ASTM D4768-11(2019)

Standard Test Method for Analysis of 2,6-Ditertiary-Butyl Para-Cresol and 2,6-Ditertiary-Butyl Phenol in Insulating Liquids by Gas Chromatography

SIGNIFICANCE AND USE
4.1 In new electrical insulating oil, this test method provides a quantitative measure of the amounts of 2,6-ditertiary-butyl para-cresol and 2,6-ditertiary-butyl phenol that have been added to the oil. In a used oil, the test measures the amount of these inhibitors remaining in the oil. This test method is suitable for manufacturing control, specification acceptance, and service evaluation.  
4.2 This test method is used to separate, identify, and quantify the inhibitors with minimal interference and matrix effects.  
4.3 This test method has also been used successfully to determine the inhibitor concentrations in other insulating liquids such as esters and high-temperature hydrocarbons.
SCOPE
1.1 This test method covers the determination by gas chromatography of 2,6-ditertiary-butyl para-cresol and 2,6-ditertiary-butyl phenol in new and used insulating liquids at concentrations up to 0.5 %. It includes the determination in Type I and II insulating mineral oils as specified in Specification D3487, but has also been used to measure these inhibitors in other insulating liquids, such as esters and high fire-point hydrocarbons.  
1.2 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2019
• ICS: 29.040.10 - Insulating oils
• Technical Committee: D27 - Electrical Insulating Liquids and Gases
• Drafting Committee: D27.03 - Analytical Tests

Relations

• Replaces: ASTM D4768-11 - Standard Test Method for Analysis of 2,6-Ditertiary-Butyl Para-Cresol and 2,6-Ditertiary-Butyl Phenol in Insulating Liquids by Gas Chromatography
• Effective Date: 01-Dec-2019
• Refers: ASTM D923-15(2023) - Standard Practices for Sampling Electrical Insulating Liquids
• Effective Date: 01-Dec-2023
• Refers: ASTM E260-96(2019) - Standard Practice for Packed Column Gas Chromatography
• Effective Date: 01-Sep-2019
• Refers: ASTM D3487-16e1 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 15-Jun-2016
• Refers: ASTM D3487-16 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 15-Jun-2016
• Refers: ASTM D923-15 - Standard Practices for Sampling Electrical Insulating Liquids
• Effective Date: 01-Oct-2015
• Refers: ASTM E260-96(2011) - Standard Practice for Packed Column Gas Chromatography
• Effective Date: 01-Nov-2011
• Refers: ASTM D3487-09 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 01-Dec-2009
• Refers: ASTM D3487-08 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 01-Nov-2008
• Refers: ASTM D5222-08 - Standard Specification for High Fire-Point Mineral Electrical Insulating Oils
• Effective Date: 01-Jan-2008
• Refers: ASTM D923-07 - Standard Practices for Sampling Electrical Insulating Liquids
• Effective Date: 15-Jul-2007
• Refers: ASTM D3487-00(2006) - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 01-Sep-2006
• Refers: ASTM E260-96(2006) - Standard Practice for Packed Column Gas Chromatography
• Effective Date: 01-Mar-2006
• Refers: ASTM E260-96 - Standard Practice for Packed Column Gas Chromatography
• Effective Date: 01-Jan-2001
• Refers: ASTM E260-96(2001) - Standard Practice for Packed Column Gas Chromatography
• Effective Date: 01-Jan-2001

Overview

ASTM D4768-11(2019) is the internationally recognized standard test method for the analysis of 2,6-ditertiary-butyl para-cresol (DBPC) and 2,6-ditertiary-butyl phenol (DBP) in insulating liquids using gas chromatography. These two compounds are crucial antioxidants, commonly used as inhibitors to extend the lifespan and performance of electrical insulating oils. This test method enables laboratories and industries to quantitatively determine the levels of these inhibitors in both new and used insulating liquids, supporting consistency, safety, and regulatory compliance in the production and maintenance of electrical equipment.

Key Topics

• Quantitative Analysis: The standard outlines procedures for the precise measurement of DBPC and DBP in concentrations up to 0.5% by weight in insulating liquids.
• Gas Chromatography Technique: Utilizes gas chromatography equipped with appropriate columns and detectors-typically flame ionization-ensuring separation and accurate quantification of inhibitors with minimal interference from matrix effects.
• Sample Preparation: Details steps including extraction using activated alumina columns, solvent washes, and preparation of working standards to eliminate nonpolar interferences and enhance chromatographic results.
• Applicability: While primarily focused on insulating mineral oils (Type I and II), the method also applies to other insulating liquids such as esters and high fire-point hydrocarbons used in electrical apparatus.
• Manufacturing and Service Evaluation: Enables manufacturing control, specification acceptance, and service evaluation by providing a reliable measure of antioxidant content in insulating fluids.

