ASTM D7795-15(2022)e1
(Test Method)Standard Test Method for Acidity in Ethanol and Ethanol Blends by Titration
Standard Test Method for Acidity in Ethanol and Ethanol Blends by Titration
SIGNIFICANCE AND USE
5.1 This test method measures acidity in ethanol or ethanol blends quantitatively. Denatured fuel ethanol may contain additives such as corrosion inhibitors and detergents as well as contaminants from manufacturing that can affect the acidity of finished ethanol fuel. Very dilute aqueous solutions of low molecular mass organic acids, such as acetic acid, are highly corrosive to many metals. It is important to keep such acids at a very low level.
5.2 Acceptable levels of acidity in ethanol or ethanol blends can vary with different specifications but in general it is below 200 mg/kg (ppm). Knowledge of the acidity can be required to establish whether the product quality meets specification.
SCOPE
1.1 This test method covers the determination of acidity as acetic acid (see Specification D4806) in commonly available grades of denatured ethanol, and ethanol blends with gasoline ranging from E95 to E30. This test method is used for determining low levels of acidity, below 200 mg/kg (ppm mass), with the exclusion of carbon dioxide.
1.1.1 Procedure A—Developed specifically for measurement of acidity by potentiometric titration. This is the referee method.
1.1.2 Procedure B—Developed specifically for measurement of acidity by color end point titration.
1.2 The ethanol and ethanol blends may be analyzed directly by this test method without any sample preparation.
1.3 Review the current and appropriate Material Safety Data Sheets (MSDS) for detailed information concerning toxicity, first aid procedures, and safety precautions and proper personal protective equipments.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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. Some specific hazards statements are given in Section 7 on Hazards.
1.6 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
Relations
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.
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Designation: D7795 − 15 (Reapproved 2022)
Standard Test Method for
Acidity in Ethanol and Ethanol Blends by Titration
This standard is issued under the fixed designation D7795; 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.
ε NOTE—Editorially updated references in Section 3 and 19.2 in May 2022.
1. Scope 2. Referenced Documents
1.1 This test method covers the determination of acidity as 2.1 ASTM Standards:
acetic acid (see Specification D4806) in commonly available D770Specification for Isopropyl Alcohol
grades of denatured ethanol, and ethanol blends with gasoline D1193Specification for Reagent Water
ranging from E95 to E30. This test method is used for D4175Terminology Relating to Petroleum Products, Liquid
determining low levels of acidity, below 200mg⁄kg (ppm Fuels, and Lubricants
mass), with the exclusion of carbon dioxide. D4806Specification for Denatured Fuel Ethanol for Blend-
1.1.1 Procedure A—Developed specifically for measure- ing with Gasolines for Use asAutomotive Spark-Ignition
ment of acidity by potentiometric titration. This is the referee Engine Fuel
method. D6299Practice for Applying Statistical Quality Assurance
1.1.2 Procedure B—Developed specifically for measure- and Control Charting Techniques to Evaluate Analytical
ment of acidity by color end point titration. Measurement System Performance
D6708Practice for StatisticalAssessment and Improvement
1.2 The ethanol and ethanol blends may be analyzed di-
of Expected Agreement Between Two Test Methods that
rectly by this test method without any sample preparation.
Purport to Measure the Same Property of a Material
1.3 ReviewthecurrentandappropriateMaterialSafetyData
E200Practice for Preparation, Standardization, and Storage
Sheets (MSDS) for detailed information concerning toxicity,
of Standard and Reagent Solutions for ChemicalAnalysis
firstaidprocedures,andsafetyprecautionsandproperpersonal
protective equipments.
3. Terminology
1.4 The values stated in SI units are to be regarded as
3.1 Definitions:
standard. No other units of measurement are included in this
3.1.1 For definitions of terms used in this test method, refer
standard.
to Terminology D4175.
3.1.2 acidity, n—the quality, state, or degree of being acid.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.1.2.1 Discussion—The amount of acid titrated with a base
(NaOH or KOH) in a sample of ethanol or ethanol blend with
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- gasoline, calculated as acetic acid in mg/kg (ppm mass).
mine the applicability of regulatory limitations prior to use.
3.2 Abbreviations:
Some specific hazards statements are given in Section 7 on
3.2.1 KHC H O —KHP-Potassium Acid Phthalate
8 4 4
Hazards.
