1、Designation: D 2268 93 (Reapproved 2003)e1An American National StandardStandard Test Method forAnalysis of High-Purity n-Heptane and Isooctane by CapillaryGas Chromatography1This standard is issued under the fixed designation D 2268; the number immediately following the designation indicates the yea
2、r 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.This standard has been approved for use by agencies of the Departm
3、ent of Defense.e1NOTEWarning notes were editorially moved into the standard text in July 2003.1. Scope1.1 This test method provides for the analysis of high-purity(greater than 99.5 % by volume) n-heptane and isooctane(2,2,4-trimethylpentane), which are used as primary referencestandards in determin
4、ing the octane number of a fuel. Indi-vidual compounds present in concentrations of less than0.01 % can be detected. Columns specified by this test methodmay not allow separation of all impurities in reference fuels.1.2 The values stated in SI units are to be regarded as thestandard. The values give
5、n in parentheses are for informationonly.1.3 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 and health practices and determine the applica-bility of regulatory
6、 limitations prior to use.2. Summary of Test Method2.1 The sample is injected into a capillary gas chromato-graphic column consisting of at least 61 m (200 ft) of stainlesssteel tubing (0.25-mm (0.010-in.) inside diameter), the innerwalls of which are coated with a thin film of stationary liquid.An
7、inert gas transports the sample through the column, inwhich it is partitioned into its individual components. As eachcomponent is eluted from the column, it is detected with ahydrogen flame ionization detector and recorded on a conven-tional strip-chart recording potentiometer. The detector re-spons
8、e from each impurity is then compared with that of aknown quantity of an internal standard. After determining thetotal impurity concentration, the n-heptane, or isooctane purityis obtained by difference.3. Significance and Use3.1 This test method is used for specification analysis ofhigh-purity n-he
9、ptane and isooctane, which are used as ASTMKnock Test Reference Fuels. Hydrocarbon impurities or con-taminants, which can adversely affect the octane number ofthese fuels, are precisely determined by this method.4. Apparatus4.1 ChromatographGas chromatograph should beequipped with a split-stream inl
10、et device for introducingminute quantities of sample without fractionation, a capillarycolumn, and a hydrogen flame ionization detector. An elec-trometer to amplify the low output signal of the hydrogen flameionization detector, and a strip-chart recorder for recording thedetector signal are needed.
11、 The time constant of neither theelectrometer nor the recorder should exceed 1 s.Aball and diskintegrator or electronic integrator for peak area measurementsshould be used. The detection system must have sufficientsensitivity to produce a recorder deflection for cyclohexane ofat least 8 divisions on
12、 a standard 0100 scale chart using 0.10volume percent of cyclohexane in n-heptane as defined in 7.1.4.2 MicrosyringeA microsyringe is needed for injectingthe sample into the split-stream inlet device.4.3 Volumetric Pipet, 0.1-mL capacity.4.4 Analytical Balance, 200-g capacity.5. Reagents and Materia
13、ls5.1 Carrier GasArgon, Nitrogen, or Helium; 99.99% orgreater purity. (WarningCompressed gases under high pres-sure.)5.2 Fuel GasHydrogen; 99.99% or greater purity.(WarningCompressed gas under high pressure. Extremelyflammable gas.)5.3 Oxidant GasAir; 99.99% or greater purity.(WarningCompressed gase
14、s under high pressure.)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 May 10, 2003. Published July 2003. Originallyapproved in 1964. Last pre
15、vious edition approved in 1998 as D 226893 (1998).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.4 CyclohexaneAt least 99 mol % pure, to be used asinternal standard. (WarningFlammable liquid and harmful ifingested or inhaled.)5.5
16、n-PentaneCommercial grade. (WarningVolatileand flammable liquid, and harmful if ingested or inhaled.)5.6 Isooctane (2,2,4-trimethylpentane)(WarningFlammable liquid and harmful if ingested or inhaled.)5.7 SqualaneLiquid phase for gas chromatographic col-umns.5.8 TubingType 316, 321, or 347 stainless
17、steel; 0.25 mm(0.010 in.) inside diameter.6. Preparation of Resolving ColumnNOTE 1There are many different procedures for coating capillarycolumns. A suitable procedure is given in 6.1 through 6.3. Other columnsmay be used provided they meet resolution and repeatability requirementsof the method.6.1
