1、Designation: D 2668 02e1Standard Test Method for2,6-di-tert-Butyl-p-Cresol and 2,6-di-tert-Butyl Phenol in ElectricalInsulating Oil by Infrared Absorption1This standard is issued under the fixed designation D 2668; the number immediately following the designation indicates the year oforiginal adopti
2、on 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.e1NOTEThe absorbance of DBPC and DBPwas corrected from 3680 cm1to 3650 cm1in 3.2 edit
3、orially in November 2005.1. Scope*1.1 This test method covers the determination of the weightpercent of 2,6-ditertiary-butyl paracresol and 2,6-ditertiary-butyl phenol in new or used electrical insulating oil inconcentrations up to 0.5 % by measuring its absorbance at thespecified wavelengths in the
4、 infrared spectrum.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 applica-bility of regulatory limitations prior to
5、use.2. Referenced Documents2.1 ASTM Standards:2D 923 Practices for Sampling Electrical Insulating LiquidsD 2144 Test Methods for Examination of Electrical Insulat-ing Oils by Infrared AbsorptionD 3487 Specification for Mineral Insulating Oil Used inElectrical Apparatus3. Significance and Use3.1 The
6、quantitative determination of 2,6-ditertiary-butylparacresol and 2,6-ditertiary-butyl phenol in a new electricalinsulating oil measures the amount of this material that hasbeen added to the oil as protection against oxidation. In a usedoil it measures the amount remaining after oxidation productshav
7、e reduced its concentration. The test is also suitable formanufacturing control and specification acceptance.3.2 When an infrared spectrum is obtained of an electricalinsulating oil inhibited with either of these compounds there isan increase in absorbance of the spectrum at several wave-lengths (or
8、 wavenumbers). 2,6 ditertiary-butyl paracresol pro-duces pronounced increases in absorbance at 2.72 m (3650cm1), and 11.63 m (860 cm1). 2,6 ditertiary-butyl phenolproduces pronounced increases in absorbance at 2.72 m (3650cm1) and 13.33 m (750 cm1).3.3 When making this test on other than a highly ox
9、idizedoil or when using a double-beam spectrophotometer, it hasbeen found convenient to obtain the spectrum between 2.5 m(4000 cm1) and 2.9 m (3450 cm1) because the instrument iscompensated for the presence of moisture and the band is notinfluenced by intermolecular forces (associations). However,wh
10、en testing a highly oxidized oil or when using a single-beaminstrument better results may be obtained if the scan is madebetween 10.90 m (918 cm1) and 14.00 m (714 cm1).3.4 Increased absorption at 11.63 m (860 cm1) or 13.33m (750 cm1) or both, will identify the inhibitor as 2,6-ditertiary-butyl para
11、cresol or 2,6-ditertiary-butyl phenol re-spectively (Note 1).NOTE 1The absorbance at 750 cm1for 2,6-ditertiary-butyl phenoland at 860 cm1for 2,6-ditertiary-butyl paracresol for equal concentra-tions will be in the approximate ratio of 2.6 to 1.4. Apparatus4.1 With equipment description referring to
12、compliance, theequipment shall be in accordance with Section 6 of TestMethods D 2144. Accordingly, the use of Fourier-transformrapid scan infrared spectrophotometers is permitted by refer-ence to that test method.5. Sampling5.1 Obtain the sample in accordance with Test MethodD 923.6. Calibration and
13、 Standardization6.1 When the manufacturer of the oil is known and the baseoil is available, use it to prepare the standards. For oils ofunknown origin, use base oils which meet the requirements of1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Ga
14、ses and is the direct responsibility of Subcom-mittee D27.03 on Analytical Tests.Current edition approved Oct. 10, 2002. Published December 2002. Originallypublished as D 2668 67. Last previous edition D 2668 96.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cus
15、tomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
16、n, PA 19428-2959, United States.Specification D 3487. Some base oils may provide a bettermatch than others and therefore it is desirable to have severalavailable.6.2 Prepare standards containing between 0.05 and 0.4weight percent of 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol diss
