ASTM_D_2268_-_93_2013.pdf

Designation:D226893(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 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 This 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%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 given 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 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 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-sponse 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-heptane and isooctane,which are used as ASTMKnock Test Reference Fuels.Hydrocarbon impurities orcontaminants,which can adversely affect the octane number ofthese fuels,are precisely determined by this method.4.Apparatus4.1 ChromatographGaschromatographshouldbeequipped with a split-stream inlet 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.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 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 Materials5.1 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 OxidantGasAir;99.99%orgreaterpurity.(WarningCompressed gases under high pressure.)5.4 CyclohexaneAt least 99 mol%pure,to be used asinternal standard.(WarningFlammable 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 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(2008).DOI:10.1520/D2268-93R13.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.7 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.Preparation of Resolving ColumnNOTE1There 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 stee