ASTM D3227-24

Standard Test Method for (Thiol Mercaptan) Sulfur in Gasoline, Kerosine, Aviation Turbine, and Distillate Fuels (Potentiometric Method)

SIGNIFICANCE AND USE
5.1 Mercaptan sulfur has an objectionable odor, an adverse effect on fuel system elastomers, and is corrosive to fuel system components.
SCOPE
1.1 This test method covers the determination of mercaptan sulfur in gasolines, kerosines, aviation turbine fuels, and distillate fuels containing from 0.0003 % to 0.01 % by mass of mercaptan sulfur. Organic sulfur compounds such as sulfides, disulfides, and thiophene, do not interfere. Elemental sulfur in amounts less than 0.0005 % by mass does not interfere. Hydrogen sulfide will interfere if not removed, as described in 10.2.  
1.2 The values in acceptable SI units are to be regarded as the standard.  
1.2.1 Exception—The values in parentheses are for information only.  
1.3 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. For specific warning statements, see Sections 7, 9, 10, and Appendix X1.  
1.4 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: 29-Feb-2024
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.03 - Elemental Analysis

Relations

• Replaces: ASTM D3227-23 - Standard Test Method for (Thiol Mercaptan) Sulfur in Gasoline, Kerosine, Aviation Turbine, and Distillate Fuels (Potentiometric Method)
• Effective Date: 01-Mar-2024
• Referred By: ASTM D4952-23 - Standard Test Method for Qualitative Analysis for Active Sulfur Species in Fuels and Solvents (Doctor Test)
• Effective Date: 01-Mar-2024
• Referred By: ASTM D235-22 - Standard Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Dry Cleaning Solvent)
• Effective Date: 01-Mar-2024
• Referred By: ASTM D7566-23b - Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons
• Effective Date: 01-Mar-2024
• Referred By: ASTM D5273-23 - Standard Guide for Analysis of Propylene Concentrates
• Effective Date: 01-Mar-2024
• Referred By: ASTM D6615-22 - Standard Specification for Jet B Wide-Cut Aviation Turbine Fuel
• Effective Date: 01-Mar-2024
• Referred By: ASTM D1655-23a - Standard Specification for Aviation Turbine Fuels
• Effective Date: 01-Mar-2024
• Referred By: ASTM D8147-17(2023) - Standard Specification for Special-Purpose Test Fuels for Aviation Compression-Ignition Engines
• Effective Date: 01-Mar-2024
• Referred By: ASTM D7223-21 - Standard Specification for Aviation Certification Turbine Fuel
• Effective Date: 01-Mar-2024
• Referred By: ASTM D6681-23 - Standard Test Method for Evaluation of Engine Oils in a High Speed, Single-Cylinder Diesel Engine-Caterpillar 1P Test Procedure
• Effective Date: 01-Mar-2024
• Referred By: ASTM D8056-18 - Standard Guide for Elemental Analysis of Crude Oil
• Effective Date: 01-Mar-2024
• Referred By: ASTM D3699-19 - Standard Specification for Kerosine
• Effective Date: 01-Mar-2024

Overview

ASTM D3227-24 is the standard test method for the determination of thiol (mercaptan) sulfur in gasoline, kerosine, aviation turbine, and distillate fuels using a potentiometric method. Developed by ASTM International, this standard outlines procedures to accurately measure low concentrations of mercaptan sulfur (from 0.0003% to 0.01% by mass) in various fuel products. Mercaptan sulfur is notable for its unpleasant odor and its corrosive and degrading effects on fuel system components and elastomers. Effective control of mercaptan content helps ensure product quality, equipment performance, and regulatory compliance in fuel processing and distribution.

Key Topics

• Scope: Applies to gasoline, kerosine, aviation turbine fuels, and distillate fuels with mercaptan sulfur content between 0.0003% and 0.01% by mass.
• Method Summary: Utilizes potentiometric titration, where a hydrogen sulfide-free fuel sample is titrated with silver nitrate solution. The endpoint is detected by the potential change between a glass electrode and silver/silver-sulfide electrode.
• Interference: Organic sulfur compounds such as sulfides, disulfides, and thiophene do not interfere. Elemental sulfur below 0.0005% by mass is not an issue. However, hydrogen sulfide must be removed prior to analysis as it does interfere.
• Precision: The standard provides repeatability and reproducibility guidelines to ensure high precision in both single-laboratory and inter-laboratory settings.
• Safety and Compliance: Users must implement suitable safety, health, and environmental protection measures and consider regulatory requirements, as handling chemicals like cadmium sulfate, lead acetate, and sulfuric acid involve health hazards.

