ASTM D7923-19

Standard Test Method for Water in Ethanol and Hydrocarbon Blends by Karl Fischer Titration

SIGNIFICANCE AND USE
5.1 Blends of fuel ethanol and hydrocarbon have a limited solvency for water that is dependent upon temperature and the ratio of ethanol to hydrocarbon. Good handling practices are important during the blending, storage, and transportation of fuel to avoid water contamination. High concentrations of water can cause haze or phase separation in ethanol and hydrocarbon blends and lead to freezing problems at low temperatures. Water has also been associated with corrosion and filter plugging.
SCOPE
1.1 This test method covers the determination of water in blends of ethanol, hydrocarbon, and corresponding blends. It is intended for measuring water content of gasoline or other hydrocarbon blendstock, denatured fuel ethanol as cited in Specification D4806, and ethanol fuel blends such as those cited in Specification D5798 and Practice D7794. This test method is not applicable to samples that are phase separated.  
1.1.1 Procedure A—For measurement of water from 0.004 % by mass to 1.63 % by mass in ethanol and hydrocarbon using coulometric Karl Fischer titration. This is the referee method for samples containing up to 1.63 % water.  
1.1.2 Procedure B—For measurement of water from 0.02 % by mass to 5.41 % by mass in ethanol and hydrocarbon using volumetric Karl Fischer titration.  
1.2 This method measures mass percent water and allows for the alternative reporting of volume percent. This test method recommends the use of pyridine-free reagents.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 8.  
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.

General Information

• Status: Published
• Publication Date: 31-May-2019
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.06 - Analysis of Liquid Fuels and Lubricants

Relations

• Replaces: ASTM D7923-17ae1 - Standard Test Method for Water in Ethanol and Hydrocarbon Blends by Karl Fischer Titration
• Effective Date: 01-Jun-2019
• Refers: ASTM D6708-24 - Standard Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material
• Effective Date: 01-Mar-2024
• Refers: ASTM E203-24 - Standard Test Method for Water Using Volumetric Karl Fischer Titration
• Effective Date: 01-Jan-2024
• Refers: ASTM E1064-24 - Standard Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
• Effective Date: 01-Jan-2024
• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM D6299-23a - Standard Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
• Effective Date: 01-Dec-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM D4806-19a - Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-Ignition Engine Fuel
• Effective Date: 15-Sep-2019
• Refers: ASTM D5798-19b - Standard Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines
• Effective Date: 01-Jul-2019
• Refers: ASTM D5798-19a - Standard Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines
• Effective Date: 01-May-2019
• Refers: ASTM D6708-19 - Standard Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material
• Effective Date: 01-May-2019
• Refers: ASTM D4806-19 - Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-Ignition Engine Fuel
• Effective Date: 01-Mar-2019
• Refers: ASTM D5798-19 - Standard Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines
• Effective Date: 01-Feb-2019
• Refers: ASTM D4806-18a - Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-Ignition Engine Fuel
• Effective Date: 01-Dec-2018
• Refers: ASTM D7794-18a - Standard Practice for Blending Mid-Level Ethanol Fuel Blends for Flexible-Fuel Vehicles with Automotive Spark-Ignition Engines
• Effective Date: 01-Dec-2018

Overview

ASTM D7923-19: Standard Test Method for Water in Ethanol and Hydrocarbon Blends by Karl Fischer Titration is an internationally recognized method for quantifying water content in blends of ethanol and hydrocarbons, including gasoline and ethanol fuel mixtures. Developed by ASTM International, this standard supports the fuel industry by providing reliable procedures for detecting water contamination-a key concern in fuel handling, storage, and transportation. The presence of excess water in ethanol-blended fuels can cause operational problems such as phase separation, haze, corrosion, and filter plugging, which compromise fuel quality and equipment performance.

Key Topics

• Water Determination Methods: Two approaches are defined:
  • Procedure A - Coulometric Karl Fischer Titration: Suited for water content ranging from 0.004% up to 1.63% by mass.
  • Procedure B - Volumetric Karl Fischer Titration: Suitable for higher water concentrations, from 0.02% up to 5.41% by mass.
• Scope and Limitations:
  • Applicable to gasoline, hydrocarbon blendstocks, denatured fuel ethanol, and ethanol blends as specified in other ASTM standards.
  • Not intended for samples that have phase separated, as stratification of water invalidates test results.
• Units and Reporting:
  • Water content is measured as mass percent, with an option to report as volume percent.
  • Results can be reported to the nearest 0.01% or 0.001% depending on the concentration.
• Sample Handling:
  • Emphasizes careful sampling to avoid atmospheric contamination due to the hygroscopic nature of ethanol.
  • Only single-phase samples are suitable for analysis to ensure accuracy.
• Quality Assurance:
  • Calibration and routine quality control are strongly encouraged using certified water standards.
  • Pyridine-free Karl Fischer reagents are recommended for improved safety and environmental compliance.

