1、Designation: D 2668 07Standard 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 adoption
2、 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. Scope*1.1 This test method covers the determination of the weightpercent of 2,6-dite
3、rtiary-butyl paracresol (DBPC) and 2,6-ditertiary-butyl phenol (DBP) in new or used electrical insu-lating oil in concentrations up to 0.5 % by measuring itsabsorbance at the specified wavelengths in the infrared spec-trum.1.2 This standard does not purport to address all of thesafety concerns, if a
4、ny, 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:2D 923 Practices for Sampling Electrical Insulatin
5、g LiquidsD 2144 Practices for Examination of Electrical InsulatingOils by Infrared AbsorptionD 3487 Specification for Mineral Insulating Oil Used inElectrical Apparatus3. Significance and Use3.1 The quantitative determination of 2,6-ditertiary-butylparacresol and 2,6-ditertiary-butyl phenol in a new
6、 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 hasreduced its concentration. The test is also suitable for manu-facturing control and specification acceptance.
7、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 wavenumbers). 2,6 ditertiary-butyl paracresol pro-duces pronounced increases in absorbance at 2.72 m (3650cm
8、1), and 11.63 m (860 cm1). 2,6 ditertiary-butyl phenolproduces pronounced increases in absorbance at 2.72 m (3650cm1) and 13.42 m (745 cm1).3.3 When making this test on other than a highly oxidizedoil or when using a double-beam spectrophotometer, it hasbeen found convenient to obtain the spectrum b
9、etween 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,when testing a highly oxidized oil or when using a single-beaminstrument better results may be obtained if the
10、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 13.42m (745 cm1) or both, will identify the inhibitor as 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol re-spectively (Note 1).NOTE 1The absorbance at 745 cm1for 2,6-ditertiar
11、y-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 compliance, theequipment shall be in accordance with Section 6 of TestMethods D 2144. Accordingly, the use of
12、 Fourier-transformrapid scan infrared (FTIR) spectrophotometers is permitted byreference to that test method.5. Sampling5.1 Obtain the sample in accordance with Practices D 923.6. Calibration and Standardization6.1 When the manufacturer of the oil is known and the baseoil is available, use it to pre
13、pare the standards. For oils ofunknown origin, use base oils which meet the requirements ofSpecification 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-dite
14、rtiary-butyl paracresol or 2,6-ditertiary-butyl phenol dissolved in an uninhibited base oil.Alternatively, the range of prepared standards may be in-creased to 0.5 weight percent if certain oils to be investigated1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulati
15、ng Liquids and Gases and is the direct responsibility of Subcom-mittee D27.03 on Analytical Tests.Current edition approved Dec. 1, 2007. Published January 2008. Originallyapproved in 1967. Last previous edition approved in 2002 as D 2668 02e1.2For referenced ASTM standards, visit the ASTM website, w
16、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.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive
17、, PO Box C700, West Conshohocken, PA 19428-2959, United States.are believed to contain greater amounts of inhibitor. Obtain aspectrum, at the desired band, of each standard in accordancewith Test Methods D 2144. Cells with a standard path length of0.3 to 1.0 mm are recommended. Other path lengths ma
18、y befound more suitable for different instruments or particularwave lengths. Other sample path lengths may be used providedthe instrument sensitivity can be adjusted to compensate forthis change. The dip in the curve for the inhibited oil shouldprovide a distinctive increase in the absorbance at the
19、 criticalwavelength or frequency (Note 3). Repeat the procedure oneach of the standards making at least three scans on eachstandard. (See Note 2) Record all settings of the spectropho-tometer used in obtaining the respective spectra (Note 4).NOTE 2The current method precision is based on manually de
20、ter-mined results where exactly three scans were determined for eachstandard. Newer instruments 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 statisticall
21、y compensate for any outliers. Laboratories willneed to determine the minimum number of scans that should be used intheir instrument 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.N
22、OTE 4In making these tests, transmission-scaled charts may beused, but in this case special rulers 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 o
