ASTM D664-11a(2017)
(Test Method)Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration
Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration
SIGNIFICANCE AND USE
5.1 New and used petroleum products, biodiesel and blends of biodiesel may contain acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products. The relative amount of these materials can be determined by titrating with bases. The acid number is a measure of this amount of acidic substance in the oil, always under the conditions of the test. The acid number is used as a guide in the quality control of lubricating oil formulations. It is also sometimes used as a measure of lubricant degradation in service. Any condemning limits must be empirically established.
5.2 Since a variety of oxidation products contribute to the acid number and the organic acids vary widely in corrosion properties, the test method cannot be used to predict corrosiveness of oil or biodiesel and blends under service conditions. No general correlation is known between acid number and the corrosive tendency of biodiesel and blends or oils toward metals.
SCOPE
1.1 This test method covers procedures for the determination of acidic constituents in petroleum products, lubricants, biodiesel and blends of biodiesel.
1.1.1 Test Method A—For petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids whose dissociation constants in water are larger than 10-9; extremely weak acids whose dissociation constants are smaller than 10-9 do not interfere. Salts react if their hydrolysis constants are larger than 10–9. The range of acid numbers included in the precision statement is 0.1 mg/g KOH to 150 mg/g KOH.
1.1.2 Test Method B—Developed specifically for biodiesel and biodiesel blends with low acidity and slightly different solubility. This test method requires the use of an automatic titrator with automatic endpoint seeking capability.
Note 1: In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak bases, acid salts of polybasic acids, and addition agents such as inhibitors and detergents.
1.2 The test method may be used to indicate relative changes that occur in oil during use under oxidizing conditions regardless of the color or other properties of the resulting oil. Although the titration is made under definite equilibrium conditions, the test method is not intended to measure an absolute acidic property that can be used to predict performance of oil under service conditions. No general relationship between bearing corrosion and acid number is known.
Note 2: The acid number obtained by this standard may or may not be numerically the same as that obtained in accordance with Test Methods D974 and D3339. There has not been any attempt to correlate this method with other non-titration methods.
Note 3: A few laboratories have made the observation that there is a difference in Test Method D664 results when aqueous versus nonaqueous buffers are used.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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 health 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.
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Designation: D664 − 11a (Reapproved 2017) British Standard 4457
Designation 177/96
Standard Test Method for
Acid Number of Petroleum Products by Potentiometric
Titration
This standard is issued under the fixed designation D664; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber 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.
D974andD3339.Therehasnotbeenanyattempttocorrelatethismethod
1. Scope
with other non-titration methods.
1.1 This test method covers procedures for the determina-
NOTE 3—A few laboratories have made the observation that there is a
tion of acidic constituents in petroleum products, lubricants, difference in Test Method D664 results when aqueous versus nonaqueous
buffers are used.
biodiesel and blends of biodiesel.
1.1.1 Test Method A—Forpetroleumproductsandlubricants
1.3 The values stated in SI units are to be regarded as
soluble or nearly soluble in mixtures of toluene and propan-2-
standard. No other units of measurement are included in this
ol. It is applicable for the determination of acids whose
standard.
-9
dissociation constants in water are larger than 10 ; extremely
1.4 This standard does not purport to address all of the
-9
weak acids whose dissociation constants are smaller than 10
safety concerns, if any, associated with its use. It is the
do not interfere. Salts react if their hydrolysis constants are
responsibility of the user of this standard to establish appro-
–9
larger than 10 . The range of acid numbers included in the
priate safety and health practices and determine the applica-
precision statement is 0.1mg⁄g KOH to 150mg⁄g KOH.
bility of regulatory limitations prior to use.
1.1.2 Test Method B—Developed specifically for biodiesel
1.5 This international standard was developed in accor-
and biodiesel blends with low acidity and slightly different
dance with internationally recognized principles on standard-
solubility. This test method requires the use of an automatic
ization established in the Decision on Principles for the
titrator with automatic endpoint seeking capability.
Development of International Standards, Guides and Recom-
NOTE 1—In new and used oils, the constituents that may be considered
mendations issued by the World Trade Organization Technical
to have acidic characteristics include organic and inorganic acids, esters,
Barriers to Trade (TBT) Committee.
phenolic compounds, lactones, resins, salts of heavy metals, salts of
ammoniaandotherweakbases,acidsaltsofpolybasicacids,andaddition
2. Referenced Documents
agents such as inhibitors and detergents.