Applications

The ASTM D3227-24 test method is widely employed in:

• Quality Control in Petroleum Refineries: Ensures produced or blended fuels meet sulfur content specifications, preventing off-odor and corrosion issues in end-use equipment.
• Aviation Fuel Certification: Verifies that aviation turbine fuels comply with international and regional mercaptan sulfur limits, critical for operational safety and reliability.
• Distribution and Storage Monitoring: Detects mercaptan pickup or degradation during transportation and storage, enabling timely corrective actions.
• Regulatory Compliance: Assists in demonstrating compliance with environmental and industry standards for fuel sulfur content.
• Research and Development: Supports product development and process optimization by providing accurate measurements of low-level sulfur compounds.

Related Standards

Several ASTM standards are referenced or are commonly used in conjunction with ASTM D3227-24:

• ASTM D1193: Specification for Reagent Water, ensuring high purity of reagents.
• ASTM D1250: Guide for Temperature and Pressure Volume Correction Factors for crude oils and refined products.
• ASTM D1298: Test Method for Density of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method.
• ASTM D4052: Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density Meter.
• ASTM D4057 / D4177: Practices for Manual and Automatic Sampling of Petroleum Products.
• ASTM D6299: Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance.
• ASTM D4175: Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants.

Practical Value

Implementing ASTM D3227-24 helps fuel producers, certifying bodies, and fuel distributors to:

• Verify Product Integrity: Prevents corrosion and operational problems associated with excess mercaptan sulfur in fuels.
• Maintain Regulatory Compliance: Ensures fuels meet mandatory sulfur content limits set by governing bodies.
• Enhance Equipment Reliability: By limiting corrosive mercaptans, the standard reduces maintenance costs and prolongs the life of fuel system components.
• Support Environmental Goals: Accurate control and monitoring of sulfur species help reduce environmental impact and support cleaner fuel initiatives.

Keywords: ASTM D3227-24, mercaptan sulfur, potentiometric titration, gasoline sulfur, kerosine sulfur, aviation fuel, distillate fuels, sulfur analysis standard, fuel quality control.