Applications

• Fuel Blending and Production: Ensures ethanol/gasoline blends meet regulatory water specifications, enhancing fuel stability and preventing phase separation.
• Quality Control in Storage and Transit: Detects and quantifies unintended water contamination before product delivery, mitigating risks of fuel system corrosion and filter issues.
• Refinery and Laboratory Analysis: Supports routine water content testing in research and operational labs, ensuring process control and compliance.
• Flexible-Fuel Vehicles: Critical in certifying water content in fuels for engines designed to run on mid- and high-level ethanol blends.
• Regulatory Compliance: Satisfies requirements for fuel ethanol and hydrocarbon blends cited in ASTM D4806, D5798, and D7794.

Related Standards

• ASTM D4806: Specification for Denatured Fuel Ethanol for blending with gasolines.
• ASTM D5798: Specification for Ethanol Fuel Blends for flexible-fuel automotive engines.
• ASTM D4057 / D4177: Practices for manual and automatic sampling of petroleum products, crucial for representative sampling in water content testing.
• ASTM E1064 / E203: Karl Fischer titration methods for water in organic liquids.
• ASTM D1193: Specification for Reagent Water used in analytical procedures.
• ASTM D6299 / D6708: Practices for statistical quality control and method comparison.

Practical Value

Implementing ASTM D7923-19 helps fuel producers, distributors, and laboratories maintain stringent control over water contamination in ethanol and hydrocarbon blends. Accurate water content determination:

• Prevents operational issues such as haze, freezing, and corrosion.
• Protects fuel infrastructure and vehicle engines.
• Ensures products meet industry and regulatory specifications.
• Supports efficient and safe fuel supply chain management.

Keywords: water content, ethanol blends, hydrocarbon fuel, Karl Fischer titration, ASTM D7923-19, fuel quality, volumetric titration, coulometric titration, pyridine-free reagents, gasoline, phase separation, fuel storage.

