1、Designation: D 4768 03Standard Test Method forAnalysis of 2,6-Ditertiary-Butyl Para-Cresol and 2,6-Ditertiary-Butyl Phenol in Insulating Liquids by GasChromatography1This standard is issued under the fixed designation D 4768; the number immediately following the designation indicates the year oforig
2、inal adoption or, in the case 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 by gaschromatography
3、 of 2,6-ditertiary-butyl para-cresol and 2,6-ditertiary-butyl phenol in new and used insulating liquids atconcentrations up to 0.5 %. It includes the determination inType I and II insulating mineral oils as specified in Specifica-tion D 3487, but has also been used to measure these inhibitorsin othe
4、r insulating liquids, such as esters and high fire-pointhydrocarbons.1.2 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
5、applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 923 Test Method for Sampling Electrical Insulating Liq-uids2D 3487 Specification for Mineral Insulating Oil Used inElectrical Apparatus2D 5222 Guide for High-Fire Point Electrical Insulating Oilsof Petr
6、oleum Origin2E 260 Practice for Packed Column Gas Chromatography33. Summary of Test Method3.1 The test specimen is placed onto a column containingactivated alumina and extracted to remove interfering sub-stances. The inhibitors are then eluted from the column withsuitable solvent and analyzed by gas
7、 chromatography. Theinhibitor type and quantity are determined by comparison ofeach component with a working standard tested under similarconditions.4. Significance and Use4.1 In new electrical insulating oil, this test method providesa quantitative measure of the amounts of 2,6-ditertiary-butylpara
8、-cresol and 2,6-ditertiary-butyl phenol that have beenadded to the oil. In a used oil, the test measures the amount ofthese inhibitors remaining in the oil. This test method issuitable for manufacturing control, specification acceptance,and service evaluation.4.2 This test method is used to separate
9、, identify, andquantify the inhibitors with minimal interference and matrixeffects.4.3 This test method has also been used successfully todetermine the inhibitor concentrations in other insulatingliquids such as esters and high-temperature hydrocarbons.5. Apparatus5.1 Gas Chromatograph, equipped wit
10、h oven temperaturecontrol constant to 1C and with heated injector port.5.1.1 Means to Record the Chromatogram, such as a penrecorder or a digital integrator to determine peak areas, isrecommended. An automated sample injector may be used.5.2 Flame Ionization Detector, with appropriate hydrogen/air g
11、as flows, is preferred over a thermal conductivity detectorto provide maximum sensitivity.5.3 Column, a suitable stainless steel or glass columnpacked with a nonpolar silicone on an appropriate support.NOTE 1A 3 % OV-14on 100/120 Mesh Supelcoport,51.83 m (6 ft)long, 3.2 mm (0.125 in.) in outside dia
12、meter has been used successfully.5.3.1 Condition columns in accordance with manufacturersrecommendations. Disconnect columns from detector prior toconditioning and reconnect after conditioning.5.4 Precision Syringe, glass, 10.0 L.5.5 Volumetric Glassware, appropriate for making dilutions.5.6 Pipets,
13、 Pasteur, disposable, 146 by 7.5 mm.5.7 Analytical Balance.5.8 Automatic Pipetter, 1 mL calibrated, adjustable.5.9 Oven, capable of maintaining a temperature of 275 65C for conditioning extraction columns.1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liqui
14、ds and Gases and is the direct responsibility of Subcom-mittee D27.03 on Analytical Tests.Current edition approved March 10, 2003. Published May 2003. Originallyapproved in 1988 as D 4768 88. Last previous edition approved in 1996 asD 4768 96.2Annual Book of ASTM Standards, Vol 10.03.3Annual Book of
15、 ASTM Standards, Vol 14.01.4Registered trademark of Ohio Valley Specialty Co.5Registered trademark of Supelco, Inc.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.10 Desiccator.6. Reagents and Materials6.1 Purity of ReagentsUse rea
16、gent grade chemicals in alltests. Unless otherwise indicated, it is intended that all reagentsshall conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society, wheresuch specifications are available.6Other grades may be used,provided it is first ascertained
17、 that the reagent is of sufficientpurity to permit its use without lessening the accuracy of thedetermination.6.2 2,6-ditertiary-butyl phenol (DBP).6.3 2,6-ditertiary-butyl para-cresol (DBPC7)Alsoknown as butylated hydroxytoluene (BHT).6.4 Glass Wool.6.5 Aluminum Oxide (Alumina), acid powder, ACS, B
18、rock-man Activity Grade 1, for chromatography.86.6 Hexane or Heptane, ACS reagent grade.6.7 Methanol, anhydrous, ACS reagent grade.6.8 Mineral Oil, inhibitor-free, transformer grade.7. Calibration and Standardization7.1 Cleanup Column PreparationPrepare cleanup col-umns by inserting a small glass wo
19、ol plug into the wide end ofa Pasteur pipet and tamping down to the narrow end. Fillcolumn to a height of approximately 35 mm (1.5 in.) withalumina and place a second glass wool plug on top ofadsorbent. Activate column by placing in 275C oven for aminimum of 12 h. Cool in a desiccator prior to use.
