EN 18051:2026

• Abstract:

  This document specifies a test method for the determination of the content of n-butyl phenyl ether (BPE, CAS: 1126-79-0, also known as butoxy-benzene) in gas oils, kerosene, diesel fuel and biodiesel blends. The method uses a two-column gas chromatograph with an FID-type of detector. The application range is 0,27 mg/l to 19,75 mg/l of BPE, with the minimum and maximum reporting levels being 0,09 mg/l and 21,89 mg/l respectively.; NOTE This corresponds to 1 % to 185 % of the average marking level of the ACCUTRACE™ Plus required by Commission Implementing Decision (EU) 2022/197 [1] of 17 January 2022 establishing a common fiscal marker for gas oils and kerosene.; The method is found to be applicable to determinations beyond this range or for specific other chemical markers that fall within the distillation temperature range of middle-distillates, but for that no precision has been determined.; WARNING — The use of this document can involve hazardous materials, operations and equipment. This document does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this document to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.

• Status: Not Published
• Publication Date: 22-Sep-2026
• ICS: 75.160.20 - Liquid fuels
• ICS: 75.160.40 - Biofuels
• Technical Committee: CEN/TC 19 - Petroleum products, lubricants and related products
• Drafting Committee: CEN/TC 19/WG 9 - Chromatographic test methods
• Current Stage: 5060 - Closure of Vote - Formal Approval
• Start Date: 02-Jul-2026
• Due Date: 07-Jul-2027
• Completion Date: 02-Jul-2026
• Ref Project: kSIST FprEN 18051:2026 - Automotive fuels - Determination of content of butoxy-benzene in middle distillates - Gas chromatographic method using a flame ionization detector (GC-FID)

• Revises: EN 18051:2024 - Automotive fuels - Determination of content of butoxy-benzene in middle distillates - Gas chromatographic method using a flame ionization detector (GC-FID)
• Effective Date: 28-May-2025

Overview

EN 18051:2026 is a European standard developed by CEN that specifies a test method for the determination of n-butyl phenyl ether (BPE, also known as butoxy-benzene) content in automotive middle distillates. The targeted products covered by this standard include gas oils, kerosene, diesel fuel, and biodiesel blends. This method employs a two-column gas chromatographic (GC) system using a flame ionization detector (FID) and is essential for ensuring compliance with EU regulations regarding fuel markers-specifically in support of the ACCUTRACE™ Plus fiscal marker as required by Commission Implementing Decision (EU) 2022/197.

The standard outlines the equipment, reagents, calibration procedures, and quality checks necessary for accurate BPE detection and quantification in relevant fuel matrices. Its application range is from 0.27 mg/l to 19.75 mg/l of BPE, with reporting levels extending from 0.09 mg/l to 21.89 mg/l.

Key Topics

• Target Analyte: n-butyl phenyl ether (BPE), also known as butoxy-benzene, used as a fiscal marker in middle distillate fuels.
• Applicable Products: Gas oils, kerosene, diesel fuel, and biodiesel blends.
• Analytical Technique: Gas chromatography with a flame ionization detector (GC-FID), utilizing a two-column system including pre-column heart-cutting for optimal separation of BPE.
• Application Range: Method suitable for detecting BPE in concentrations from 0.27 mg/l to 19.75 mg/l; reporting range is 0.09 mg/l to 21.89 mg/l.
• Calibration and Validation: Includes procedures for preparing stock and working calibration solutions, linearity checks, validation analyses, and determination of response factors.
• Precision Requirements: Repeatability and reproducibility criteria are outlined in accordance with EN ISO 4259-1.
• Safety Notice: Use of this standard may involve hazardous materials; adherence to safety and regulatory protocols is required.

