SIST EN 15721:2026

• Abstract:

  This document specifies a gas chromatographic method for ethanol, in which higher alcohols (propan-1-ol, butan-1-ol, butan-2-ol, 2-methylpropan-1-ol (iso-butanol), 2-methylbutan-1-ol, and 3-methylbutan-1-ol) from (0,1 up to 2,5) mass percentage, methanol from (0,1 up to 3) mass percentage and other impurities, in the range from (0,1 up to 2) mass percentage are determined.; NOTE 1 The European ethanol blending component specification [1] sets a limit for the combined result of ethanol + higher alcohols, not the ethanol content itself.; The method is developed for non-denatured ethanol samples. With sufficient attention to correct separation of the higher alcohols and other components, determination of hydrocarbons in ethanol that contains denaturants as per EN 15376 [1] is possible.; NOTE 2 For the purposes of this document, the term “% (m/m)” is used to represent the mass percentage or mass fraction (ω).

• Status: Published
• Public Enquiry End Date: 03-Jul-2025
• Publication Date: 15-Jun-2026
• ICS: 71.040.50 - Physicochemical methods of analysis
• ICS: 71.080.60 - Alcohols. Ethers
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: NAD - Petroleum products, lubricants and related products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 03-Jun-2026
• Due Date: 08-Aug-2026
• Completion Date: 16-Jun-2026
• Ref Project: EN 15721:2026 - Ethanol as a blending component for petrol - Determination of higher alcohols, methanol and other impurities - Gas chromatographic method

• Replaces: SIST EN 15721:2013 - Ethanol as a blending component for petrol - Determination of higher alcohols, methanol and volatile impurities - Gas chromatographic method
• Effective Date: 01-Jul-2026
• Refers: SIST EN ISO 3170:2025 - Hydrocarbon Liquids - Manual Sampling (ISO 3170:2025)
• Effective Date: 12-Aug-2026
• Refers: SIST EN ISO 3696:1998 - Water for analytical laboratory use - Specification and test methods (ISO 3696:1987)
• Effective Date: 12-Aug-2026

SIST EN 15721:2026 is the Slovenian adoption of EN 15721:2026, published by SIST and prepared within CEN. It specifies a gas chromatographic (GC) method for determining higher alcohols, methanol and other impurities in ethanol used as a blending component for petrol, so laboratories can measure the groups needed for fuel-specification checks.

What does SIST EN 15721:2026 specify?

SIST EN 15721:2026 specifies a GC method for ethanol samples, with defined ranges for higher alcohols, methanol and other impurities. The method is written for non-denatured ethanol, and it can also be applied to ethanol containing denaturants when the separation is managed carefully.

The standard is organized into Clauses 1 to 11, covering scope, normative references, terms and definitions, principle, reagents and materials, apparatus, sampling, procedure, calculation, precision and the test report. Annex A is informative and gives chromatogram examples and peak assignments.

Annex	What it covers
Annex A	Informative examples of chromatograms for typical column systems, with peak identification and retention times

The scope matters in practice because it tells a laboratory exactly which impurity groups the method is meant to quantify and that the result set is group-based, not just a single ethanol value.

What are the key requirements of SIST EN 15721:2026?

Sampling and sample handling

SIST EN 15721:2026 requires laboratory samples to be taken according to EN ISO 3170 unless otherwise specified. Samples are to be collected in clean, dry glass bottles, rinsed with the product before use, and protected from contamination, especially water.

That matters because this method is sensitive to light volatile compounds and to moisture contamination. Poor sampling can change the measured impurity profile before the sample even reaches the chromatograph.

Two procedure variants

SIST EN 15721:2026 defines two alternatives: Procedure A uses direct injection of the test portion, while Procedure B includes a water-dilution step before injection. The laboratory chooses the procedure, but Procedure B is recommended when ethyl acetate may be present, while Procedure A is recommended when non-polar compounds are present.

In practice, this choice is about peak separation and interference control. A lab needs to select the variant that gives the cleanest chromatogram for the material being tested.

Preparation of solutions and internal standards

SIST EN 15721:2026 requires stock and calibration solutions to be prepared gravimetrically and handled to minimize loss of volatile compounds. The document also sets out the internal standards used for each procedure and requires calibration solutions to be stored at 4 °C and used for no more than six months.

This matters because the method depends on comparing analyte peaks with an internal standard. If the solutions are prepared inconsistently, the calculated contents can drift even when the instrument is working correctly.

GC equipment and separation performance

SIST EN 15721:2026 requires a GC system with a flame ionization detector (FID), a split injector and suitable data handling. The column must separate the specified compounds, and the internal standard must be fully separated from all other peaks; the two isomeric alcohols 2-methylbutan-1-ol and 3-methylbutan-1-ol must achieve at least the stated minimum resolution.