2.1 ASTM Standards:
1.2 The test method may be used to indicate relative
D974Test Method for Acid and Base Number by Color-
changesthatoccurinoilduringuseunderoxidizingconditions
Indicator Titration
regardless of the color or other properties of the resulting oil.
D1193Specification for Reagent Water
Although the titration is made under definite equilibrium
D3339TestMethodforAcidNumberofPetroleumProducts
conditions, the test method is not intended to measure an
by Semi-Micro Color Indicator Titration
absolute acidic property that can be used to predict perfor-
D4057Practice for Manual Sampling of Petroleum and
mance of oil under service conditions. No general relationship
Petroleum Products
between bearing corrosion and acid number is known.
D4177Practice for Automatic Sampling of Petroleum and
NOTE2—Theacidnumberobtainedbythisstandardmayormaynotbe
numerically the same as that obtained in accordance with Test Methods
Petroleum Products
E177Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
This test method is under the jurisdiction of ASTM Committee D02 on
3. Terminology
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.
3.1 Definitions:
Current edition approved May 1, 2017. Published June 2017. Originally
ɛ1
approved in 1942. Last previous edition approved in 2011 as D664 – 11a . DOI:
10.1520/D0664-11AR17. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method was adopted as a jointASTM-IPstandard in 1964.ASTM Test contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Method D4739 has been developed as an alternative to the base number portion of Standards volume information, refer to the standard’s Document Summary page on
D664. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D664 − 11a (2017)
3.1.1 acid number, n—the quantity of a specified base, 6. Apparatus
expressed in milligrams of potassium hydroxide per gram of
6.1 Manual Titration Apparatus:
sample, required to titrate a sample in a specified solvent to a
6.1.1 Meter, a voltmeter or a potentiometer that will operate
specified endpoint using a specified detection system.
with an accuracy of 60.005V and a sensitivity of 60.002V
3.1.1.1 Discussion—Thistestmethodexpressesthequantity
overarangeofatleast 60.5Vwhenthemeterisusedwiththe
of base as milligrams of potassium hydroxide per gram of
electrodes specified in 6.1.2 and 6.1.3 and when the resistance
sample, that is required to titrate a sample in a mixture of
between the electrodes falls within the range from 0.2MΩ to
toluene and propan-2-ol to which a small amount of water has
20MΩ. The meter shall be protected from stray electrostatic
been added from its initial meter reading in millivolts to a
fields so that no permanent change in the meter readings over
meter reading in millivolts corresponding to an aqueous basic
the entire operating range is produced by touching, with a
buffersolutionorawell-definedinflectionpointasspecifiedin
grounded lead, any part of the exposed surface of the glass
the test method.
electrode, the glass electrode lead, the titration stand, or the
3.1.1.2 Discussion—This test method provides additional
meter.
information. The quantity of base, expressed as milligrams of
NOTE 4—A suitable apparatus could consist of a continuous-reading
potassium hydroxide per gram of sample, required to titrate a
−
electronic voltmeter designed to operate on an input of less than 5×10
sampleinthesolventfromitsinitialmeterreadinginmillivolts
12A, when an electrode system having 1000MΩ resistance is connected
to a meter reading in millivolts corresponding to a freshly
across the meter terminals and provided with a metal shield connected to
the ground, as well as a satisfactory terminal to connect the shielded
prepared aqueous acidic buffer solution or a well-defined
connectionwirefromtheglasselectrodetothemeterwithoutinterference
inflectionpointasspecifiedinthetestmethodshallbereported
from any external electrostatic field.
as the strong acid number.
6.1.2 Sensing Electrode,StandardpH,suitablefornonaque-
3.1.1.3 Discussion—The causes and effects of the so-called
ous titrations.
strongacidsandthecausesandeffectsoftheotheracidscanbe
6.1.3 Reference Electrode, Silver/Silver Chloride (Ag/
very significantly different. Therefore, the user of this test
AgCl) Reference Electrode, filled with 1M–3M LiCl in etha-
method shall differentiate and report the two, when they are
nol.
found.