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.
Designation: D7923 − 19
Standard Test Method for
Water in Ethanol and Hydrocarbon Blends by Karl Fischer
Titration
This standard is issued under the fixed designation D7923; 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* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of water in
D1152 Specification for Methanol (Methyl Alcohol)
blends of ethanol, hydrocarbon, and corresponding blends. It is
D1193 Specification for Reagent Water
intended for measuring water content of gasoline or other
D4057 Practice for Manual Sampling of Petroleum and
hydrocarbon blendstock, denatured fuel ethanol as cited in
Petroleum Products
Specification D4806, and ethanol fuel blends such as those
D4175 Terminology Relating to Petroleum Products, Liquid
cited in Specification D5798 and Practice D7794. This test
Fuels, and Lubricants
method is not applicable to samples that are phase separated.
D4177 Practice for Automatic Sampling of Petroleum and
1.1.1 Procedure A—For measurement of water from
Petroleum Products
0.004 % by mass to 1.63 % by mass in ethanol and hydrocar-
D4806 Specification for Denatured Fuel Ethanol for Blend-
bon using coulometric Karl Fischer titration.This is the referee
ing with Gasolines for Use as Automotive Spark-Ignition
method for samples containing up to 1.63 % water.
Engine Fuel
1.1.2 Procedure B—For measurement of water from 0.02 %
D5798 Specification for Ethanol Fuel Blends for Flexible-
by mass to 5.41 % by mass in ethanol and hydrocarbon using
Fuel Automotive Spark-Ignition Engines
volumetric Karl Fischer titration.
D6299 Practice for Applying Statistical Quality Assurance
and Control Charting Techniques to Evaluate Analytical
1.2 This method measures mass percent water and allows
Measurement System Performance
for the alternative reporting of volume percent. This test
D6708 Practice for StatisticalAssessment and Improvement
method recommends the use of pyridine-free reagents.
of Expected Agreement Between Two Test Methods that
1.3 The values stated in SI units are to be regarded as
Purport to Measure the Same Property of a Material
standard. No other units of measurement are included in this
D7794 Practice for Blending Mid-Level Ethanol Fuel
standard.
BlendsforFlexible-FuelVehicleswithAutomotiveSpark-
Ignition Engines
1.4 This standard does not purport to address all of the
E203 Test Method for Water Using Volumetric Karl Fischer
safety concerns, if any, associated with its use. It is the
Titration
responsibility of the user of this standard to establish appro-
E1064 Test Method for Water in Organic Liquids by Coulo-
priate safety, health, and environmental practices and deter-
metric Karl Fischer Titration
mine the applicability of regulatory limitations prior to use.
Specific precautionary statements are given in Section 8.
3. Terminology
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
3.1 For general terminology, refer to Terminology D4175.
ization established in the Decision on Principles for the
3.2 Definitions:
Development of International Standards, Guides and Recom-
3.2.1 denatured fuel ethanol, n—fuel ethanol made unfit for
mendations issued by the World Trade Organization Technical
beverage use by the addition of denaturants under formula(s)
Barriers to Trade (TBT) Committee.
approved by the applicable regulatory agency to prevent the
imposition of beverage alcohol tax. D4806
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 June 1, 2019. Published June 2019. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ɛ1
approved in 2016. Last previous edition approved in 2017 as D7923 – 17a . DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7923-19. 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
D7923 − 19
3.2.2 hydrocarbon, n—a compound composed solely of generator electrode assembly, and magnetic stirrer. The instru-
hydrogen and carbon. D5798 ment is designed to coulometrically generate iodine that reacts
3.2.2.1 Discussion—The hydrocarbon mixtures used in stoichiometrically with the water present in the sample solu-
ethanol fuel blends will be unleaded gasoline, gasoline blend- tion. The coulombs of electricity required to generate the
stock for oxygenate blending (BOB), natural gasoline, or other reagent are converted to micrograms of water, which is
hydrocarbons in the gasoline boiling range. The hydrocarbon obtained as a direct digital readout.
blend components will also contain trace quantities of other 7.1.2 Volumetric Automatic Titrator, consisting of a control
elements. unit, titration vessel, dual platinum sensing electrode, dispens-
ing buret, and magnetic stirrer. The instrument is designed to
3.3 Definitions of Terms Specific to This Standard:
accurately dose an iodine containing titrant into the titration
3.3.1 coulometric titration, n—in reference to Karl Fischer
vessel that reacts stoichiometrically with the water present in
titration methods, a process of measuring the water content of
the sample solution. The titrant solution is standardized to
a sample using an electrolytic process to generate iodine in
determine milligrams of water per milliliter of Karl Fischer
situ.
reagent it will neutralize in the sample.
3.3.2 pre-titration, n—the process of adding titrant to react
7.2 Gas-tight Syringe, fitted with a cannula needle of
with any water in the Karl Fischer system so the system is
appropriate length and gauge for introducing sample into the
totally dry prior to addition of a test sample.
titration chamber or removing excess solution from titration
3.3.3 volumetric titration, n—in reference to Karl Fischer
chamber (see Note 1). The syringe shall be made of glass or
titration methods, a process of measuring the water content of
other suitably inert material. The volume of the syringe will
a sample by the physical delivery of a titration reagent
depend on the sample size. When injecting by volume, the
containing iodine.
sample should occupy at least 25 % of the syringe volume.
7.2.1 Rinseallglasssyringesandneedleswithdrymethanol
4. Summary of Test Method
or ethanol after cleaning, then dry in an oven at 100 °C for at
4.1 This test method is based on the Karl Fischer (KF)
least 1 h and store in a desiccator.
reaction for determining water. Iodine is consumed by water in
7.3 Sample Bottle, suitable for collecting sample and main-
a one to one molar ratio in the presence of sulfur dioxide,
taining an air-tight enclosure to prevent intrusion of atmo-
organic base, and methanol or other alcohols. The coulometric
spheric moisture.
methodgeneratesiodinefromiodidebyanodicoxidationwhile
7.4 Oven, temperature 100 °C 6 5 °C.
the iodine is already present in the volumetric KF reagents.
7.5 Desiccator, standard laboratory type with desiccant
