1、Designation: D6550 10 (Reapproved 2015)Standard Test Method forDetermination of Olefin Content of Gasolines bySupercritical-Fluid Chromatography1This standard is issued under the fixed designation D6550; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he 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. Scope1.1 This test method covers the determination of the totalamount of olefins in blended mo
3、tor gasolines and gasolineblending stocks by supercritical-fluid chromatography (SFC).Results are expressed in terms of mass % olefins. Theapplication range is from 1 mass % to 25 mass % total olefins.1.2 This test method can be used for analysis of commercialgasolines, including those containing va
4、rying levels ofoxygenates, such as methyl tert/butyl ether (MTBE), diisopro-pyl ether (DIPE), methyl tert/amyl ether (TAME), and ethanol,without interference.NOTE 1This test method has not been designed for the determinationof the total amounts of saturates, aromatics, and oxygenates.1.3 The values
5、stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 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 establish appro-priate safety
6、 and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1319 Test Method for Hydrocarbon Types in Liquid Petro-leum Products by Fluorescent Indicator AdsorptionD4052 Test Method for Density, Relative Density, and APIGr
7、avity of Liquids by Digital Density MeterD5186 Test Method for Determination of the AromaticContent and Polynuclear Aromatic Content of DieselFuels and Aviation Turbine Fuels By Supercritical FluidChromatographyD6296 Test Method for Total Olefins in Spark-ignitionEngine Fuels by Multidimensional Gas
8、 ChromatographyD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6839 Test Method for Hydrocarbon Types, OxygenatedCompounds, and Benzene in Spark Ignition Engine Fuelsby Gas Chromatography3. Terminology3.1 D
9、efinitions of Terms Specific to This Standard:3.1.1 critical pressure, nthe pressure needed to condensea gas to a liquid at the critical temperature.3.1.2 critical temperature, nthe highest temperature atwhich a gaseous fluid can be condensed to a liquid by meansof compression.3.1.3 supercritical fl
10、uid, na fluid maintained above itscritical temperature and critical pressure.3.1.4 supercritical-fluid chromatography (SFC), na typeof chromatography that employs a supercritical fluid as themobile phase.4. Summary of Test Method4.1 A small aliquot of the fuel sample is injected onto a setof two chr
11、omatographic columns connected in series andtransported using supercritical carbon dioxide (CO2)asthemobile phase. The first column is packed with high-surface-area silica particles. The second column contains either high-surface-area silica particles loaded with silver ions or strong-cation-exchang
12、e material loaded with silver ions.4.2 Two switching valves are used to direct the differentclasses of components through the chromatographic system tothe detector. In a forward-flow mode, saturates (normal andbranched alkanes, cyclic alkanes) pass through both columns tothe detector, while the olef
13、ins are trapped on the silver-loadedcolumn and the aromatics and oxygenates are retained on thesilica column. Aromatic compounds and oxygenates are sub-sequently eluted from the silica column to the detector in aback-flush mode. Finally, the olefins are back-flushed from thesilver-loaded column to t
14、he detector.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.04.0C on Liquid Chromatography.Current edition approved April 1, 2015. Published June 2015. Originallyapproved in 2000.