Applications

EN 18051:2026 offers significant practical value in the following areas:

• Regulatory Compliance: Supports implementation of EU directives for fiscal marking of fuels, aiding in market control and prevention of tax fraud.
• Customs and Excise Control: Enables accurate identification of fuel markers in middle distillates, facilitating enforcement by customs and tax authorities.
• Quality Assurance in Refineries and Blending Facilities: Provides laboratories a standardized methodology for verifying correct fuel marker levels in production and distribution.
• Environmental and Forensic Analysis: Offers a reliable tool for traceability of fuel sources and investigation of fuel misuse or adulteration.
• Fuel Distribution Chain Monitoring: Ensures that marked fuels remain identifiable throughout the supply chain, bolstering transparency and regulatory checks.

Laboratories employing this standard benefit from:

• Clear procedures for sample handling and preparation
• Guidance on equipment setup and calibration
• Repeatable, traceable GC-FID analysis aligned with recognized European standards

Related Standards

Professionals using EN 18051:2026 may also find the following standards of interest:

• EN ISO 3170: Hydrocarbon Liquids - Manual Sampling
• EN ISO 3171: Petroleum liquids - Automatic pipeline sampling
• EN ISO 4259-1: Petroleum and related products - Determination of precision data
• ILIADe 606: Determination of n-Butylphenyl Ether (BPE) in gas oil and kerosene by 2D-GC-MS
• Commission Implementing Decision (EU) 2022/197: Establishing a common fiscal marker for gas oils and kerosene

---

By following EN 18051:2026, stakeholders in the petroleum industry ensure robust, compliant, and reliable analysis of fiscal markers in automotive fuels, contributing to effective market control and regulatory oversight in the European Union.

SLOVENSKI STANDARD
oSIST prEN 18051:2025
01-september-2025
Motorna goriva - Določanje vsebnosti butoksibenzena v srednjih destilatih -
Metoda plinske kromatografije z uporabo plamensko ionizacijskega detektorja
(GC-FID)
Automotive fuels - Determination of content of butoxy-benzene in middle distillates - Gas
chromatographic method using a flame ionization detector (GC-FID)
Kraftstoffe - Bestimmung des Gehalts von Butoxybenzol in Mitteldestillaten -
Gaschromatographisches Verfahren mit Flammenionisationsdetektor (GC-FID)
Carburants pour automobiles - Détermination de la teneur en butoxybenzène dans les
distillats moyens - Méthode par chromatographie en phase gazeuse utilisant un
détecteur à ionisation de flamme (CPG-DIF)
Ta slovenski standard je istoveten z: prEN 18051
ICS:
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
75.160.20 Tekoča goriva Liquid fuels
oSIST prEN 18051:2025 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 18051:2025
oSIST prEN 18051:2025
DRAFT
EUROPEAN STANDARD
prEN 18051
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2025
ICS 75.160.20; 75.160.40 Will supersede EN 18051:2024
English Version
Automotive fuels - Determination of content of butoxy-
benzene in middle distillates - Gas chromatographic
method using a flame ionization detector (GC-FID)
Carburants pour automobiles - Détermination de la Kraftstoffe - Bestimmung des Gehalts von
teneur en butoxybenzène dans les distillats moyens - Butoxybenzol in Mitteldestillaten -
Méthode par chromatographie en phase gazeuse Gaschromatographisches Verfahren mit
utilisant un détecteur à ionisation de flamme (CPG- Flammenionisationsdetektor (GC-FID)
DIF)
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 19.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 18051:2025 E
worldwide for CEN national Members.