5. Significance and Use
containing color change indicator.
5.1 Blends of fuel ethanol and hydrocarbon have a limited
7.6 Analytical Balance, capable of weighing to 60.0001 g.
solvency for water that is dependent upon temperature and the
ratio of ethanol to hydrocarbon. Good handling practices are
8. Safety Precautions
important during the blending, storage, and transportation of
8.1 The reagents contain one or more of the following:
fuel to avoid water contamination. High concentrations of
iodine, organic base, sulfur dioxide, and methanol or other
water can cause haze or phase separation in ethanol and
alcohol. Wear chemically resistant gloves when mixing the
hydrocarbon blends and lead to freezing problems at low
reagents and removing solution from the titration chamber.
temperatures. Water has also been associated with corrosion
Exercise care to avoid inhalation of reagent vapors, or direct
and filter plugging.
contact of the reagent with the skin.
6. Interferences
9. Sampling
6.1 A number of functional groups are known to interfere
9.1 Sampling is defined as all of the steps required to obtain
with Karl Fischer titrations. In hydrocarbons, the most com-
an aliquot representative of the contents of any pipe, tank or
mon interferences are mercaptans and sulfides. In ethanol,
other system and to place the sample into a container for
aldehydes and ketones are known to interfere with the Karl
analysis by a laboratory or test facility. Sampling practices are
Fischer reagent. Some interferences can be mitigated with the
covered in Practices D4057 and D4177.
use of applicable reagents. For fuel grade ethanol and gasoline
9.2 Due to the low concentration of water to be measured,
in areas with stringent environmental regulations, the magni-
andthehygroscopicnatureofethanol,exercisecareatalltimes
tude of the interference should be negligible under most
to avoid contaminating the sample with moisture from the
circumstances. A list of several additional functional groups
sample container, the atmosphere, or transfer equipment.
that can interfere with Karl Fischer titrations is included in the
9.3 Samples shall be at room temperature at time of analy-
Appendix (X1.1.1).
sis.
7. Apparatus
9.4 Verify that samples are single phase before taking an
7.1 Automatic Titrator: aliquot to test. Water or water/ethanol blend will separate from
7.1.1 Coulometric Automatic Titrator, consisting of a con- hydrocarbon if the solubility limit is exceeded. The solubility
trol unit, titration vessel, dual platinum sensing electrode, limitdependsonthegasolinemakeup,concentrationofethanol
D7923 − 19
or other emulsifiers, and sample temperature. Water is infi- diaphragm-less generator cell or as the anolyte solution in a
nitely soluble in ethanol. diaphragm cell if specified by the manufacturer.
9.4.1 For a transparent container, this observation can be 10.3.4 Water Standards, 0.1 % by mass and 1 % by mass,
determinedbyvisualinspection.Ifthematerialhastwophases, commercially prepared in organic solvent recommended for
shake the sample vigorously to combine. If the separate layer this method.
re-forms, the sample is not suitable for testing.
9.4.2 If the sample is contained in a non-transparent 11. Preparation of Apparatus
container, mix the sample and immediately pour a portion of
11.1 Clean, dry, and assemble the titration chamber as
the remaining sample into a clear glass container and observe
directed in the manufacturer’s instructions. Care should be
for evidence of phase separation. If the separate layer forms,
taken to ensure the vessel is sealed from atmospheric moisture.
the sample is not suitable for testing.
Replace the desiccant if saturated. Connect the leads from the
9.4.3 Because of the volatile and hygroscopic nature of the
sensing and generator electrodes to the titrator.
samples, mixing with a mechanical or electronic mixer is not
11.2 Add catholyte solution (10.3.1) to the generator elec-
recommended.
trode assembly and reseal the vessel according to manufacturer
9.5 Remove the test specimens for analysis from the sample
instructions.
bottle with a dry, inert gas-tight syringe.
11.3 Fill the anode reservoir with anolyte solution (10.3.2)
PROCEDURE A (COULOMETRIC) as directed by the manufacturer. The level of the catholyte
solution in the inner chamber shall be maintained slightly
10. Reagents
below the level of the anolyte solution to prevent backflow
contamination of the titration (anolyte) solution. As samples
10.1 Purity of Reagents—Unless otherwise indicated, it is
areanalyzed,thevolumeoftheanolytewillincrease.Thismay
intended that all reagents shall conform to the specifications of
slowreactivityofthecatholyteduetoincreasedpressureacross
theCommitteeonAnalyticalReagentsoftheAmericanChemi-
themembrane.Aportionoftheanolytesolutionmayhavetobe
cal Society, where such specifications are available. Other
removed periodically to maintain the correct level. (Note 1)
grades may be used, provided it is first ascertained that the
NOTE 1—A coulometric system with a diaphragm-less generator elec-
reagent is of sufficiently high purity to permit its use without
trode should be filled with the appropriate one component solution.
lessening the accuracy of the determination.
11.4 Agitate the titration solution by gently swirling the
10.2 Purity of Water—Unless otherwise indicated, reference
titration chamber to remove any residual moisture from the
to water shall be understood to mean Type II or Type III
walls. Allow the solution to stir until inner atmosphere mois-
reagent water, conforming to Specification D1193, or better.
ture is removed and the baseline has been established.
10.3 Karl Fischer Reagents—Commercial coulometric KF
reagents and reagent systems of various types are available for 12. Verification of Calibration and Quality Control
use with autotitrators for water determination. Traditionally,
12.1 Autotitrators vary in calibration procedures by manu-
pyridine was the organic base used in KF reagents. Pyridine-
facturer. Consult the operating manual for the autotitrator in
free formulations are available and are preferred by most KF
use. Stable, prepackaged quality control (QC) water standards
instrument manufacturers for use with their equipment. The
are commercially available with 0.1 % by mass and 1 % by
pyridine-free reagents are less toxic, less odorous, and more
mass water content for this purpose. It is desirable to verify
stable than those containing pyridine. The use of pyridine-free
calibration with a standard solution that approximates the same
reagents is recommended whenever possible. Coulometric
range of water expected to be in the samples.
titrations normally require two reagent solutions: an anolyte
