ASTM D8488-22

Standard Test Method for Determination of Hydrogen Sulfide (H<inf>2</inf>S) in Natural Gas by Tunable Diode Laser Spectroscopy (TDLAS)

SIGNIFICANCE AND USE
5.1 H2S measurements in natural gas are performed to ensure concentrations satisfy gas purchase contract criteria and to prevent pipeline and associated component corrosion.  
5.2 Using TDLAS for the measurement of H2S in natural gas enables a high degree of selectivity with minimal interference from common constituents in natural gas streams. The TDLAS analyzer can detect changes in concentration with a relatively rapid response compared to other methods so that operators may take swift action when designated H2S concentrations are exceeded.  
5.3 Primary applications covered in this test method are listed in 5.3.1 and 5.3.2. Each application may have differing requirements and methods for gas sampling. Additionally, different natural gas applications may require unique spectroscopic considerations.  
5.3.1 Raw natural gas is found in production, gathering sites, and inlets to gas-processing plants characterized by potentially high levels of water (H2O), carbon dioxide (CO2), H2S, and heavy hydrocarbons. Gas-conditioning plants and skids are normally used to remove H2O, CO2, H2S, and other contaminants.  
5.3.2 High-quality “sales gas” is found in transportation pipelines, natural gas distribution (utilities), and natural gas power plant inlets. The gas is characterized by a very high percentage of methane (90 to 100 %) with small quantities of other hydrocarbons and trace levels of contaminants.
SCOPE
1.1 This test method is for the online determination of hydrogen sulfide (H2S) in natural gas using tunable diode laser absorption spectroscopy (TDLAS) analyzers also known as a “TDL analyzers.” The particular wavelength for H2S measurement varies by manufacturer, typically between 1000 and 10 000 nm with an individual laser having a tunable range of less than 10 nm. The H2S concentration ranges can be anywhere from 0-5 ppm(v) to 0-90 % by volume.  
1.2 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. TDLAS analyzers inherently output concentrations in unitless molar ratios such as ppm(v).
Note 1: Weight-per-volume units such as milligrams or grains of H2S per cubic foot or cubic meter can be derived from ppm(v) at “standard conditions” or standard temperature and pressure.  
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.  
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: 31-Oct-2022
• ICS: 75.060 - Natural gas
• Technical Committee: D03 - Gaseous Fuels
• Drafting Committee: D03.12 - On-Line/At-Line Analysis of Gaseous Fuels

Relations

• Refers: ASTM D4150-19 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 15-Dec-2019
• Refers: ASTM D4150-08(2016) - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 01-Jul-2016
• Refers: ASTM D7833-12 - Standard Test Method for Determination of Hydrocarbons and Non-Hydrocarbon Gases in Gaseous Mixtures by Gas Chromatography
• Effective Date: 01-Nov-2012
• Refers: ASTM D6228-10 - Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Flame Photometric Detection (Withdrawn 2019)
• Effective Date: 01-Dec-2010
• Refers: ASTM D7551-10 - Standard Test Method for Determination of Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases and Natural Gas by Ultraviolet Fluorescence
• Effective Date: 01-May-2010
• Refers: ASTM D1945-03(2010) - Standard Test Method for Analysis of Natural Gas by Gas Chromatography
• Effective Date: 01-Jan-2010
• Refers: ASTM D6968-03(2009) - Standard Test Method for Simultaneous Measurement of Sulfur Compounds and Minor Hydrocarbons in Natural Gas and Gaseous Fuels by Gas Chromatography and Atomic Emission Detection
• Effective Date: 01-Jun-2009
• Refers: ASTM D5503-94(2008) - Standard Practice for Natural Gas Sample-Handling and Conditioning Systems for Pipeline Instrumentation (Withdrawn 2017)
• Effective Date: 01-Dec-2008
• Refers: ASTM D4150-08 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 01-Dec-2008
• Refers: ASTM D5504-08 - Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence
• Effective Date: 15-Jun-2008
• Refers: ASTM D5504-01(2006) - Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence
• Effective Date: 01-Jun-2006
• Refers: ASTM D6968-03 - Standard Test Method for Simultaneous Measurement of Sulfur Compounds and Minor Hydrocarbons in Natural Gas and Gaseous Fuels by Gas Chromatography and Atomic Emission Detection
• Effective Date: 01-Oct-2003
• Refers: ASTM D4150-03 - Standard Terminology Relating to Gaseous Fuels
• Effective Date: 10-Aug-2003
• Refers: ASTM D1945-03 - Standard Test Method for Analysis of Natural Gas by Gas Chromatography
• Effective Date: 10-May-2003
• Refers: ASTM D5503-94(2003) - Standard Practice for Natural Gas Sample-Handling and Conditioning Systems for Pipeline Instrumentation
• Effective Date: 10-May-2003

