SIST 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: Published
• Public Enquiry End Date: 30-Sep-2025
• Publication Date: 09-Sep-2026
• ICS: 71.040.50 - Physicochemical methods of analysis
• ICS: 75.160.20 - Liquid fuels
• ICS: 75.160.40 - Biofuels
• Technical Committee: NAD - Petroleum products, lubricants and related products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 31-Aug-2026
• Due Date: 05-Nov-2026
• Completion Date: 10-Sep-2026
• Ref Project: EN 18051:2026 - Automotive fuels - Determination of content of butoxy-benzene in middle distillates - Gas chromatographic method using a flame ionization detector (GC-FID)

• Replaces: SIST EN 18051:2025 - Automotive fuels - Determination of content of butoxy-benzene in middle distillates - Gas chromatographic method using a flame ionization detector (GC-FID)
• Effective Date: 01-Oct-2026

SIST EN 18051:2026 is the Slovenian adoption of EN 18051:2026 from CEN. It specifies a GC-FID test method for measuring n-butyl phenyl ether (BPE), also called butoxy-benzene, in middle distillates such as gas oils, kerosene, diesel fuel and biodiesel blends. The method is intended for laboratories and fuel-control teams that need to check marker content in these fuels within the stated application range.

What does SIST EN 18051:2026 specify?

SIST EN 18051:2026 specifies a test method and the supporting procedure for determining BPE in middle-distillate fuels. It covers the analytical setup, solution preparation, calibration checks, calculation and reporting needed to run the method consistently.

The document is organized into clauses on scope, normative references, abbreviations, principle, reagents and materials, apparatus, sampling, preparation of working solutions, apparatus preparation, procedure, calculation, expression of results, precision and test report, plus one normative annex.

Annex	What it covers
Annex A	Typical GC settings, including the column arrangement and operating conditions used for the method

The scope also states that the method may be used beyond the stated range, or for other chemical markers in the middle-distillate boiling range, but without a precision statement for those cases.

What are the key requirements of SIST EN 18051:2026?

Clause 7 says samples are to be taken according to EN ISO 3170 or EN ISO 3171 unless the product specification says otherwise. In practice, this ties the analysis to recognized sampling methods, because poor sampling can distort the result before the GC run even starts.

Clause 5 requires reagent-grade chemicals and clean carrier and detector gases, with the method using helium or hydrogen as carrier gas and hydrogen, nitrogen and compressed air for the FID. This matters because trace contamination or gas impurities can affect sensitivity and peak shape.

Clause 6 requires a two-column GC arrangement with at least one FID, a split inlet and Deans-switching technology or another heart-cut technique. The method depends on separating the marker from the bulk fuel before it reaches the analytical column, so the instrument setup is part of the measurement, not just the hardware.

Clauses 8 and 9 require preparation of a stock calibration solution, a working calibration solution and a set of linearity working solutions (LWS), followed by system checks. The method uses a heart-cutting time check, a peak skew check, a linearity check and a response-factor determination, which in practice means the laboratory must prove the system is correctly separating and measuring BPE before routine testing starts.

Clause 10 requires neat injection of samples and solutions, with a validation analysis using a reference material at the start of a sequence or daily. This gives day-to-day control of the method and helps show that the instrument response still matches the calibration.

Clause 11 calculates BPE concentration from the measured peak area and the absolute response factor, and Clause 12 requires reporting to the nearest 0,01 mg/l. Clause 13 gives repeatability and reproducibility statements from inter-laboratory data, which is what buyers and laboratories use to judge whether two results should agree.

What terms does SIST EN 18051:2026 define?

The document uses these abbreviations in the method and calculations:

• BPE - n-butyl phenyl ether, the marker measured by this method.
• FID - flame ionization detector, the detector used for quantification.
• GC - gas chromatograph, the instrument used for the analysis.
• LWS - linearity working solution, used to check linearity across the working range.
• RF - absolute response factor, used in the concentration calculation.
• SCS - stock calibration solution, the concentrated calibration solution prepared first.
• WCS - working calibration solution, the diluted calibration solution used for routine calibration and checks.

Who uses SIST EN 18051:2026?

