1、Designation: D2685 11Standard Test Method forAir and Carbon Tetrafluoride in Sulfur Hexafluoride by GasChromatography1This standard is issued under the fixed designation D2685; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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. Scope1.1 This test method covers the determination of air (Note1) and carbon tetrafluoride as impurities in sulfur hexafl
3、uoride.NOTE 1Nitrogen, oxygen, or any of their mixtures is considered to beair. Commercial grade air or nitrogen is used for standardization.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
4、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:2D2472 S
5、pecification for Sulfur HexafluorideE260 Practice for Packed Column Gas ChromatographyE355 Practice for Gas Chromatography Terms and Rela-tionships3. Summary of Test Method3.1 Air and carbon tetrafluoride are separated physically bygas chromatography and compared to corresponding compo-nents separat
6、ed under similar conditions from a referencestandard mixture of known composition. The individual com-pounds of air are not separated. The composition of the sampleis calculated from its chromatogram by comparing the area ofthe peak of each component with the area of the peak of thecorresponding com
7、ponent on the reference standard chromato-gram.4. Significance and Use4.1 Air and carbon tetrafluoride (CF4) are two contaminantsof interest in sulfur hexafluoride (SF6). Both of these contami-nants adversely affect the performance of SF6when used as anelectrical insulating gas. Specification for ma
8、ximum levels ofthese contaminants are given in Specification D2472.4.2 Gas chromatography is used to separate these contami-nants from a sample of SF6and to determine their concentra-tion.5. Apparatus5.1 Gas Chromatograph, consisting of a sample inlet sys-tem, adsorption column, flow meter, detector
9、, and data han-dling system. Ensure that the column material of constructionand sample components are compatible. The apparatus mustcompletely separate air, carbon tetrafluoride, and sulfurhexafluoride as indicated by return of the recorded peak to thebase line between each successive peak. Chromato
10、grams mustbe reproducible so that successive runs of a reference standardagree on each component peak area or height within 5 %. Foradditional information on gas chromatography see PracticesE260 and E355.6. Reagents and Materials6.1 Cylinder of Helium Gas.6.2 Reference Standard MixtureA gas mixture
11、that con-tains known percentages of air and carbon tetrafluoride inhelium or air and carbon tetrafluoride in sulfur hexafluoride isrequired. The concentration of a component in the referencesample should not be less than 50 % nor more than 300 % ofthe concentration of the corresponding component in
12、theunknown.7. Calibration and Standardization7.1 Apparatus PreparationPrepare the gas chromato-graph for use as directed by the manufacturer. The followingoperating conditions have been found satisfactory. However,any combination of conditions that result in complete separa-tions as indicated in the
13、 apparatus section will be satisfactory.Carrier gas helium, 40 to 50 mL/minColumn Porapak Q-80/100 mesh or Porapak R 50/80 meshColumn size 6 to 10 Ft (23.5 m) by in. (6.4 mm) nominal1This test method is under the jurisdiction of ASTM Committee D27 ElectricalInsulating Liquids and Gases and is the di
14、rect responsibility of SubcommitteeD27.03 on Analytical Tests.Current edition approved May 1, 2011. Published May 2011. Originallyapproved in 1968. Last previous edition approved in 2003 as D2685 95(2003).DOI: 10.1520/D2685-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orc
15、ontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Column temperature
16、40 to 50CDetector temperature 70 to 80CSample volume 2 to 5 mL approximatelyAttenuation lowest which will keep peaks on a scale may be variedduring runDetector thermal conductivity7.2 Example of Chromatography ConditionsSpecific con-ditions used by one laboratory which produces acceptablechromatogra
17、ms are as follows:Carrier gas helium, 50 mL/minColumn packing Porapak R 50/80 meshColumn size and material 0.25 in. (6.4 mm) nominal ID,10 ft (3.5 m) long, copperColumn temperature 48CDetector thermal conductivityDetector temperature 75CSample volume 5 mL7.3 Reference Standard Introduction and Separ
