1、Designation: D4768 11Standard 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 D4768; the number immediately following the designation indicates the year oforigin
2、al 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. Scope1.1 This test method covers the determination by gaschromatography of
3、 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 D3487, but has also been used to measure these inhibitorsin other in
4、sulating 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 appl
5、ica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D923 Practices for Sampling Electrical Insulating LiquidsD3487 Specification for Mineral Insulating Oil Used inElectrical ApparatusD5222 Specification for High Fire-Point Mineral ElectricalInsulating OilsE26
6、0 Practice for Packed Column Gas Chromatography3. 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 chromatography. T
7、heinhibitor 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-cresol and 2,6-di
8、tertiary-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, identify, andqua
9、ntify 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 with oven temperature
10、control 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 gas flows, is prefe
11、rred 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 orequivalent capillary column.NOTE 1A 3 % OV-13on 100/120 Mesh Supelcoport,41.83 m (6 ft)long, 3.2 mm (0.125 in.) in
12、 outside diameter has been used successfully.A SPB-1430 m by 0.53 mm 1m film column has also been usedsuccessfully.5.3.1 Condition columns in accordance with manufacturersrecommendations. Disconnect columns from detector prior toconditioning and reconnect after conditioning.5.4 Precision Syringe, gl
13、ass, 10.0 L.5.5 Volumetric Glassware, appropriate for making dilutions.5.6 Pipets, Pasteur, disposable, 146 by 7.5 mm.5.7 Analytical Balance.1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D
14、27.03 on Analytical Tests.Current edition approved Aug. 1, 2011. Published September 2011. Originallyapproved in 1988 as D4768 88. Last previous edition approved in 2003 asD4768 03. DOI: 10.1520/D4768-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Se
15、rvice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Registered trademark of Ohio Valley Specialty Co.4Registered trademark of Supelco, Inc.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, We
16、st Conshohocken, PA 19428-2959, United States.5.8 Automatic Pipetter, 1 mL calibrated, adjustable.5.9 Oven, capable of maintaining a temperature of 325 65C for conditioning extraction columns.5.10 Desiccator.6. Reagents and Materials6.1 Purity of ReagentsUse reagent grade chemicals in alltests. Unle
17、ss 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.5Other grades may be used,provided it is first ascertained that the reagent is of sufficientpuri
18、ty 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 (DBPC6)Alsoknown as butylated hydroxytoluene (BHT).6.4 Glass Wool.6.5 Aluminum Oxide (Alumina), acid powder, ACS, Brock-man Activity Grade 1, for chromat
19、ography.76.6 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 wool plug into the wide end ofa Pasteur
20、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 325C oven for aminimum of 12 h. Cool in a desiccator prior to use. Aftercolumn has cooled, purge column w
21、ith 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,and 0.40 % (w/w) of both DBP and DBPC
22、. 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 check standard containing 0.30 % (w/w
23、)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 volume of thisworking standard into the gas
24、 chromatograph.7.3.3 Inject a volume (equal to that used in 7.3.2)ofthediluted 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 as follows:AICI3 W0.30ACCC3 VC3 DC3 100
25、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 (specific gravity) of methanolused in ch
26、eck standard preparation, andW0.30= weight of 0.30 % working standard as recorded in7.4.1.VC= volume of check standard diluted to 5 mL in 7.3.1(=0.25 mL)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
27、, 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
28、 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 W0.4
29、0 %,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 in
30、hibitors 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
31、equilibrated 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 analys
32、es 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:5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washi
33、ngton, DC. For suggestions on the 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.6Registered Trademark of Rhone-Poulenc, Inc.7Available from J.T. Baker C
34、hemical Co., Phillipsburg, NJ 08865.D4768 112Si= weight normalized, %.7.5.1.1 If the correlation coefficient for the regression analy-ses (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 resu
35、lts alone. Ifthe 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
36、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 or Capillary Column TemperatureA columnoven temperature held isothermally at 150C for 5 minfollowed by te
37、mperature ramping at 20C/min to 250C and ahold period at that temperature for 2 min gives satisfactoryresults. Although the inhibitors are resolved by the isothermalportion of the run, higher temperatures are required to purgethe column of interfering substances for successive runs.8.3 Detector Temp
38、eratureA 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. P
39、rocedure9.1 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
40、taken to 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 approxima
41、tely 5 mL 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 theelu
42、ate in a 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
43、) of inhibitors 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 co
44、ntent(s) 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 i
45、nhibitor 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 the
46、same sample 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 p
47、osition 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 validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsib
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49、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 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 copies) of this standard may be obtained by contacting ASTM at the a
