ISO 25121

• Abstract:

  This document specifies a ultraviolet fluorescence method for the determination of trace sulfur in light olefins. This document is applicable to the determination of sulfur in ethylene, propylene, butadiene and other C4 olefins. The detection range for sulfur is from 0,2 mg/kg to 100 mg/kg.

• Status: Not Published
• ICS: 71.040.40 - Chemical analysis
• ICS: 71.080.10 - Aliphatic hydrocarbons
• Technical Committee: ISO/TC 47 - Chemistry
• Drafting Committee: ISO/TC 47/WG 2 - Light Olefins
• Current Stage: 6000 - International Standard under publication
• Start Date: 09-Sep-2026
• Completion Date: 12-Sep-2026

Overview

ISO 25121: Light olefins for industrial use - Determination of trace sulfur - Ultraviolet fluorescence method is an international standard developed by ISO for the precise measurement of trace sulfur in light olefins such as ethylene, propylene, butadiene, and other C4 olefins. This standard specifies the ultraviolet fluorescence (UVF) method for detecting sulfur levels ranging from 0.2 mg/kg to 100 mg/kg. Accurate sulfur detection is essential in petrochemical industries to ensure product quality, optimize catalyst performance, protect equipment, and comply with environmental and safety regulations.

Key Topics

• Ultraviolet Fluorescence Method: The standard outlines the use of a UVF analyzer for quantifying sulfur content. In the method, sulfur compounds in the sample are oxidized to sulfur dioxide (SO₂) in a high-temperature combustion tube. The resulting SO₂ absorbs ultraviolet light, emits fluorescence, and is measured to determine sulfur concentration.
• Sample Types: Applicable to both liquid and vapor samples of ethylene, propylene, butadiene, and other C4 light olefins.
• Reagents and Calibration: Requires high-purity sulfur compounds to prepare calibration standards, with strict protocols for solvents and gases to prevent contamination.
• Instrumentation and Apparatus: Specifies the use of a pyrolysis furnace, quartz combustion tube, flow controllers, vapor drier, calibrated sampling syringes, and an ultraviolet fluorescence detector for accurate sulfur analysis.
• Sampling and Analysis Procedure: Details sampling protocols according to referenced ISO standards to preserve sample integrity, including temperature control and swift sample handling.
• Calculation and Reporting: Provides formulas for converting analyzer output into sulfur concentration and sets requirements for reporting results with repeatability and reproducibility benchmarks.

Applications

The practical value of ISO 25121 lies in supporting:

• Petrochemical Production and Quality Control: Ensures that raw materials meet industry requirements for ultra-low sulfur content, essential for downstream chemical processes and compliance with technical specifications.
• Catalyst Protection: Trace sulfur can poison catalysts used in olefin polymerization and other processes, so accurate detection prevents operational disruptions and extends catalyst lifetime.
• Environmental and Regulatory Compliance: Many regions regulate sulfur emissions from chemical manufacturing. Routine use of this method helps organizations verify compliance with environmental standards.
• Research and Development: Supports analytical labs in developing new light olefin processes by providing a reliable method for tracking trace sulfur throughout experiments and pilot-scale operations.
• Supply Chain and Customer Assurance: Documentation and certification of low sulfur content are often required for product acceptance in international markets.

Related Standards

• ISO 7382: Ethylene for industrial use - Sampling in the liquid and the gaseous phase
  • Provides standardized procedures for sampling ethylene, ensuring representative samples for analysis.
• ISO 8563: Propylene and butadiene for industrial use - Sampling in the liquid phase
  • Specifies liquid phase sampling methods critical for accurate sulfur determination in propylene and butadiene.
• ISO 17034: General requirements for the competence of reference material producers
  • Cited for certified reference materials used in calibration, ensuring traceability and accuracy.

By implementing ISO 25121, organizations can achieve reliable trace sulfur determination in light olefins, enhancing product quality, process safety, and regulatory compliance across the chemical and petrochemical industry.