oSIST prEN 18051:2025
prEN 18051:2025 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviations . 5
3.1 Terms and definitions . 5
3.2 Abbreviations . 5
4 Principle . 6
5 Reagents and materials . 6
6 Apparatus . 6
7 Sampling . 8
8 Preparation and handling of working solutions . 8
8.1 Preparation of stock calibration solution . 8
8.2 Preparation of working calibration solution (WCS) . 8
8.3 Preparation of linearity working solution (LWS) . 9
8.4 Storage of solutions . 9
9 Apparatus preparation . 9
9.1 Gas chromatograph preparation . 9
9.2 System performance check . 9
9.2.1 Determine heart-cutting time . 9
9.2.2 Peak skew check. 10
9.2.3 Linearity check . 11
9.2.4 Determine response factor . 11
10 Procedure . 11
10.1 Initial step . 11
10.2 Validation analysis . 12
10.3 Sample analysis . 12
11 Calculation . 12
12 Expression of results . 13
13 Precision . 13
13.1 General. 13
13.2 Repeatability . 13
13.3 Reproducibility . 13
14 Test report . 14
Annex A (normative) Typical GC settings . 15
A.1 Recommended GC setting . 15
A.2 Exemplary chromatograms . 16
Bibliography . 17

oSIST prEN 18051:2025
prEN 18051:2025 (E)
European foreword
This document (prEN 18051:2025) has been prepared by Technical Committee CEN/TC 19 “Gaseous and
liquid fuels, lubricants and related products of petroleum, synthetic and biological origin”, the secretariat
of which is held by NEN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 18051:2024. After a second interlaboratory study using better
controlled samples, new precision statements have been developed, and a slight change of scope
application has been introduced. Also, some more detail on the test procedure is presented.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supports implementation in the market of the Decision [1] of the European Commission
with regards to common distillate fuel marking.

oSIST prEN 18051:2025
prEN 18051:2025 (E)
Introduction
For the proper functioning of the internal market, the European Commission has established Directives
providing for a common marking system to identify gas oils and kerosene, which have been released for
consumption exempt from excise duty, or which are subject to a reduced excise duty rate. In a review in
2019, the Commission’s evaluation identified the shortcomings of the actual marker (Solvent Yellow 124)
in terms of its lack of resilience to common removal methods.
Consequently, a new, colourless chemical marker, Butoxybenzene (CAS Registry Number 1126-79-0),
was chosen to replace Solvent Yellow 124 as of 18 January 2024. This product or fiscal marker is
TM 1
commercially available as ACCUTRACE PLUS from DOW.
At the time of publication of the decision [1], a gas chromatography technique using a mass spectrometer
(GC-MS) as detector was promoted by DOW. That technique didn’t have a full precision. The first contacts
in 2022 with the European Commission and the EU Customs laboratories led CEN to conclude that the
GC-MS would not be further standardized.
This document has then been developed to present a simpler alternative to the market compared to the
GC-MS method.
The test method described in this document is based on a standard [2] previously prepared for a former
fuel marker, ACCUTRACE™ S101 (3-secbutyl-4-decyloxyphenylmethanetriyltribenzene), which is used in
a few European countries.
To determine the initial method precision, CEN cooperated with the EU Customs laboratories (CLEN) who
studied an improvement of the GC-MS method. The two organizations used the same samples to develop
precision. Bias of this document against the ILIAD 606 method [3] has not been determined in that study.
As for some reasons the sample distribution in the combined study didn’t go as could be expected, the
initial precision was not as expected via the pilot study by CEN. Hence a new study was performed that
resulted in an improved precision and better-defined scope of application.