15、 Last previous edition approved in 2010 as D6550 10. DOI:10.1520/D6550-10R15.2For 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 ont
16、he ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.3 A flame-ionization detector (FID) is used for quantita-tion. Calibration is based on the area of the chromatographicsignal for olefins, relative to standard reference
17、 materials,which contain a known mass % of total olefins as corrected fordensity.5. Significance and Use5.1 Gasoline-range olefinic hydrocarbons have been dem-onstrated to contribute to photochemical reactions in theatmosphere, which result in the formation of photochemicalsmog in susceptible urban
18、areas.5.2 The California Air Resources Board (CARB) has speci-fied a maximum allowable limit of total olefins in motorgasoline. This necessitates an appropriate analytical testmethod for determination of total olefins to be used both byregulators and producers.5.3 This test method compares favorably
19、 with Test MethodD1319 (FIA) for the determination of total olefins in motorgasolines. It does not require any sample preparation, has acomparatively short analysis time of about 10 min, and isreadily automated. Alternative methods for determination ofolefins in gasoline include Test Methods D6839 a
20、nd D6296.6. Apparatus6.1 Supercritical-fluid Chromatograph (SFC)Any SFCinstrumentation can be used that has the following character-istics and meets the performance requirements specified inSection 8.NOTE 2The SFC instruments suitable for Test Method D5186 aresuitable for this test method, if equipp
21、ed with two switching valves, asdescribed under 6.1.7.6.1.1 PumpThe SFC pump shall be able to operate at therequired pressures (typically up to about 30 MPa) and delivera sufficiently stable flow to meet the requirements of retention-time precision (better than 0.3 %) and detection background(see Se
22、ction 8). The characteristics of the pump will largelydetermine the optimum column diameter. The use of 4.6 mminternal diameter (i.d.) columns requires a pump capacity of atleast 1 mL min of liquid CO2. Columns with an insidediameter of 2 mm and 1 mm require minimum pump capacitiesof 200 L min and 5
23、0 L min, respectively.6.1.2 DetectorsA FID is required for quantitation. A flowrestrictor shall be installed immediately before the FID. Thisrestrictor serves to maintain the required pressure in thecolumn, while allowing the pump and detector to perform asspecified. A (diode-array or variable wavel
24、ength) UV detectorfor establishing optimum switching times (see Sections 8 and9) is optional. Such a detector can be incorporated in twodifferent manners.6.1.2.1 AUV detector with a very small dead volume can beinserted between the column and the FID and operated inseries.6.1.2.2 A post-column split
25、ting device, consisting of aT-junction with an appropriate flow restrictor to the FID, can beinserted between the column and the UV detector. Using theT-junction, the two detectors can be operated in parallel. Thecombination of restrictors (before the FID and after the UVdetector) shall allow the pu
26、mp and detector to perform asspecified.6.1.3 Sample-inlet SystemA liquid-sample injectionvalve3is required, capable of introducing (sub-)microlitrevolume with a precision better than 0.5 %. A 1 L injectionvolume was found to be adequate in combination with 4.6 mminside diameter columns. Correspondin
27、g injection volumes are200 nL and 50 nL for columns with inside diameters of 2 mmand 1 mm, respectively. The sample inlet system shall beinstalled and operated in a manner such that the chromato-graphic separation is not negatively affected.6.1.4 ColumnsTwo columns of equal inside diameter arerequir
28、ed:6.1.4.1 A high-surface-area-silica column, capable of sepa-rating alkanes and olefins from aromatics as specified inSection 8. Typically, one or several 250 mm long columns areused. These columns are packed with particles having anaverage diameter of 5 m or less, 600 nm (60 ) pores, and asurface
29、area of 350 m2/g.NOTE 3Columns suitable for Test Method D5186 are also suitable forthe present method. A typical example is shown in Table 1.6.1.4.2 A silver-loaded-silica column or a cation-exchangecolumn in the silver form. Cation-exchange columns areclaimed4to yield more stable columns. Typically
30、, one 50 mmor 100 mm long column packed with particles with an averagediameter of 5 m is used for the analysis.NOTE 4Some columns that have been used successfully are shown inTable 1.6.1.5 Column-temperature ControlThe chromatographshall be capable of column temperature control to within0.5 C or les
31、s.6.1.6 Computor or Electronic IntegratorMeans shall beprovided for the determination of accumulated peak areas. Thiscan be done by means of a computer or electronic integrator.The computer or integrator shall have the capability of correct-ing for baseline shifts during the run.3Sample valves with