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: D3227 − 24
Designation: 342/20
Standard Test Method for
(Thiol Mercaptan) Sulfur in Gasoline, Kerosine, Aviation
1,2
Turbine, and Distillate Fuels (Potentiometric Method)
This standard is issued under the fixed designation D3227; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of mercaptan
D1193 Specification for Reagent Water
sulfur in gasolines, kerosines, aviation turbine fuels, and
D1250 Guide for the Use of the Joint API and ASTM
distillate fuels containing from 0.0003 % to 0.01 % by mass of
Adjunct for Temperature and Pressure Volume Correction
mercaptan sulfur. Organic sulfur compounds such as sulfides,
Factors for Generalized Crude Oils, Refined Products, and
disulfides, and thiophene, do not interfere. Elemental sulfur in
Lubricating Oils: API MPMS Chapter 11.1
amounts less than 0.0005 % by mass does not interfere.
D1298 Test Method for Density, Relative Density, or API
Hydrogen sulfide will interfere if not removed, as described in
Gravity of Crude Petroleum and Liquid Petroleum Prod-
10.2.
ucts by Hydrometer Method
1.2 The values in acceptable SI units are to be regarded as
D4052 Test Method for Density, Relative Density, and API
the standard.
Gravity of Liquids by Digital Density Meter
1.2.1 Exception—The values in parentheses are for informa-
D4057 Practice for Manual Sampling of Petroleum and
tion only.
Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid
1.3 This standard does not purport to address all of the
Fuels, and Lubricants
safety concerns, if any, associated with its use. It is the
D4177 Practice for Automatic Sampling of Petroleum and
responsibility of the user of this standard to establish appro-
Petroleum Products
priate safety, health, and environmental practices and deter-
D6299 Practice for Applying Statistical Quality Assurance
mine the applicability of regulatory limitations prior to use.
and Control Charting Techniques to Evaluate Analytical
For specific warning statements, see Sections 7, 9, 10, and
Measurement System Performance
Appendix X1.
1.4 This international standard was developed in accor-
3. Terminology
dance with internationally recognized principles on standard-
3.1 Definitions:
ization established in the Decision on Principles for the
3.1.1 For definitions of terms used in this test method, refer
Development of International Standards, Guides and Recom-
to Terminology D4175.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
4. Summary of Test Method
4.1 The hydrogen sulfide-free sample is dissolved in an
alcoholic sodium acetate titration solvent and titrated potentio-
This test method is under the jurisdiction of ASTM International Committee
D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct
metrically with silver nitrate solution, using as an indicator the
responsibility of ASTM Subcommittee D02.03 on Elemental Analysis. The techni-
potential between a glass reference electrode and a silver/
cally equivalent standard as referenced is under the jurisdiction of the Energy
silver-sulfide indicating electrode. Under these conditions, the
Institute Subcommittee SC-G-5.
Current edition approved March 1, 2024. Published March 2024. Originally
approved in 1973. Last previous edition approved in 2023 as D3227 – 23. DOI:
10.1520/D3227-24.
2 3
This test method has been developed through the cooperative effort between For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ASTM and the Energy Institute, London. ASTM and IP standards were approved by contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ASTM and EI technical committees as being technically equivalent but that does not Standards volume information, refer to the standard’s Document Summary page on
imply both standards are identical. 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
D3227 − 24
mercaptan sulfur is precipitated as silver mercaptide and the 7.2 Water—Reagent grade, Type I, Specification D1193.
end point of the titration is shown by a large change in cell
7.3 Cadmium Sulfate, Acid Solution (150 g ⁄L)—Dissolve
potential.
150 g of cadmium sulfate (3CdSO ·8H O) in water.
4 2
(Warning—Poison. May be fatal if swallowed or inhaled. A
5. Significance and Use
known carcinogen (animal positive).) Add 10 mL of dilute
5.1 Mercaptan sulfur has an objectionable odor, an adverse
H SO (Warning—Poison. Causes severe burns. Harmful or
2 4
effect on fuel system elastomers, and is corrosive to fuel
fatal if swallowed or inhaled) and dilute to 1 L with water.
system components.
7.4 Potassium Iodide, Standard Solution (approximately
0.1 mol ⁄L)—Dissolve 17 g of KI (weigh to 0.01 g) in 100 mL
6. Apparatus
of water in a 1 L volumetric flask and dilute to 1 L. Calculate
6.1 As described in 6.2 – 6.5; alternatively, any automatic
the exact molarity.
titration system may be used that, using the same electrode pair
7.5 Propan-2-ol—(Warning—Flammable. Warning—
described in 6.3, is capable of performing the titration as
Unless inhibited against it, peroxides can form in propan-2-ol
described in Section 10 and selecting the endpoint specified in
when stored in the same container that is exposed to air. When
12.1 with a precision that meets or is better than that given in