The carrier gas is helium for the precision data in the standard, although hydrogen or nitrogen are allowed. This is important because different gases can change retention times and resolution, so a laboratory must confirm that its chosen setup still meets the separation criteria.

Calibration, response factors and calculation

SIST EN 15721:2026 requires response factors to be determined from the calibration solution under the same chromatographic conditions used for samples. Clause 9 then uses those response factors, together with peak areas and the dilution factor where relevant, to calculate the content of each compound.

The standard also gives typical response factors for common denaturants and allows a default response factor for components not listed. In practice, this means the laboratory must not rely on peak area alone - it must calculate content using the calibration relationship for the actual compounds present.

Group reporting and treatment of water

SIST EN 15721:2026 requires reported results for impurities, methanol, higher alcohols, and ethanol including higher alcohols. Compounds below the stated summation threshold are excluded from group totals, and water is not part of the chromatographic result because it is not visible in the chromatogram.

This matters because the final report is not just a list of peaks. The method is designed to produce the grouped values that feed into the ethanol specification, while water has to be considered separately if the specification asks for alcohol content.

Precision checks and test report

SIST EN 15721:2026 gives repeatability and reproducibility expressions for the main reported quantities and states that precision was established from inter-laboratory testing. Clause 11 also requires the test report to identify the standard, the product, the procedure used, the result, any deviations, any unusual features and the test date.

That gives laboratories a common way to judge whether two results are close enough and ensures the reported result is traceable to the procedure actually used.

What terms does SIST EN 15721:2026 define?

• Impurities - compounds that are not assigned to the higher alcohols group or to methanol.
• Gas chromatograph (GC) - the instrument used to separate the compounds in the ethanol sample before detection.
• Flame ionization detector (FID) - the detector used to measure the separated compounds after GC separation.
• Internal standard - a compound added before injection so the analyte peaks can be measured against a known reference response.
• Procedure A - the variant with direct injection of the test portion.
• Procedure B - the variant that includes a water dilution step before injection.
• % (m/m) - the notation used in the document for mass percentage or mass fraction.

Who uses SIST EN 15721:2026?

SIST EN 15721:2026 is used by laboratories that test ethanol for use as a petrol blending component. It is relevant to fuel producers, fuel blenders, quality control teams, and third-party analytical laboratories that need to measure methanol, higher alcohols and other impurities against fuel specifications.

It is also useful for buyers, suppliers and auditors who need a shared test method for checking compliance with ethanol quality requirements in the automotive fuel chain.

What changed in SIST EN 15721:2026 from the previous edition?

SIST EN 15721:2026 supersedes SIST EN 15721:2013 and EN 15721:2013. The foreword states two significant technical changes: response factors are now self-determined in the calculation for all components, with recommendations given for commonly used denaturants, and the need for good separation to avoid overlap between ethanol and petrol components is emphasized.

Which standards are used with SIST EN 15721:2026?

Standard	What it contributes
EN ISO 3170	Sampling procedure for obtaining laboratory samples
EN ISO 3696	Water quality for analytical laboratory use
EN 15376	The petrol-blending ethanol specification that uses the results from this method
EN ISO 4259:2006	Precision data approach used in the inter-laboratory evaluation described in Clause 11

These references matter because they connect the analytical method to sampling practice, laboratory water quality, product specification and precision evaluation.

What does the SIST EN 15721:2026 document contain?

SIST EN 15721:2026 contains the analytical principle, reagent and apparatus requirements, and detailed preparation steps for the calibration and sample solutions used in Procedure A and Procedure B. It also includes the calculation formulas for response factors and compound contents, plus the rules for summing group contents and expressing results.

Annex A provides example chromatograms and peak assignments for typical column systems. The figures and tables there are there to help analysts identify peaks, confirm retention behavior and check that their separation is fit for the method.

SLOVENSKI STANDARD
01-julij-2026
Nadomešča:
SIST EN 15721:2013
Etanol kot komponenta za dodajanje motornemu bencinu - Določanje višjih
alkoholov, metanola ter drugih nečistoč - Metoda plinske kromatografije
Ethanol as a blending component for petrol — Determination of higher alcohols,
methanol and other impurities - Gas chromatographic method
Ethanol zur Verwendung als Blendkomponente in Ottokraftstoff - Bestimmung von
höheren Alkoholen, Methanol und andere Verunreinigungen - Gaschromatographisches
Verfahren
Ethanol comme base de mélange à l'essence — Détermination de la teneur des alcools
supérieurs, méthanol et autres impuretés — Méthode par chromatographie en phase
gazeuse
Ta slovenski standard je istoveten z: EN 15721:2026
ICS:
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
71.080.60 Alkoholi. Etri Alcohols. Ethers
75.160.20 Tekoča goriva Liquid fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 15721
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2026
EUROPÄISCHE NORM
ICS 75.160.20 Supersedes EN 15721:2013
English Version
Ethanol as a blending component for petrol -
Determination of higher alcohols, methanol and other
impurities - Gas chromatographic method
Éthanol comme base de mélange à l'essence - Ethanol zur Verwendung als Blendkomponente in
Détermination de la teneur en alcools supérieurs, Ottokraftstoff - Bestimmung von höheren Alkoholen,
méthanol et autres impuretés - Méthode par Methanol und andere Verunreinigungen -
chromatographie en phase gazeuse Gaschromatographisches Verfahren
This European Standard was approved by CEN on 17 May 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 15721:2026 E
worldwide for CEN national Members.