Overview

ASTM D8488-22 is the Standard Test Method for the Determination of Hydrogen Sulfide (H₂S) in Natural Gas by Tunable Diode Laser Spectroscopy (TDLAS). This internationally recognized standard, developed by ASTM, creates a reliable and selective approach for the online measurement of H₂S in natural gas streams. Accurate H₂S measurement is essential to meet contractual obligations and protect pipeline systems and associated components from corrosion. By employing TDLAS, operators benefit from fast response times, high sensitivity, and minimal interference from common gas stream constituents.

Key Topics

• Purpose and Importance
  • Ensures H₂S concentrations meet gas purchase agreement criteria.
  • Protects pipelines and components from corrosion caused by sulfur compounds.
• Principle of Operation
  • Utilizes tunable diode lasers to scan specific spectral regions where H₂S absorbs light.
  • Achieves selective H₂S detection even in complex gas mixtures.
• Measurement Capabilities
  • Applicable to a wide range of H₂S concentrations, from trace (ppm(v)) up to high percentage levels.
  • Provides real-time, continuous, online monitoring.
• Instrumentation and Sampling
  • Requires proper sample extraction, transport, and conditioning to deliver a representative, contaminant-free gas sample to the analyzer.
  • Sampling hardware must maintain sample integrity and avoid condensation or adsorption losses.
• Validation and Calibration
  • Routine validation is recommended to ensure consistent analytical performance.
  • Factory calibration is standard, with field validation supported as per operational needs.

Applications

ASTM D8488-22 is used extensively across the natural gas supply chain where accurate and reliable H₂S measurement is critical:

• Raw Gas Monitoring:

  • At production sites, gathering stations, and gas-processing plant inlets, H₂S levels may be significantly elevated and require continuous monitoring.
  • Supports operation of gas conditioning systems to remove H₂S, CO₂, water, and heavy hydrocarbons.

• Sales Gas Assurance:

  • In transportation pipelines, gas distribution networks, and power plant inlets, high-purity natural gas (“sales gas”) must meet strict specifications.
  • Fast-acting TDLAS analyzers enable prompt intervention if H₂S exceeds set limits, protecting downstream assets and ensuring compliance.

• Process Safety and Environmental Compliance:

  • Monitors for leaks or abnormal H₂S concentrations, supporting safety protocols and regulatory requirements.
  • Essential in detecting trace levels that could otherwise go unnoticed due to interference in traditional measurement methods.