this happens and the propan-2-ol evaporates to dryness, an
Section 15.
explosion can occur. When peroxides are suspected, they may
6.2 Meter—An electronic voltmeter, operating on an input
be removed by percolation through an activated alumina
−12
of less than 9 × 10 A and having a sensitivity of 62 mV
column.)
over a range of at least 61 V. The meter shall be electrostati-
7.6 Silver Nitrate, Standard Alcoholic Solution
cally shielded, and the shield shall be connected to the ground.
(0.1 mol ⁄L)—Dissolve 17 g of AgNO in 100 mL of water in a
6.3 Cell System, consisting of a reference and indicating
1 L volumetric flask and dilute to 1 L with propan-2-ol (99 %)
electrode. The reference is a glass electrode. The indicating
(see Note 1). Store in a dark bottle and standardize at intervals
electrode shall be a silver wire or billet electrode with a
frequent enough to detect a change of 0.0005 or greater in
silver/silver-sulfide coating. Combination electrodes consisting
molarity.
of a glass and silver electrode pair, where silver is coated with
NOTE 1—It is important to pass the propan-2-ol through a column of
sulfide (Ag S), may also be used. Shielded electrode cables
activated alumina to remove peroxides that may have formed on storage;
must be used.
failure to remove peroxides will lead to low results. It is not necessary to
6.4 Buret, 10 mL capacity, graduated in 0.05 mL intervals,
perform this step if the alcohol is tested and found free of peroxides.
with a tip that extends approximately 120 mm (5 in.) below the
7.6.1 Standardization—Add six drops of concentrated
stopcock.
HNO (relative density 1.42) (Warning—Poison. Causes
severe burns. Harmful or fatal if swallowed or inhaled) to
6.5 Titration Stand, preferably built as an integral part of the
100 mL of water in an appropriately sized beaker (for example,
meter housing and provided with supports for the electrodes
and electrical stirrer, all connected to ground. No permanent a 200 mL, 250 mL, or 300 mL size beaker is typically large
enough). Remove oxides of nitrogen by boiling for 5 min. Cool
change in meter reading should be noticeable upon connecting
or disconnecting the stirring motor. to ambient temperature. Pipet 5 mL of 0.1 mol ⁄L KI solution
into the beaker and titrate with the AgNO solution choosing
7. Reagents and Materials
the end point at the inflection of the titration curve.
7.1 Purity of Reagents—Reagent grade chemicals shall be
7.7 Silver Nitrate, Standard Alcoholic Solution
used in all tests. Unless otherwise indicated, it is intended that
(0.010 mol ⁄L)—Prepare daily when the test is being performed
all reagents shall conform to the specifications of the Commit-
by dilution of the 0.1 N standard. Pipet 100 mL of the
tee on Analytical Reagents of the American Chemical Society,
0.1 mol ⁄L standard into a 1 L volumetric flask and dilute to
where such specifications are available. Other grades may be
volume with propan-2-ol. Calculate the exact molarity.
used, provided it is first ascertained that the reagent is of
7.8 Sodium Sulfide Solution (10 g ⁄L)—Dissolve 10 g of
sufficiently high purity to permit its use without lessening the
Na S in water and dilute to 1 L with water. Prepare fresh as
accuracy of the determination.
needed.
7.1.1 Commercially available solutions may be used in
place of prepared laboratory solutions, when they are certified NOTE 2—Anhydrous sodium sulfide is not widely available, and is
expensive. An aqueous solution of hydrated sodium sulfide (Na S·9H O)
2 2
to meet the required concentrations.
at 30.6 g ⁄L is satisfactory.
7.1.2 Alternate volumes of solutions and solvents may be
7.9 Sulfuric Acid, dilute. Cautiously dilute five volumes of
prepared, when an equivalent concentration is maintained.
water with one volume of sulfuric acid (relative density 1.84).
(Warning—Adding the acid will generate heat: mix well. If
Any apparatus that will give equal or better precision is acceptable.
water begins to boil, cool before adding more acid.) Note that
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
only limited volumes are required because only 10 mL are
Standard-Grade Reference Materials, American Chemical Society, Washington,
DC. For suggestions on the testing of reagents not listed by the American Chemical needed for each litre of cadmium sulfate solution.
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
7.10 Titration Solvent—Low molecular weight mercaptans,
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
copeial Convention, Inc. (USPC), Rockville, MD. as usually found in gasoline, are readily lost from the titration
D3227 − 24
solution if an acidic titration solvent is used. For the determi- 9.2.2 As triggered by the analysis of a quality control (QC)
nation of the higher molecular weight mercaptan as normally sample (see Section 13), prepare a fresh silver sulfide coating
encountered in kerosines, aviation turbine fuels, and distillate on the electrode by the following method:
fuels, the acidic titration solvent is used to achieve more rapid 9.2.2.1 Burnish electrode with polishing paper or cloth until
equilibrium between successive additions of the titrant. a clean, polished silver surface shows.
