ISO 21846:2018

Vegetable fats and oils - Determination of composition of triacylglycerols and composition and content of diacylglycerols by capillary gas chromatography

This document specifies the determination of composition of triacylglycerols and the determination of the composition and content of diacylglycerols by capillary gas chromatography in vegetable oils with a lauric acid content below 1 %. Applying certain technological processing 1,2-diacylglycerols (1,2-DAGs) are transformed to the more stable isomeric 1,3-diacylglycerols (1,3-DAGs) due to acidic catalysed reaction. During storage, the speed and amount of this rearrangement depends on the acidity of the oil. The transformation normally reaches an equilibrium between the two isomeric forms. The relative amount of 1,2-DAGs is related to oil freshness or to a possible technological treatment. Therefore, it is possible to use the ratio of 1,2-DAGs to 1,3-DAGs as a quality criterion for vegetable fats and oils. The triacylglycerols profile is of potential interest for the fingerprint of each vegetable oil and may help the detection of certain types of adulteration, such as the addition of high oleic sunflower oil or palm olein in olive oil. NOTE This document is based on Reference [3].

Corps gras d'origine végétale — Détermination de la composition des triacylglycérols et de la teneur en diacylglycérols par chromatographie en phase gazeuse sur colonne capillaire, dans les huiles végétales

General Information

• Status: Published
• Publication Date: 06-Aug-2018
• ICS: 67.200.10 - Animal and vegetable fats and oils
• Technical Committee: ISO/TC 34/SC 11 - Animal and vegetable fats and oils
• Drafting Committee: ISO/TC 34/SC 11 - Animal and vegetable fats and oils
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 22-Oct-2025
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO/TS 19468:2022 - Intelligent transport systems - Data interfaces between centres for transport information and control systems - Platform-independent model specifications for data exchange protocols for transport information and control systems
• Effective Date: 06-Jun-2022
• Revised: ISO 21846:2025 - Vegetable fats and oils - Determination of composition of triacylglycerols and composition and content of diacylglycerols by capillary gas chromatography
• Effective Date: 25-Jan-2025

Overview

ISO 21846:2018 specifies a capillary gas chromatography (GC) method for determining the composition of triacylglycerols (TAGs) and the composition and total content of diacylglycerols (DAGs) in vegetable fats and oils with a lauric acid content below 1%. The method uses silylation, an internal standard, and separation on a short fused‑silica capillary column with flame‑ionization detection to produce TAG and DAG profiles used for quality assessment and oil fingerprinting.

Key topics and technical requirements

• Scope: Applicable to vegetable oils with <1% lauric acid; evaluates TAG classes (C46–C64) and DAG isomers (1,2‑ and 1,3‑structures, e.g. C32–C36).
• Sample preparation: Addition of an internal standard (dinonadecanoin), silylation with BSTFA/TMCS in pyridine, dilution in n‑heptane or methyl tert‑butyl ether prior to injection.
• Chromatography:
  • Capillary column: fused silica, 6–8 m length, 0.25–0.32 mm i.d., SE‑52/SE‑54 stationary phase, film 0.10–0.15 µm.
  • Injection: on‑column cold injection or programmed temperature vaporizer.
  • Detector: flame‑ionization detector (FID); carrier gas hydrogen or helium.
  • Typical oven program and detector temperatures defined for reliable separation of TAG classes and DAG isomers.
• Peak identification and quantification:
  • TAGs identified by carbon atom number (elution order C46 → C64) and normalized to 100% for percentage profiles.
  • DAGs separated by isomeric structure (1,2 elute earlier than 1,3); percent of each DAG isomer is area/% of total DAG area.
  • Total DAG content (g/100 g) calculated using the internal standard and measured peak areas.
• Performance and reporting:
  • Method precision given in terms of repeatability and reproducibility (interlaboratory evaluation included).
  • Test report must document sample ID, sampling method, method reference (ISO 21846), operating details, results, and repeatability checks if performed.

Applications

• Quality control and shelf‑life monitoring: the 1,2‑DAG to 1,3‑DAG ratio is an indicator of oil freshness and acidic or thermal processing (1,2 → 1,3 rearrangement).
• Authentication and adulteration detection: TAG profiles can act as oil fingerprints to help detect adulteration (e.g., addition of high‑oleic sunflower oil or palm olein into olive oil).
• Process control and research: monitoring DAG levels during refining, storage studies, and formulation of fat blends.

Who uses this standard

• Food testing laboratories and quality control analysts
• Vegetable oil producers, refiners and packers
• Regulatory agencies and food authenticity labs
• Research groups studying lipid chemistry and oil stability

Related standards

ISO 21846:2018 complements other standard methods for fat and oil analysis and general chromatographic practice; laboratories should use it alongside established sampling and traceability standards when reporting compliance and authenticity results.