Related Standards

To ensure comprehensive gas quality assessment and measurement accuracy, ASTM D8488-22 should be used in conjunction with other relevant standards:

• ASTM D1945: Test Method for Analysis of Natural Gas by Gas Chromatography
• ASTM D5504: Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence
• ASTM D6228: Determination of Sulfur Compounds and Minor Hydrocarbons in Natural Gas and Gaseous Fuels by Gas Chromatography and Flame Photometric Detection
• ASTM D6968: Simultaneous Measurement of Sulfur Compounds and Minor Hydrocarbons in Natural Gas by Gas Chromatography and Atomic Emission Detection
• ASTM D7551: Determination of Total Volatile Sulfur in Gaseous Hydrocarbons by Ultraviolet Fluorescence
• ASTM D7833: Determination of Hydrocarbons and Non-Hydrocarbon Gases in Gaseous Mixtures by Gas Chromatography

Summary

Adopting ASTM D8488-22 for H₂S determination in natural gas via TDLAS delivers robust, accurate, and interference-resistant results. This standard supports gas producers, pipeline operators, and utilities in maintaining product quality, operational safety, and regulatory compliance. Its integration with related ASTM standards ensures a comprehensive framework for natural gas quality monitoring and control.

Keywords: hydrogen sulfide, H₂S, natural gas, TDLAS, tunable diode laser absorption spectroscopy, gas quality, pipeline safety, ASTM D8488-22