32、loop volumes down to 50 nL are commercially availablefrom Valco (Houston, TX).4Anderson, P. E., Demirbueker, M., and Blomberg, L. G., Journal ofChromatography, 596, 1991, pp. 301-311.TABLE 1 Typical ColumnsSilica Column Silver-loaded ColumnVendor Merck Vendor Hypersil, Phenomenex, SelerityPacking ma
33、terial Lichrospher SI 60 Packing material Hypersil SCX, Selectosil SCX, Ag+ formParticle size, m 5 Particle size, m 5Length, mm 250 Length, mm 100 or 50Internal diameter, mm 4.6 Internal diameter, mm 4.6D6550 10 (2015)26.1.7 Switching ValvesTwo six-way switching valves areconfigured in accordance wi
34、th the scheme shown in Fig. 1.This configuration allows four different valve positions, de-fined as follows:6.1.7.1 Position ASilica column (forward-flush mode) andsilver-loaded column (forward-flush mode) connected in se-ries. This position is used (1) to inject the sample on the twocolumns, (2) to
35、 elute the saturates, (3) to trap the olefins on thesilver-loaded column, and (4) to retain the aromatics andoxygenates on the silica column.6.1.7.2 Position BSilica column (backflush mode) con-nected in-line; silver-loaded column not in flow path. Thisposition is used to elute the aromatics and pol
36、ar compounds.6.1.7.3 Position CSilica column not in flow path; silver-loaded column (backflush mode) connected in-line. This posi-tion is used to elute the olefins.6.1.7.4 Position DSilica column (forward-flush mode)connected in-line; silver-loaded column not in flow path. Thisposition is used to op
37、timize the separation. Also, this positionallows Test Method D5186 to be performed without changingthe system.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of
38、 the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.5Other grades 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.7.2 AirZero-grad
39、e (hydrocarbon-free) air is used as theFID oxidant. (Warning Air is usually supplied as a com-pressed gas under high pressure, and it supports combustion.)7.3 Calibration SolutionAmixture of hydrocarbons with aknown mass % of olefins of the type and concentration foundin typical gasolines. This olef
40、in mixture can be diluted byweight with olefin-free components, such as alkylate, toluene,xylenes, and oxygenates, such as MTBE, as appropriate toapproximate the composition of the fuels being tested.7.4 Carbon Dioxide (CO2)Supercritical-fluid-chromatographic grade, 99.99 % minimum purity, suppliedp
41、ressurized in a cylinder with a dip tube for removal of liquidCO2.(WarningLiquid at high pressure. Release of pressureresults in production of extremely cold, solid CO2and gas,which can dilute available atmospheric oxygen.)7.5 HydrogenHydrogen of high quality (hydrocarbon-free) is used as the fuel f
42、or the FID. (WarningHydrogen isusually supplied under high pressure and is extremely flam-mable.)7.6 Loading-time MixtureA mixture of a typical alkaneand an olefin, which can be used to determine the loading time(see 8.2.2.3 ( 1) and 8.2.2.3 (2) while protecting the silver-loaded column from exposur
43、e to aromatic compounds.7.7 Performance MixtureA mixture of a typical alkane, amono-aromatic (usually toluene), and a typical mono-olefincan be used to fine-tune this test method and to check itsperformance. A mixture of n-heptane, toluene, and 3-methyl-2-pentene has been successfully used for this
44、purpose.7.8 Quality Control SampleA motor gasoline containingolefins to be used to establish and monitor the precision of theanalytical measurement system.8. Preparation of Apparatus8.1 Install the SFC instrumentation in accordance with themanufacturers instructions. System operating conditions will
45、5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacope
46、iaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.FIG. 1 Configuration of Switching Valves (Shown in Position A)D6550 10 (2015)3depend on the column used and optimization of performance.The conditions listed in Table 1 have been used successfully. Ifthe performance c
47、haracteristics in terms of retention andresolution, specified in 8.2, are not achieved, the temperature,pressure, or mobile-phase flow rate can be modified to achievecompliance. A silica column of low activity can be reactivatedby solvent rinsing, using accepted liquid-chromatographicactivation stra
48、tegies.8.2 System Performance:8.2.1 System OptimizationThe operation of the SFC sys-tem shall be optimized in order to achieve the requiredseparation on the silica column. This process is different if anoptional UV detector is available.8.2.1.1 When the optional UV detector is installed, theseparati
49、on between the three different classes of compoundscan be monitored directly. Saturates show no UV absorption.Olefins show significant absorption at wavelengths up to about220 nm but no absorption at 250 nm or higher.Aromatics showconsiderable absorption at low wavelengths, extended to awavelength of 250 nm and higher. The onset of the elution ofthe olefin fraction (following the saturates fraction) can bemonitored at 220 nm. The elution of the aromatic fraction canbe monitored at 250 nm. In this case, the performance mixture(see 7.6)