12.2 It is recommended that a control chart measuring a QC
and a catholyte or generator solution. However, with the use of
standard sample be established and maintained according to
an integrated or diaphragm-less cell, a single solution that
generally accepted guidelines. Practice D6299 may be used for
contains all of the reagents needed for a KF titration may be
this purpose. Measure the control sample each day a sample(s)
used.
is tested. If the measured value exceeds 65 % of the known
10.3.1 Catholyte solution, contains ammonium salts and
amount, take appropriate action before proceeding with the
methanol.
sample test (see Note 2).
10.3.2 Anolyte solution, contains iodide, sulfur dioxide and
NOTE 2—This may require replacing the reagent solutions.
imidazole buffer in a suitable solvent.
10.3.3 One component solution, iodide, sulfur dioxide, imi-
13. Procedure
dazolebuffer,andbasesinasuitablesolvent.Thissolutionmay
13.1 Assemble a dry syringe and needle. Withdraw 1 mLto
be used as the only solution in a coulometric system with a
2 mL of the sample into the syringe and discard the contents
into a waste container. Repeat rinsing the syringe with sample
two additional times to assure a representative sample and
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
remove any residual moisture from the syringe. During
listed by the American Chemical Society, see Analar Standards for Laboratory
sampling, minimize sample exposure to atmospheric moisture.
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Using the following table as a guide, withdraw the proper
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. amount of test sample into the syringe. Invert the syringe and
D7923 − 19
eject to remove any air. Wipe any excess liquid from the µg water
~water content, mass percent! 5 (1)
needle. Obtain a mass to 60.1 mg (W1). See Table 1. ~W 1 2 W 2! 310000
13.1.1 A 1 mL gas tight syringe is suggested for single
water content, volume percent 5
coulometric injections. If replicates of the same sample are
density of sample at t
(2)
water content, mass percent 3
required, a larger syringe with suitable volume may be used. ~ !
density of water at t
The sample volume should occupy at least 25 % of the syringe
where:
volume. For increased precision, it is not recommended to
inject less than 0.25 mL of sample into the coulometric cell. t = test temperature,
W1 = mass of sample and syringe before injection, g, and
13.2 With the analyzer stabilized, carefully insert the needle
W2 = mass of sample and syringe after injection, g.
of the sample syringe through the septum and slightly below
the level of solution in the titration chamber. Inject the sample
15. Report
carefully into the titration solution and begin titration per
manufacturer directions. Withdraw the syringe needle and 15.1 For samples with 1.00 % water or greater, report the
percentageofwatertothenearest0.01 %bymass.Forsamples
weigh to the nearest 60.1 mg (W2) to determine the exact
sample mass.Allow the titration to proceed until the end-point containing less than 1.00 % water, report the percentage of
is indicated. water to the nearest 0.001 %.Alternatively, report the percent-
13.2.1 After numerous analyses, the level of solvent accu- age of water by volume.
mulated in the titration chamber may have to be reduced. This
15.2 Report the water concentration in one of the defined
can be accomplished with a syringe of capacity of 20 mLor by
units as obtained by Test Method D7923, Procedure A.
partially draining the solution of the titration chamber. Discard
the solution and replace with fresh anolyte solution if a stable
16. Precision and Bias
reading cannot be obtained.
16.1 The statistical precision of this procedure, as deter-
13.2.2 When a stable reading cannot be obtained, replace
mined by statistical examination of the 2015 interlaboratory
the reagents and follow the manufacturer procedure to condi-
test results, obtained from 12 laboratories on 12 samples, is as
tion the reagents.
follows:
13.3 End Point Detection:
16.1.1 Repeatability—The difference between successive
13.3.1 During coulometric titrations, iodine is generated
results obtained by the same operator with the same apparatus
electrochemically by anodic oxidation of iodide to iodine.
under constant operating conditions on identical test material,
There is a quantitative relationship between the amount of
would in the long run, in the normal and correct operation of
electric current passed through the generator electrode and the
the test method, exceed the following values in one case in
amount of iodine generated. Iodine will be consumed as long
twenty.
as water is present.
0.5746
r 5 2.216E-02 3 X % by mass (3)
13.3.2 End point is detected automatically and the water
content is calculated based on the sample weight entered.
where:
During the titration a small constant polarization current is
X = the calculated result for percentage of water expressed
applied to the double platinum electrode and the voltage
as percent by mass.
required to maintain this current is measured. When water is
present in the titration vessel, the voltage required is high. 16.1.2 Reproducibility—The difference between two single
Once there is a slight excess of iodine, the voltage required is and independent results, obtained by different operators work-
reduced.Thislargechangeinvoltageindicatesthetitrationend ing in different laboratories on identical material, would be in
point. the long run, in the normal and correct operation of the test
method, exceed the following values only in one case in
13.4 Record the micrograms of water determined for the
twenty.
sample titration.
0.5746
R 5 3.356E-02 3 X % by mass (4)
14. Calculation
where:
14.1 The water content is manually calculated in percent by
X = the calculated result for percentage of water expressed
mass using Eq 1 or percent by volume using Eq 2. Most
as percent by mass.
instruments are equipped to provide a calculated result based
NOTE 3—The data in Table 2 shows repeatabilities and reproducibilities
upon the measured sample size.
for water values obtained using the formulas given in 16.1.1 and 16.1.2.
16.1.3 The precision statement was determined through
TABLE 1 Recommended Sample Size (Coulometric)
statistical examination of 11 materials with blind duplicates
Expected Water Content Sample Size
from 12 laboratories. The materials included one sample of
(mass percent) (g)
anhydrous ethanol, six ethanol blends ranging from a nominal
0to0.2 3to5
0.2to0.5 1to2 5 % to 85 % ethanol, three samples of denatured fuel ethanol,
0.5 to 1.0 0.5 to1.0
and one sample of gasoline. Water contents of the samples
1.0to2.0 0.5
ranged from 0.002 % by mass to 1.63 % by mass by Procedure
>2.0 Please use Procedure B
A.
...

