1、Designation: D 6920 07An American National StandardStandard Test Method forTotal Sulfur in Naphthas, Distillates, ReformulatedGasolines, Diesels, Biodiesels, and Motor Fuels byOxidative Combustion and Electrochemical Detection1This standard is issued under the fixed designation D 6920; the number im
2、mediately 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1
3、This test method covers the determination of total sulfurin liquid hydrocarbons, boiling in the range from approxi-mately 25 to 400C, with viscosities between approximately0.2 and 10 cSt (mm/S) at room temperature. This test methodis applicable to naphthas, distillates, and motor fuels such asgasoli
4、nes, reformulated gasolines, gasohols, diesels and biodie-sels containing approximately 1 to 100 mg/kg total sulfur ingasoline type products, and approximately 1 to 40 mg/kg sulfurin diesel type products.1.2 The detector response for this technique within thescope of this test method is linear with
5、sulfur concentration.1.3 Based on interlaboratory study, the pooled limit ofquantitation of this test method is 3 mg/kg for gasoline and900C) where oxygen is introduced. Sulfur compounds,present in the specimen are converted to sulfur dioxide (SO2).Sulfur dioxide is reacted with the sensing electrod
6、e in a3-electrode electrochemical cell. This reaction produces a1This 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 Dec. 1, 2007. Published January
7、2008. Originallyapproved in 2003. Last previous edition approved in 2003 as D 692003.2For 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
8、page onthe ASTM website.3Withdrawn.4Available from U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C
9、700, West Conshohocken, PA 19428-2959, United States.measurable current that is directly proportional to the amountof sulfur in the original sample material. The reactions thatoccur are as follows:Combustion:R-S+O2.900CCO2+H2O+SO2+ oxidesDetection:SO2+2H2OElectrolyteH2SO4+2H+2e5. Significance and Us
10、e5.1 All sulfur present in petroleum products is converted tosulfur oxides upon combustion, which is a significant pollutantof the atmosphere. This test method can be used to monitor thetotal sulfur levels in these fuels.NOTE 1Virtually all sulfur compounds will be detected by thistechnique.6. Inter
11、ferences6.1 Moisture produced during the combustion step caninterfere if not removed prior to the detector.6.2 Equivalent amounts of nitrogen in the sample may alsointerfere.7. Apparatus7.1 Pyrolysis Furnace, a furnace capable of maintaining atemperature sufficient to volatilize and combust all of t
12、hesample and oxidize the sulfur to SO2.The furnace temperaturesfor petroleum substances shall be as recommended by themanufacturer.7.2 Quartz Combustion Tube, capable of withstanding 900to 1200C. The inlet end of the tube holds a septum for syringeentry of the sample and has inlet fittings or side a
13、rms for theintroduction of oxygen (O2) and inert gas. The construction issuch that the inert gas (or inert gas and oxygen mixture) sweepsthe inlet zone transporting all of the volatilized sample into ahigh temperature oxidation zone. The oxidation section shallbe large enough to ensure complete oxid
14、ation of the sample.7.3 Drier TubeThe reaction products include water vaporthat must be removed prior to measurement by the electro-chemical detector. This can be accomplished with a magne-sium perchlorate scrubber or a membrane drying tube (perme-ation drier), or both.7.4 Electrochemical Detector,
15、capable of measuring SO2inthe combustion gas stream.7.5 Data Reduction System, having the capability of mea-suring, amplifying, and integrating the current from the elec-trochemical detector. The amplified or integrated output signalshall be applied to a digital display or some other data reportingd
16、evice.7.6 Microlitre Syringe, of 5, 10, 25, 50, or 100 L capacitycapable of accurately delivering microlitre quantities is re-quired. The needle should be long enough to reach the hottestportion of the inlet section of the furnace when injecting thesample.7.7 Recorder (Optional).7.8 Constant Rate In
17、jector or Automatic Sampler System(s)(Optional), capable of delivering a sample at a preciselycontrolled rate.8. Reagents8.1 Purity of ChemicalsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Co
18、mmit-tee onAnalytical Reagents of theAmerican Chemical Society,5where such specifications are available. Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Magnesium Perchlo