6.1.3.1 Combination Electrodes—Sensing electrodes may
have the Ag/AgCl reference electrode built into the same
4. Summary of Test Method
electrode body, which offers the convenience of working with
4.1 Thesampleisdissolvedinatitrationsolventandtitrated
andmaintainingonlyoneelectrode.Thecombinationelectrode
potentiometrically with alcoholic potassium hydroxide using a
shall have a sleeve junction on the reference compartment and
glass indicating electrode and a reference electrode or a
shall use an inert ethanol electrolyte, for example, 1M–3M
combination electrode. The meter readings are plotted manu-
LiCl in ethanol. These combination electrodes shall have the
allyorautomaticallyagainsttherespectivevolumesoftitrating
same response or better response than a dual electrode system.
solution and the end points are taken only at well-defined
They shall have removable sleeves for easy rinsing and
inflections in the resulting curve. When no definite inflections
addition of electrolyte.
are obtained and for used oils, end points are taken at meter
NOTE 5—Athird electrode, such as a platinum electrode, may be used
readings corresponding to those found for aqueous acidic and
to increase the electrode stability in certain systems.
basic buffer solutions.
6.1.4 Variable-Speed Mechanical Stirrer, a suitable type,
equipped with a propeller-type stirring paddle. The rate of
5. Significance and Use
stirringshallbesufficienttoproducevigorousagitationwithout
5.1 New and used petroleum products, biodiesel and blends
spatteringandwithoutstirringairintothesolution.Apropeller
of biodiesel may contain acidic constituents that are present as
with blades 6mm in radius and set at a pitch of 30° to 45° is
additives or as degradation products formed during service,
satisfactory. A magnetic stirrer is also satisfactory.
such as oxidation products. The relative amount of these
6.1.4.1 If an electrical stirring apparatus is used, it shall be
materials can be determined by titrating with bases. The acid
electrically correct and grounded so that connecting or discon-
number is a measure of this amount of acidic substance in the
necting the power to the motor will not produce a permanent
oil,alwaysundertheconditionsofthetest.Theacidnumberis
change in the meter reading during the course of the titration.
used as a guide in the quality control of lubricating oil
6.1.5 Burette, 10mL capacity, graduated in 0.05mL divi-
formulations. It is also sometimes used as a measure of
sions and calibrated with an accuracy of 60.02mL. The
lubricant degradation in service. Any condemning limits must
buretteshallhaveatipthatextends100mmto130mmbeyond
be empirically established.
thestopcockandshallbeabletodelivertitrantdirectlyintothe
5.2 Since a variety of oxidation products contribute to the titration vessel without exposure to the surrounding air or
vapors.TheburetteforKOHshallhaveaguardtubecontaining
acid number and the organic acids vary widely in corrosion
soda lime or other CO -absorbing substance.
properties,thetestmethodcannotbeusedtopredictcorrosive-
6.1.6 Titration Beaker, 250mL capacity, made of borosili-
nessofoilorbiodieselandblendsunderserviceconditions.No
general correlation is known between acid number and the cate glass or other suitable material.
corrosive tendency of biodiesel and blends or oils toward 6.1.7 Titration Stand, suitable for supporting the electrodes,
metals. stirrer, and burette.
D664 − 11a (2017)
NOTE6—Anarrangementthatallowstheremovalofthebeakerwithout
column, discarding the first 5% of material distilling overhead
disturbing the electrodes and stirrer is desirable.
and using the 95% remaining. Drying can also be accom-
6.2 Automatic Titration Apparatus: plished using molecular sieves such as Linde Type 4A, by
6.2.1 Automatic titration systems shall be able to carry out passing the solvent upward through a molecular sieve column
the necessary analyses as prescribed in the method. As a using one part of molecular sieve per ten parts of solvent.
NOTE 7—It has been reported that, if not originally inhibited against it,
minimum, the automatic titration system shall meet the perfor-
propan-2-ol can contain peroxides. When this occurs, an explosion is
mance and specification requirements listed in 6.1 as war-
possible when the storage of the vessel or other equipment such as a
ranted.
dispensing bottle, is near empty and approaching dryness.