17、olved in an uninhibited base oil.Obtain a spectrum, at the desired band, of each standard inaccordance with Test Methods D 2144. Cells with a standardpath length of 0.3 to 1.0 mm are recommended. Other pathlengths may be found more suitable for different instruments orparticular wave lengths. Other
18、sample path lengths may beused provided the instrument sensitivity can be adjusted tocompensate for this change. The dip in the curve for theinhibited oil should provide a distinctive increase in theabsorbance at the critical wavelength or frequency (Note 3).Repeat the procedure on each of the stand
19、ards making at leastthree scans on each standard. (See Note 2) Record all settingsof the spectrophotometer used in obtaining the respectivespectra (Note 4).NOTE 2The current method precision is based on manually deter-mined results where exactly three scans were determined for eachstandard. Newer in
20、struments are capable of automatically performingscans much more rapidly, which can reduce the variability of resultsdetermined. In such cases, it is recommended that the number of scans beincreased to statistically compensate for any outliers. Labs will need todetermine the minimum number of scans
21、that should be used in theirinstrument standardization and test specimen analyses to satisfy theirtesting needs.NOTE 3Where desired, a chart having a non-linear wavelength scaleas the abscissa may be used.NOTE 4In making these tests, transmission-scaled charts may beused, but in this case special ru
22、lers and nomographs or logarithmic tableswill be necessary for determining the intensity measurements. Alterna-tively, instrument software capable of recording all settings of thespectrophotometer used in obtaining the respective spectra, may be used.6.3 The quantitative determination is made from t
23、he follow-ing equation which is derived from Beers law:Absorbance 5 A 2 Aowhere:Ao= absorbance units of base oil, andA = absorbance units of oil containing 2,6-ditertiary-butylparacresol or 2,6-ditertiary-butyl phenol.6.4 Manual Plotting Routine for Generating CalibrationCurveDesignate the point of
24、maximum absorbance of theabsorbance band as Point A. Draw a tangent to the spectrumcurve and a second line through Point A perpendicular to theabsorbance lines, as shown in Fig. 1. Designate the intersectionof these two lines as Point Ao. Read the values of absorbanceat these points on the charts of
25、 the three scans made on eachtest specimen to the nearest 0.001 absorbance unit (with the aidof a reading glass) and subtract the values of Aofrom those ofA. When the average of the three values for each of thespecially prepared test specimens is plotted against the con-centration, a straight line i
26、s obtained. The best straight linethrough the calibration data points should be drawn or deter-mined by linear regression analysis. This is the calibrationcurve from which the unknown concentration of the 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol in atest specimen may be determi
27、ned. One such calibration curveis shown as Fig. 2. Fig. 3 and Fig. 4 illustrate sections ofdifferential scans.6.4.1 Automatic Plotting Routine for Generating Calibra-tion CurveFor instruments capable of automatically gener-ating a standard calibration curve, follow manufacturersinstructions. Perform
28、 at least three scans for each standardanalyzed across the calibration range of interest (see Note 2).Develop a calibration curve which has a minimum correlationvalue of 0.99 to ensure the linearity of the calibration curve.6.5 When frequent determinations are made on a routinebasis, periodic checks
29、 of one or more standards are recom-mended, since the characteristics of electronics components inspectrophotometers change with time. If the absorbance of thestandards differ from the calibration curve by more than thelimits given in 8.2, a new curve should be obtained. Somelaboratories have develo
30、ped tighter limits than these. A newcurve should also be obtained whenever there is a change inoperating conditions, such as a change in light source, scanspeed, and so forth.NOTE 5It is recommended that the solutions of known concentrationbe stored in amber-colored bottles for a period not to excee
31、d one year inorder to facilitate a quick check of the characteristics of the spectropho-tometer in relation to the calibration curve.7. Procedure7.1 Using the quantitative scan mode, make at least threescans (see Note 2) of the test specimen on which the determi-nation of the 2,6-ditertiary-butyl pa
