles in the film will affect
29、 the number ofsulfur X-rays transmitted. Therefore, the importance of thefilms tautness and cleanliness cannot be over stressed. Reca-librate the analyzer when you change the type or thickness ofthe window film.8.3 Polyester films often contain impurities that may affectthe measurement of low levels
30、 of sulfur and may vary from lotto lot. Therefore, if using a polyester film, check the calibrationwith the start of each new roll.8.4 X-ray films may vary in thickness from batch to batch.Check the calibration when starting a new roll of any film.8.5 Samples of high aromatic count may dissolve poly
31、esterand polycarbonate films. In these cases, other materials besidesthese films may be used for X-ray windows, provided that theydo not contain any elemental impurities that can adverselyaffect the results obtained by this test method.9. Calibration9.1 Prepare calibration standards by the careful p
32、reparationby mass of a 50:50 mixture (based on sulfur content) of thecertified thiophene and 2-methylthiophene or n-butyl sulfidewith 20 to 80 % mixture of tolueneisooctane or other suitablebase material (see 5.1). Exact standards of the nominal sulfurconcentrations listed in Table 1 are recommended
33、.9.2 Preparation of Stock Standard:Weigh approximately 0.657 g of thiophene and 0.767 g of2-methylthiophene and record the masses to the nearest 0.1 mg,or weigh 2.286 of n-butyl sulfide to the nearest 0.1 mg. Add thestandard materials to a tared 100 mL volumetric flask. Addmixed solvent of 20 % tolu
34、ene and 80 % isooctane (by volume)or other base material (see 5.1) to a net mass of 50.000 + 0.010TABLE 1 Nominal Sulfur StandardsRange 1Sulfur Concentration,mg/kgRange 2Sulfur Concentration,mg/kg0 1005 25010 50050 1000100 D 6334 98 (2003)e12g. This stock standard contains approximately 10 mg/g sulf
35、ur.Correct the concentration by multiplying the measured massesby the sulfur equivalency in each of the standards, that isthiophene grams 3 0.3803 3 purity plus 2-methylthiophenegrams 3 0.3260 3 purity (or n-butyl sulfide grams 3 0.21913 purity) = weight of sulfur in the standard solution. Dividethi
36、s number by the total mass of the standards and basematerial added to them, multiply by 1000 mg/g and the resultis the actual sulfur concentration in mg/g. This calculation is asfollows:S, mg/g 5 1000 3T 3 0.3803 3 P 1 M 3 0.3260 3 PF(1)S, mg/g 5 1000 3DB 3 0.2187 3 PF(2)where:S = final sulfur conce
37、ntration,T = mass of thiophene added,M = mass of 2-methylthiophene added,DB = mass of di-n-butyl sulfide added,P = purity of the standard material, andF = final mass of mixture.9.3 Preparation of Diluted Standard:Dilute 25.0 mL of stock standard to 250 mL using the basematerial. This gives a standar
38、d of approximately 1000 mg/kg.Divide the standard concentration calculated in 9.2 by 10 todetermine the actual concentration.9.4 Serial Dilutions:Prepare serial dilutions of the diluted standard by diluting thefollowing volumes to 100 mL using the base material:0.5 mL = 5 mg/kg1.0 mL = 10 mg/kg5.0 m
39、L = 50 mg/kg10.0 mL = 100 mg/kg25.0 mL = 250 mg/kg50.0 mL = 500 mg/kgDiluted Standard = 1000 mg/kgNOTE 2Prepare calibrations up to 1000 mg/kg sulfur, and dilutesamples with higher concentrations of sulfur to within this concentrationrange.9.5 Establish calibration curve data by carefully measuringth
40、e net intensity of the emitted sulfur radiation from each of thestandards by the procedure described in Sections 10 and 11.9.6 Construct a calibration model by:9.6.1 Using the software and algorithms supplied by theinstrument manufacturer.9.6.2 Fitting the data to an equation of the type:S 5 aR 1 b
41、(3)where:S = sulfur concentration, mg/kg,R = net intensity for the sulfur radiation,a = slope of the calibration curve, andb = intercept of the calibration curve.9.6.3 Plot corrected net intensity in counts per second (cps)versus sulfur concentration. Plot data in two ranges listed inTable 1.9.7 Dur
42、ing collection of calibration data, measure the inten-sity of the drift monitor standards. Use the intensities fromthese standards to correct for day to day instrument sensitivity.This value corresponds to A in Eq 5, Section 11. Manyinstrument manufacturers have built drift correction proceduresinto
43、 their software.9.8 At the completion of the calibration, measure one ormore independent calibration check standards to verify theaccuracy of the calibration curve. These standards (see 7.7) areindependent of the calibration set. The measured value shallagree with the standard value within 62 % rela
44、tive or 2 ppm,whichever is greater.NOTE 3NIST traceable gasoline standards are available at the 1, 10,40, and 300 mg/kg levels. Other concentrations may be prepared bydilution of these standards with a solvent of similar matrix to the standardspreviously prepared.10. Procedure10.1 Measure the intens
45、ity of the drift correction monitor(s)used in 9.7. The value determined corresponds to B in Eq 5,Section 11. This measurement may not be required on highstability instrumentation. Determine the value of F8 in Eq 6,Section 11 at regular intervals by measuring the peak andbackground count rates on the
46、 solvent blank. This measure-ment may not be needed on some instruments.10.2 Place the sample in an appropriate cell using tech-niques consistent with good practice for the particular instru-ment being used. Although sulfur radiation will penetrate onlya small distance into the sample, scatter from
47、the sample cupand the sample may vary to such an extent that a specificamount or a minimum amount of sample shall be used.Generally, filling the cup to one-half capacity is sufficient.Once this amount is established for each instrument, thisvolume of sample is used for each measurement.10.3 Place th
48、e sample in the X-ray beam, and allow theX-ray optical atmosphere to come to equilibrium.10.4 Determine the intensity of the sulfur Karadiation at5.373 by making counting rate measurements at the preciseangular settings for this wavelength.NOTE 4Take a sufficient number of counts to satisfy at least
49、 a 1.0 %expected coefficient of variation when practical. When sensitivity orconcentration, or both, make it impractical to collect a sufficient numberof counts to achieve a 1.0 % coefficient of variation, accepted techniques,which will allow the greatest statistical precision in the time allotted foreach analysis, should be used. Calculate the coefficient of variation asfollows:Coefficient of variation,%5 100 =Ns1 Nb!/Ns2 Nb! (4)where:Ns= gross number of counts collected at sulfur line, andNb= gross number of counts collected at background wavelength (onthe ba
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