Accutrace PLUS and ACCUTRACE S10 are the trade names of products supplied by DOW Chemicals. This
information is given for the convenience of users of this document and does not constitute an endorsement by CEN
of the product named. Equivalent products may be used.
oSIST prEN 18051:2025
prEN 18051:2025 (E)
1 Scope
This document specifies a test method for the determination of the content of n-butyl phenyl ether (BPE,
CAS: 1126-79-0, also known as butoxy-benzene) in gas oils, kerosene, diesel fuel and biodiesel blends.
The method uses a two-column gas chromatograph with an FID-type of detector. The application range
is 0,27 mg/l to 19,75 mg/l of BPE, with the minimum and maximum reporting levels being 0,09 mg/l,
respectively 21,89 mg/l.
NOTE This corresponds to 1 % to 185 % of the average marking level of the ACCUTRACE™ Plus required by
Commission Implementing Decision (EU) 2022/197 [1] of 17 January 2022 establishing a common fiscal marker
for gas oils and kerosene.
The method is found to be applicable to determinations beyond this range or for specific other chemical
markers that fall within the distillation temperature range of middle-distillates, but for that no precision
has been determined.
WARNING — The use of this document can involve hazardous materials, operations and equipment. This
document does not purport to address all of the safety problems associated with its use. It is the
responsibility of the user of this document to establish appropriate safety and health practices and to
determine the applicability of regulatory limitations prior to use.
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.
EN ISO 3170, Hydrocarbon Liquids — Manual Sampling (ISO 3170)
EN ISO 3171, Petroleum liquids — Automatic pipeline sampling (ISO 3171)
3 Terms, definitions and abbreviations
3.1 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/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.2 Abbreviations
BPE n-butyl phenyl ether
FID flame ionization detector
GC gas chromatograph
LWS linearity working solution
MS mass spectrometry
RF absolute response factor
SCS stock calibration solution
WCS Working calibration solution
oSIST prEN 18051:2025
prEN 18051:2025 (E)
4 Principle
A test portion is run neat on a two-column gas-chromatographic system. A pre-separation takes place on
a non-polar pre-column. The middle-distillate part with the component, n-butyl phenyl ether or BPE, that
is the main part of the ACCUTRACE™ PLUS fuel marker, is transferred towards a polar analytical column
by using a heart-cut technique. The GC is set towards optimum flow and temperature setting for the
analytical column.
The response areas for the BPE-specific sequential time interval over the entire chromatogram is
determined in a pre-calibration, linearity check step. A flame-ionization detector (FID) is used for
assignment and quantification by reference to an external standard using a BPE-free diesel-type fuel.
5 Reagents and materials
5.1 Purity of reagents and gasses
Reagent grade chemicals shall be used in all tests.
Any hydrocarbon, oxygen or water present in the gasses used (5.2, 5.3 and 5.4), shall be removed by
applying an appropriate filter.
5.2 Carrier gas, helium or hydrogen, minimum 99,995 %(V/V) purity.
NOTE Helium and hydrogen have been proven to achieve the required level of detection, detection and were
used during the interlaboratory study, see 13.1, but nitrogen is an option as well.
5.3 Hydrogen gas, minimum purity 99,995 % (V/V), for use as FID combustion gas.
5.4 Nitrogen gas, minimum purity 99,995 % (V/V) or better, for use as FID make-up gas.
5.5 Compressed air, for use as FID combustion gas.
5.6 Diesel fuel, free of BPE.
5.7 Solvent, purity ≥ 99 %. It has been proven that with m-Xylene the required level of detection can
be achieved, but lower hazard solvents such as cyclohexane or heptane are suitable as well.
5.8 Fuel marker, n-butyl phenyl ether (CAS: 1126-79-0) with known analytical purity.
This product is also known as BPE and is commercially available as the EU fiscal marker or as
TM 1
ACCUTRACE Plus solution.
6 Apparatus
6.1 Gas chromatograph (GC), accommodating two capillary columns and equipped with at least one
Flame Ionization Detector (FID) and one split inlet, and Deans-switching technology, capable to be
operated under the typical conditions given in Annex A (see also Figure 1).
Heart-cut techniques other than Deans-switches are allowed. If these are placed outside the oven, one
shall ensure that no condensation occurs.
oSIST prEN 18051:2025
prEN 18051:2025 (E)
Key
a aux d monitor column
b pre-column e FID back detector
c analysis column f FID front detector
Figure 1 — Schematic overview of the configuration
6.1.1 Sample inlet system, consisting of a split inlet, able to be operated under the typical conditions
given in Annex A.
6.1.2 Column temperature programmer, able to be operated under the typical conditions given in
Annex A.
NOTE Columns are heated in the same oven compartment or in separate oven compartments.
6.1.3 Flame ionization detector(s), able to be operated under the typical conditions given in Annex
...