23、btaining the respective spectra, may be used.6.3 The quantitative determination is made from the 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-b
24、utyl phenol.6.4 Manual Plotting Routine for Generating CalibrationCurveDesignate the point of 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 intersectio
25、nof these two lines as Point Ao. Read the values of absorbanceat these points on the charts of 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
26、 thespecially prepared test specimens is plotted against the con-centration, a straight line is 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
27、,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol in atest specimen may be determined. One such calibration curveis shown as Fig. 2. Fig. 3 and Fig. 4 illustrate sections ofdifferential scans. Figs. 5-7 show FTIR scans of uninhibited, asimilar oil with 0.55 % DBPC and the resulting FTIR
28、differ-ential scan.6.4.1 Automatic Plotting Routine for Generating Calibra-tion CurveFor instruments capable of automatically gener-ating a standard calibration curve, follow manufacturersinstructions. Perform at least three scans for each standardanalyzed across the calibration range of interest (s
29、ee 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 of one or more standards are recom-mended, since the characteristics of electronics compon
30、ents 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 developed tighter limits than these. A newcurve should also be obtained whenever there is a chang
31、e 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 exceed one year inorder to facilitate a quick check of the characteristics of the spectropho-tom
32、eter 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 paracresol or 2,6-ditertiary-butyl phenol content is to be made, at the desired band. Do this
33、in accordance with Test Methods D 2144, except that cellsFIG. 1 Spectrum of an Electrical Insulating Oil Inhibited with 2,6-Ditertiary-ButylParacresol Showing Location Points Aoand AD 2668 072having path lengths as specified in 6.2 are preferred. Use thesame cell that was used in obtaining the spect
34、ra for thecalibration curve. For the Differential 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 obtaini
35、ng the spectra forthe calibration curve. In particular, it should be noted thatFourier-transform rapid scan infrared spectrophotometers mayalso be used and in some cases are preferred for the measure-ment.7.2 For routine tests, a single scan of the test specimen isadequate as long as the instrument
36、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 samenumber of scans used to standardize the instrument for the testspecimen, if performed automatica
37、lly.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 value, determine the concen-tration from the calibration curve.7.4 Automatically Determined
38、 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, determine the concentration of the test specimenfrom the calibration curve.FIG. 2 Calibration
39、Curve for Determining the Percent by Weight of 2,6-Ditertiary-ButylParacresol in Electrical Insulating OilFIG. 3 Section of Differential Scan-AD 2668 0738. Precision and Bias8.1 Checking Limits of Range (A Ao)Determine thehighest and lowest values of A Aoresulting from the three ormore scans and sub
40、tract one from the other. If the resultingquantity exceeds 0.010, reject the results as excessively vari-able 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
41、-tor with the same apparatus under constant operating condi-tions on identical test material would, in the 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
42、DBP, each obtained from the average ofthree scans determined manually, obtained by different opera-tors in 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 stat
43、ement is made about bias of this test method formeasuring ditertiary-butyl paracresol or ditertiary-butyl phenolas it has not been determined.9. Keywords9.1 2,6-ditertiary-butyl paracresol; 2,6-ditertiary-butyl phe-nol; electrical insulating oil; infrared absorptionFIG. 4 Section of Differential Sca
44、n-BFIG. 5 Example of a FTIR Scan of an Uninhibited Transformer OilD 2668 074SUMMARY OF CHANGESCommittee D27 has identified the location of selected changes to this standard since the last issue(D 266802e1) that may impact the use of this standard.(1) The absorption band for DBP has been changed from
45、 750cm-1(13.33 m) to 745 cm-1(13.42 m).(2) FTIR references and Figs. 5-7 were added.FIG. 6 Example of a FTIR Scan on a Transformer Oil with 0.55 % DBPCFIG. 7 Example of the Differential Scan Showing 0.542 % WT % DBPC InhibitorD 2668 075ASTM International takes no position respecting the validity of
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49、yrighted 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 076