6.2.2 A dynamic mode of titrant addition shall be used.
7.9 Commercial Aqueous pH 4, pH 7 and pH 11 Buffer
Duringthetitration,thespeedandvolumeoftheadditionshall
Solutions—These solutions shall be replaced at regular inter-
vary depending on the rate of change of the system. The
vals consistent with their stability or when contamination is
recommended maximum volume increment is 0.5mL and the
suspected. Information relating to their stability should be
recommended minimum volume increment is 0.05mL.
obtained from the manufacturer.
6.2.3 Graduated Cylinder—50mL, or dispensing device
capable of delivering 50mL 6 0.5mL.
8. Electrode System
6.2.4 Pipette—2.0mL, Class A.
8.1 Preparation of Electrodes—When a Ag/AgCl reference
6.2.5 Titration Beaker—250 mL, 125 mL, or suitable
electrode is used for the titration and it contains an electrolyte
capacity, made of borosilicate glass or other suitable material.
which is not 1M–3M LiCl in ethanol, replace the electrolyte.
Drain the electrolyte from the electrode, wash away all the salt
7. Reagents
(if present) with water and then rinse with ethanol. Rinse
7.1 Purity of Reagents—Reagent grade chemicals shall be
severaltimeswiththeLiClelectrolytesolution.Finally,replace
used in all tests. Unless otherwise indicated, it is intended that
the sleeve and fill the electrode with the LiCl electrolyte to the
all reagents shall conform to the specifications of the commit-
filling hole. When refitting the sleeve ensure that there will be
tee onAnalytical Reagents of theAmerican Chemical Society,
3 a free flow of electrolyte into the system. A combination
where such specifications are available. Other grades may be
electrodeshallbepreparedinthesamemanner.Theelectrolyte
used, provided it is first ascertained that the reagent is of
in a combination electrode can be removed with the aid of a
sufficiently high purity to permit its use without lessening the
vacuum suction.
accuracy of the determination.
8.2 Testing of Electrodes—Test the meter-electrode combi-
7.1.1 Commercially available solutions may be used in
nation when first put into use, or when new electrodes are
place of laboratory preparations provided the solutions have
installed, and retest at intervals thereafter. Rinse the electrodes
been certified as being equivalent.
withsolventthenwithwater,anddipthemintoapH4aqueous
7.1.2 Alternate volumes of the solutions may be prepared,
buffer solution. Read the mV value after stirring one minute.
provided the final solution concentration is equivalent.
Removetheelectrodesandrinsewithwater.Diptheelectrodes
7.2 Purity of Water—Unless otherwise indicated, reference
into a pH 7 aqueous buffer. Read the mV value after stirring
to water shall be understood to mean reagent water that meets
one minute. Calculate the mV difference. A good electrode
the requirements of either Type I, II, or III of Specification
syst
...
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.
´1
Designation: D664 − 11a D664 − 11a (Reapproved 2017) British Standard 4457
Designation 177/96
Standard Test Method for
Acid Number of Petroleum Products by Potentiometric
Titration
This standard is issued under the fixed designation D664; 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.
ε NOTE—Subsection 14.5 was corrected editorially in September 2016.
1. Scope*Scope
1.1 This test method covers procedures for the determination of acidic constituents in petroleum products, lubricants, biodiesel
and blends of biodiesel.
1.1.1 Test Method A—For petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-ol.
-9
It is applicable for the determination of acids whose dissociation constants in water are larger than 10 ; extremely weak acids
-9 -9–9
whose dissociation constants are smaller than 10 do not interfere. Salts react if their hydrolysis constants are larger than 10 .
The range of acid numbers included in the precision statement is 0.10.1 mg mg/g ⁄g KOH to 150150 mg mg/g ⁄g KOH.
1.1.2 Test Method B—Developed specifically for biodiesel and biodiesel blends with low acidity and slightly different solubility.
This test method requires the use of an automatic titrator with automatic endpoint seeking capability.
NOTE 1—In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters,
phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak bases, acid salts of polybasic acids, and addition agents
such as inhibitors and detergents.
1.2 The test method may be used to indicate relative changes that occur in oil during use under oxidizing conditions regardless
of the color or other properties of the resulting oil. Although the titration is made under definite equilibrium conditions, the test
method is not intended to measure an absolute acidic property that can be used to predict performance of oil under service
conditions. No general relationship between bearing corrosion and acid number is known.
