ASTM D2896-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D2896 − 15 D2896 − 21
Standard Test Method for
Base Number of Petroleum Products by Potentiometric
Perchloric Acid Titration
This standard is issued under the fixed designation D2896; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the determination of basic constituents in petroleum products by titration with perchloric acid in
glacial acetic acid.
1.2 Procedures A and B use different titration solvent volumes and sample weights.
NOTE 1—A round robin on a series of new and used oils and additive concentrates has shown that the two procedures give statistically equivalent results.
1.3 Appendix X2 provides the use of an alternative solvent system which eliminates the use of chlorobenzene in this test method.
The use of the alternative solvent gives statistically equivalent results; however, the precision is worse. Paragraph X2.5.5 provides
guidance when comparing results using the two different solvents.
1.4 The constituents that may be considered to have basic characteristics include organic and inorganic bases, amino compounds,
salts of weak acids (soaps), basic salts of polyacidic bases, and salts of heavy metals.
NOTE 2—This test method is applicable to both fresh oils and used oils as described in Sections 16, 17, and 19 and Appendix X1.
1.5 This test method can be used to determine base number >300 mg KOH/g. However, the precision statement in Section 19 has
been obtained only on base number ≤300 mg KOH/g.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific warning statements, see Section 7, Section 10, and X2.2.
1.8 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.
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 Dec. 1, 2015Nov. 1, 2021. Published February 2016November 2021. Originally approved in 1970. Last previous edition approved in 20112015
as D2896 – 11.D2896 – 15. DOI: 10.1520/D2896-15.10.1520/D2896-21.
This test method has been approved by the sponsoring committees and accepted by the cooperating societies in accordance with established procedures.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2896 − 21
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
3. Terminology
3.1 Definitions:
3.1.1 base number—number, n—the quantity of a specified acid, expressed in terms of the equivalent number of 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.
4. Summary of Test Method
4.1 The sample is dissolved in an essentially anhydrous mixture of chlorobenzene and glacial acetic acid and titrated with a
solution of perchloric acid in glacial acetic acid using potentiometric titrimeter. A glass indicating electrode and a reference
electrode are used, the latter being connected with the sample solution by means of a salt bridge. The meter readings are plotted
against the respective volumes of titrating solution, and the end point is taken at the inflection in the resulting curve.
4.2 Procedure A uses 120 mL of titration solvent. Procedure B uses 60 mL of titration solvent. In addition, the two procedures use
different equations for the calculation of appropriate sample weights. Since many portions of the test method are identical for
Procedures A and B, only the unique sections will be described separately for the two versions of the test method.
4.3 Occasionally certain used oils give no inflection in the forward titration mode, in which case a back titration modification with
sodium acetate titrant is employed.
5. Significance and Use
5.1 New and used petroleum products can contain basic constituents that are present as additives. The relative amounts of these
materials can be determined by titration with acids. The base number is a measure of the amount of basic substance in the oil,
always under the conditions of the test. It is sometimes used as a measure of lubricant degradation in service; however, any
condemning limits must be empirically established.
6. Apparatus
6.1 Potentiometric Titrimeters, either automatic recording or manual.
6.2 Glass Electrode, pH 0 to 11, general-purpose type.
6.3 Reference Electrode, silver/silver chloride (Ag/AgCl) reference electrode with a nonaqueous bridge as described in Section 10.
(See also 19.1.)
NOTE 3—Some reference electrodes with fritted or fiber diaphragms and some combined glass plus reference electrodes systems are commercially
available, such as the single-rod glass plus silver/silver chloride electrode assembly. During the development of this test method, the use of electrodes
of these types gave problems in some laboratories, but not in others. Accordingly, these electrodes are permitted in this test method, provided that the
sodium perchlorate bridge is used; however, when stability or other problems arise with their use, the sleeve-type electrode should be used.
6.4 Stirrer, either mechanical or electrical, with variable speeds and with propeller or paddle of chemically inert material. When
an electrical stirrer is used, it must be grounded so that disconnecting or connecting the power to the motor will not produce a
permanent change in meter reading during the course of a titration. A magnetic stirrer with stirring bar can be used provided it
meets these conditions.
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volume information, refer to the standard’s Document Summary page on the ASTM website.
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6.5 Buret, 10 mL or 20 mL, graduated in 0.05 mL divisions and calibrated with an accuracy of 60.02 mL, or an automatic buret
of similar accuracy.
6.6 Titration Beaker, made of borosilicate glass or other suitable titration beaker, tall form recommended.
6.6.1 For Procedure A, use a beaker of 250 mL or 300 mL capacity. For Procedure B, use a beaker of about 150 mL capacity such
that 60 mL of titration solvent will cover the electrodes.
NOTE 4—Other beakers of suitable size capacity may be used.
