1、Designation: D2268 93 (Reapproved 2013)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 Department of Defense.1. Scope1.1 This te
3、st 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 % can
4、 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 given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety
5、 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 limitations prior to use.2. Summary of Test Method2.1 The sample is injected into a capillary gas chro
6、mato-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 column, inwhich it is partitioned into its individual compo
7、nents. 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 that of aknown quantity of an internal standard. After deter
8、mining 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 ASTMKnock Test Reference Fuels. Hydrocarbon impurities orcontami
9、nants, 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 sample without fractionation, a capillarycolumn, and a hydr
10、ogen 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 nor the recorder should exceed 1 s.Aball and diskintegrator
11、 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 using 0.10volume percent of cyclohexane in n-heptane as defined in 7.1.4.2 M
12、icrosyringeA 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% orgreater purity. (WarningCompressed gases under high
13、 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 gases under high pressure.)5.4 CyclohexaneAt least 99 mol % pure, to be used asinternal standard. (WarningFla
14、mmable liquid and harmful ifingested 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.)1This test method is under the jurisdiction of
15、 ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility ofSubcommittee D02.04.0L on Gas Chromatography Methods.Current edition approved Oct. 1, 2013. Published October 2013. Originallyapproved in 1964. Last previous edition approved in 2008 as D2268 93(
16、2008).DOI: 10.1520/D2268-93R13.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.7 SqualaneLiquid phase for gas chromatographic col-umns.5.8 TubingType 316, 321, or 347 stainless steel; 0.25 mm(0.010 in.) inside diameter.6. Preparatio
17、n 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 Connect a 229 mm (9-in.) section of stainless steeltub
18、ing 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 (0.010-in.) inside diameter) to the 229-mmsection of 6
19、4 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 capillary tubing through a 1.6 mm (116-in.) Swagelok union.6.
20、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 and allow the pressure in the tubing to return toatmos
21、pheric.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) until the solution begins issuing from the end of thecap
22、illary 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 psiggage) and allow gas to pass through the column for 1 to
23、 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, and the widths of the peaks at thebaseline, Y1and Y2.R 5
24、 2d12 d2!/Y11Y2! (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 Weigh the sample. Using a 0.10-mL volumetric pipet,add 0
25、.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 (specific gravities) of cyclohexane andn-heptane or iso
26、octane, 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-trimethylpen-tane = 0.6919.)Cyclohexane, volume% 5 wt cyclohexane/rel dens cyclohexane (2) wt
27、 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 to 250C, column at optimum temperature and detectorgreater than 100C. Adjust the excess gas flow through thesplitter to
28、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. Volumes entering the column in the range of0.002 to 0.005
29、 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 isooctane are shown inFig. 2. Relative retention time
30、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 are commonly found as impurities inASTM n-heptane and AS
31、TM iso octane 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. Calculate the volume percent of each impurity asfollows:VI5VS
32、3PAIPAS3SI3 100 2 VS!3100 (3)where:FIG. 1 Column Resolution (R).D2268 93 (2013)2VI= volume percent of the impurity to be determined,VS= volume percent of the internal standard, cyclohexane,PAI= peak area of the impurity to be determined,PAS= peak area of the internal standard, cyclohexane, andSI= th
33、e 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 cyclohexane in Table 3.Report the volume percent of each impurity.9.
34、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 interlaboratory results is as follows:10.1.1 RepeatabilityThe
35、 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, exceed the following values onlyone case in twenty:0.010 volume
36、% 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 normal and correct operation of the testmethod, exceed the followin
37、g 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 electronic integrationand triangulation were employed.10.3 Since there
38、are no acceptable reference test methodsfor comparison, no statement of bias can be made.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: hydroge
39、n flame ionizationSample Size: 0.2 L split 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-Meth
40、ylpentane 0.243-Methylpentane 0.27n-Hexane 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-Dimet
41、hylcyclopentane 0.811-trans-3-Dimethylcyclopentane 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 1.36Ethyl
42、cyclopentane 1.392,4-Dimethylhexane 1.422,2,3-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-Hepta
43、ne and IsooctaneImpurities in ASTM n-HeptaneMajor 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-D
44、imethylhexane2,5-Dimethylhexane2,4-Dimethylhexane2,2,3-Trimethylpentane2,3,4-Trimethylpentane2,3,3-TrimethylpentaneTolueneD2268 93 (2013)311. Keywords11.1 ASTM knock test reference fuels; capillary column;gas chromatography; isooctane; n-heptaneASTM International takes no position respecting the val
45、idity 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 rights, are entirely their own responsibility.This standard is sub
46、ject 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 additional standardsand should be addressed to ASTM International Headqua
47、rters. 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 standa
48、rd 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 aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serv
49、iceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).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