7.10.1 Alkaline Titration Solvent—Dissolve 2.7 g of sodium 9.2.2.2 Place electrode in operating position and immerse it
acetate trihydrate (NaC H O ·3H O) or 1.6 g of anhydrous in 100 mL of titration solvent containing 8 mL of Na S
2 3 2 2
sodium acetate (NaC H O ) in 25 mL of water free of dis- solution.
2 3 2
solved oxygen and pour into 975 mL of propan-2-ol (99 %) 9.2.2.3 Add slowly (for example, from a buret), with
(Note 1). When necessary, remove dissolved oxygen by purg- stirring, 10 mL of 0.1 mol ⁄L AgNO solution over a period
ing the solution with a rapid stream of nitrogen for 10 min each from 10 min to 15 min.
day prior to use; keep protected from the atmosphere. To 9.2.2.4 Remove electrode from solution, wash with water,
minimize oxygen from dissolving in the solution during and wipe with a soft, clean tissue.
storage, an option exists to nitrogen blanket the solution prior
9.3 Combination Electrodes—After each titration, rinse
to sealing the solvent container.
with a suitable solvent such as toluene or 2-propanol followed
7.10.2 Acidic Titration Solvent—Dissolve 2.7 g of
by a rinse with water. Rinse with water before each use.
NaC H O ·3H O or 1.6 g of NaC H O in 20 mL of water free
2 3 2 2 2 3 2
9.3.1 When not in use, immerse the glass membrane portion
of dissolved oxygen and pour into 975 mL of propan-2-ol
of the combination electrode in distilled water. Rinse with
(99 %) (Note 1) and add 4.6 mL of glacial acetic acid. When
water before use.
necessary, remove dissolved oxygen by purging the solution
with a rapid stream of nitrogen for 10 min each day prior to
10. Procedure
use; keep protected from the atmosphere. To minimize oxygen
10.1 Determination of Density—If the sample is to be
from dissolving in the solution during storage, an option exists
measured volumetrically, determine the density by Test
to nitrogen blanket the solution prior to sealing the solvent
Method D1298 or Test Method D4052 at the temperature at
container.
which the test portion will be taken, either directly or from the
7.11 Polishing Paper or Cloth, 6 μm to 20 μm average
density determined at a reference temperature and converted to
particle size abrasive.
the transfer temperature by use of the Petroleum Measurement
Tables (Guide D1250).
8. Sampling
10.2 Removal of Hydrogen Sulfide—Test the sample quali-
8.1 Take the sample in accordance with Practice D4057 or
tatively for hydrogen sulfide (H S) by mixing 5 mL of the
Practice D4177. sample with 5 mL of the acid CdSO solution. If no precipitate
appears, proceed with the analysis of the sample as described
8.2 Methanethiol (methyl mercaptan) has a boiling point of
in 10.3. If a yellow precipitate appears, remove the H S in the
6.2 °C and may be expected to be present in light untreated
following manner: Place a quantity of the sample, three to four
gasolines. Therefore, when the presence of this low boiling
times that required for the analysis, in a separatory funnel
thiol (mercaptan) is known or expected, specimen to be tested
containing a volume of the acid CdSO solution equal to one
shall be kept below 4 °C to prevent the loss of mercaptan from
half that of the sample and shake vigorously. Draw off and
such samples.
discard the aqueous phase containing the yellow precipitate.
8.3 Light naphtha fractions of high thiol content
Repeat the extraction with another portion of the CdSO
(>100 mg ⁄kg) boiling below 85 °C have been shown to be very
solution. Again draw off the aqueous phase, and wash the
sensitive to the titration temperatures.
sample with three 25 mL to 30 mL portions of water, with-
drawing the water after each washing. Filter the hydrocarbon
NOTE 3—Samples with a thiol content above 0.010 % by mass may be
analyzed by an appropriate reduction in test portion mass, ensuring that through a rapid paper. Test a small portion of the washed
the minimum volume of titration solvent plus test portion exceeds
sample, such as in a test tube or vial, with a few millilitres of
120 mL. If additional titration solvent is used to maintain this requirement,
the CdSO solution as described previously. If no further
a similar volume should be used for the blank titration. No precision has
precipitate is formed, proceed as directed in 10.3. If a precipi-
been determined for thiol contents above 0.01 % by mass.
tate appears, repeat the extraction with the CdSO solution
until all of the H S has been removed. (Warning—Certain
9. Preparation of Apparatus 2
straight run gasolines can contain significant amounts of both
9.1 Glass Electrode—After each titration, rinse with a
low molecular weight mercaptans and dissolved elemental
suitable solvent such as toluene or 2-propanol followed by a
sulfur, which, when heated under total reflux conditions, may
rinse with water. Rinse with water before use.
produce H S by the inter-reaction of both. This phenomenon is
9.1.1 When not in use, keep the glass membrane of the
particularly noticed in straight run gasolines produced from
electrode immersed in water.
some natural gas condensates. Therefore, it is advisable that
9.2 Silver-Sulfide Electrode—After each titration, rinse with
during the removal of H S (and after all H S has been