32、racresol or 2,6-ditertiary-butyl phenol content is to be made, at the desired band. Do thisin accordance with Test Methods D 2144, except that cellshaving path lengths as specified in 6.2 are preferred. Use thesame cell that was used in obtaining the spectra for thecalibration curve. For the Differe
33、ntial Method, fill the referencecell with an appropriate base oil free of oxidation inhibitors.Use a spectrophotometer which meets the requirements speci-fied in Section 6 of Test Methods D 2144 and instrumentalconditions identical to those used in obtaining the spectra forthe calibration curve.7.2
34、For routine tests, a single scan of the test specimen isadequate as long as the instrument is capable of meeting thecriteria of 8.2 using single scans to replace average values. Forreferee purposes, use the average of three scans of the testspecimen performed manually or the average of the samenumbe
35、r of scans used to standardize the instrument for the testspecimen, if performed automatically.7.3 Manually Determined ResultsRead the values of ab-sorbance at points Aoand A on each of the three spectra to thenearest 0.001 absorbance unit; obtain the differences andaverage them. Using this average
36、value, determine the concen-tration from the calibration curve.7.4 Automatically Determined ResultsUsing the averagevalue of the absorbance difference between A and Aothat isdetermined automatically by the instrument for the samenumber of scans performed on the test specimen as for thestandards, det
37、ermine the concentration of the test specimenfrom the calibration curve.D 2668 02e12FIG. 1 Spectrum of an Electrical Insulating Oil Inhibited with 2,6-Ditertiary-ButylParacresol Showing Location Points Aoand AFIG. 2 Calibration Curve for Determining the Percent by Weight of 2,6-Ditertiary-ButylParac
38、resol in Electrical Insulating OilD 2668 02e138. Precision and Bias8.1 Checking Limits of Range (A Ao)Determine thehighest and lowest values of A Aoresulting from the three ormore scans and subtract one from the other. If the resultingquantity exceeds 0.010, reject the results as excessively vari-ab
39、le and repeat the test.8.2 RepeatabilityThe difference between two determina-tions for DBPC and DBP, each obtained from the average ofthree scans determined manually, obtained by the same opera-tor with the same apparatus under constant operating condi-tions on identical test material would, in the
40、long run, in thenormal and correct operation of the test method, exceed thevalue of 0.04 % by only one case in twenty.8.3 ReproducibilityThe difference between two determi-nations for DBPC and DBP, each obtained from the average ofthree scans determined manually, obtained by different opera-tors in
41、different laboratories on identical test material would, inthe long run, in the normal and correct operation of the testmethod, exceed the value of 0.04 % by only one case in twenty.8.4 No statement is made about bias of this test method formeasuring ditertiary-butyl paracresol or ditertiary-butyl p
42、henolas it has not been determined.FIG. 3 Section of Differential Scan-AFIG. 4 Section of Differential Scan-BD 2668 02e149. Keywords9.1 2,6-ditertiary-butyl paracresol; 2,6-ditertiary-butyl phe-nol; electrical insulating oil; infrared absorption; paracresolSUMMARY OF CHANGESCommittee D27 has identif
43、ied the location of selected changes to this standard since the last issue (D 266896)that may impact the use of this standard.(1) Added a sentence to section 4.1 permitting use of FTIRinstruments.(2) Updated sections 6.2, 6.4, 7.1, 7.2, 7.3, 8.1, 8.2, and 8.3.Added a new section 6.4.1 and 7.4.(3) Ad
44、ded a new Note 2 and renumbered subsequent Notesaccordingly. Updated initial Note 3 to Note 4 and added asecond sentence.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 expres
45、sly advised that determination of 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,
46、 either reapproved or withdrawn. 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 at
47、tend. 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 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 2668 02e15