1.6 This international standard was developed in accor-
4. Summary of Test Method
dance with internationally recognized principles on standard-
4.1 Samples are purged with nitrogen prior to and during
ization established in the Decision on Principles for the
titrationfortheeliminationofcarbondioxideandthenaknown
Development of International Standards, Guides and Recom-
amount of ethanol or ethanol blend sample is analyzed poten-
mendations issued by the World Trade Organization Technical
tiometrically either using a monotonic or dynamic end point
Barriers to Trade (TBT) Committee.
titrant addition, as specified in Procedure A, or by color end
point titration, as specified in Procedure B, using a base
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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2022. Published May 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2012. Last previous edition approved in 2015 as D7795–15. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7795-15R22E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7795 − 15 (2022)
(NaOH) solution. Acid content is calculated as milligrams of intervals (monotonic) or variable titrant increments with elec-
acetic acid per kilogram of sample. trode stability between increment additions (dynamic) with
endpoint seeking capabilities as prescribed in the method. At
5. Significance and Use
the very least, the automatic titration system shall meet the
5.1 This test method measures acidity in ethanol or ethanol
performance and specification requirements as warranted by
blends quantitatively. Denatured fuel ethanol may contain
the manufacturer.
additives such as corrosion inhibitors and detergents as well as
contaminants from manufacturing that can affect the acidity of 8.2 A monotonic or dynamic mode of titrant addition shall
finished ethanol fuel. Very dilute aqueous solutions of low be used. During the titration, the speed and volume of the
molecular mass organic acids, such as acetic acid, are highly
addition may vary depending on the rate of change of the
corrosive to many metals. It is important to keep such acids at
system. The recommended minimum volume increment is
a very low level.
0.05mL for low acidity samples such as E30, and the recom-
mended maximum volume increment is 0.1 mL.Asignal drift
5.2 Acceptablelevelsofacidityinethanolorethanolblends
can vary with different specifications but in general it is below of 10 mV/min and endpoint recognition set to last is recom-
200mg/kg(ppm).Knowledgeoftheaciditycanberequiredto mendedtoensureendpointdetection.Whenusingamonotonic
establish whether the product quality meets specification.
titrant addition the waiting time between increment additions
shall be sufficient to allow for mixing and a stable electrode
6. Interferences
response. Wait at least 10 s between additions.
6.1 Basic solutions will absorb carbon dioxide from the air
8.3 Buret, 5 mL capacity, capable of delivering titrant in
to produce carbonate ions in the titrant and change the
concentration of the titrant. Care should be taken to minimize 0.02mLorlargerincrements.Theburettipshalldelivertitrant
exposure of basic titrants to the air as much as possible.Verify directly into the titration vessel without exposure to the
the concentration of the titrant (standardize the titrant) fre-
surrounding air. The buret used for base solutions shall have a
quently enough to detect concentration changes of
guard tube containing carbon dioxide absorbent.
0.0005mol⁄L (M) and especially if prolonged exposure to the
8.4 Titration Stand, suitable for supporting the electrode,
air occurs.
stirrer and buret tip.
6.2 Minimize exposure of the ethanol or ethanol blend
samples to the air to avoid contamination by carbon dioxide. 8.5 Sensing Electrode, standard pH, suitable for non-
aqueous titrations.
7. Hazards
8.6 Reference Electrode—Silver/Silver Chloride (Ag/AgCl)
7.1 Each analyst shall be acquainted with the potential
Reference Electrode, filled with 1M-3M LiCl in ethanol.
hazards of the equipment, reagents, products, solvents and
procedures before beginning laboratory work. Sources of
8.7 Combination pH Electrodes—Sensing electrodes may
information include: instrument manuals, MSDS, various
have the Ag/AgCl reference electrode built into the same
literature, and other related sources. Safety information should
electrode body, which offers the convenience of working with
be requested from the supplier. Disposal of waste materials,
and maintaining only one electrode. A combination pH elec-
reagents, reactants, and solvents shall comply with all the laws
trode designed for nonaqueous titrations of organic solvents is
and regulations from all applicable governmental agencies.
needed for titration of ethanol and ethanol blends. The combi-
7.2 Ethanol or ethanol blend products are intended for
nation pH electrode shall have a sleeve junction on the
industrial use only.
reference compartment and shall use an inert ethanol
7.3 The following hazards are associated with the applica-
electrolyte, 1 mol/L to 3 mol/L (M) LiCl in ethanol. Combi-
tion of this test method and the use of an automatic titrator.
nation pH electrodes shall have the same or better response
7.3.1 Chemical Hazard:
thanadualelectrodesystem.Theyshallhaveamovablesleeve
7.3.1.1 A solution of potassium hydroxide or sodium hy-
for easy rinsing and addition of electrolyte.
droxide is corrosive and shall be handled with the appropriate
8.8 Titration Beaker, borosilicate glass or plastic beaker of
personal protective equipment such as gloves, chemical
suitable size for the titration.
goggles, and lab coat or chemical-resistant apron.Always add
the base to water when diluting 50 % NaOH.
8.9 Sparging System, a gas delivery system suitable to
7.3.1.2 Ethanolisaflammableandtoxicsolventthatisused
deliver directly into the liquid sample, with an external
to prepare the lithium chloride electrolyte solution for the
pressure of 69 kPa (10 psi).
referenceelectrode.When handling a flammable solvent,work
in a well-ventilated area away from all sources of ignition.
