1、Designation: D2268 93 (Reapproved 2017)Standard Test Method forAnalysis of High-Purity n-Heptane and Isooctane byCapillary Gas Chromatography1This standard is issued under the fixed designation D2268; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 Th
3、is test method covers and provides for the analysis ofhigh-purity (greater than 99.5 % by volume) n-heptane andisooctane (2,2,4-trimethylpentane), which are used as primaryreference standards in determining the octane number of a fuel.Individual compounds present in concentrations of less than0.01 %
4、 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.1.2.1 ExceptionThe values given in parentheses are forinformation only.1.3 This standard does not purport to addres
5、s all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was develop
6、ed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Summary of Test M
7、ethod2.1 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 inert gas transports the sample through the co
8、lumn, 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-sponse from each impurity is then compared with tha
9、t 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-heptane and isooctane, which are used as ASTMKno
10、ck Test Reference Fuels. Hydrocarbon impurities orcontaminants, 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 inlet device for introducingminute quantities of sa
11、mple 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. The time constant of neither theelectrometer no
12、r 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 a standard 0100 scale chart using0.10 % by volu
13、me of cyclohexane in n-heptane as defined in7.1.4.2 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 Materials5.1 Carrier GasArgon, Nitrogen, or Helium; 99.99 %
14、 orgreater purity. (WarningCompressed gases under high pres-sure.)5.2 Fuel GasHydrogen; 99.99 % or greater purity.(WarningCompressed gas under high pressure. Extremelyflammable gas.)1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants a
15、nd is the direct responsibility ofSubcommittee D02.04.0L on Gas Chromatography Methods.Current edition approved Oct. 1, 2017. Published November 2017. Originallyapproved in 1964. Last previous edition approved in 2013 as D2268 93 (2013).DOI: 10.1520/D2268-93R17.Copyright ASTM International, 100 Barr
16、 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recomme
17、ndations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15.3 Oxidant GasAir; 99.99 % or greater purity.(WarningCompressed gases under high pressure.)5.4 CyclohexaneAt least 99 mol % pure, to be used asinternal standard. (WarningFlammable liquid and harmful ifinges
18、ted or inhaled.)5.5 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, 32
19、1, or 347 stainless 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 requireme
20、ntsof the method.6.1 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
21、steeltubing (0.25 mm (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 m to 9 m
22、to 12 m(40 ft) of capillary tubing through a 1.6 mm (116 in.) Swagelokunion.6.2 Clean the tubing by passing 25 mL to 30 mL (5 to 6reservoir volumes) of n-pentane through the tubing with about1.7 MPa to 2.1 MPa (250 psig to 300 psig gage) of inert gas.After the column has been cleaned, disconnect the
23、 upstreamend of the reservoir tube and allow the pressure in the tubingto return to atmospheric.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
24、column at 500 psig (3.5 MPagage) until 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 of40 drops min to 60 drops min. When the coating solution hasbeen expelled from the column, r
25、educe the inlet pressure to345 kPa (50 psig gage) and allow gas to pass through thecolumn for 1 h to 2 h. Disconnect the 9 m to 12 m (30 ft to40 ft) tail section and then mount the column in the chromato-graph.6.4 To test column resolution use Fig. 1 and calculate R,from the distance between the cyc
26、lohexane and n-heptanepeaks at the peak maxima, d, and the widths of the peaks at thebaseline, Y1and Y2.R 5 2d12 d2!/Y11Y2! (1)Resolution (R), using the above equation, must exceed avalue of 10.7. Sample Preparation7.1 Place 20 mL to 30 mL of the reference fuel (n-heptaneor isooctane) into a 100 mL
27、volumetric flask which has beenpreviously weighed.7.2 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
28、g. From these weights (masses) and therelative density (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 at20 C = 0.7786; n-heptane =
