ASTM D5770-23

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Designation: D5770 − 11 (Reapproved 2017) D5770 − 23
Standard Test Method for
Semiquantitative Micro Determination of Acid Number of
Lubricating Oils During Oxidation Testing
This standard is issued under the fixed designation D5770; 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 Scope*
1.1 This test method is a semiquantitative micro method intended for monitoring the changes in acidic constituents occurring in
lubricating oils during oxidation testing, when the acid number of such oils falls within the range from 0.02 mg to 1.0 mg of
potassium hydroxide per gram of sample. It is applicable to such oils as turbine oils, hydraulic oils, and other circulating oils.
NOTE 1—This test method is a micro version of Test Method D974 and it produces results similar to that method.
1.2 This test method is designed for use where sample size is limited. It shall not be used as a replacement for higher precision
methods such as Test Methods D974 or D664. It shall not be used to monitor oils in-service.
1.3 The values stated in SI units are to be regarded as the standard.
1.3.1 Exception—The values given in parentheses are for information only.
1.4 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 healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D664 Test Method for Acid Number of Petroleum Products by Potentiometric Titration
D943 Test Method for Oxidation Characteristics of Inhibited Mineral Oils
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D3339 Test Method for Acid Number of Petroleum Products by Semi-Micro Color Indicator Titration
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4871 Guide for Universal Oxidation/Thermal Stability Test Apparatus
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.06 on Analysis of Liquid Fuels and Lubricants.
Current edition approved May 1, 2017July 1, 2023. Published June 2017August 2023. Originally approved in 1995. Last previous edition approved in 20112017 as
D5770 – 11.D5770 – 11 (2017). DOI: 10.1520/D5770-11R17.10.1520/D5770-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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D5770 − 23
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.2 Definitions:Definitions of Terms Specific to This Standard:
3.2.1 acid number, n—the quantity of a specified base, expressed in milligrams of potassium hydroxide per gram of sample,
required to titrate a sample in a specified solvent to a specified endpoint using a specified detection system.
3.2.1.1 Discussion—
In this test method, the acid number is calculated from the number of drops required to produce a change in solution color from
blue-green to orange, compared to the number of drops required to produce an identical color change using a reference standard.
Because this is a direct comparison method, the acid number value can be reported in milligrams of potassium hydroxide per gram
of sample.
4. Summary of Test Method
4.1 A 2.0 mL portion of the titration solution is titrated with a sample using a dropping pipet. The number of drops of sample
required to turn the blue-green titration solution to a persistent orange color is noted.
4.2 A second 2.0 mL portion of the titration solution is titrated with an acid number reference solution of known acid number. The
number of drops of the reference solution required to turn the blue-green titration solution to a persistent orange color is noted.
4.3 The estimated acid number of the sample is calculated using the acid number of the reference solution and the ratio of the
number of drops of the reference solution required to effect the color change to the number of drops of the sample required for
the same change.
5. Significance and Use
5.1 This test method provides a semiquantitative estimate of the acid number of lubricating oils obtained from laboratory oxidation
tests using smaller amounts of sample than Test Methods D974, D664, or D3339. It has specific application in Test Method D943
and in Test Method D4871. This test method, therefore, provides a means of monitoring the relative oxidation of lubricating oils
by measuring changes in acid number, at different time intervals and under various oxidizing test conditions.
5.2 Since this test method is semiquantitative, each laboratory shall develop its own criteria for each oxidation test method for
determining when to switch from this semiquantitative test method to a more precise test method for acid number.
6. Apparatus
6.1 Glass Beakers, 10 mL capacity, or glass vials, 4 dram or 6 dram.
6.2 Glass Syringe, 2 mL to 5 mL capacity. A 5 mL interchangeable syringe with a 20 gage, 12 cm needle is satisfactory.
6.3 Dropping Pipet, glass with rubber bulb, capable of delivering 35 drops to 40 drops of oil.
7. Reagents
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless indicated otherwise, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades can be used provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent
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