20、Aftercolumn has cooled, purge column with approximately 2 mLhexane or heptane. Do not allow column to dry out prior to use.7.2 Standard Solution PreparationStandard solutions areprepared containing both DBP and DBPC from inhibitor-freemineral oil. Prepare oil solutions of 0, 0.040, 0.080, 0.15, 0.30
21、,and 0.40 % (w/w) of both DBP and DBPC. Determine therelative density (specific gravity) of the oil used in standardsolution preparation (DI) to 0.001.7.3 Column Extraction EffciencyVerify by the followingprocedure that the extraction efficiency of the prepared col-umns is acceptable.7.3.1 Prepare a
22、 check standard containing 0.30 % (w/w)DBP and 0.30 % (w/w) DBPC in methanol. Dilute 0.25 mL ofcheck standard to 5.0 mL with methanol.7.3.2 Prepare a working standard in accordance with 7.4,using the 0.30 % (w/w) oil standard and the cleanup columnwhose efficiency is to be determined. Inject a volum
23、e of thisworking standard into the gas chromatograph.7.3.3 Inject a volume (equal to that used in 7.3.2) of thediluted check standard into the chromatograph using the samechromatographic conditions used to analyze the working stan-dards.7.3.4 Calculate the extraction efficiency for both DBP andDBPC
24、as follows:AICI3 W0.30ACCC3 VC3 DC3 100 5AI3 CC3 VC3 DCAC3 CI3 W0.305 extraction efficiency,%where:AI= area (or height) of 0.30 % working standard,AC= area (or height) of 0.30 % check standard,CI= known concentration of working standard,CC= known concentration of check standard,DC= relative density
25、(specific gravity) of methanol used incheck standard preparation, andDI= relative density (specific gravity) of oil used inworking standard preparation.7.3.5 The minimum acceptable extraction efficiency is 70 %for DBPC and 60 % for DBP. If the prepared columns do notachieve this level of efficiency,
26、 make and test new cleanupcolumns until acceptable extraction efficiency is achieved. Ifunable to obtain this, purchase a new lot of acid powderalumina or verify that extraction columns are being activatedproperly as in 7.1.7.4 Working Standard Preparation:7.4.1 Accurately weigh a cleanup column to
27、0.001 g. Pipet0.25 mL of the 0 % standard solution onto the top of thecleanup column. Weigh the cleanup column to 0.001 g. Recordthe difference as W0%. Repeat for the remaining standardsolutions utilizing different cleanup columns and recordingweights as W0.040 %, W0.080 %, W0.15 %, W0.30 %and W0.40
28、 %,respectively.7.4.2 To remove nonpolar interferences, wash the standardsolutions with approximately 5 mL of hexane or heptane,collecting the eluate in a waste container. Remove as much ofthe solvent as possible by using pipet bulb pressure, but do notallow the column to dry out.7.4.3 Elute the inh
29、ibitors from the column with threewashes consisting of 1 mL of methanol each, collecting theeluate in a clean 5 mL volumetric flask. Dilute to 5 mL withmethanol and mix well. These are the working standards.7.5 Working Standard ChromatographyInject a volume ofthe working standard solution into the e
30、quilibrated chromato-graph as described in Section 8. Recommended injectionvolumes are 2 to 10 L, depending on individual detectorresponse. Measure the response, Ax, (peak height or area inintegrator counts) for each peak (excluding the solvent front).7.5.1 Perform separate linear regression analyse
31、s of theresponses resulting from both DBPC and DBP working stan-dards by plotting Siversus area, Ax (or height) where:Si5Concentration of Working Standard, weight %Mass of Working Standard Used 7.4.1!where:Si= weight normalized, %.7.5.1.1 If the correlation coefficient for the regression analy-ses (
32、7.5.1) is less than 0.995, prepare new working standards(7.4), repeat the chromatographic measurements (7.5) andperform the data analysis (7.5.1) on the new results alone. If6Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the
33、 testing of reagents notlisted by the American Chemical Society, see “Reagent Chemicals and Standards,”by Joseph Rosin, D. Van Nostrand Co., Inc., New York, NY and the“ United StatesPharmacopeia.7Registered Trademark of Rhone-Poulenc, Inc.8Available from J.T. Baker Chemical Co., Phillipsburg, NJ 088