29、0.6838, and 2,2,4-trimethylpen-tane = 0.6919.)Cyclohexane, volume% 5 wt cyclohexane/rel dens cyclohexane (2) wt reference fuel/rel dens reference fuel! 31008. Procedure8.1 Adjust the operating variables to optimum conditions.Temperatures should be as follows: Injection port and splitter150 C to 250
30、C, column at optimum temperature and detectorgreater than 100 C. 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 cons
31、idered in choosing the correct volume ofsample to inject. Volumes entering the column in the range of0.002 L 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
32、 conditions. Typical chromato-grams of ASTM n-heptane and ASTM isooctane are shown inFig. 2. Relative retention time data for a number of hydrocar-bons over squalane at 30 C are given in Table 1. The retentiontime data of Table 1 are corrected for the gas holdup of thecolumn and are relative to n-he
33、ptane. Argon was used as thecarrier gas.8.4 Hydrocarbons that are commonly found as impurities inASTM n-heptane and ASTM isooctane are listed in Table 2.FIG. 1 Column Resolution (R).D2268 93 (2017)29. Calculation9.1 After identifying the various impurities, measure thepeak area of each impurity peak
34、 and that of the internalstandard, cyclohexane, by ball and disk integrator or electronicintegrator. Calculate the volume percent of each impurity asfollows:VI5VS3PAIPAS3SI3 100 2 VS!3100 (3)where:VI= volume percent of the impurity to be determined,VS= volume percent of the internal standard, cycloh
35、exane,PAI= peak area of the impurity to be determined,PAS= 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 respo
36、nse is givenfor several hydrocarbons relative to cyclohexane 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
37、 test method as determined bystatistical examination of 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 testColumn: 0.25 mm (0.010 in.) inside
38、 diameter by 61 m (200 ft) stainless steelCoating: squalaneTemperature: 30 CInlet Pressure: 110 kPa (16 psi gage) argonFlow Rate: 0.85/minLinear Velocity: 150 mmDetector: hydrogen flame ionizationSample Size: 0.2 L split 100 to 1FIG. 2 Chromatogram of ASTM n-Heptane and ASTM IsooctaneTABLE 1 Relativ
39、e Retention Data for Various Hydrocarbons OverSqualane at 30 C(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-Hexane 0.332,2-Dimethylpentane 0.43Methylcyclopentane 0.432,4-Dimethylpentane 0.46Ben
40、zene 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-Dimethylcyclopentane 0.843-Ethylpentane 0.851-trans-2-Dimethylcyclopentane 0.852,2,4-Trimet
41、hylpentane (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 1.422,2,3-Trimethylpentane 1.481-trans-2-cis-4-Trimethylcyclopentane 1.52Toluene 1.54
42、3,3-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-HeptaneMajor Minor1-cis-2-Dimethylcyclopentane 2-Methylhexane2,3-DimethylpentaneMeth
43、ylcyclohexane 1,1-Dimethylcyclopentane2,2,4-Trimethylpentane (isooctane) 3-Methylhexane1-trans -2-Dimethylcyclopentane3-EthylpentaneImpurities in ASTM IsooctaneMajorn-Heptane2,2-Dimethylhexane2,5-Dimethylhexane2,4-Dimethylhexane2,2,3-Trimethylpentane2,3,4-Trimethylpentane2,3,3-TrimethylpentaneToluen
44、eD2268 93 (2017)3material would, in the long run, in the normal and correctoperation of the test method, exceed the following values onlyone case in twenty:0.010% by volume at levels . 99.5 % by volume (4)10.1.2 ReproducibilityThe difference between two singleand independent results obtained by diff
45、erent operators work-ing in different laboratories on identical test material would, inthe long run, in the normal and correct operation of the testmethod, exceed the following values only one case in twenty:0.054 % by volume at levels . 99.5 % by volume (5)10.2 The above precision values are based
46、on cooperativedata from seven laboratories using five samples. Calculationswere performed using peak area. Both electronic integrationand triangulation were employed.10.3 Since there are no acceptable reference test methodsfor comparison, no statement of bias can be made.11. Keywords11.1 ASTM knock
47、test reference fuels; capillary column;gas chromatography; isooctane; 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 vali
48、dity of any such patent rights, and the riskof infringement of such 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 comm
49、ents are invited either for revision of this standard or for additional 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 ASTM 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,Unite
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