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: D7923 − 17a D7923 − 19
Standard Test Method for
Water in Ethanol and Hydrocarbon Blends by Karl Fischer
Titration
This standard is issued under the fixed designation D7923; 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.
ε NOTE—The title of Table 3 was corrected editorially in July 2018.
1. Scope*
1.1 This test method covers the determination of water from 0.05 % to 5.0 % by mass in blends of ethanol, hydrocarbon, and
corresponding blends. It is intended for measuring water content of gasoline or other hydrocarbon blendstock, denatured fuel
ethanol as cited in Specification D4806, and ethanol fuel blends such as those cited in Specification D5798 and Practice D7794.
This test method is not applicable to samples that are phase separated.
1.1.1 Procedure A—For measurement of water up to 2 %from 0.004 % by mass to 1.63 % by mass in ethanol and hydrocarbon
blends using coulometric Karl Fischer titration. This is the referee method for samples containing up to 2 %1.63 % water.
1.1.2 Procedure B—For measurement of water up to 5.4 %from 0.02 % by mass to 5.41 % by mass in ethanol and hydrocarbon
blends using volumetric Karl Fischer titration.
1.2 This method measures mass percent water and allows for the alternative reporting of volume percent. This test method
recommends the use of pyridine-free reagents.
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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Specific precautionary statements are given in Section 8.
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:
D1152 Specification for Methanol (Methyl Alcohol)
D1193 Specification for Reagent Water
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4806 Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-Ignition Engine Fuel
D5798 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
D6708 Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport
to Measure the Same Property of a Material
D7794 Practice for Blending Mid-Level Ethanol Fuel Blends for Flexible-Fuel Vehicles with Automotive Spark-Ignition
Engines
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 1, 2017June 1, 2019. Published July 2017June 2019. Originally approved in 2016. Last previous edition approved in 2017 as
ɛ1
D7923 – 17.D7923 – 17a . DOI: 10.1520/D7923-17AE01.10.1520/D7923-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
D7923 − 19
E203 Test Method for Water Using Volumetric Karl Fischer Titration
E1064 Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
3. Terminology
3.1 For general terminology, refer to Terminology D4175.
3.2 Definitions:
3.2.1 denatured fuel ethanol, n—fuel ethanol made unfit for beverage use by the addition of denaturants under formula(s)
approved by the applicable regulatory agency to prevent the imposition of beverage alcohol tax. D4806
3.2.2 hydrocarbon, n—a compound composed solely of hydrogen and carbon. D5798
3.2.2.1 Discussion—
The hydrocarbon mixtures used in ethanol fuel blends will be unleaded gasoline, gasoline blendstock for oxygenate blending
(BOB), natural gasoline, or other hydrocarbons in the gasoline boiling range. The hydrocarbon blend components will also contain
trace quantities of other elements.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 coulometric titration, n—in reference to Karl Fischer titration methods, a process of measuring the water content of a
sample using an electrolytic process to generate iodine in situ.
3.3.2 pre-titration, n—the process of adding titrant to react with any water in the Karl Fischer system so the system is totally
dry prior to addition of a test sample.
3.3.3 volumetric titration, n—in reference to Karl Fischer titration methods, a process of measuring the water content of a
sample by the physical delivery of a titration reagent containing iodine.
4. Summary of Test Method
4.1 This test method is based on the Karl Fischer (KF) reaction for determining water. Iodine is consumed by water in a one
to one molar ratio in the presence of sulfur dioxide, organic base, and methanol or other alcohols. The coulometric method
generates iodine from iodide by anodic oxidation while the iodine is already present in the volumetric KF reagents.
5. Significance and Use
5.1 Blends of fuel ethanol and hydrocarbon have a limited solvency for water that is dependent upon temperature and the ratio
of ethanol to hydrocarbon. Good handling practices are important during the blending, storage, and transportation of fuel to avoid
water contamination. High concentrations of water can cause haze or phase separation in ethanol and hydrocarbon blends and lead
to freezing problems at low temperatures. Water has also been associated with corrosion and filter plugging.
6. Interferences
6.1 A number of functional groups are known to interfere with Karl Fischer titrations. In hydrocarbons, the most common
interferences are mercaptans and sulfides. In ethanol, aldehydes and ketones are known to interfere with the Karl Fischer reagent.
Some interferences can be mitigated with the use of applicable reagents. For fuel grade ethanol and gasoline in areas with stringent
environmental regulations, the magnitude of the interference should be negligible under most circumstances. A list of several
additional functional groups that can interfere with Karl Fischer titrations is included in the Appendix (X1.1.1).
7. Apparatus
7.1 Automatic Titrator:
7.1.1 Coulometric Automatic Titrator, consisting of a control unit, titration vessel, dual platinum sensing electrode, generator
electrode assembly, and magnetic stirrer. The instrument is designed to coulometrically generate iodine that reacts stoichiometri-
cally with the water present in the sample solution. The coulombs of electricity required to generate the reagent are converted to
micrograms of water, which is obtained as a direct digital readout.
7.1.2 Volumetric Automatic Titrator, consisting of a control unit, titration vessel, dual platinum sensing electrode, dispensing
buret, and magnetic stirrer. The instrument is designed to accurately dose an iodine containing titrant into the titration vessel that
reacts stoichiometrically with the water present in the sample solution. The titrant solution is standardized to determine milligrams
of water per milliliter of Karl Fischer reagent it will neutralize in the sample.