19、rate, Mg(ClO4)2(WarningMagnesium perchlorate is a strong oxidizer, and is an irritant)for drying products of the combustion (if a permeation drier isnot used).8.3 Inert GasEither argon (Ar) or helium (He) may beused. The purity should be no less than 99.99 mol %.8.4 OxygenThe purity should be no les
20、s than 99.99 mol %(WarningOxygen of this purity will vigorously acceleratecombustion).8.5 SolventThe solvent chosen should be capable ofdissolving the sulfur-containing compound used to prepare thestandard and, if necessary, the samples. The solvent of choiceshould have a boiling point similar to th
21、e samples beinganalyzed and it should contain less sulfur than is in the lowestsample to be analyzed. Suggested possibilities include, but arenot limited to: toluene, iso-octane, methanol, cetane, or othersolvent similar to the compound present in the sample to beanalyzed (WarningFlammable solvents)
22、.NOTE 2A quick screening can be conducted by injecting the solventand sample once or twice and comparing relative integral response.8.6 Sulfur Stock Solution, 1000 g S/mLPrepare a stocksolution by accurately weighing to the nearest 0.1 mg, 0.576 gof dibenzothiophene into a tared 100-mL volumetric fl
23、ask.Dilute to volume with selected solvent. This stock may befurther diluted to desired sulfur concentrations.g S/mL 5 (1)exact weight of dibenzothiophene mg!332.06 3 1000 g/mg!100 mL 3 184.27NOTE 3Dibenzothiophene may be used for calibration throughout theboiling range of this test method.8.7 Diben
24、zothiophene (C12H8S), CAS 132650(WarningDibenzothiophene is an irritant) molecular weight184.27, purity 99.8 %.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society
25、, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.TABLE 1 Dilutions for Working StandardsDesired g S/mL mL to pipet From g/mL Dilution volume, mL100.0 10.0
26、1000.0 100.010.0 10.0 100.0 100.01.0 10.0 10.0 100.00.5 5.0 10.0 100.00.05 5.0 1.0 100.0D69200728.8 Sulfur Working Standard Solutions, 0.5, 1.0, 10.0, and100.0 g S/mLThe working standards are prepared byaccurately pipetting and diluting each to volume with solvent.To obtain the following concentrati
27、ons 100.0, 10.0, 1.0, and 0.5g S/mL see Table 1.NOTE 4Working standards should be prepared fresh on a regularbasis, depending upon frequency of use and age.9. Hazards9.1 Consult current OSHA regulations, suppliers MaterialsSafety Data Sheets, and local regulations for all materials usedin this test
28、method.9.2 High temperature is employed in this test method. Extracare must be exercised when using flammable materials nearthe high temperature furnace.10. Sample Handling10.1 Collect the samples in accordance with PracticeD 4057 or Practice D 4177 as appropriate.10.2 To preserve sample integrity (
29、consistency) and preventthe loss of volatile components, which may be present in somesamples, do not uncover samples any longer than necessary.Analyze samples as soon as possible after taking from the bulksupplies to prevent loss of sulfur or contamination.10.3 Since this procedure is intended for t
30、race levels, caremust be taken to ensure the containers used for the sample, thespecimen, and the working standards do not alter the sampleresult.11. Preparation of Apparatus11.1 Assemble the apparatus in accordance with manufac-turers instructions.11.2 Adjust the gas flows and the combustion temper
31、ature tothe desired operating conditions.12. Calibration and Standardization12.1 Prepare a series of calibration standards using a stocksolution covering the range of operation as described in8.6-8.8, and consisting of sulfur type and matrix similar tosamples to be analyzed.12.2 Volumetric measureme
32、nt of the injected sample can beobtained by filling the syringe to the 80 % level, retracting theplunger so that the lower liquid meniscus falls on the 10 %scale mark, and recording volume of liquid in the syringe.Afterthe sample has been injected, again retract the plunger so thatthe lower liquid m
33、eniscus falls on the 10 % scale mark, andrecord the volume of liquid in the syringe. The differencebetween the two volume readings is the volume of sampleinjected.12.3 Alternatively, the sample injection device may beweighed before and after injection to determine the amount ofsample injected. This
34、test method provides greater precisionthan the volume delivery method, provided a balance with aprecision of 6 0.01 mg is used.12.4 Insert the syringe needle through the inlet septum up tothe syringe barrel and inject the sample or standard at auniform rate of 0.2 to 1.0 L/s. Rate of injection is de
35、pendenton such factors as viscosity, sample type, and sulfur concen-tration. Each user must adopt a method whereby a consistentand uniform injection rate is ensured.NOTE 5For the most consistent injection rate and best analyticalresults, a constant rate injection system or automatic sampling system