2 2
a suitable solvent such as toluene or 2-propanol followed by a extracted), that no heat should be applied to the sample.)
rinse with water. Rinse with water before use.
10.2.1 When the test results obtained are not for referee
9.2.1 When not in use, the silver electrode may be kept dry. purposes and Quality Assurance/Quality Control (QA/QC)
D3227 − 24
protocol permits, an alternative test for, and a procedure for the 10.3.3 Continue the titration until the meter reading change
remo
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D3227 − 23 D3227 − 24
Designation: 342/00342/20
Standard Test Method for
(Thiol Mercaptan) Sulfur in Gasoline, Kerosine, Aviation
1,2
Turbine, and Distillate Fuels (Potentiometric Method)
This standard is issued under the fixed designation D3227; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the determination of mercaptan sulfur in gasolines, kerosines, aviation turbine fuels, and distillate
fuels containing from 0.0003 % to 0.01 % by mass of mercaptan sulfur. Organic sulfur compounds such as sulfides, disulfides, and
thiophene, do not interfere. Elemental sulfur in amounts less than 0.0005 % by mass does not interfere. Hydrogen sulfide will
interfere if not removed, as described in 10.2.
1.2 The values in acceptable SI units are to be regarded as the standard.
1.2.1 Exception—The values in parentheses are for information only.
1.3 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. For specific warning statements, see Sections 7, 9, 10, and Appendix X1.
1.4 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:
D1193 Specification for Reagent Water
D1250 Guide for the Use of the Joint API and ASTM Adjunct for Temperature and Pressure Volume Correction Factors for
Generalized Crude Oils, Refined Products, and Lubricating Oils: API MPMS Chapter 11.1
D1298 Test Method for Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products by
Hydrometer Method
D4052 Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density Meter
This test method is under the jurisdiction of ASTM International Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility
of ASTM Subcommittee D02.03 on Elemental Analysis. The technically equivalent standard as referenced is under the jurisdiction of the Energy Institute Subcommittee
SC-G-5.
Current edition approved May 1, 2023March 1, 2024. Published June 2023March 2024. Originally approved in 1973. Last previous edition approved in 20162023 as
D3227 – 16.D3227 – 23. DOI: 10.1520/D3227-23.10.1520/D3227-24.
This test method has been developed through the cooperative effort between ASTM and the Energy Institute, London. ASTM and IP standards were approved by ASTM
and EI technical committees as being technically equivalent but that does not imply both standards are identical.
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
D3227 − 24
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
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
4. Summary of Test Method
4.1 The hydrogen sulfide-free sample is dissolved in an alcoholic sodium acetate titration solvent and titrated potentiometrically
with silver nitrate solution, using as an indicator the potential between a glass reference electrode and a silver/silver-sulfide
indicating electrode. Under these conditions, the mercaptan sulfur is precipitated as silver mercaptide and the end point of the
titration is shown by a large change in cell potential.
5. Significance and Use
5.1 Mercaptan sulfur has an objectionable odor, an adverse effect on fuel system elastomers, and is corrosive to fuel system
components.
6. Apparatus
6.1 As described in 6.2 – 6.5; alternatively, any automatic titration system may be used that, using the same electrode pair
described in 6.3, is capable of performing the titration as described in Section 10 and selecting the endpoint specified in 12.1 with
a precision that meets or is better than that given in Section 15.
−12
6.2 Meter—An electronic voltmeter, operating on an input of less than 9 × 10 A and having a sensitivity of 62 mV over a range
of at least 61 V. The meter shall be electrostatically shielded, and the shield shall be connected to the ground.
6.3 Cell System, consisting of a reference and indicating electrode. The reference electrode should be a sturdy, pencil-type glass
electrode, having a shielded lead connected to ground. is a glass electrode. The indicating electrode shall be made from a silver
wire, 2 mm (0.08 in.) in diameter or larger, mounted in an insulated support. Silver billet electrodes can a silver wire or billet
electrode with a silver/silver-sulfide coating. Combination electrodes consisting of a glass and silver electrode pair, where silver
is coated with sulfide (Ag S), may also be used. Shielded electrode cables must be used.
6.4 Buret, 10 mL capacity, graduated in 0.05 mL intervals, with a tip that extends approximately 120 mm (5 in.) below the
stopcock.
6.5 Titration Stand, preferably built as an integral part of the meter housing and provided with supports for the electrodes and
electrical stirrer, all connected to ground. No permanent change in meter reading should be noticeable upon connecting or