SIST EN 18051:2026 is used by fuel-testing laboratories, customs and fiscal-marker laboratories, and quality control teams in the fuels sector. It fits the work of analysts who prepare calibration mixtures, run GC-FID sequences, verify marker content and document results for gas oils, kerosene, diesel fuel and biodiesel blends. It is also relevant to organizations that need to confirm compliance with marker-based fuel marking programs.

What changed in SIST EN 18051:2026 from the previous edition?

SIST EN 18051:2026 replaces SIST EN 18051:2025, and EN 18051:2026 supersedes EN 18051:2024. The European foreword states three technical changes:

• improved precision statements after a second interlaboratory study
• modified scope application
• more detail in the test procedure

Which standards are used with SIST EN 18051:2026?

The method refers to these standards for supporting tasks:

• EN ISO 3170 - manual sampling of hydrocarbon liquids.
• EN ISO 3171 - automatic pipeline sampling of petroleum liquids.
• EN ISO 4259-1:2026 - used for determining and expressing precision data in line with the repeatability and reproducibility statements.

What does the SIST EN 18051:2026 document contain?

The document contains the full workflow for the analysis: reagent requirements, GC configuration, sample handling, solution preparation, system checks, calibration, validation, calculation and reporting. It includes Table 1 for the linearity working solutions, formulas for solution concentration, response factor and result calculation, and precision formulas for repeatability and reproducibility.

Annex A gives typical GC settings, including the oven program, injector and detector temperatures, inlet pressure profile, split ratio, column dimensions and examples of analytical columns used in the interlaboratory studies. The figures show the GC configuration, peak skew assessment, heart-cut timing and example chromatograms. These parts are used mainly for method setup, verification and routine analytical work.

SLOVENSKI STANDARD
01-oktober-2026
Nadomešča:
SIST EN 18051:2025
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: EN 18051:2026
ICS:
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
75.160.20 Tekoča goriva Liquid fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 18051
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2026
EUROPÄISCHE NORM
ICS 75.160.20; 75.160.40 Supersedes 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 European Standard was approved by CEN on 3 August 2026.

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. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists 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.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 18051:2026 E
worldwide for CEN national Members.

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 . 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 Heart-cutting time determination . 9
9.2.2 Peak skew check. 10
9.2.3 Linearity check . 10
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, r . 13
13.3 Reproducibility, R . 13
14 Test report . 13
Annex A (normative) Typical GC settings . 15
Bibliography . 17

European foreword
This document (EN 18051:2026) 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 European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2027, and conflicting national standards shall be
withdrawn at the latest by March 2027.
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 supersedes EN 18051:2024.
— after a second interlaboratory study, improved precision statements have been developed;
— modification of scope application has been introduced;
— more detail on the test procedure is presented.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: 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 the United
Kingdom.
Introduction
This document supports implementation in the market of Commission Implementing Decision (EU)
2022/197 [1] of the European Commission with regards to common distillate fuel marking.
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, butoxy-benzene (CAS Registry Number 1126-79-0),
was chosen to replace Solvent Yellow 124 as of 18 January 2024. This product or fiscal marker is
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 did not have a precision statement in line
with ISO 4259-1. 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™ S10 (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 the test method described in 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 encountered issues and 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 products named. Equivalent products may be used.
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 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.
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
For the purposes of this document, the following abbreviations apply:
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
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 gases used (5.2, 5.3 and 5.4), shall be removed by
applying an appropriate filter.
5.2 Carrier gas, helium or hydrogen, minimum volume fraction of 99,995 % purity.
NOTE Helium and hydrogen have been proven to achieve the required level of detection, and were used during
the interlaboratory study (see 13.1), but nitrogen is an option as well.
5.3 Hydrogen gas, minimum volume fraction of 99,995 % purity, for use as FID combustion gas.
5.4 Nitrogen gas, minimum volume fraction of 99,995 % purity 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
ACCUTRACE™ Plus solution.
6 Apparatus
6.1 Gas chromatograph (GC)
6.1.1 Gas chromatograph, 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.
Key
a aux
b pre-column
c analysis column
d monitor column
e FID back detector
f
...