36、maybe helpful. Consult manufacturer for recommendations.NOTE 6With direct injection below 2 mg/kg of sulfur, the needle-septum blank may become increasingly important. Error due to this can beavoided by inserting the syringe needle into the hot inlet and allowing theneedle-septum blank to dissipate
37、before injecting the sample.12.5 For the method blank, rinse the syringe thoroughlywith the solvent blank, Then inject the same amount of solventblank as utilized with standards and obtain the reading.Measure the blank a second time and average the results. Thesolvent blank should contain less than
38、0.05 mg/kg of sulfur.12.6 If the system features an automatic calibration proce-dure, repeat the measurement of each calibration standard threetimes. All calibration points shall be used to construct acalibration curve. System performance shall be checked with asuitable calibration standard each day
39、 and when changingconcentration ranges.12.7 For those analyzers not equipped with an automaticcalibration procedure, construct a standard curve as follows:Repeat the determination of each calibration standard and theblank three times to determine the average net response foreach standard. Construct
40、a curve plotting mg/kg of sulfurinjected versus detector response (integration count). Theresponse curve should be linear and shall be checked at leastonce per week.13. Procedure13.1 Sample sizes ranging from 3 to 40 Lare acceptable. Itis advisable that the size of injected sample shall be similar t
41、othe size of injected standard.13.2 Experience dictates the best sample size. Typicalsample sizes are shown in Table 2.13.3 Flush the microlitre syringe several times with theunknown sample. Determine the sample size as described in13.2 and inject it at an even rate as described in 12.4.14. Calculat
42、ion14.1 For analyzers equipped with an automatic calibration,calculate the sulfur content of the sample in parts per millionby weight (mg/kg) by either of the following equations:Sulfur, mg/kg 5 I 2 B! 3 K / V 3 D! (2)Sulfur, mg/kg 5 I 2 B! 3 K / M (3)where:D = density of sample, g/mL,K = dilution f
43、actor,V = volume of sample, L,M = mass of sample, mg,I = visual display reading of sample, andTABLE 2 Concentrations for Suggested Sample SizesSulfur, mg/kg Sample Size, L1 and less up to 2010 up to 10100 up to 5D6920073B = average of visual display readings of blank.14.2 For analyzers not equipped
44、with automatic calibration,calculate the sulfur content of the sample in parts per millionby weight (mg/kg) as follows:Sulfur, mg/kg 5 I 3 S 3 K / V 3 D! (4)where:D = density of sample, g/mL,S = slope of standard curve, mg S/count,V = volume of sample, L,I = detector response, integration counts, an
45、dK = dilution factor (when applicable).15. Precision and Bias615.1 PrecisionThe precision of this test method as deter-mined by the statistical examination of the interlaboratory testresults is as follows. These data were produced from aninterlaboratory study involving 16 laboratories that analyzed
46、atotal of 16 samples for gasoline and 16 samples for diesel. Twoinstruments were used in this interlaboratory study, one fromAPS Technologies and one from Antek Instruments. Since theresults from these instruments were statistically different,precision statements are provided for each of the instrum
47、ents.15.1.1 RepeatabilityThe difference between successiveresults obtained on the same day by the same operator with thesame apparatus under constant operating conditions on identi-cal test material would, in the long run, in the normal andcorrect operation of the test method, exceed the followingva
48、lues in Table 3 only in one case in twenty.15.1.2 ReproducibilityThe difference between two singleand independent results obtained by different operators work-ing in different laboratories on identical test material would inthe long run, exceed the values in Table 4 only in one case intwenty.15.2 Bi
49、asBased on the analysis of NIST Standard Refer-ence Materials (SRM), there was no significant bias for the testmethod on either instrument between the results by this testmethod and the certified values by NISTfor diesel SRM 2723a.For gasoline SRMs, there was no bias for SRM 2299 contain-ing 13.6 mg/kg sulfur. However, for gasoline SRM 2298containing 4.6 mg/kg total sulfur there was a bias of 0.78mg/kg for the test method on both instruments.16. Quality Control16.1 Confirm the performance of the instrument or the testprocedure by re
