ASTM D2668 - 07(2013)

    Standard Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6-di-tert-Butyl Phenol in Electrical Insulating Oil by Infrared Absorption

    Active Standard ASTM D2668 | Developed by Subcommittee: D27.03

    Book of Standards Volume: 10.03


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    Significance and Use

    3.1 The quantitative determination of 2,6-ditertiary-butyl paracresol and 2,6-ditertiary-butyl phenol in a new electrical insulating oil measures the amount of this material that has been added to the oil as protection against oxidation. In a used oil it measures the amount remaining after oxidation has reduced its concentration. The test is also suitable for manufacturing control and specification acceptance.

    3.2 When an infrared spectrum is obtained of an electrical insulating oil inhibited with either of these compounds there is an increase in absorbance of the spectrum at several wavelengths (or wavenumbers). 2,6 ditertiary-butyl paracresol produces pronounced increases in absorbance at 2.72 μm (3650 cm−1), and 11.63 μm (860 cm−1 ). 2,6 ditertiary-butyl phenol produces pronounced increases in absorbance at 2.72 μm (3650 cm−1) and 13.42 μm (745 cm −1).

    3.3 When making this test on other than a highly oxidized oil or when using a double-beam spectrophotometer, it has been found convenient to obtain the spectrum between 2.5 μm (4000 cm−1) and 2.9 μm (3450 cm−1) because the instrument is compensated for the presence of moisture and the band is not influenced by intermolecular forces (associations). However, when testing a highly oxidized oil or when using a single-beam instrument better results may be obtained if the scan is made between 10.90 μm (918 cm−1) and 14.00 μm (714 cm−1).

    3.4 Increased absorption at 11.63 μm (860 cm −1) or 13.42 μm (745 cm−1) or both, will identify the inhibitor as 2,6-ditertiary-butyl paracresol or 2,6-ditertiary-butyl phenol respectively (Note 1).

    Note 1The absorbance at 745 cm−1 for 2,6-ditertiary-butyl phenol and at 860 cm−1 for 2,6-ditertiary-butyl paracresol for equal concentrations will be in the approximate ratio of 2.6 to 1.

    1. Scope

    1.1 This test method covers the determination of the weight percent of 2,6-ditertiary-butyl paracresol (DBPC) and 2,6-ditertiary-butyl phenol (DBP) in new or used electrical insulating oil in concentrations up to 0.5 % by measuring its absorbance at the specified wavelengths in the infrared spectrum.

    1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

    1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    D923 Practices for Sampling Electrical Insulating Liquids

    D2144 Practices for Examination of Electrical Insulating Oils by Infrared Absorption

    D3487 Specification for Mineral Insulating Oil Used in Electrical Apparatus


    ICS Code

    ICS Number Code 29.040.10 (Insulating oils)

    UNSPSC Code

    UNSPSC Code 15121505(Transformer oil or insulating oil)


    Referencing This Standard

    DOI: 10.1520/D2668

    ASTM International is a member of CrossRef.

    Citation Format

    ASTM D2668-07(2013), Standard Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6-di-tert-Butyl Phenol in Electrical Insulating Oil by Infrared Absorption, ASTM International, West Conshohocken, PA, 2013, www.astm.org

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