ASTM_D_1945_-_14.pdf

Designation:D194514Standard Test Method forAnalysis of Natural Gas by Gas Chromatography1This standard is issued under the fixed designation D1945;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.1.Scope*1.1 This test method covers the determination of the chemi-cal composition of natural gases and similar gaseous mixtureswithin the range of composition shown in Table 1.This testmethod may be abbreviated for the analysis of lean naturalgases containing negligible amounts of hexanes and higherhydrocarbons,or for the determination of one or morecomponents,as required.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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.Referenced Documents2.1 ASTM Standards:2D2597 Test Method for Analysis of Demethanized Hydro-carbon Liquid Mixtures Containing Nitrogen and CarbonDioxide by Gas ChromatographyE260 Practice for Packed Column Gas Chromatography3.Summary of Test Method3.1 Components in a representative sample are physicallyseparated by gas chromatography(GC)and compared tocalibration data obtained under identical operating conditionsfrom a reference standard mixture of known composition.Thenumerous heavy-end components of a sample can be groupedinto irregular peaks by reversing the direction of the carrier gasthrough the column at such time as to group the heavy endseither as C5and heavier,C6and heavier,or C7and heavier.Thecomposition of the sample is calculated by comparing eitherthe peak heights,or the peak areas,or both,with the corre-sponding values obtained with the reference standard.4.Significance and Use4.1 This test method is of significance for providing data forcalculating physical properties of the sample,such as heatingvalue and relative density,or for monitoring the concentrationsof one or more of the components in a mixture.5.Apparatus5.1 DetectorThe detector shall be a thermal-conductivitytype,or its equivalent in sensitivity and stability.The thermalconductivity detector must be sufficiently sensitive to producea signal of at least 0.5 mV for 1 mol%n-butane in a 0.25-mLsample.5.2 Recording InstrumentsEither strip-chart recorders orelectronic integrators,or both,are used to display the separatedcomponents.Although a strip-chart recorder is not requiredwhen using electronic integration,it is highly desirable forevaluation of instrument performance.5.2.1 The recorder shall be a strip-chart recorder with afull-range scale of 5 mV or less(1 mV preferred).The width ofthe chart shall be not less than 150 mm.A maximum penresponse time of 2 s(1 s preferred)and a minimum chart speedof 10 mm/min shall be required.Faster speeds up to 100mm/min are desirable if the chromatogram is to be interpretedusing manual methods to obtain areas.5.2.2 Electronic or Computing IntegratorsProof of sepa-ration and response equivalent to that for a recorder is requiredfor displays other than by chart recorder.Baseline trackingwith tangent skim peak detection is recommended.5.3 AttenuatorIf the chromatogram is to be interpretedusing manual methods,an attenuator must be used with thedetector output signal to maintain maximum peaks within therecorder chart range.The attenuator must be accurate to within0.5%between the attenuator range steps.5.4 Sample Inlet System:5.4.1 The sample inlet system shall be constructed ofmaterials that are inert and nonadsorptive with respect to thecomponents in the sample.The preferred material of construc-tion is stainless steel.Copper,brass,and other copper-bearingalloys are unacceptable.The sample inlet system from the1This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.07 on Analysis ofChemical Composition of Gaseous Fuels.Current edition approved Nov.1,2014.Published November 2014.Originallyapproved in 1962.Last previous edition approved in 2010 as D1945-96(2010).DOI:10.1520/D1945-14.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 cylinder valve to the GC column inlet must be maintained at atemperature constant to 61 C.5.4.2 Provision must be made to introduce into the carrie