disconnecting the stirring motor.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
Any apparatus that will give equal or better precision is acceptable.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D3227 − 24
7.1.1 Commercially available solutions may be used in place of prepared laboratory solutions, when they are certified to meet the
required concentrations.
7.1.2 Alternate volumes of solutions and solvents may be prepared, when an equivalent concentration is maintained.
7.2 Water—Reagent grade, Type I, Specification D1193.
7.3 Cadmium Sulfate, Acid Solution (150 g ⁄L)—Dissolve 150 g of cadmium sulfate (3CdSO ·8H O) in water. (Warning—Poison.
4 2
May be fatal if swallowed or inhaled. A known carcinogen (animal positive).) Add 10 mL of dilute H SO (Warning—Poison.
2 4
Causes severe burns. Harmful or fatal if swallowed or inhaled) and dilute to 1 L with water.
7.4 Potassium Iodide, Standard Solution (approximately 0.1 mol ⁄L)—Dissolve 17 g of KI (weigh to 0.01 g) in 100 mL of water
in a 1 L volumetric flask and dilute to 1 L. Calculate the exact molarity.
7.5 Propan-2-ol—(Warning—Flammable. Warning—Unless inhibited against it, peroxides can form in propan-2-ol when stored
in the same container that is exposed to air. When this happens and the propan-2-ol evaporates to dryness, an explosion can occur.
When peroxides are suspected, they may be removed by percolation through an activated alumina column.)
7.6 Silver Nitrate, Standard Alcoholic Solution (0.1 mol ⁄L)—Dissolve 17 g of AgNO in 100 mL of water in a 1 L volumetric flask
and dilute to 1 L with propan-2-ol (99 %) (see Note 1). Store in a dark bottle and standardize at intervals frequent enough to detect
a change of 0.0005 or greater in molarity.
NOTE 1—It is important to pass the propan-2-ol through a column of activated alumina to remove peroxides that may have formed on storage; failure
to remove peroxides will lead to low results. It is not necessary to perform this step if the alcohol is tested and found free of peroxides.
7.6.1 Standardization—Add six drops of concentrated HNO (relative density 1.42) (Warning—Poison. Causes severe burns.
Harmful or fatal if swallowed or inhaled) to 100 mL of water in an appropriately sized beaker (for example, a 200 mL, 250 mL,
or 300 mL size beaker is typically large enough). Remove oxides of nitrogen by boiling for 5 min. Cool to ambient temperature.
Pipet 5 mL of 0.1 mol ⁄L KI solution into the beaker and titrate with the AgNO solution choosing the end point at the inflection
of the titration curve.
7.7 Silver Nitrate, Standard Alcoholic Solution (0.010 mol ⁄L)—Prepare daily when the test is being performed by dilution of the
0.1 N standard. Pipet 100 mL of the 0.1 mol ⁄L standard into a 1 L volumetric flask and dilute to volume with propan-2-ol. Calculate
the exact molarity.
7.8 Sodium Sulfide Solution (10 g ⁄L)—Dissolve 10 g of Na S in water and dilute to 1 L with water. Prepare fresh as needed.
NOTE 2—Anhydrous sodium sulfide is not widely available, and is expensive. An aqueous solution of hydrated sodium sulfide (Na S·9H O) at 30.6 g ⁄L
2 2
is satisfactory.
7.9 Sulfuric Acid, dilute. Cautiously dilute five volumes of water with one volume of sulfuric acid (relative density 1.84).
(Warning—Adding the acid will generate heat: mix well. If water begins to boil, cool before adding more acid.) Note that only
limited volumes are required because only 10 mL are needed for each litre of cadmium sulfate solution.
7.10 Titration Solvent—Low molecular weight mercaptans, as usually found in gasoline, are readily lost from the titration solution
if an acidic titration solvent is used. For the determination of the higher molecular weight mercaptan as normally encountered in
kerosines, aviation turbine fuels, and distillate fuels, the acidic titration solvent is used to achieve more rapid equilibrium between
successive additions of the titrant.
7.10.1 Alkaline Titration Solvent—Dissolve 2.7 g of sodium acetate trihydrate (NaC H O ·3H O) or 1.6 g of anhydrous sodium
2 3 2 2
acetate (NaC H O ) in 25 mL of water free of dissolved oxygen and pour into 975 mL of propan-2-ol (99 %) (Note 1). When
2 3 2
necessary, remove dissolved oxygen by purging the solution with a rapid stream of nitrogen for 10 min each day prior to use; keep
protected from the atmosphere. To minimize oxygen from dissolving in the solution during storage, an option exists to nitrogen
blanket the solution prior to sealing the solvent container.
D3227 − 24
7.10.2 Acidic Titration Solvent—Dissolve 2.7 g of NaC H O ·3H O or 1.6 g of NaC H O in 20 mL of water free of dissolved
2 3 2 2 2 3 2
oxygen and pour into 975 mL of propan-2-ol (99 %) (Note 1) and add 4.6 mL of glacial acetic acid. When necessary, remove
dissolved oxygen by purging the solution with a rapid stream of nitrogen for 10 min each day prior to use; keep protected from
the atmosphere. To minimize oxygen from dissolving in the solution during storage, an option exists to nitrogen blanket the
solution prior to sealing the solvent container.
7.11 Polishing Paper or Cloth, 6 μm to 20 μm average particle size abrasive.
8. Sampling
8.1 Take the sample in accordance with Practice D4057 or Practice D4177.