6.7 Titration Stand, suitable to support the beaker, electrodes, stirrer, and buret. An arrangement that allows for the removal of the
beaker without disturbing the electrodes, buret, and stirrer is desirable.
NOTE 5—Some apparatus may be sensitive to interference by static electricity, shown by erratic movements of recorder pen or meter indicator, when the
titration assembly (beaker and electrodes) is approached by the operator. In this case surround the beaker closely with a cylinder of copper gauze that
is electrically grounded.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, 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 may 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.
7.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean reagent water that meets the
requirement of either Type I, II, or III of Specification D1193.
7.3 Acetic Acid, glacial (Warning—Toxic and irritant).
7.4 Acetic Anhydride (Warning—Toxic and irritant).
7.5 Chlorobenzene (Warning—Toxic and irritant).
7.6 Perchloric Acid, Standard Solution in Acetic Acid (0.1 N) (Warning—Powerful oxidant when dry or heated. Great care
should be taken to avoid contact with organic matter under conditions that may result in subsequent drying or heating, and spills
should be washed immediately and thoroughly with water)—Mix 8.5 mL of 70 % to 72 % perchloric acid (HClO , 70 % to 72 %)
(or 10.2 mL of 60 % to 62 % HClO solution) with 500 mL of glacial acetic and 30 mL (or 35 mL if the 60 % to 62 % HClO
4 4
solution is used) of acetic anhydride. Dilute to 1 L with glacial acetic acid. Allow the solution to stand for 24 h.
NOTE 6—Excess acetic anhydride should be avoided to prevent acetylation of any primary or secondary amines that may be present.
7.7 Potassium Hydrogen Phthalate—(KHC H O ).
8 4 4
7.8 Sodium Perchlorate Electrolyte—(Warning—Sodium perchlorate is toxic and an irritant. It is also a powerful oxidizing agent
when heated. Great care should be taken to avoid contact with organic matter under conditions that may result in subsequent drying
or heating, and spills should be washed immediately and thoroughly with water.) Prepare a saturated solution of sodium perchlorate
(NaClO ) in glacial acetic acid. An excess of undissolved NaClO shall always be present at the bottom of the solution.
4 4
Reagent Chemicals, American Chemical Society SpecificationsACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, , American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for
Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC),
Rockville, MD.
Available commercially for purchase already prepared.
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7.9 Titration Solvent—Add one volume of glacial acetic acid to two volumes of chlorobenzene.
7.10 Sodium Carbonate, anhydrous (Na CO ).
2 3
7.11 Sodium Acetate Solution, 0.1 N in acetic acid (for back titration, see Sections 16 and 17)—Dissolve 5.3 g of anhydrous
Na CO in 300 mL of glacial acetic acid. Dilute to 1 L with acetic acid after solution is complete.
2 3
8. Standardization of Reagents
8.1 Perchloric Acid Solution—The standardization of the perchloric acid solution (HClO ) differs for the two procedures as
follows:
8.1.1 Procedure A (120 mL)—Heat a quantity of potassium hydrogen phthalate in an oven at 120 °C for 2h2 h and allow it to cool.
Take 0.1 g to 0.2 g of the potassium hydrogen phthalate weighed to the nearest 0.1 mg and dissolve it in 40 mL of warm glacial
acetic acid. Add 80 mL of chlorobenzene, cool, and titrate with 0.1 N HClO solution, using the electrode system and procedures
given in 10.1 to 10.4 and 11.4 to 11.7. Detect the end point by the same procedure used for base number determination (see 14.2).
Carry out a blank titration on 40 mL of glacial acetic acid plus 80 mL of chlorobenzene (see 11.8).
8.1.2 Procedure B (60 mL)—Heat a quantity of potassium hydrogen phthalate in an oven at 120 °C for 2 h and allow it to cool.
Take 0.05 g to 0.1 g of the potassium hydrogen phthalate weighed to the nearest 0.1 mg and dissolve it in 20 mL of warm glacial
acetic acid. Add 40 mL of chlorobenzene, cool, and titrate with 0.1 N HClO solution as described in 8.1.1. Carry out a blank
titration on 20 mL of glacial acetic acid and 40 mL of chlorobenzene (see 11.8).
8.1.3 Calculate the normality, N , of the HClO solution as follows:
A 4
N 5 1000W/@204.23·~V 2 b!# (1)
A
where:
W = potassium hydrogen phthalate, g,
V = HClO solution used, mL, and
b = volume corresponding to V for the blank titration, mL.
NOTE 7—Because of the relatively large coefficient of volumetric expansion of organic liquids, the acetous HClO solution should be used within 65 °C
of the temperature at which it was standardized. If used at a temperature more than 5 °C higher, multiply the volume used by the factor 1 − (t·0.001).