8.10 Variable-Speed Mechanical Stirrer, a suitable type,
equipped with a propeller-type stirring paddle. The rate of
stirringshallbesufficienttoproducevigorousagitationwithout
PROCEDURE A—POTENTIOMETRIC TITRATION
spatteringandwithoutstirringairintothesolution.Apropeller
8. Apparatus
with blades 6 mm in radius and set at a pitch of 30 to 45° is
satisfactory. A magnetic stirrer and stirring bars is also satis-
8.1 Potentiometric Titrator—Automatic titration systems
capable of adding fixed increments of titrant at fixed time factory.
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D7795 − 15 (2022)
8.10.1 If an electrical stirring apparatus is used, it shall be 9.5.1 Alternatively, KOH (0.01 N) in isopropyl alcohol
electrically correct and grounded so that connecting or discon- solution may be used instead of 0.01 N) NaOH.
necting the power to the motor will not produce a permanent
9.6 Alcohols, refined, ethyl or isopropyl.
change in the instrument reading during the course of the
NOTE 1—Isopropyl alcohol (99 % grade) conforming to Specification
titration.
D770, or 190 proof ethyl alcohol conforming to formula No. 3A of the
U.S, Bureau of Alcohol, Tobacco, and Firearms as defined in Title 27,
9. Reagents and Materials
Code of Federal Regulations (or equivalent regulations in other jurisdic-
tions) is suitable for use as the solvent. The use of methyl alcohol is not
9.1 Purity of Reagents—Reagent grade chemicals shall be
recommended.
used in all tests. Unless otherwise indicated, it is intended that
9.7 Lithium Chloride Electrolyte—Prepare a 1 mol/L to
all reagents shall conform to the specifications of the commit-
3mol⁄L(M) solution of lithium chloride (LiCl) in ethanol per
tee onAnalytical Reagents of theAmerican Chemical Society,
the electrode manufacturer’s recommendation.
where such specifications are available. Other grades may be
used, provided it is pure enough to be used without lessening
9.8 Nitrogen, 99.9 % pure.
the accuracy of the determination.
9.9 Commercial Aqueous pH 4 and pH 7 Buffer Solutions—
9.1.1 Commercially-available solutions may be used in
Thesesolutionsshallbereplacedatregularintervalsconsistent
place of laboratory preparations provided the solutions have
with their stability or when contamination is suspected. Infor-
been certified as being equivalent.
mation relating to their stability is provided by the manufac-
9.1.2 Alternate volumes of the solutions may be prepared,
turer.
provided the final solution concentration is equivalent.
9.2 Purity of Water—Unless otherwise indicated, reference 10. Preparation of Apparatus
to water shall be understood to mean reagent water that meets
10.1 Prepare the titrator in accordance with the manufactur-
the requirements of either Type II or III of Specification
er’s instructions. Any visible air bubbles in the buret tip shall
D1193.
be eliminated prior to titration since this can lead to errors.
9.2.1 Prepare CO free water by sparging 1 Lof water (9.2)
10.2 Preparation of Electrodes—When the combination pH
with nitrogen (9.8) for no less than 3 min.
electrode contains Ag/AgCl reference with an electrolyte
9.3 Potassium Acid Phthalate (KHC H O ), primary
8 4 4
which is not 1 mol/L to 3 mol/L (M) LiCl in ethanol, the
standard, dried—Place4gto5gof primary standard potas-
electrolyte shall be replaced. Drain the electrolyte from the
sium acid phthalate KHC H O of 100 mesh fineness, in a
8 4 4
electrode (vacuum suction), wash away all the salt (if present)
weighing bottle at 120°C for 2 h. Stopper the container and
with water and then rinse with ethanol. Rinse several times
cool it in a desiccator.
with LiCl electrolyte solution. Finally, replace the sleeve and
9.4 Potassium Hydrogen Phthalate (KHP) Solution— fill the electrode with the LiCl electrolyte to the filling hole.
Accuratelyweighapproximately1.0gofdriedKHPandrecord When refitting the sleeve, ensure that there will be a free flow
the mass to the nearest 60.0001 g and transfer it to a 500 mL of electrolyte into the system.
Class A volumetric flask swept free of carbon dioxide. Add
10.3 Maintenance and Storage of Electrodes:
200mL of Type II DI water that is free of carbon dioxide,
10.3.1 Follow the manufacturer’s instructions for storage
stopper and swirl gently until it is dissolved. Dilute to 500 mL
and use of the electrode.
and mix thoroughly. Express the concentration of KHP in
10.3.2 Prior to each titration soak the prepared electrode in
solution as Molarity in moles of KHPper litre of solution.The
water for at least 2 min. Rinse the electrode with deionized
use of a volumetric flask can be avoided by weighing 1.0 g of
water immediately prior to use. The glass membrane needs to
driedKHPtothenearest0.0001gintoabeakerandadding500
be rehydrated after titration of non-aqueous solutions.
g of Type II carbon dioxide free DI water. Record the total
10.3.3 When not in use, immerse the lower half of the
mass of water and KHPto the nearest 60.01 g and express the
combination electrode in LiCl electrolyte. Do not allow elec-
concentration of KHP
...
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