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:D8488 −22
Standard Test Method for
Determination of Hydrogen Sulfide (H S) in Natural Gas by
Tunable Diode Laser Spectroscopy (TDLAS)
This standard is issued under the fixed designation D8488; 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 D5503 Practice for Natural Gas Sample-Handling and Con-
ditioning Systems for Pipeline Instrumentation (With-
1.1 This test method is for the online determination of
drawn 2017)
hydrogen sulfide (H S) in natural gas using tunable diode laser
D5504 TestMethodforDeterminationofSulfurCompounds
absorption spectroscopy (TDLAS) analyzers also known as a
in Natural Gas and Gaseous Fuels by Gas Chromatogra-
“TDLanalyzers.” The particular wavelength for H S measure-
phy and Chemiluminescence
ment varies by manufacturer, typically between 1000 and
D6228 TestMethodforDeterminationofSulfurCompounds
10 000 nm with an individual laser having a tunable range of
in Natural Gas and Gaseous Fuels by Gas Chromatogra-
less than 10 nm. The H S concentration ranges can be any-
phy and Flame Photometric Detection
where from 0-5 ppm(v) to 0-90 % by volume.
D6968 Test Method for Simultaneous Measurement of Sul-
1.2 Units—The values stated in SI units are to be regarded
fur Compounds and Minor Hydrocarbons in Natural Gas
as the standard. No other units of measurement are included in
and Gaseous Fuels by Gas Chromatography and Atomic
this standard. TDLAS analyzers inherently output concentra-
Emission Detection
tions in unitless molar ratios such as ppm(v).
D7551 Test Method for Determination of Total Volatile
Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum
NOTE 1—Weight-per-volume units such as milligrams or grains of H S
per cubic foot or cubic meter can be derived from ppm(v) at “standard Gases and Natural Gas by Ultraviolet Fluorescence
conditions” or standard temperature and pressure.
D7833 Test Method for Determination of Hydrocarbons and
1.3 This standard does not purport to address all of the Non-Hydrocarbon Gases in Gaseous Mixtures by Gas
safety concerns, if any, associated with its use. It is the
Chromatography
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Definitions—For definitions of general terms used in
1.4 This international standard was developed in accor-
D03 Gaseous Fuels standards, refer to Terminology D4150.
dance with internationally recognized principles on standard-
3.2 Definitions of Terms Specific to This Standard:
ization established in the Decision on Principles for the
3.2.1 absorption spectroscopy, n—refers to spectroscopic
Development of International Standards, Guides and Recom-
techniques that measure the absorption of electromagnetic
mendations issued by the World Trade Organization Technical
radiation as a function of frequency or wavelength because of
Barriers to Trade (TBT) Committee.
its interaction with a sample.
2. Referenced Documents
3.2.2 adsorption, n—adhesion of molecules to a solid sur-
face forming a molecular or atomic film.
2.1 ASTM Standards:
D1945 Test Method for Analysis of Natural Gas by Gas
3.2.3 chemometrics, n—field of science relating measure-
Chromatography
ments made on a chemical system or process to the state of the
D4150 Terminology Relating to Gaseous Fuels
system via application of mathematical or statistical methods.
3.2.4 desorption, n—phenomenon whereby a substance is
1 released from a surface (the opposite of adsorption).
ThistestmethodisunderthejurisdictionofASTMCommitteeD03onGaseous
Fuels and is the direct responsibility of Subcommittee D03.12 on On-Line/At-Line
3.2.5 heat trace, n—ribbon-shaped tape that uses electrical
Analysis of Gaseous Fuels.
resistance or tubing carrying steam to generate heat.
Current edition approved Nov. 1, 2022. Published November 2022. DOI:
10.1520/D8488-22.
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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8488−22
3.2.5.1 Discussion—Heat trace tape is attached to sample laser temperature. The laser generates a near-infrared beam of
tubing and other sample-conditioning components to avoid light that passes through the cell window, which is typically
condensation and stabilize the temperature of the wetted reflected using a mirror (or mirrors) within the cell, and then
components and the gas stream. returns through the window and into a photodiode detector.
The photodiode signal is used to determine how much light is
3.2.6 selectivity, n—refers to the extent to which a measure-
absorbed at specific wavelengths.
ment of concentration can be made in a mixture of various
chemicals without significant influence from other components
4.3 Fig. 2 is a graph of typical regions in the near-infrared
in the mixture.
spectrum where H S will be absorbed. In the graph, the x-axis
indicates the wavelength.The y-axis indicates the “absorption”
3.2.7 tunable diode laser absorption spectroscopy (TDLAS),
of light in which 1.0 (or 100 %) is the maximum. Where the
n—technique for measuring the concentration of a specific
absorption is more than 0, H S is indicated. The vertical lines
componentsuchashydrogensulfide(H S)inagaseoussample 2
within the graph indicate the magnitude of absorption at
by absorption spectrometry using tunable diode lasers.
specific wavelengths. Each individual absorption line can be
3.3 Abbreviations:
potentially used for TDLAS H S measurement. The actual
3.3.1 CO —carbon dioxide
wavelength used will vary based on manufacturer, background
3.3.2 H O—water
2 composition, measurement specification requirements, and la-
3.3.3 H S—hydrogen sulfide ser availability.
3.3.4 TDLAS—tunable diode laser absorption spectroscopy 4.4 The sensitivity of the measurement is determined by the
absorption as well as the length of the laser beam path (path
4. Summary of Test Method
length) within the sample cell. The path length is fixed and can
range from about 30 cm to 30 m depending on the measure-