NOTE 2—The acid number obtained by this standard may or may not be numerically the same as that obtained in accordance with Test Methods D974
and D3339. There has not been any attempt to correlate this method with other non-titration methods.
NOTE 3—A few laboratories have made the observation that there is a difference in Test Method D664 results when aqueous versus nonaqueous buffers
are used.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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 health 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:
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D1193 Specification for Reagent Water
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 July 15, 2011May 1, 2017. Published August 2011June 2017. Originally approved in 1942. Last previous edition approved in 2011 as D664 –
ɛ1
11.11a . DOI: 10.1520/D0664-11AE01.10.1520/D0664-11AR17.
This test method was adopted as a joint ASTM-IP standard in 1964. ASTM Test Method D4739 has been developed as an alternative to the base number portion of D664.
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
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D664 − 11a (2017)
D3339 Test Method for Acid Number of Petroleum Products by Semi-Micro Color Indicator Titration
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
3. Terminology
3.1 Definitions:
3.1.1 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.
3.1.1.1 Discussion—
This test method expresses the quantity of base as milligrams of potassium hydroxide per gram of sample, that is required to titrate
a sample in a mixture of toluene and propan-2-ol to which a small amount of water has been added from its initial meter reading
in millivolts to a meter reading in millivolts corresponding to an aqueous basic buffer solution or a well-defined inflection point
as specified in the test method.
3.1.1.2 Discussion—
This test method provides additional information. The quantity of base, expressed as milligrams of potassium hydroxide per gram
of sample, required to titrate a sample in the solvent from its initial meter reading in millivolts to a meter reading in millivolts
corresponding to a freshly prepared aqueous acidic buffer solution or a well-defined inflection point as specified in the test method
shall be reported as the strong acid number.
3.1.1.3 Discussion—
The causes and effects of the so-called strong acids and the causes and effects of the other acids can be very significantly different.
Therefore, the user of this test method shall differentiate and report the two, when they are found.
4. Summary of Test Method
4.1 The sample is dissolved in a titration solvent and titrated potentiometrically with alcoholic potassium hydroxide using a
glass indicating electrode and a reference electrode or a combination electrode. The meter readings are plotted manually or
automatically against the respective volumes of titrating solution and the end points are taken only at well-defined inflections in
the resulting curve. When no definite inflections are obtained and for used oils, end points are taken at meter readings
corresponding to those found for aqueous acidic and basic buffer solutions.
5. Significance and Use
5.1 New and used petroleum products, biodiesel and blends of biodiesel may contain acidic constituents that are present as
additives or as degradation products formed during service, such as oxidation products. The relative amount of these materials can
be determined by titrating with bases. The acid number is a measure of this amount of acidic substance in the oil, always under
the conditions of the test. The acid number is used as a guide in the quality control of lubricating oil formulations. It is also
sometimes used as a measure of lubricant degradation in service. Any condemning limits must be empirically established.
5.2 Since a variety of oxidation products contribute to the acid number and the organic acids vary widely in corrosion properties,
the test method cannot be used to predict corrosiveness of oil or biodiesel and blends under service conditions. No general
correlation is known between acid number and the corrosive tendency of biodiesel and blends or oils toward metals.
6. Apparatus
6.1 Manual Titration Apparatus:
6.1.1 Meter, a voltmeter or a potentiometer that will operate with an accuracy of 60.005 V and a sensitivity of 60.002 V over
a range of at least 60.5 V when the meter is used with the electrodes specified in 6.1.2 and 6.1.3 and when the resistance between
the electrodes falls within the range from 0.2 MΩ to 20 MΩ. The meter shall be protected from stray electrostatic fields so that
no permanent change in the meter readings over the entire operating range is produced by touching, with a grounded lead, any part
of the exposed surface of the glass electrode, the glass electrode lead, the titration stand, or the meter.
− 12
NOTE 4—A suitable apparatus could consist of a continuous-reading electronic voltmeter designed to operate on an input of less than 5 × 10 A, when
an electrode system having 1000 MΩ resistance is connected across the meter terminals and provided with a metal shield connected to the ground, as
well as a satisfactory terminal to connect the shielded connection wire from the glass electrode to the meter without interference from any external
electrostatic field.