7.2 Gas-tight Syringe, fitted with a cannula needle of appropriate length and gauge for introducing sample into the titration
chamber or removing excess solution from titration chamber (see Note 1). The syringe shall be made of glass or other suitably inert
material. The volume of the syringe will depend on the sample size. When injecting by volume, the sample should occupy at least
25 % of the syringe volume.
7.2.1 Rinse all glass syringes and needles with dry methanol or ethanol after cleaning, then dry in an oven at 100 °C for at least
1 h and store in a desiccator.
D7923 − 19
7.3 Sample Bottle, suitable for collecting sample and maintaining an air-tight enclosure to prevent intrusion of atmospheric
moisture.
7.4 Oven, temperature 100 °C 6 5 °C.
7.5 Desiccator, standard laboratory type with desiccant containing color change indicator.
7.6 Analytical Balance, capable of weighing to 60.0001 g.
8. Safety Precautions
8.1 The reagents contain one or more of the following: iodine, organic base, sulfur dioxide, and methanol or other alcohol. Wear
chemically resistant gloves when mixing the reagents and removing solution from the titration chamber. Exercise care to avoid
inhalation of reagent vapors, or direct contact of the reagent with the skin.
9. Sampling
9.1 Sampling is defined as all of the steps required to obtain an aliquot representative of the contents of any pipe, tank or other
system and to place the sample into a container for analysis by a laboratory or test facility. Sampling practices are covered in
Practices D4057 and D4177.
9.2 Due to the low concentration of water to be measured, and the hygroscopic nature of ethanol, exercise care at all times to
avoid contaminating the sample with moisture from the sample container, the atmosphere, or transfer equipment.
9.3 Samples shall be at room temperature at time of analysis.
9.4 Verify that samples are single phase before taking an aliquot to test. Water or water/ethanol blend will separate from
hydrocarbon if the solubility limit is exceeded. The solubility limit depends on the gasoline makeup, concentration of ethanol or
other emulsifiers, and sample temperature. Water is infinitely soluble in ethanol.
9.4.1 For a transparent container, this observation can be determined by visual inspection. If the material has two phases, shake
the sample vigorously to combine. If the separate layer re-forms, the sample is not suitable for testing.
9.4.2 If the sample is contained in a non-transparent container, mix the sample and immediately pour a portion of the remaining
sample into a clear glass container and observe for evidence of phase separation. If the separate layer forms, the sample is not
suitable for testing.
9.4.3 Because of the volatile and hygroscopic nature of the samples, mixing with a mechanical or electronic mixer is not
recommended.
9.5 Remove the test specimens for analysis from the sample bottle with a dry, inert gas-tight syringe.
PROCEDURE A (COULOMETRIC)
10. Reagents
10.1 Purity of Reagents—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.
10.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean Type II or Type III reagent
water, conforming to Specification D1193, or better.
10.3 Karl Fischer Reagents—Commercial coulometric KF reagents and reagent systems of various types are available for use
with autotitrators for water determination. Traditionally, pyridine was the organic base used in KF reagents. Pyridine-free
formulations are available and are preferred by most KF instrument manufacturers for use with their equipment. The pyridine-free
reagents are less toxic, less odorous, and more stable than those containing pyridine. The use of pyridine-free reagents is
recommended whenever possible. Coulometric titrations normally require two reagent solutions: an anolyte and a catholyte or
generator solution. However, with the use of an integrated or diaphragm-less cell, a single solution that contains all of the reagents
needed for a KF titration may be used.
10.3.1 Catholyte solution, contains ammonium salts and methanol.
10.3.2 Anolyte solution, contains iodide, sulfur dioxide and imidazole buffer in a suitable solvent.
10.3.3 One component solution, iodide, sulfur dioxide, imidazole buffer, and bases in a suitable solvent. This solution may be
used as the only solution in a coulometric system with a diaphragm-less generator cell or as the anolyte solution in a diaphragm
cell if specified by the manufacturer.
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 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.
D7923 − 19
10.3.4 Water Standards, 0.1 % by mass and 1 % by mass, commercially prepared in organic solvent recommended for this
method.
11. Preparation of Apparatus
11.1 Clean, dry, and assemble the titration chamber as directed in the manufacturer’s instructions. Care should be taken to
ensure the vessel is sealed from atmospheric moisture. Replace the desiccant if saturated. Connect the leads from the sensing and
generator electrodes to the titrator.
11.2 Add catholyte solution (10.3.1) to the generator electrode assembly and reseal the vessel according to manufacturer
instructions.
11.3 Fill the anode reservoir with anolyte solution (10.3.2) as directed by the manufacturer. The level of the catholyte solution
in the inner chamber shall be maintained slightly below the level of the anolyte solution to prevent backflow contamination of the
titration (anolyte) solution. As samples are analyzed, the volume of the anolyte will increase. This may slow reactivity of the
catholyte due to increased pressure across the membrane. A portion of the anolyte solution may have to be removed periodically
to maintain the correct level. (Note 1)
NOTE 1—A coulometric system with a diaphragm-less generator electrode should be filled with the appropriate one component solution.
11.4 Agitate the titration solution by gently swirling the titration chamber to remove any residual moisture from the walls. Allow
the solution to stir until inner atmosphere moisture is removed and the baseline has been established.
12. Verification of Calibration and Quality Control
12.1 Autotitrators vary in calibration procedures by manufacturer. Consult the operating manual for the autotitrator in use.