18、 Connect a 229 mm (9-in.) section of stainless steeltubing 6.4 mm (14-in.) outside diameter, total volume ofapproximately 5 mL) to a high-pressure cylinder of argon,helium, or nitrogen through a pressure regulator. Connect atleast 61 m (200 ft) of Type 316, 321, or 347 stainless steeltubing (0.25-mm
19、 (0.010-in.) inside diameter) to the 229-mmsection of 64 mm tubing which is to be used as a reservoir forthe coating solution. The capillary column is generally coiledon a suitable mandrel before coating. To the other end of thecapillary column, connect an additional 30 to 9 to 12 m (40 ft)of capill
20、ary tubing through a 1.6 mm (116-in.) Swagelok union.6.2 Clean the tubing by passing 25 to 30 mL (5 to 6reservoir volumes) of n-pentane through the tubing with about1.7 to 2.1 MPa ( 250 to 300 psig gage) of inert gas. After thecolumn has been cleaned, disconnect the upstream end of thereservoir tube
21、 and allow the pressure in the tubing to return toatmospheric.6.3 Prepare a solution containing 6 volume percent ofsqualane in n-pentane. Fill the reservoir tube with the coatingsolution and promptly connect to the gas cylinder. Pass thecoating solution through the column at 500 psig (3.5 MPagage) u
22、ntil the solution begins issuing from the end of thecapillary tubing; gradually reduce the inlet pressure in order tokeep the flow of the solution at a relatively even rate of 40 to60 drops/min. When the coating solution has been expelledfrom the column, reduce the inlet pressure to 345 kPa (50 psig
23、gage) and allow gas to pass through the column for 1 to 2 h.Disconnect the 9 to 12-m (30 to 40-ft) tail section and thenmount the column in the chromatograph.6.4 To test column resolution use Fig. 1 and calculate R,from the distance between the cyclohexane and n-heptanepeaks at the peak maxima, d, a
24、nd the widths of the peaks at thebaseline, Y1and Y2.R 5 2d12 d2!/Y11 Y2! (1)Resolution (R), using the above equation, must exceed avalue of 10.7. Sample Preparation7.1 Place 20 to 30 mL of the reference fuel (n-heptane orisooctane) into a 100-mL volumetric flask which has beenpreviously weighed.7.2
25、Weigh the sample. Using a 0.10-mL volumetric pipet,add 0.10 mL of the internal standard cyclohexane (99 mol %,min) and reweigh. Dilute to the mark with the n-heptane orisooctane sample and weigh. Use a 200-g analytical balanceaccurate to 60.0002 g. From these weights (masses) and therelative density
26、 (specific gravities) of cyclohexane andn-heptane or isooctane, calculate the volume percent of thecyclohexane internal standard to the nearest 0.001 volumepercent. (Relative density (specific gravity) of cyclohexane at20C = 0.7786; n-heptane = 0.6838, and 2,2,4-trimethylpentane = 0.6919.)Cyclohexan
27、e, volume % 5 wt cyclohexane/rel dens cyclohexane4wt reference fuel/rel dens reference fuel!3100 (2)8. Procedure8.1 Adjust the operating variables to optimum conditions.Temperatures should be as follows: Injection port and splitter150 to 250C, column at optimum temperature and detectorgreater than 1
28、00C. Adjust the excess gas flow through thesplitter to provide a proper sample size to the column.8.2 Using the microsyringe, inject sufficient sample contain-ing the internal standard. Both the sample volume and the splitratio must be considered in choosing the correct volume ofsample to inject. Vo
29、lumes entering the column in the range of0.002 to 0.005 L have been found satisfactory.8.3 The various impurities present in the primary referencestandards can be identified from retention time data obtained atthe same gas chromatographic conditions. Typical chromato-grams of ASTM n-heptane and ASTM
30、 isooctane are shown inFig. 2. Relative retention time data for a number of hydrocar-bons over squalane at 30C are given in Table 1. The retentiontime data of Table 1 are corrected for the gas holdup of thecolumn and are relative to n-heptane. Argon was used as thecarrier gas.8.4 Hydrocarbons that a
31、re commonly found as impurities inASTM n-heptane and ASTM isooctane are listed in Table 2.9. Calculation9.1 After identifying the various impurities, measure thepeak area of each impurity peak and that of the internalstandard, cyclohexane, by ball and disk integrator or electronicintegrator. Calcula
32、te the volume percent of each impurity asfollows:VI5VS3 PAIPAS3 SI3 100 2 VS!3 100 (3)FIG. 1 Column Resolution (R).D 2268 93 (2003)e12where:VI= volume percent of the impurity to be determined,VS= volume percent of the internal standard, cyclohex-ane,PAI= peak area of the impurity to be determined,PA