Contents Page
European Foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 5
5 Reagents and materials . 6
6 Apparatus . 6
7 Sampling . 8
8 Procedure. 8
8.1 General . 8
8.2 General considerations for preparation and handling of solutions . 9
8.3 Preparation of solutions for Procedure A . 9
8.3.1 Calibration stock solution (E) for Procedure A . 9
8.3.2 Internal standard stock solution (ES) for Procedure A . 9
8.3.3 Calibration solution (FS1) for Procedure A . 9
8.3.4 Preparation of sample (S) for Procedure A . 10
8.4 Preparation of solutions for Procedure B . 10
8.4.1 Calibration stock solution (E) for Procedure B . 10
8.4.2 Internal standard stock solution (ES) for Procedure B . 10
8.4.3 Calibration solution (FS1) for Procedure B . 10
8.4.4 Preparation of sample (S) for Procedure B . 10
8.5 Determination . 11
8.5.1 Gas chromatograph analysis conditions . 11
8.5.2 Determination of response factors . 12
8.5.3 Recording the chromatogram . 12
8.5.4 Performance checks . 12
9 Calculation . 12
9.1 Content of individual compounds . 12
9.2 Calculation of group contents . 13
9.3 Expression of results . 13
10 Precision . 14
10.1 General . 14
10.2 Repeatability . 14
10.3 Reproducibility . 14
11 Test report . 15
Annex A (informative) Examples of chromatograms . 16
Bibliography . 22
European foreword
This document (EN 15721:2026) 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 January 2027, and conflicting national standards shall
be withdrawn at the latest by January 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 will supersede EN 15721:2013, and includes the following significant technical changes
with respect to that edition:
— the requirement to use self-determined response factors in the calculation (9.1) for all components,
whereas recommendations are given for the commonly used denaturants;
— the need for a good separation, to prevent peak overlap between ethanol and petrol components, is
underlined (8.5.3).
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 specifies a gas chromatographic (GC) test method for the determination of a number of
compounds present in ethanol for use as a blending component in petrol according to the CEN ethanol
blending component specification EN 15376 [1]. The test method comprises of GC identification and
analysis of a number of molecules, which are then attributed to several classes (“impurities”, “methanol”,
“higher alcohols”), which are needed for calculation of the specified values as required in EN 15376.
The method described in this document was prepared by CEN/TC 19’s Working Group 9 and is based on
two methods ([2] and [3]) published from a European Regulation on wine and on other internationally
published analytical methods on spirits [4]. The method was modified for determinations in non-
denatured ethanol for automotive applications. When ethanol blending in petrol became more common
outside the refinery, it appeared to be necessary to generalize the test method more towards denatured
ethanol.
1 Scope
This document specifies a gas chromatographic method for ethanol, in which higher alcohols (propan-1-
ol, butan-1-ol, butan-2-ol, 2-methylpropan-1-ol (iso-butanol), 2-methylbutan-1-ol, and 3-methylbutan-1-
ol) from (0,1 up to 2,5) mass percentage, methanol from (0,1 up to 3) mass percentage and other
impurities, in the range from (0,1 up to 2) mass percentage are determined.
NOTE 1 The European ethanol blending component specification [1] sets a limit for the combined result of
ethanol + higher alcohols, not the ethanol content itself.
The method is developed for non-denatured ethanol samples. With sufficient attention to correct
separation of the higher alcohols and other components, determination of hydrocarbons in ethanol that
contains denaturants as per EN 15376 [1] is possible.
NOTE 2 For the purposes of this document, the term “% (m/m)” is used to represent the mass percentage or
mass fraction (ω).
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 3696, Water for analytical laboratory use — Specification and test methods (ISO 3696)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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/
3.1
impurities
compounds not attributed to the groups of higher alcohols or methanol
4 Principle
The compounds specified in the scope are determined by direct injection of a test portion into a gas
chromatograph (GC) system. An internal standard is added to the sample prior to the injection. The
compounds are separated with suitable GC equipment using temperature programming with the option
to also use flow programming on a suitable column. They are detected using a flame ionization detector
(FID). The concentration of each compound is determined from response factors with respect to the
internal standard.
Water, if present in the sample, is not included in this analysis, because a signal for water is not visible in
the chromatogram.
The response factors are obtained during calibration using the same chromatographic conditions as those
for the analysis of the ethanol samples.
Two procedures (“Procedure A” and “Procedure B”) are specified which differ mainly in the optional use
of a water dilution step prior to the analysis. Both variants have been validated to produce identical
results and precision in extensive Round Robin tests.
5 Reagents and materials
All reagents shall be of recognized analytical grade (minimum 99 %) or of higher purity, if commercially
available. They shall be stored in closed dark glass bottles. Other internal standards may also be used
when there is sufficient proof that their GC signal does not interfere with the other signals in the
chromatogram.
5.1 Water which, for analytical laboratory use, shall conform to grade 2 of EN ISO 3696.
5.2 Compounds
The compounds used for calibration and peak identification are listed in Table 1.
Table 1 — Compounds for calibration, used as solvents and other related information
Compound Attributed to group
Calibration compounds
Methanol Methanol
Propan-1-ol Higher Alcohols
Butan-1-ol Higher Alcohols
Butan-2-ol Higher Alcohols
2-Methylpropan-1-ol Higher Alcohols
2-Methylbutan-1-ol Higher Alcohols
3-Methylbutan-1-ol Higher Alcohols
Internal standards
Pentan-3-ol Internal standard for Procedure A
4-Methylpentan-2-ol Internal standard for Procedure B
Solvent
a
Ethanol Solvent
a
Ethanol is needed in Procedure “A” and “B” as a solvent for the calibration
solutions. The purity of the ethanol should be considered when preparing
the mixtures. It should not contain any impurities that may interfere with
the analysis and the results shall be corrected for the purity of the ethanol.