D664 − 11a (2017)
6.1.2 Sensing Electrode, Standard pH, suitable for nonaqueous titrations.
6.1.3 Reference Electrode, Silver/Silver Chloride (Ag/AgCl) Reference Electrode, filled with 1M–3M LiCl in ethanol.
6.1.3.1 Combination Electrodes—Sensing electrodes may have the Ag/AgCl reference electrode built into the same electrode
body, which offers the convenience of working with and maintaining only one electrode. The combination electrode shall have a
sleeve junction on the reference compartment and shall use an inert ethanol electrolyte, for example, 1M–3M LiCl in ethanol.
These combination electrodes shall have the same response or better response than a dual electrode system. They shall have
removable sleeves for easy rinsing and addition of electrolyte.
NOTE 5—A third electrode, such as a platinum electrode, may be used to increase the electrode stability in certain systems.
6.1.4 Variable-Speed Mechanical Stirrer, a suitable type, equipped with a propeller-type stirring paddle. The rate of stirring shall
be sufficient to produce vigorous agitation without spattering and without stirring air into the solution. A propeller with blades
6 mm in radius and set at a pitch of 30° to 45° is satisfactory. A magnetic stirrer is also satisfactory.
6.1.4.1 If an electrical stirring apparatus is used, it shall be electrically correct and grounded so that connecting or disconnecting
the power to the motor will not produce a permanent change in the meter reading during the course of the titration.
6.1.5 Burette, 10 mL capacity, graduated in 0.05 mL divisions and calibrated with an accuracy of 60.02 mL. The burette shall
have a tip that extends 100 mm to 130 mm beyond the stopcock and shall be able to deliver titrant directly into the titration vessel
without exposure to the surrounding air or vapors. The burette for KOH shall have a guard tube containing soda lime or other
CO -absorbing substance.
6.1.6 Titration Beaker, 250 mL capacity, made of borosilicate glass or other suitable material.
6.1.7 Titration Stand, suitable for supporting the electrodes, stirrer, and burette.
NOTE 6—An arrangement that allows the removal of the beaker without disturbing the electrodes and stirrer is desirable.
6.2 Automatic Titration Apparatus:
6.2.1 Automatic titration systems shall be able to carry out the necessary analyses as prescribed in the method. As a minimum,
the automatic titration system shall meet the performance and specification requirements listed in 6.1 as warranted.
6.2.2 A dynamic mode of titrant addition shall be used. During the titration, the speed and volume of the addition shall vary
depending on the rate of change of the system. The recommended maximum volume increment is 0.5 mL and the recommended
minimum volume increment is 0.05 mL.
6.2.3 Graduated Cylinder—50 mL, or dispensing device capable of delivering 50 mL 6 0.5 mL.
6.2.4 Pipette—2.0 mL, Class A.
6.2.5 Titration Beaker—250 mL, 125 mL, or suitable capacity, made of borosilicate glass or other suitable material.
7. Reagents
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.
7.1.1 Commercially available solutions may be used in place of laboratory preparations provided the solutions have been
certified as being equivalent.
7.1.2 Alternate volumes of the solutions may be prepared, provided the final solution concentration is equivalent.
7.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean reagent water that meets the
requirements of either Type I, II, or III of Specification D1193.
7.3 Primary Standard—Where specified, these samples, or samples of commercially available primary standards, are to be used
in standardizing the volumetric solutions.
7.4 Ethanol, (Warning—Flammable and toxic, especially when denatured.)
7.5 Lithium Chloride, LiCl.
7.6 Lithium Chloride Electrolyte , Prepare a 1M–3M solution of lithium chloride (LiCl) in ethanol.
7.7 Potassium Hydroxide, (Warning—Causes severe burns.)
7.8 Propan-2-ol, Anhydrous, (less than 0.1 % H O). (Warning—Flammable.) If adequately dry reagent cannot be procured, it
can be dried by distillation through a multiple plate column, discarding the first 5 % of material distilling overhead and using the
95 % remaining. Drying can also be accomplished using molecular sieves such as Linde Type 4A, by passing the solvent upward
through a molecular sieve column using one part of molecular sieve per ten parts of solvent.
NOTE 7—It has been reported that, if not originally inhibited against it, propan-2-ol can contain peroxides. When this occurs, an explosion is possible
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by
the American Chemical Society, see Annua
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