Keywords: ISO 21846:2018, triacylglycerols, diacylglycerols, capillary gas chromatography, DAG/TAG profile, oil authenticity, olive oil adulteration, silylation, flame‑ionization detector.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21846
First edition
2018-08
Vegetable fats and oils —
Determination of composition of
triacylglycerols and composition and
content of diacylglycerols by capillary
gas chromatography
Corps gras d'origine végétale — Détermination de la composition
des triacylglycérols et de la teneur en diacylglycérols par
chromatographie en phase gazeuse sur colonne capillaire, dans les
huiles végétales
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus . 2
6 Reagents . 2
7 Procedure. 3
7.1 Gas chromatographic apparatus and capillary column condition . 3
7.2 Choice of operating conditions . 3
7.3 Performance of the analysis . 3
7.4 Peak identification . 3
7.5 Determination of percentage content of each triacylglycerol class . 4
7.6 Determination of percentage content of each 1,2 diacylglycerol . 4
7.7 Determination of weight percentage total content of diacylglycerols . 4
8 Expression of results . 5
9 Precision of the method . 5
9.1 Repeatability, r .5
9.2 Reproducibility, R .5
10 Test report . 5
Annex A (informative) Examples of a typical chromatograms . 6
Annex B (informative) Results of an interlaboratory test .11
Bibliography .13
Foreword
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This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 11,
Animal and vegetable fats and oils.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 21846:2018(E)
Vegetable fats and oils — Determination of composition
of triacylglycerols and composition and content of
diacylglycerols by capillary gas chromatography
1 Scope
This document specifies the determination of composition of triacylglycerols and the determination of
the composition and content of diacylglycerols by capillary gas chromatography in vegetable oils with
a lauric acid content below 1 %.
Applying certain technological processing 1,2-diacylglycerols (1,2-DAGs) are transformed to the more
stable isomeric 1,3-diacylglycerols (1,3-DAGs) due to acidic catalysed reaction. During storage, the
speed and amount of this rearrangement depends on the acidity of the oil. The transformation normally
reaches an equilibrium between the two isomeric forms. The relative amount of 1,2-DAGs is related to
oil freshness or to a possible technological treatment. Therefore, it is possible to use the ratio of 1,2-
DAGs to 1,3-DAGs as a quality criterion for vegetable fats and oils.
The triacylglycerols profile is of potential interest for the fingerprint of each vegetable oil and may help
the detection of certain types of adulteration, such as the addition of high oleic sunflower oil or palm
olein in olive oil.
NOTE This document is based on Reference [3].
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Principle
After the addition of an internal standard the oil sample is silylated, dissolved in a suitable reagent and
directly injected in the gas chromatographic apparatus. Triacyglycerols are separated into classes on
the basis of their carbon atom number, while diacylglycerols are separated in function of their carbon
atom number and structure, as 1,2 structures show a lower retention time than 1,3 ones.
Unsaturated diacylglycerol structures do not affect retention time. Therefore, saturated and
unsaturated diacylglycerols elute together, so 1,2 and 1,3-diacylglycerol structures are identified by
their peak retention time. The percentage content of 1,2 structure is determined through the ratio of
1,2-diacylglycerol areas to the sum of areas of all the diacylglycerol peaks.
The diacylglycerol total content is calculated by means of an internal standard.
The percentage content for each triacylglycerol class is calculated after normalization to 100 % of all
the triacylglycerol peaks.
5 Apparatus
5.1 Analytical balance suitable to perform weighing to an accuracy of within +/−0,1 mg.
5.2 Gas chromatograph for use with a capillary column, equipped with a system for direct on-column
for cold injection or a programmed temperature vaporizer.
5.3 Thermostat-controlled oven with temperature programming.
5.4 Cold injector for on-column injection or programmed temperature vaporizer.
5.5 Flame-ionization detector and converter-amplifier.
5.6 Recorder-integrator for use with the converter-amplifier (5.5), with a rate of response below 1 s
and variable paper speed, or any suitable device for data capture and handling.
5.7 Capillary column, fused silica, 6 m to 8 m length, 0,25 mm to 0,32 mm internal diameter,
internally coated with SE 52, SE 54 liquid phase to a uniform thickness of 0,10 μm to 0,15 μm.
5.8 Microsyringe, 10 μl, with a hardened needle for on-column injector.
5.9 Microsyringe, 100 μl, with a hardened needle.
5.10 Usual laboratory glassware.
6 Reagents
WARNING — Attention is drawn to the regulations which specify the handling of hazardous
substances. Technical, organizational and personal safety measures shall be followed.
Unless otherwise stated analytically pure reagents shall be used.
6.1 Carrier gas: hydrogen or helium, pure, for gas chromatography.
6.2 Auxiliary gases:
— hydrogen, pure, for gas chromatography;
— air, pure, for gas chromatography.
6.3 Silylating reagent, mix equal volumes of
— pyridine, and
— bistrimethy
...