33、S= peak area of the internal standard, cyclohexane, andSI= the response per unit volume of the hydrogen flameionization detector to the impurity relative to theresponse per unit volume to cyclohexane.9.2 Hydrogen flame ionization detector response is givenfor several hydrocarbons relative to cyclohe
34、xane in Table 3.Report the volume percent of each impurity.9.3 Total the concentrations of the individual impurities andthen calculate the purity of the n-heptane or isooctane sampleby difference.10. Precision and Bias10.1 The precision of this test method as determined bystatistical examination of
35、interlaboratory results is as follows:10.1.1 RepeatabilityThe difference between successivetest results obtained by the same operator with the sameapparatus under constant operating conditions on identical testmaterial would, in the long run, in the normal and correctoperation of the test method, ex
36、ceed the following values onlyone case in twenty:0.010 volume % at levels . 99.5 volume %. (4)10.1.2 ReproducibilityThe difference between two singleand independent results obtained by different operators work-ing in different laboratories on identical test material would, inthe long run, in the nor
37、mal and correct operation of the testmethod, exceed the following values only one case in twenty:0.054 volume % at levels . 99.5 volume %. (5)10.2 The above precision values are based on cooperativedata from seven laboratories using five samples. Calculationswere performed using peak area. Both elec
38、tronic integrationand triangulation were employed.Column: 0.25 mm (0.010-in.) inside diameter by 61-m (200-ft) stainless steelCoating: squalaneTemperature: 30CInlet Pressure: 110 kPa (16 psi gage) argonFlow Rate: 0.85/minLinear Velocity: 150 mmDetector: hydrogen flame ionizationSample Size: 0.2 L sp
39、lit 100 to 1FIG. 2 Chromatogram of ASTM n-Heptane and ASTM IsooctaneTABLE 1 Relative Retention Data for Various Hydrocarbons OverSqualane at 30C(n-Heptane = 1.00)Isopentane 0.08n-Pentane 0.112,2-Dimethylbutane 0.16Cyclopentane 0.222,3-Dimethylbutane 0.232-Methylpentane 0.243-Methylpentane 0.27n-Hexa
40、ne 0.332,2-Dimethylpentane 0.43Methylcyclopentane 0.432,4-Dimethylpentane 0.46Benzene 0.482,2,3-Trimethylbutane 0.503,3-Dimethylpentane 0.62Cyclohexane 0.632-Methylhexane 0.692,3-Dimethylpentane 0.721,1-Dimethylcyclopentane 0.713-Methylhexane 0.761-cis-3-Dimethylcyclopentane 0.811-trans-3-Dimethylcy
41、clopentane 0.843-Ethylpentane 0.851-trans-2-Dimethylcyclopentane 0.852,2,4-Trimethylpentane (isooctane) 0.87n-heptane 1.001-cis-2-Dimethylcyclopentane 1.202,2-Dimethylhexane 1.221,1,3-Trimethylcyclopentane 1.24Methylcyclohexane 1.252,5-Dimethylhexane 1.36Ethylcyclopentane 1.392,4-Dimethylhexane 1.42
42、2,2,3-Trimethylpentane 1.481-trans-2-cis-4-Trimethylcyclopentane 1.52Toluene 1.543,3-Dimethylhexane 1.561-trans-2-cis-3-Trimethylcyclopentane 1.632,3,4-Trimethylpentane 1.712,3,3-Trimethylpentane 1.81TABLE 2 Hydrocarbon Impurities Commonly Found in ASTMn-Heptane and IsooctaneImpurities in ASTM n-Hep
43、taneMajor Minor1-cis-2-Dimethylcyclopentane 2-Methylhexane2,3-DimethylpentaneMethylcyclohexane 1,1-Dimethylcyclopentane2,2,4-Trimethylpentane (isooctane) 3-Methylhexane1-trans-2-Dimethylcyclopentane3-EthylpentaneImpurities in ASTM IsooctaneMajorn-Heptane2,2-Dimethylhexane2,5-Dimethylhexane2,4-Dimeth
44、ylhexane2,2,3-Trimethylpentane2,3,4-Trimethylpentane2,3,3-TrimethylpentaneTolueneD 2268 93 (2003)e1310.3 Since there are no acceptable reference test methodsfor comparison, no statement of bias can be made.11. Keywords11.1 ASTM knock test reference fuels; capillary column;gas chromatography;isooctan
45、e;n-heptaneASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such
46、rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additio
47、nal standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the A
48、STM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the ab
49、oveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).TABLE 3 Hydrogen Flame Ionization Detector Relative ResponseData (Response per Unit Volume Relative to Cyclohexane)CompoundRelativeResponseper UnitVolumeIsopentane 0.84n-Pentane 0.842,2-Dimethylbutane 0.87Cyclopentane 1.002,3-Dimethylbutane 0.882-Methylpentane 0.873-Methylpentane 0.89n-Hexane 0.872,2-Dimethylpentane 0.88Methylcyclopentane 0.972,4-Dimethylpentane 0.88Benzene 1.272,2,3-Trimethylbutane 0.913,3-Dimethylpentan
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