1、Designation: D 2685 95 (Reapproved 2003)Standard Test Method forAir and Carbon Tetrafluoride in Sulfur Hexafluoride by GasChromatography1This standard is issued under the fixed designation D 2685; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 impuri
3、ties in sulfur hexafluoride.NOTE 1Nitrogen, oxygen, or any of their mixtures is considered to beair. Commercial grade air or nitrogen is used for standardization.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the u
4、ser 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:2D 2472 Specification for Sulfur Hexafluoride3. Summary of Test Method3.1 Air and carbon tetrafluoride are sepa
5、rated physically bygas chromatography and compared to corresponding compo-nents separated 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
6、the area ofthe peak of each component with the area of the peak of thecorresponding component 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 affe
7、ct the performance of SF6when used as anelectrical insulating gas. Specification for maximum levels ofthese contaminants are given in Specification D 2472.4.2 Gas chromatography is used to separate these contami-nants from a sample of SF6and to determine their concentra-tion.5. Apparatus5.1 Gas Chro
8、matograph, consisting of a sample inlet sys-tem, adsorption column, flow meter, detector, 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 indicat
9、ed by return of the recorded peak to thebase line between each successive peak. Chromatograms mustbe reproducible so that successive runs of a reference standardagree on each component peak area or height within 5 %.6. Reagents and Materials6.1 Cylinder of Helium Gas.6.2 Reference Standard MixtureA
10、gas mixture 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 c
11、omponent in 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 indi
12、cated in the 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) nominalColumn temperature 40 to 50CDetector temperature 70 to 80CSample volume 2 to 5 mL approximatelyAttenuation
13、 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 acceptablechromatograms are as follows:1This test method is under the jurisdiction of ASTM Committee D27 Ele
14、ctricalInsulating Liquids and Gases and is the direct responsibility of SubcommitteeD27.03 on Analytical Tests.Current edition approved Sept. 10, 1995. Published November 1995. Originallypublished as D 2685 68. Last previous edition D 2685 94.2For referenced ASTM standards, visit the ASTM website, w
15、ww.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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Car
16、rier 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 SeparationConnect the refe
17、rence 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 sampling valve with ani
18、ntervening 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 sample of the gas into th
19、ecolumn 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 needlevalve and disconne
20、ct 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 half height of eachcom
21、ponent 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 component peak,b = peak
22、 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 component in the samp
23、leS = 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 be converted to awei
24、ght 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 hexafluoride.NOTE 3If nitr
25、ogen 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 thelowest value exceeds 0.0
26、04 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 BiasBias for this test met
27、hod has not been deter-mined, as there is not a sufficient number of laboratoriesperforming this test method.11. Keywords11.1 air; carbon tetrafluoride; sulfur hexafluorideD 2685 95 (2003)2APPENDIX(Nonmandatory Information)X1. SINGLE LABORATORY TYPICAL RESULTSX1.1 On the basis of data taken during t
28、he 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 described in this
29、 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 of the validit
30、y 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 comment
31、s 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
32、 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 multiple copi
33、es) 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).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 %D 2685 95 (2003)3