If used at a temperature more than 5 °C lower, multiply by the factor 1 + (t·0.001), where t is the difference in degrees Celsius between temperatures of
standardization and use and is always positive.
8.2 Sodium Acetate Solution—The standardization of the sodium acetate solution (Na CO ) differs for the two procedures as
2 3
follows:
8.2.1 Procedure A (120 mL)—Use 120 mL of titration solvent and 8.00 mL of 0.1 N HClO solution. Titrate with 0.1 N sodium
acetate solution, using the electrode system and procedure given in 10.1 to 10.4 and 11.4 to 11.7. Detect the end point by the same
procedure as will be used for base number determination (see 14.2). Calculate the normality, N , of the sodium acetate solution
B
as follows:
N 5 8.00 2 b N /G (2)
@~ ! #
B A
where:
b = volume corresponding to V for the blank titration,
N = normality of the HClO solution, and
A 4
G = volume of standard sodium acetate used in the standardization, mL.
8.2.2 Procedure B (60 mL)—Use 60 mL of titration solvent and 4.00 mL of 0.1 N HClO solution. Titrate as described in 8.2.1.
Calculate the normality, N , of the sodium acetate solution as follows:
B
N 5 4.00 2 b N /G (3)
@~ ! #
B A
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where:
b = volume corresponding to V for the blank titration,
N = normality of the HClO solution, and
A 4
G = volume of standard acetous sodium acetate used in the standardization, mL.
9. Preparation of Sample
9.1 It is essential to ensure thatWhen applicable, refer to Practice D4057 the sample is representative since any sediment can be
acidic or basic or(Manual Sampling) or Practice D4177 have adsorbed acidic or basic material from the sample. When necessary,
samples are warmed to aid mixing. Used oils should be vigorously shaken to ensure homogeneity before sampling. (Automatic
Sampling) for proper sampling techniques.
NOTE 8—As used oils can change appreciably in storage, samples should be tested as soon as possible after removal from the lubricating system and the
dates of sampling and testing, if known, should be noted.
9.1.1 When sampling used lubricants, the specimen shall be representative of the system sampled and shall be free of
contamination from external sources.
9.1.2 Agitate used oil samples thoroughly to ensure that any sediment present is homogeneously suspended before analysis, as the
sediment can be acidic or basic or have adsorbed acidic or basic material from the sample. When necessary, samples are warmed
to aid mixing.
NOTE 8—As used oils can change appreciably in storage, samples should be tested as soon as possible after removal from the lubricating system and the
dates of sampling and testing, if known, should be noted.
10. Preparation of Electrode System
10.1 Preparation of Electrodes—When the reference electrode is to be changed from aqueous bridge to nonaqueous, drain out the
aqueous solution, wash out all crystals of KCl with water, then rinse the outer jacket (salt bridge) several times with NaClO
electrolyte solution. Finally fill the outer jacket with NaClO electrolyte solution up to the filling hole. When using the sleeve-type
electrode, carefully remove the ground-glass sleeve and thoroughly wipe both ground surfaces. Replace the sleeve loosely and
allow a few drops of electrolyte to drain through to flush the ground-glass joint and to wet the ground surfaces thoroughly with
electrolyte. Set the sleeve firmly in place, refill the outer jacket with the NaClO electrolyte solution, and rinse the electrode with
chlorobenzene. When in use, the electrolyte level in the reference electrode should be kept above that of the liquid in the titration
beaker to prevent entry of contaminants into the salt bridge. When not in use, fill the reference electrode with the NaClO
electrolyte solution, leave the bung in the filling orifice, and immerse both electrodes in distilled water, keeping the level of the
electrolyte above that of the distilled water.
10.2 Testing of Electrodes—Test the meter-electrode combination when first put into use or when new electrodes are installed and
retest at intervals thereafter as follows:
10.2.1 Procedure A—Dip the electrodes into a well-stirred mixture of 100 mL of glacial acetic acid plus 0.2 g of KHC H O and
8 4 4
record the reading given by the meter. Rinse the electrodes with chlorobenzene and immerse in 100 mL of glacial acetic acid plus
1.5 mL of 0.1 N HClO solution. The difference between readings is to be at least 0.3 V.
10.2.2 Procedure B—Dip the electrodes into a well-stirred mixture of 60 mL of glacial acetic acid plus 0.1 g of KHC H O and
8 4 4
record the reading vein by the meter. Rinse the electrodes with chlorobenzene and immerse in 50 mL of glacial acetic acid plus
solution. The difference between readings is to be at least 0.3 V.
0.75 mL of 0.1 N HClO
NOTE 9—See Appendix X4 for a possible procedure to check the electrode performance.