International
Standard
First edition
Light olefins for industrial use —
Determination of trace sulfur —
Ultraviolet fluorescence method
PROOF/ÉPREUVE
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and Materials . 1
6 Apparatus . 2
6.1 Ultraviolet fluorescence analyzer .2
6.1.1 Pyrolysis Furnace .2
6.1.2 Combustion tube .2
6.1.3 Flow controller .2
6.1.4 Vapour drier .2
6.1.5 Ultraviolet fluorescence (UV) detector.3
6.2 Sampling Syringe for calibration standards .3
6.3 Inlet system for vaporized light olefin sample .3
6.4 Vaporization apparatus .3
6.5 Analytical Balance . .3
6.6 Flask .3
7 Sampling . 3
8 Procedure . 3
8.1 Preparation of Apparatus .3
8.2 Calibration .4
8.3 Vaporization of liquid light olefin samples .4
8.4 Vaporized light olefin sample analysis .4
9 Calculation . 4
10 Reporting . 5
11 Precision . 5
11.1 Repeatability (r) .5
11.2 Reproducibility(R) .5
12 Test report . 5
Bibliography . 7
PROOF/ÉPREUVE
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 47, Chemistry.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE
iv
International Standard ISO 25121:2026(en)
Light olefins for industrial use — Determination of trace
sulfur — Ultraviolet fluorescence method
1 Scope
This document specifies a ultraviolet fluorescence method for the determination of trace sulfur in light
olefins.
This document is applicable to the determination of sulfur in ethylene, propylene, butadiene and other C4
olefins. The detection range for sulfur is from 0,2 mg/kg to 100 mg/kg.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 7382, Ethylene for industrial use — Sampling in the liquid and the gaseous phase
ISO 8563, Propylene and butadiene for industrial use — Sampling in the liquid phase
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following ad
...

ISO/DISPRF 25121:2026(en)
ISO/TC 47
Secretariat: JISC
Date: 2026-06-1608-11
Light olefins for industrial use — Determination of trace sulfur —
Ultraviolet fluorescence method
PROOF
ISO/PRF 25121:2026(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO/CD 25121 2026 – All rights reserved
ii
ISO/DISPRF 25121:2026(en)
Contents
Foreword . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and Materials . 1
6 Apparatus . 2
6.1 Ultraviolet fluorescence analyzer . 2
6.2 Sampling Syringe for calibration standards . 3
6.3 Inlet system for vaporized light olefin sample . 3
6.4 Vaporization apparatus . 3
6.5 Analytical Balance . 3
6.6 Flask . 3
7 Sampling . 3
8 Procedure . 3
8.1 Preparation of Apparatus . 3
8.2 Calibration . 4
8.3 Vaporization of liquid light olefin samples . 4
8.4 Vaporized light olefin sample analysis . 4
9 Calculation . 4
10 Reporting . 5
11 Precision . 5
11.1 Repeatability (r) . 5
11.2 Reproducibility(R) . 5
12 Test report . 5
Bibliography . 7

Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Sampling . 3
8 Procedure . 4
9 Calculation . 5
10 Reporting . 5
11 Precision . 5
iii
ISO/PRF 25121:2026(en)
12 Test report . 6
iv © ISO/CD 25121 2026 – All rights reserved
iv
ISO/DISPRF 25121:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 47, Chemistry.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.

v
DRAFT International Standard ISO/DIS 25121:2026(en)

Light olefins for industrial use — Determination of trace sulfur —
Ultraviolet fluorescence method
1 Scope
This document specifies a ultraviolet fluorescence method for the determination of trace sulfur in light olefins.
This document is applicable to the determination of sulfur in ethylene, propylene, butadiene and other C4
olefins. The detection range for sulfur is from 0,2 mg/kg to 100 mg/kg.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 7382, Ethylene for industrial use — Sampling in the liquid and the gaseous phase
ISO 8563, Propylene and butadiene for industrial use — Sampling in the liquid phase
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
4 Principle
The gaseous sample is injected to high temper
...