ASTM D6423-99
(Test Method)Standard Test Method for Determination of pHe of Ethanol, Denatured Fuel Ethanol, and Fuel Ethanol (Ed75-Ed85)
Standard Test Method for Determination of pHe of Ethanol, Denatured Fuel Ethanol, and Fuel Ethanol (Ed75-Ed85)
SCOPE
1.1 This test method covers a procedure to determine a measure of the acid strength of high ethanol content fuels. These include ethanol, denatured fuel ethanol, and fuel ethanol (Ed75-Ed85). The test method is applicable to fuels containing nominally 70 volume % ethanol, or higher, as described in Specifications D 4806 and D 5798.
1.2 Acid strength as measured in this test method is defined as pHe. A pHe value for alcohol solutions is not directly comparable to pH values of water solutions.
1.3 The value of pHe will depend somewhat on the fuel blend, the stirring rate, and the time the electrode is in the fuel.
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.
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An American National Standard
Designation: D 6423 – 99
Standard Test Method for
Determination of pHe of Ethanol, Denatured Fuel Ethanol,
and Fuel Ethanol (Ed75-Ed85)
This standard is issued under the fixed designation D 6423; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.4 fuel ethanol (Ed75-Ed85), n—a blend of ethanol and
hydrocarbons of which the ethanol portion is nominally 75 to
1.1 This test method covers a procedure to determine a
85 volume % denatured ethanol.
measure of the acid strength of high ethanol content fuels.
3.2 Definitions of Terms Specific to This Standard:
These include ethanol, denatured fuel ethanol, and fuel ethanol
3.2.1 pHe, n—a measure of the acid strength of alcohol
(Ed75-Ed85). The test method is applicable to fuels containing
fuels defined by this apparatus and procedure.
nominally 70 volume % ethanol, or higher, as described in
Specifications D 4806 and D 5798.
4. Summary of Test Method
1.2 Acid strength as measured in this test method is defined
4.1 The sample is analyzed at room temperature using a
as pHe. A pHe value for alcohol solutions is not directly
specified electrode system and a pH meter with a sufficiently
comparable to pH values of water solutions.
high impedance and recommended for use with ion specific
1.3 The value of pHe will depend somewhat on the fuel
electrodes.
blend, the stirring rate, and the time the electrode is in the fuel.
4.2 Readings are taken at exactly 30 s because the meter
1.4 This standard does not purport to address all of the
reading will drift throughout the analysis due to solvent effects
safety concerns, if any, associated with its use. It is the
on the electrode.
responsibility of the user of this standard to establish appro-
4.3 The electrode is soaked in water-based pH 7 buffer
priate safety and health practices and determine the applica-
between readings to prepare it for the next sample. This
bility of regulatory limitations prior to use.
rehydrates the glass electrode, a necessary step to preserve the
2. Referenced Documents electrode’s response characteristics.
2.1 ASTM Standards:
5. Significance and Use
D 4806 Specification for Denatured Fuel Ethanol for Blend-
5.1 The acid strength, as measured by pHe, is a good
ing with Gasolines for Use as Automotive Spark-Ignition
2 predictor of the corrosion potential of ethanol fuels. It is
Engine Fuel
preferable to total acidity because total acidity does not
D 5798 Specification for Fuel Ethanol (Ed75-Ed85) for
3 measure acid strength; overestimates the contribution of weak
Automotive Spark-Ignition Engines
acids, such as carbonic acid; and may underestimate the
3. Terminology corrosion potential of low concentrations of strong acids, such
as sulfuric acid.
3.1 Definitions:
3.1.1 ethanol, n—ethyl alcohol, the chemical compound,
6. Apparatus
C H OH.
2 5
6.1 pH meter—All types of commercially available pH
3.1.2 denaturants, n—natural gasoline, gasoline compo-
meters with a sufficiently high impedance and recommended
nents, unleaded gasoline, or toxic or noxious materials added to
for use with ion specific electrodes are acceptable for this test
fuel ethanol to make it unsuitable for beverage use but not
method. Temperature compensation and readability to 0.01 pH
unsuitable for automotive fuel use.
unit are recommended.
3.1.3 denatured fuel ethanol, n—fuel ethanol made unfit for
6.2 Electrode—ORION Ross Sure-Flow combination elec-
beverage use by the addition of denaturants.
trode with a glass body shall be used. Because the measure-
ment is (of necessity) not made at equilibrium, it is essential
This test method is under the jurisdiction of ASTM Committee D-2 on
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.A on Gasoline and Oxygenated Fuels. The specified electrode (ORION Cat. No. 8172BN) is available from many
Current edition approved June 10, 1999. Published August 1999. laboratory supply companies or from the manufacturer: Orion Research Incorpo-
Annual Book of ASTM Standards, Vol 05.02. rated, Laboratory Products Group, The Schrafft Center, 529 Main Street, Boston,
Annual Book of ASTM Standards, Vol 05.03. MA 02129.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6423–99
that this exact electrode be used to ensure the reproducibility of 8.2 Rinse the container with a portion of the fuel to be
results. Other electrodes (even those of similar design) will sampled before taking the sample.
likely give different results under some or all conditions due to
the use of a different size or type of glass membrane for the pH 9. Standardization of Assembly
electrode, a different type of salt bridge junction, or other small
9.1 Turn on the pH meter and allow it to warm up
differences, which may affect their nonequilibrium response.
thoroughly in accordance with the manufacturer’s instructions.
6.3 Temperature Compensator—The thermocompensator is
Note the temperature of the sample to be tested. If temperature
a temperature-sensitive resistance element immersed in the
compensation is to be manual, adjust the temperature dial of
sample with the electrodes. The thermocompensator automati-
the meter to correspond to the temperature of the sample to be
cally corrects for the change in slope of the glass electrode
tested and allow time for all buffers, solutions, and the
response (with change in temperature) but does not correct for
electrode to equilibrate thermally.
actual changes in sample pH with temperature. Because
9.2 Clean/rehydrate the electrode after every ten samples
temperature compensation corrects only for changes in pH
and new electrodes before first use in alcohol solutions by
electrode response with temperature, the fuel sample must be at
alternately soaking several times in 1 M NaOH solution and 1
22 6 2°C.
MH SO (or 1 M HCl) for about 30 s each. Remove the
2 4
6.4 Beakers, borosilicate glass, 100 mL.
electrode and rinse it well with distilled water into a waste
6.5 Magnetic Stirrer—Any laboratory magnetic stirrer can
container.
be used, along with a TFE-fluorocarbon-coated stirring bar
9.3 Calibrate the pH meter to pH=7.00 with a water-based
approximately 19 to 25-mm long.
pH=7.00 buffer solution. Remove the electrode and rinse it
6.6 Timer, capable of measuring seconds.
with distilled water into a waste container.
9.4 Calibrate the pH meter to pH=4.00 with a water-based
7. Reagents and Materials
pH=4.00 buffer solution, using the slop
...
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