18、ationConnect the reference standard cylinder to the needle valve andproceed in accordance with Section 8. Repeat the standardiza-tion in accordance with the laboratorys quality assuranceprocedures.8. Procedure8.1 Sample Introduction and SeparationConnect thesample cylinder to the inlet of the gas sa
19、mpling valve with anintervening valve. Support the sample cylinder in an invertedposition so the sample will be taken from the liquid phase andopen the sample cylinder valve. Open the needle valve so thatthe vaporized sample purges the sampling valve at a rate of 20to 100 mL/min. Injecta2to5-mL samp
20、le of the gas into thecolumn and record the chromatogram.8.2 Under the conditions given in Section 7, the approxi-mate elution times are air, 1.2 min; CF4, 2 min; and SF6, 4 min.Elution times will vary in accordance with column size andsample size.8.3 Close the sample cylinder valve and then the nee
21、dlevalve and disconnect the sample cylinder.9. Calculation9.1 Determine the concentration of sample components bycomparison of the areas or heights of the corresponding peaks.The calculations shown are for peak areas. Calculations usingpeak heights are analogous.9.2 Measure the height and width at h
22、alf height of eachcomponent peak in the standard sample chromatograms inmillimetres, and calculate the average area of each componentpeak as follows:NOTE 2The area of the component peaks may be determined directlywith an integrator, if available.A 5 (b 3 h 3 a!/n (1)where:A = average area of each co
23、mponent peak,b = peak width at half height,h = peak height above base line.a = attenuation,n = number of peaks included in average, and( = summation of the individual peak areas.9.3 Calculate the concentration of each component in thesample as follows:C 5 S 3 As!/Ar(2)where:C = mole percent of each
24、component in the sampleS = mole percent of the corresponding component in thereference standard (see Appendixes),As= average area of the corresponding component peaks inthe sample, andAr= average area of the corresponding component peaks inthe reference standard.9.4 The composition of the sample can
25、 be converted to aweight percent basis as follows (see Note 3):CWair5 2898 Cair/28.98 Cair1 88 CCF41 146 CSF6!CWCF45 8800 CCF4/28.98 Cair1 88 CCF41 146 CSF6! (3)CWSF65 100 2 CWair1 CWCF4!where:CWair= weight percent air,CWCF4= weight percent carbon tetrafluoride, andCWSF6= weight percent sulfur hexaf
26、luoride.NOTE 3If nitrogen is used instead of air, molecular weights should beadjusted accordingly.10. Precision and Bias10.1 RepeatabilityThree measurements made in the samelaboratory using a single reference sample should be consid-ered suspect if the difference between the highest value and thelow
27、est value exceeds 0.004 weight % (40 ppm by weight). SeeAppendix X1 for typical results from one laboratory.10.2 ReproducibilityReproducibility between laboratorieshas not been determined for this test method, as there are nota sufficient number of laboratories performing this test method.10.3 BiasB
28、ias for this test method has not been deter-mined, as there is not a sufficient number of laboratoriesperforming this test method.11. Keywords11.1 air; carbon tetrafluoride; sulfur hexafluorideD2685 112APPENDIX(Nonmandatory Information)X1. SINGLE LABORATORY TYPICAL RESULTSX1.1 On the basis of data t
29、aken during the methoddevelopment of the liquid phase analysis of SF6, a coefficientof variation of 65 % relative to the mean values of the air andCF4concentrations may be achieved. This standard develop-ment is applicable to both electronic peak area and manualmeasurements of the peak areas as desc
30、ribed in this testmethod.X1.2 Table X1.1 shows the results of six runs of the samesample.ASTM 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 o
31、f the validity 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.
32、 Your comments 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 comm
33、ents 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,United States. Individual reprints (single or
34、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 serviceastm.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 X1.1 Repeatability DataAir, ppm (wt) CF4, ppm (wt)101 255105 265101 25595 24299 25197 247Mean 100 253Standard Deviation 3.2 7.2Coefficient of Variation 3.2 % 2.9 %D2685 113