Stable, prepackaged quality control (QC) water standards are commercially available with 0.1 % by mass and 1 % by mass water
content for this purpose. It is desirable to verify calibration with a standard solution that approximates the same range of water
expected to be in the samples.
12.2 It is recommended that a control chart measuring a QC standard sample be established and maintained according to
generally accepted guidelines. Practice D6299 may be used for this purpose. Measure the control sample each day a sample(s) is
tested. If the measured value exceeds 65 % of the known amount, take appropriate action before proceeding with the sample test
(see Note 2).
NOTE 2—This may require replacing the reagent solutions.
13. Procedure
13.1 Assemble a dry syringe and needle. Withdraw 1 mL to 2 mL of the sample into the syringe and discard the contents into
a waste container. Repeat rinsing the syringe with sample two additional times to assure a representative sample and remove any
residual moisture from the syringe. During sampling, minimize sample exposure to atmospheric moisture. Using the following
table as a guide, withdraw the proper amount of test sample into the syringe. Invert the syringe and eject to remove any air. Wipe
any excess liquid from the needle. Obtain a mass to 60.1 mg (W1). See Table 1.
13.1.1 A 1 mL gas tight syringe is suggested for single coulometric injections. If replicates of the same sample are required, a
larger syringe with suitable volume may be used. The sample volume should occupy at least 25 % of the syringe volume. For
increased precision, it is not recommended to inject less than 0.25 mL of sample into the coulometric cell.
13.2 With the analyzer stabilized, carefully insert the needle of the sample syringe through the septum and slightly below the
level of solution in the titration chamber. Inject the sample carefully into the titration solution and begin titration per manufacturer
directions. Withdraw the syringe needle and weigh to the nearest 60.1 mg (W2) to determine the exact sample mass. Allow the
titration to proceed until the end-point is indicated.
13.2.1 After numerous analyses, the level of solvent accumulated in the titration chamber may have to be reduced. This can be
accomplished with a syringe of capacity of 20 mL or by partially draining the solution of the titration chamber. Discard the solution
and replace with fresh anolyte solution if a stable reading cannot be obtained.
13.2.2 When a stable reading cannot be obtained, replace the reagents and follow the manufacturer procedure to condition the
reagents.
13.3 End Point Detection:
TABLE 1 Recommended Sample Size (Coulometric)
Expected Water Content Sample Size
(mass percent) (g)
0 to 0.2 3 to 5
0.2 to 0.5 1 to 2
0.5 to 1.0 0.5 to1.0
1.0 to 2.0 0.5
>2.0 Please use Procedure B
D7923 − 19
13.3.1 During coulometric titrations, iodine is generated electrochemically by anodic oxidation of iodide to iodine. There is a
quantitative relationship between the amount of electric current passed through the generator electrode and the amount of iodine
generated. Iodine will be consumed as long as water is present.
13.3.2 End point is detected automatically and the water content is calculated based on the sample weight entered. During the
titration a small constant polarization current is applied to the double platinum electrode and the voltage required to maintain this
current is measured. When water is present in the titration vessel, the voltage required is high. Once there is a slight excess of
iodine, the voltage required is reduced. This large change in voltage indicates the titration end point.
13.4 Record the micrograms of water determined for the sample titration.
14. Calculation
14.1 The water content is manually calculated in percent by mass using Eq 1 or percent by volume using Eq 2. Most instruments
are equipped to provide a calculated result based upon the measured sample size.
μg water
water content, mass percent 5 (1)
~ !
W 1 2 W 2 310000
~ !
water content, volume percent 5
density of sample at t (2)
water content, mass percent 3
~ !
density of water at t
where:
t = test temperature,
W1 = mass of sample and syringe before injection, g, and
W2 = mass of sample and syringe after injection, g.
15. Report
15.1 Report For samples with 1.00 % water or greater, report the percentage of water to the nearest 0.01 % by mass.
Alternatively, For samples containing less than 1.00 % water, report the percentage of water to the nearest 0.01 % 0.001 %.
Alternatively, report the percentage of water by volume.
15.2 Report the water concentration in one of the defined units as obtained by Test Method D7923, Procedure A.
16. Precision and Bias
16.1 The statistical precision of this procedure, as determined by statistical examination of the 2015 interlaboratory test results,
obtained from 12 laboratories on 12 samples, is as follows:
16.1.1 Repeatability—The difference between successive results obtained by the same operator with the same apparatus under
constant operating conditions on identical test material, would in the long run, in the normal and correct operation of the test
method, exceed the following values in one case in twenty.
0.5746
r5 2.216E-02 3X % by mass (3)
where:
X = the calculated result for percentage of water expressed as percent by mass.
16.1.2 Reproducibility—The difference between two single and independent results, obtained by different operators working in
different laboratories on identical material, would be in the long run, in the normal and correct operation of the test method, exceed
the following values only in one case in twenty.
0.5746
R5 3.356E-02 3X % by mass (4)
where:
X = the calculated result for percentage of water expressed as percent by mass.
NOTE 3—The data in Table 2 shows repeatabilities and reproducibilities for water values obtained using the formulas given in 16.1.1 and 16.1.2.
16.1.3 The precision statement was determined through statistical examination of 11 materials with blind duplicates from 12
laboratories. The materials included one sample of anhydrous ethanol, six ethanol blends ranging from a nominal 5 % to 85 %
ethanol, three samples of denatured fuel ethanol, and one sample of gasoline. Water contents of the samples ranged from 0.002 %
by mass to 1.63 % by mass by Procedure A.
16.2 Bias—This test m
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