34、65.D 4768 032the situation is not improved, repeat the procedure usingworking standards made from newly prepared standard solu-tions (7.2).8. Chromatograph Operating Conditions8.1 GeneralThe characteristics of individual chromato-graphs and columns differ. Choose particular operating condi-tions to
35、give a complete separation and good quantification ofthe peaks obtained. Temperatures and flow rates with whichsatisfactory separations have been obtained are listed in 8.2through 8.5.8.2 Packed Column TemperatureA column oven tempera-ture held isothermally at 150C for 5 min followed bytemperature r
36、amping at 20C/min to 250C and a hold periodat that temperature for 2 min gives satisfactory results. Al-though the inhibitors are resolved by the isothermal portion ofthe run, higher temperatures are required to purge the columnof interfering substances for successive runs.8.3 Detector TemperatureA
37、detector temperature of300C has been found to be satisfactory.8.4 Injector Port TemperatureAn injector port tempera-ture of 275C has been found to be satisfactory.8.5 Carrier GasA carrier gas of high purity helium at aflow of 20 to 40 mL/min gives satisfactory results for packedcolumns.9. Procedure9
38、.1 Test Specimen Preparation:9.1.1 Accurately weigh a cleanup column to 0.001 g. Pipet0.25 mL of the test specimen onto the top of the cleanupcolumn. Weigh the cleanup column to 0.001 g. Record thedifference as Wx.9.1.1.1 Due to variances between different batches of alu-mina, care must be taken to
39、prepare both the working standardsand test specimens by using the same batch of cleanupcolumns. The same “batch” should be interpreted to mean thesame lot number of alumina, preparation date, and conditioningtime.9.1.2 To remove nonpolar interferences, wash the test speci-men with approximately 5 mL
40、 of hexane or heptane, collectingthe eluate in a waste container. Remove as much of the solventas possible by using pipet bulb pressure, but do not allow thecolumn to dry out.9.1.3 Elute the inhibitor(s) from the column with threewashes consisting of 1 mL of methanol each, collecting theeluate in a
41、clean 5-mL volumetric container. Dilute to 5 mLvolume with methanol and mix well.9.2 Test Specimen ChromatographyInject a volume oftest specimen into the chromatograph under the same chro-matographic conditions used to analyze the working stan-dard(s).10. Calculation10.1 Identify the type(s) of inhi
42、bitors present by comparingthe retention time obtained from the test specimens to thoseobtained for the working standards.10.2 Using the results of the regression analyses (7.5.1),determine the uncorrected weight percent (Cu) of the inhibitorin the test specimens. Calculate the inhibitor content(s)
43、asfollows:C 5 Cu3 Wxwhere:C = weight of inhibitor in test specimen, %,Cu= weight normalized, obtained from regression analy-ses of working standards, %, andWx= mass of 0.25 mL test specimen as recorded in 9.1.1.11. Report11.1 Report the following information:11.1.1 Type and amount of each inhibitor
44、found, and11.1.2 Total amount of inhibitor as the sum of the individualinhibitors found.12. Precision and Bias12.1 The single operator coefficient of variation has beenfound not to exceed 11 % for inhibitor content between 0.06and 0.45 %. Therefore, the results of two tests conducted on thesame samp
45、le by the same operator using the same equipmentshould not differ from each other by more than 30.8 % of theaverage of the two tests.13. Keywords13.1 2,6-ditertiary-butyl para-cresol; 2,6-ditertiary-butylphenol; dbp; dbpc; inhibitor; mineral oil; transformer oilASTM International takes no position r
46、especting 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 validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.Thi
47、s 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 comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM Inte
48、rnational 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 received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown
49、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 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).D 4768 033
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