8.2 Methanethiol (methyl mercaptan) has a boiling point of 6.2 °C and may be expected to be present in light untreated gasolines.
Therefore, when the presence of this low boiling thiol (mercaptan) is known or expected, specimen to be tested shall be kept below
4 °C to prevent the loss of mercaptan from such samples.
8.3 Light naphtha fractions of high thiol content (>100 mg ⁄kg) boiling below 85 °C have been shown to be very sensitive to the
titration temperatures.
NOTE 3—Samples with a thiol content above 0.010 % by mass may be analyzed by an appropriate reduction in test portion mass, ensuring that the
minimum volume of titration solvent plus test portion exceeds 120 mL. If additional titration solvent is used to maintain this requirement, a similar volume
should be used for the blank titration. No precision has been determined for thiol contents above 0.01 % by mass.
9. Preparation of Apparatus
9.1 Glass Electrode—After each manual titration, or batch of titrations, in the case of automatic titration systems, wipe the
electrode with a soft, clean tissue and titration, rinse with a suitable solvent such as toluene or 2-propanol followed by a rinse with
water. Clean the electrode at frequent intervals (at least once a week) by stirring in cold chromic acid solution (Rinse
Warning—Causes severe burns. A recognized carcinogen. Strong oxidizer—contact with other material may cause fire.
Hygroscopic. An equivalent, chromium-free cleaning solution may be used) for a few seconds (10 s maximum). When not in use,
keep lower half of the electrode immersed in water.with water before use.
9.1.1 When not in use, keep the glass membrane of the electrode immersed in water.
9.2 Silver/Silver-SulfideSilver-Sulfide Electrode—Each day prior to use, or as triggered by the analysis of a quality control (QC)
sample (see SectionAfter each titration, rinse with a suitable solvent such as toluene or 2-propanol followed by a rinse with water.
Rinse with water 13), prepare a fresh silver sulfide coating on the electrode by the following method:before use.
9.2.1 Burnish electrode with polishing paper or cloth until a clean, polished silver surface shows.When not in use, the silver
electrode may be kept dry.
9.2.2 Place electrode in operating position and immerse it in 100 mL of titration solvent containing 8 mL of Na S solution.
9.2.2 Add slowly (for example, from a buret), with stirring, 10 mL of 0.1 molAs triggered by the analysis of a quality control (QC)
sample (see Section⁄L 13AgNO), solution over a period from 10 min to 15 min.prepare a fresh silver sulfide coating on the
electrode by the following method:
9.2.2.1 Burnish electrode with polishing paper or cloth until a clean, polished silver surface shows.
9.2.2.2 Place electrode in operating position and immerse it in 100 mL of titration solvent containing 8 mL of Na S solution.
9.2.2.3 Add slowly (for example, from a buret), with stirring, 10 mL of 0.1 mol ⁄L AgNO solution over a period from 10 min to
15 min.
9.2.2.4 Remove electrode from solution, wash with water, and wipe with a soft, clean tissue.
D3227 − 24
9.2.4 Remove electrode from solution, wash with water, and wipe with a soft, clean tissue.
9.2.5 Between manual titrations, or batches of titrations in the case of automatic titration systems, store the electrode a minimum
of 5 min in 100 mL of titration solvent containing 0.5 mL of the 0.1 mol ⁄L AgNO solution.
9.3 Combination Electrodes—After each titration, rinse with a suitable solvent such as toluene or 2-propanol followed by a rinse
with water. Rinse with water before each use.
9.3.1 When not in use, immerse the glass membrane portion of the combination electrode in distilled water. Rinse with water
before use.
10. Procedure
10.1 Determination of Density—If the sample is to be measured volumetrically, determine the density by Test Method D1298 or
Test Method D4052 at the temperature at which the test portion will be taken, either directly or from the density determined at
a reference temperature and converted to the transfer temperature by use of the Petroleum Measurement Tables (Guide D1250).
10.2 Removal of Hydrogen Sulfide—Test the sample qualitatively for hydrogen sulfide (H S) by mixing 5 mL of the sample with
5 mL of the acid CdSO solution. If no precipitate appears, proceed with the analysis of the sample as described in 10.3. If a yellow
precipitate appears, remove the H S in the following manner: Place a quantity of the sample, three to four times that required for
the analysis, in a separatory funnel containing a volume of the acid CdSO solution equal to one half that of the sample and shake
vigorously. Draw off and discard the aqueous phase containing the yellow precipitate. Repeat the extraction with another portion
of the CdSO solution. Again draw off the aqueous phase, and wash the sample with three 25 mL to 30 mL portions of water,
withdrawing the water after each washing. Filter the hydrocarbon through a rapid paper. Test a small portion of the washed sample,
such as in a test tube or vial, with a few millilitres of the CdSO solution as described previously. If no further precipitate is formed,
proceed as directed in 10.3. If a precipitate appears, repeat the extracti
...