Applications

This ASTM standard is essential in several practical contexts:

• Electrical Equipment Maintenance: Regular testing of transformer oils and other insulating liquids helps assess the remaining concentration of inhibitors, supporting proactive maintenance and avoiding equipment failures due to oxidation and degradation.
• Quality Assurance in Manufacturing: During production, ensuring the correct dosage of DBPC and DBP in insulating oils guarantees compliance with industry specifications, such as ASTM D3487 for mineral insulating oils or ASTM D5222 for high fire-point insulating oils.
• Regulatory Compliance: Meets internationally recognized quality and standardization principles, as established by the World Trade Organization’s Technical Barriers to Trade (TBT) Committee, helping organizations comply with global trade and operational requirements.
• Performance Optimization: By monitoring inhibitor levels, industries can optimize the lifetime performance and efficiency of electrical apparatus, reducing downtime and extending the service life of critical infrastructure.

Related Standards

• ASTM D923 - Practices for Sampling Electrical Insulating Liquids
  Provides guidance for collecting representative oil samples, critical for accurate chromatographic analysis.
• ASTM D3487 - Specification for Mineral Insulating Oil Used in Electrical Apparatus
  Specifies quality requirements for mineral oil used in transformers and switchgear.
• ASTM D5222 - Specification for High Fire-Point Mineral Electrical Insulating Oils
  Details requirements for insulating oils designed for high-temperature applications.
• ASTM E260 - Practice for Packed Column Gas Chromatography
  Offers general guidelines for performing gas chromatography with packed columns.

Summary

ASTM D4768-11(2019) plays a vital role in the analysis and management of antioxidants in insulating liquids, ensuring reliability and safety in electrical power systems. By adhering to standardized testing methods, laboratories and utilities gain accurate, reproducible results that support informed decisions in manufacturing, maintenance, and compliance. For manufacturers, service providers, and testing laboratories in the electrical industry, following this standard ensures high-quality insulating oils, optimized equipment performance, and alignment with international best practices.

