1、Designation: D 6550 05An American National StandardStandard Test Method forDetermination of Olefin Content of Gasolines bySupercritical-Fluid Chromatography1This standard is issued under the fixed designation D 6550; 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.1. Scope*1.1 This test method covers the determination of the totalamount of olefin
3、s in blended motor gasolines and gasolineblending stocks by supercritical-fluid chromatography (SFC).Results are expressed in terms of mass % olefins. Theapplication range is from 1 to 25 mass % total olefins.1.2 This test method can be used for analysis of commercialgasolines, including those conta
4、ining varying levels of oxygen-ates, such as methyl tert/butyl ether (MTBE), diisopropyl ether(DIPE), methyl tert/amyl ether (TAME), and ethanol, withoutinterference.NOTE 1This test method has not been designed for the determinationof the total amounts of saturates, aromatics, and oxygenates.1.3 The
5、 values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.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-pria
6、te safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1319 Test Method for Hydrocarbon Types in LiquidPetroleum Products by Fluorescent Indicator AdsorptionD 4052 Test Method for Density and Relative Densit
7、y ofLiquids by Digital Density MeterD 5186 Test Method for Determination of the AromaticContent and PolynuclearAromatic Content of Diesel Fuelsand Aviation Turbine Fuels by Supercritical Fluid Chro-matographyD 6293 Test Method for Oxygenates and Paraffin, Olefin,Naphthene, Aromatic (O-PONA) Hydrocar
8、bon Types inLow-Olefin Spark Ignition Engine Fuels by Gas Chroma-tographyD 6296 Test Method for Total Olefins in Spark-ignitionEngine Fuels by Multi-dimensional Gas ChromatographyD 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformance
9、3. Terminology3.1 Definitions 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
10、.3 supercritical fluid, 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 o
11、nto a setof two chromatographic 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 st
12、rong-cation-exchange 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 detec
13、tor, while the olefins 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
14、-loaded column to the detector.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.04 on Hydrocarbon Analysis.Current edition approved Nov. 1, 2005. Published November 2005. Originallyapproved in 20
15、00. Last previous edition approved in 2000 as D 655000.2For 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 Su
16、mmary of 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.4.3 A flame-ionization detector (FID) is used for quantita-tion. Calibration is based on the area of the chromatographicsigna
17、l for olefins, relative to standard reference 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 formati
18、on of photochemicalsmog in susceptible urban 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 prod
19、ucers.5.3 This test method compares favorably with Test MethodD 1319 (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 ofol
20、efins in gasoline include Test Methods D 6293 and D 6296.6. 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 D
21、 5186 aresuitable for this test method, if equipped 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 (b
22、etter than 0.3 %) and detection background(see Section 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 inside diameterof 2 and 1 mm req
23、uire minimum pump capacities of 200 and50 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 asspe
24、cified. A (diode-array or variable wavelength) 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 opera
25、ted inseries.6.1.2.2 A post-column splitting 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
26、after the UVdetector) shall allow the pump 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
27、-mminside diameter columns. Corresponding injection volumes are200 and 50 nL for columns with inside diameters of 2 and 1mm, respectively. The sample inlet system shall be installedand operated in a manner such that the chromatographicseparation is not negatively affected.6.1.4 ColumnsTwo columns of
28、 equal inside diameter arerequired: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, 6
29、00-nm (60-) pores, and asurface area of $350 m2/g.NOTE 3Columns suitable for Test Method D 5186 are also suitablefor the 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 yi
30、eld more stable columns. Typically, one 50 or100-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 temperatur
31、e control to within 0.5Cor less.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 durin
32、g the run.3Sample valves with loop volumes down to 50 nL are commercially availablefrom Valco (Houston, TX).4Anderson, P. E., Demirbueker, M., and Blomberg, L. G., Journal of Chroma-tography, 596, 1991, pp. 301-311.TABLE 1 Typical ColumnsSilica Column Silver-loaded ColumnVendor Merck Vendor Hypersil
33、, Phenomenex, SelerityPacking material 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 4.6D65500526.1.7 Switching ValvesTwo six-way switching valves arecon
34、figured in accordance with 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)and silver-loaded column (forward-flush mode) connected inseries. This position is used (1) to inject the sample on
35、the twocolumns, (2) to 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
36、 the aromatics and polar 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. This
37、position is used to optimize the separation. Also, this positionallows Test Method D 5186 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 t
38、o the specifications of 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 determi
39、nation.7.2 AirZero-grade (hydrocarbon-free) air is used as theFID oxidant. (WarningAir is usually supplied as a com-pressed gas under high pressure, and it supports combustion.)7.3 Calibration SolutionA mixture of hydrocarbons witha known mass % of olefins of the type and concentration foundin typic
40、al gasolines. This olefin 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 % mi
41、nimum purity, suppliedpressurized 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
42、) is used as the fuel for 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-load
43、ed column from exposure 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 succe
44、ssfully used for this 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 ope
45、rating conditions willdepend on the column used and optimization of performance.The conditions listed in Table 1 have been used successfully. Ifthe performance characteristics in terms of retention and5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington,
46、 DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, 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.FIG. 1 Configura
47、tion of Switching Valves (Shown in Position A)D6550053resolution, 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-chromatographica
48、ctivation strategies.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 installe
49、d, theseparation 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