5.3 Carrier gas, helium for use with flame ionization detectors (FIDs).
Use of hydrogen or nitrogen is allowed, however can result in slightly different retention times, relative
retention times (RRT) and peak resolutions. Precision in this document (see Clause 10) is acquired using
only helium as carrier gas.
CAUTION — Helium and nitrogen are compressed gases under high pressure. Hydrogen is an extremely
flammable gas under high pressure. The use of a hydrogen sensor in the gas chromatography oven is
strongly recommended to shut off the hydrogen source in case of a high concentration build-up of
hydrogen that exceeds the explosive limit.
6 Apparatus
6.1 Gas chromatograph, equipped with a Flame Ionization Detector (FID), a split injector and
connected to a PC or other system permitting the recording of chromatograms and execution of
quantitative calculations.
6.2 Gas chromatographic column
6.2.1 General
Bonded capillary column with a suited phase, permitting the complete separation of all requested
compounds for the analysis, except for 2-methylbutan-1-ol and 3-methylbutan-1-ol, for which a
minimum peak resolution of 1,0 (see 6.2.2) is required. The internal standard shall be perfectly separated
from all other compounds. Additional detail, including sample chromatograms, is given in Annex A.
6.2.2 Chromatographic resolution
The column resolution (as measured for 2-methylbutan-1-ol and 3-methylbutan-1-ol) shall be at least
1,0. Determine the column resolution, C , with the calibration solutions (8.3) or (8.4) for the 2-
R
methylbutan-1-ol and 3-methylbutan-1-ol peaks using the following Formula (1):
2 tt−
( )
2 1
(1)
C =
R
1,699 W + W
( )
1 2
where
t is the retention time, in seconds, for the 2-methylbutan-1-ol peak;
t is the retention time, in seconds, for the 3-methylbutan-1-ol peak;
W is the width, in seconds, at half-height of 2-methylbutan-1-ol peak;
W is the width, in seconds, at half-height of 3-methylbutan-1-ol peak.
Figure 1 presents further clarification on the calculation of column resolution, C , of 2-methylbutan-1-ol
R
and 3-methylbutan-1-ol according to procedure “B” (example: C = 1,30).
R
Key
1 pentan-3-ol (retention time 12,292 min) X retention time (min)
2 2-methylbutan-1-ol (retention time 13,741 min) Y FID signal
3 3-methylbutan-1-ol (retention time 13,820 min)
Figure 1 — Typical chromatogram for calculation of column resolution
6.3 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.4 Vials, having seals and used for test portions and calibration solutions.
7 Sampling
Unless otherwise specified, laboratory samples shall be obtained by the procedures specified in
EN ISO 3170.
Glass bottles shall be used for taking samples. The glass bottles shall be meticulously cleaned and dried,
rinsed at least twice with the product to be sampled. Special care shall be taken during all further
manipulations with the samples to avoid any risk of further contamination, e.g. with water.
8 Procedure
8.1 General
Two method variants are defined in this document:
a
...