4.1 A representative sample of the gas is extracted from a
ment range and the wavelength used. By optimizing the path
process pipe or pipeline and is transferred by a sample
length and wavelength, linearity less than 0.1 % can be readily
transport line through an appropriately designed sample-
achieved. The TDLAS manufacturer must be consulted for
handlingsystemtotheinletofananalyzer.Thesampleshallbe
actual linearity specifications.
conditioned with a minimum, preferably negligible, impact on
the H S concentration. The gas flows continuously through the
4.5 This test method can be used as a guideline for produc-
analyzer and is vented to atmosphere, or a flare, or back to the
ing H S measurement data of a known and defensible quality
process stream depending on application and regulatory re-
when using a TDLAS analyzer. A procedure is outlined below
quirements.
for validating measurement integrity.
4.2 The gas sample stream flows through the measurement
5. Significance and Use
portionoftheanalyzer.AnoveralldiagramofasimpleTDLAS
system is shown in Fig. 1. A solid-state laser with a narrow 5.1 H S measurements in natural gas are performed to
wavelength range is used as a light source. Electronics drive ensure concentrations satisfy gas purchase contract criteria and
the laser and a thermoelectric cooler precisely stabilizes the to prevent pipeline and associated component corrosion.
FIG. 1Main Components of the TDLAS System
D8488−22
FIG. 2H S Absorption in the Near Infrared (NIR) Spectrum (Source: Pacific Northwest National Laboratory Northwest Infrared Database)
5.2 Using TDLAS for the measurement of H S in natural scrubber) may be used. Since hundreds of possible wave-
gas enables a high degree of selectivity with minimal interfer- lengths are available in the near-infrared band for measuring
ence from common constituents in natural gas streams. The H S, it is not practical to list the potential interferences. The
TDLAS analyzer can detect changes in concentration with a
manufacturer should indicate the intended stream composition
relatively rapid response compared to other methods so that for the analyzer and the allowable variations in the stream to
operators may take swift action when designated H S concen-
the end user.
trations are exceeded.
6.2 Protection from liquid carryover such as from heavy
5.3 Primary applications covered in this test method are
hydrocarbons, amines, and water in the sample lines is neces-
listed in 5.3.1 and 5.3.2. Each application may have differing
sary to prevent liquid pooling in the cell or the sample system
requirements and methods for gas sampling. Additionally,
components. Liquid carryover is especially a concern on the
different natural gas applications may require unique spectro-
outlet of gas-sweetening processes that use aqueous solutions
scopic considerations.
such as amines.
5.3.1 Raw natural gas is found in production, gathering
sites, and inlets to gas-processing plants characterized by
7. Apparatus
potentially high levels of water (H O), carbon dioxide (CO ),
2 2
7.1 A TDLAS analyzer system includes the following sub-
H S, and heavy hydrocarbons. Gas-conditioning plants and
systems: (1) sample extraction, (2) sample transport, (3)
skids are normally used to remove H O, CO,H S, and other
2 2 2
sample-conditioningsystem,(4)TDLASanalyzer,and(5)vent
contaminants.
line.
5.3.2 High-quality “sales gas” is found in transportation
pipelines, natural gas distribution (utilities), and natural gas 7.1.1 Sample Extraction Hardware—Sample extraction is
power plant inlets. The gas is characterized by a very high
requiredtoobtainarepresentativesamplefromthepipeline.To
percentage of methane (90 to 100 %) with small quantities of
maximize the response speed, it is recommended to reduce the
other hydrocarbons and trace levels of contaminants.
pressure at the sample point. To avoid condensation that may
occur from expanding the gas when it is depressurized (espe-
6. Interferences
cially when the pipeline pressure is high), it is important to
6.1 TDLAS analyzers can be highly selective. They can understand the phase diagram of all the components in the gas
measure target component with very little interference from (for example, hydrocarbons, alcohols, and water). Use an
background composition with some limitations. There may be extraction probe and a regulator as shown in Fig. 3 mounted so
some interference from background components, for example, that the tip of the probe is in the center third of the pipe
at some wavelengths, methane, ethane, and carbon dioxide diameter. If the dew point of the gas is lower than the ambient
may absorb at the same wavelength as H S. If interferences temperature after consideration for temperature reduction be-
exist at a particular wavelength, a different wavelength can be cause of gas expansion through the regulator (approximately
used and other techniques such as chemometrics, compensa- 3 °C per 6 bar), all sampling apparatus such as the probe and
tion algorithms, vacuum pumps (to separate the spectroscopy regulator may need to be heat traced or enclosed in a heated
peaks), or differential measurements (a technique using an H S chamber, or both.According to Practice D5503, “vapor sample
D8488−22
FIG. 3Sample Probe with Integrated Pressure Regulator (Left) and Sample Probe with No Regulator (External Pressure Regulator to be
Used) (Right)
must be kept at least 10 °C above the hydrocarbon dew point desorption affects. Typically, if heat tracing is required, a
temperature to prevent condensation of the sample.” sample panel will be installed in a heated building or a heated
7.1.2 Sample Transport Hardware—The sample transport
enclosure. Components such as valves, regulators, and fittings
line carries the sample from the sample extraction point to the
that are used in the sample extraction, sample transport, an
...