Keywords: insulating liquids, transformer oil, antioxidant analysis, gas chromatography, 2,6-ditertiary-butyl para-cresol, 2,6-ditertiary-butyl phenol, DBPC, DBP, ASTM D4768, electrical equipment, mineral oil inhibitors, quality control.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4768 − 11 (Reapproved 2019)
Standard Test Method for
Analysis of 2,6-Ditertiary-Butyl Para-Cresol and 2,6-
Ditertiary-Butyl Phenol in Insulating Liquids by Gas
Chromatography
This standard is issued under the fixed designation D4768; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Summary of Test Method
1.1 This test method covers the determination by gas 3.1 The test specimen is placed onto a column containing
chromatography of 2,6-ditertiary-butyl para-cresol and 2,6-
activated alumina and extracted to remove interfering sub-
ditertiary-butyl phenol in new and used insulating liquids at
stances. The inhibitors are then eluted from the column with
concentrations up to 0.5 %. It includes the determination in
suitable solvent and analyzed by gas chromatography. The
Type I and II insulating mineral oils as specified in Specifica-
inhibitor type and quantity are determined by comparison of
tion D3487, but has also been used to measure these inhibitors
each component with a working standard tested under similar
in other insulating liquids, such as esters and high fire-point
conditions.
hydrocarbons.
4. Significance and Use
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4.1 Innewelectricalinsulatingoil,thistestmethodprovides
responsibility of the user of this standard to establish appro-
a quantitative measure of the amounts of 2,6-ditertiary-butyl
priate safety, health, and environmental practices and deter-
para-cresol and 2,6-ditertiary-butyl phenol that have been
mine the applicability of regulatory limitations prior to use.
added to the oil. In a used oil, the test measures the amount of
1.3 This international standard was developed in accor-
these inhibitors remaining in the oil. This test method is
dance with internationally recognized principles on standard-
suitable for manufacturing control, specification acceptance,
ization established in the Decision on Principles for the
and service evaluation.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical 4.2 This test method is used to separate, identify, and
Barriers to Trade (TBT) Committee. quantify the inhibitors with minimal interference and matrix
effects.
2. Referenced Documents
4.3 This test method has also been used successfully to
2.1 ASTM Standards:
determine the inhibitor concentrations in other insulating
D923 Practices for Sampling Electrical Insulating Liquids
liquids such as esters and high-temperature hydrocarbons.
D3487 Specification for Mineral Insulating Oil Used in
Electrical Apparatus
5. Apparatus
D5222 Specification for High Fire-Point Mineral Electrical
5.1 Gas Chromatograph, equipped with oven temperature
Insulating Oils
control constant to 1 °C and with heated injector port.
E260 Practice for Packed Column Gas Chromatography
5.1.1 Means to Record the Chromatogram, such as a pen
recorder or a digital integrator to determine peak areas, is
recommended. An automated sample injector may be used.
This test method is under the jurisdiction of ASTM Committee D27 on
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
5.2 Flame Ionization Detector, with appropriate hydrogen/
mittee D27.03 on Analytical Tests.
Current edition approved Dec. 1, 2019. Published December 2019. Originally air gas flows, is preferred over a thermal conductivity detector
approved in 1988 as D4768 – 88. Last previous edition approved in 2011 as
to provide maximum sensitivity.
D4768 – 11. DOI: 10.1520/D4768-11R19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.3 Column, a suitable stainless steel or glass column
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
packed with a nonpolar silicone on an appropriate support or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. equivalent capillary column.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4768 − 11 (2019)
3 4
NOTE 1—A 3 % OV-1 on 100/120 Mesh Supelcoport, 1.83 m (6 ft)
minimum of 12 h. Cool in a desiccator prior to use. After
long, 3.2 mm (0.125 in.) in outside diameter has been used successfully.
column has cooled, purge column with approximately 2 mL
A SPB-1 30 m by 0.53 mm 1µm film column has also been used
hexaneorheptane.Donotallowcolumntodryoutpriortouse.
successfully.
7.2 Standard Solution Preparation—Standard solutions are
5.3.1 Condition columns in accordance with manufacturer’s
prepared containing both DBP and DBPC from inhibitor-free
recommendations. Disconnect columns from detector prior to
mineral oil. Prepare oil solutions of 0, 0.040, 0.080, 0.15, 0.30,
conditioning and reconnect after conditioning.
and 0.40 % (w/w) of both DBP and DBPC. Determine the
5.4 Precision Syringe, glass, 10.0 µL.
relative density (specific gravity) of the oil used in standard
5.5 Volumetric Glassware, appropriate for making dilutions. solution preparation (D ) to 0.001.
I
7.3 Column Extraction Effıciency—Verify by the following
5.6 Pipets, Pasteur, disposable, 146 by 7.5 mm.
procedure that the extraction efficiency of the prepared col-
5.7 Analytical Balance.
umns is acceptable.
5.8 Automatic Pipetter, 1 mL calibrated, adjustable.
7.3.1 Prepare a check standard containing 0.30 % (w/w)
DBP and 0.30 % (w/w) DBPC in methanol. Dilute 0.25 mL of
5.9 Oven, capable of maintaining a temperature of 325 6 5
check standard to 5.0 mL with methanol.
°C for conditioning extraction columns.
7.3.2 Prepare a working standard in accordance with 7.4,
5.10 Desiccator.
using the 0.30 % (w/w) oil standard and the cleanup column
whose efficiency is to be determined. Inject a volume of this
6. Reagents and Materials
working standard into the gas chromatograph.
6.1 Purity of Reagents—Use reagent grade chemicals in all
7.3.3 Inject a volume (equal to that used in 7.3.2)ofthe
tests. Unless otherwise indicated, it is intended that all reagents
diluted check standard into the chromatograph using the same
shall conform to the specifications of the Committee on
chromatographic conditions used to analyze the working stan-
Analytical Reagents of theAmerican Chemical Society, where
dards.
such specifications are available. Other grades may be used,
7.3.4 Calculate the extraction efficiency for both DBP and
provided it is first ascertained that the reagent is of sufficient
DBPC as follows:
purity to permit its use without lessening the accuracy of the
A
I
determination.
C 3 W A 3 C 3 V 3 D
I 0.30 I C C C
3100 5 5 extraction efficiency,%
6.2 2,6-ditertiary-butyl phenol (DBP).
A A 3 C 3 W
C C I 0.30
6.3 2,6-ditertiary-butyl para-cresol (DBPC )—Alsoknown
C 3 V 3 D
C C C
as butylated hydroxytoluene (BHT).
where:
6.4 Glass Wool.
A = area (or height) of 0.30 % working standard,
I
A = area (or height) of 0.30 % check standard,
6.5 Aluminum Oxide (Alumina), acid powder, ACS, Brock-
C
C = known concentration of working standard,
man Activity Grade 1, for chromatography.
I
C = known concentration of check standard,
C
6.6 Hexane or Heptane, ACS reagent grade.
D = relative density (specific gravity) of methanol used
C
6.7 Methanol, anhydrous, ACS reagent grade.
in check standard preparation, and
W = weight of 0.30 % working standard as recorded in
0.30
6.8 Mineral Oil, inhibitor-free, transformer grade.
7.4.1.
V = volume of check standard diluted to 5 mL in 7.3.1
7. Calibration and Standardization C
(=0.25 mL)
7.1 Cleanup Column Preparation—Prepare cleanup col-
7.3.5 The minimum acceptable extraction efficiency is 70 %
umns by inserting a small glass wool plug into the wide end of
for DBPC and 60 % for DBP. If the prepared columns do not
a Pasteur pipet and
...