10.3 Cleaning of Electrodes—Following a titration, it is necessary that the electrodes are properly cleaned before proceeding with
a subsequent titration. One such way that has been found suitable is to first wash the electrodes with titration solvent to remove
any adhering oily material from the previous titration. Then wash the electrodes with water to dissolve any NaClO that may have
formed around the sleeve of the reference electrode and to restore the aqueous gel layer of the glass electrode. Rinse again with
the titration solvent. Before starting a series of sample titrations, follow this rinsing procedure, then run one or two blank titrations
on the solvent to condition the electrodes. Repeat the blank titrations if necessary.
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10.4 Maintenance of Electrodes—When there is reason to believe that the glass electrode has become contaminated, it can be
cleaned by immersion in cold chromic acid (Warning—Corrosive and carcinogenic) or an alternative non-chromium-containing
strongly-oxidizing acid cleaning solution for 5 min, followed by thorough water washing. After this cleaning treatment, test the
electrode as described in 10.2. The reference electrode can be cleaned by draining and refilling with fresh NaClO solution.
Maintain the electrolyte level in the reference electrode above that of the liquid in the titration beaker at all times. Do not allow
the electrodes to remain immersed in titration solvent for any appreciable period of time between titrations. While the electrodes
are not extremely fragile, handle them carefully at all times and particularly avoid scratching the glass electrode.
11. Procedure A (120 mL)
11.1 Calculate the quantity of sample required from its expected base number, BN, as follows:
Approximate weight of sample, g5 28/expected BN (4)
NOTE 10—For the back titration procedure (see 16.2), or when analyzing used oils, it may be necessary to use a smaller sample weight.
11.1.1 Weigh the sample into the titration beaker, applying the limits shown as follows. A maximum of 20 g should be taken for
analysis.
Precision of
Sample Weight, g Weighing, g
10 to 20 0.05
5 to 10 0.02
1 to 5 0.005
0.25 to 1.0 0.001
0.1 to 0.25 0.0005
11.2 Add 120 mL of titration solvent to the sample.
11.3 Place the beaker on the titration stand and stir the solution until the sample is dissolved.
NOTE 11—If solution of the sample proves difficult, dissolve it in 80 mL of chlorobenzene in the titration beaker, then add 40 mL of glacial acetic acid.
Many used oils contain some solid materials that will not dissolve. This is a frequently observed condition.
11.4 Prepare the electrodes as directed in 10.1, 10.2, and 10.3. Position the electrodes in the solution so that they are immersed
as far as possible. Continue stirring throughout the determination at a rate sufficient to produce vigorous agitation without
spattering and without stirring air into the solution. Adjust the meter so that it reads in the upper part of the millivolt scale; for
example, 700 mV. For simple meters without this adjustment, it is necessary to incorporate a source of potential in series with the
electrode. A 1.5 V dry cell and potential divider is suitable.
11.5 Fill the buret with 0.1 N HClO solution and place the buret in position in the titration assembly, taking care that the tip is
immersed below the level of the surface of the liquid in the beaker. Record the initial buret and meter (cell potential) readings.
11.6 Titration:
11.6.1 Manual Titration—Add suitable small portions of titrant and, after waiting until a constant potential has been established
(Note 12), record the buret and meter readings. At the start of the titration and in any subsequent regions (inflections) where 0.1 mL
of titrant consistently produces a total change of more than 0.03 V (corresponding to 0.5 pH scale unit) in the cell potential, add
0.05 mL portions. In the intermediate regions (plateaus) where 0.1 mL increments change the potential by less than 0.03 V, add
large portions sufficient to produce a total potential change approximately equal to, but not greater than, 0.03 V. Titrate in this
manner until the potential changes less than 0.005 V (corresponding to 0.1 pH scale unit) per 0.1 mL.
NOTE 12—Consider the cell potential constant when it changes less than 0.005 V ⁄min.
11.6.2 Automatic Recording Titration—Adjust the instrument in accordance with the manufacturer’s instructions and set the
titration speed at 1.0 mL ⁄min maximum.
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11.7 On completion of the titration, remove the beaker and rinse the electrodes and buret tip with titration solvent, then with water,
then again with titration solvent (see 10.3). Store in water when not in use (see 10.1).
11.8 For each set of samples make a blank titration using 120 mL of titration solvent. For a manual titration add 0.1 N HClO
solution in 0.05 mL increments, waiting between each addition until a constant cell potential is established. Record meter and buret
readings after each increment. Follow the procedure in 11.6.2 for an automatic titration.
12. Procedure B (60 mL)
12.1 Calculate the quantity of sample required from its expected base number as follows:
Approximate weight of sample, g5 10/expected BN (5)
NOTE 13—For the back titration procedure (see 17.2) it may be necessary to use a smaller sample weight.
12.1.1 Weigh the sample into the titration beaker, applying the limits shown as follows. A maximum of 10 g should be taken for
analysis.
Precision of
Sample Weight, g Weighing, g
5 to 10 0.02
1 to 5
...