⛽ Ester and linolenic acid methyl ester contents in FAME — gas chromatography
In short
GC-FID with a Carbowax 20M capillary column (30 m × 0. 25 mm × 0. The test is performed according to PN-EN 14103:2020-06; Range: Esters > 90 % (m/m); C18:3 1–15 % (m/m); FAME C6–C24; the precision established for 95 % and 100 % of esters. The procedure comprises 6 steps (about 3 h in total); it is used for: Quality control of FAME (biodiesel) — an ester content above 90 % (m/m), Determination of linolenic acid methyl ester (the limit 1–15 % m/m) in rapeseed and other esters, Assessment of FAME blending components for B7–B10 diesel fuels (studies at the Oil and Gas Institute).
At a glance
- Standard: PN-EN 14103:2020-06
- Category: Petrochemistry
- Procedure steps: 6
- Total time of stages: 3 h
- Range: Esters > 90 % (m/m); C18:3 1–15 % (m/m); FAME C6–C24; the precision established for 95 % and 100 % of esters
- Internal standard: Nonadecanoic acid methyl ester C19:0, GC purity ≥ 99.0 % (m/m), water < 0.2 % (m/m) (Karl Fischer)
- Test portions: ≈ 250 mg of FAME + ≈ 100 mg of C19:0 (± 0.1 mg) in 10 ml of toluene; the samples and the standard ≥ 3 h at ambient temperature before weighing
Overview
The standard describes a procedure for determining the ester content in fatty acid methyl esters (FAME) intended for incorporation into diesel fuel and the content of linolenic acid methyl ester; it makes it possible to check that the ester content of a FAME exceeds 90 % (m/m) and that the linolenic acid methyl ester content lies between 1 % and 15 % (m/m). The precision was established on FAME with ester contents of 95 % and 100 % (m/m), that is around the limiting value; the method is also suitable outside that range, but the precision for lower concentrations requires further work. The method applies to FAME containing methyl esters from C6 to C24.
The 2020 edition replaced EN 14103:2011: a note on naturally occurring nonadecanoic acid methyl ester was added, a new procedure for checking the GC purity of the internal standard was introduced (the minimum purity was lowered from 99.5 to 99.0 % (m/m)), the theoretical correction factor of the flame ionisation detector (TCF), which improves the accuracy for short-chain esters, was brought into the calculations, a new interlaboratory study was carried out, the integration was changed (all the peaks and not only the identified FAME) and the test portion was increased from 100 mg to 250 mg. For FAME from an unidentified feedstock a solution without the standard is prepared in addition, to check for the absence of natural C19:0 or of other substances co-eluting with the standard.
The contents of fatty acid methyl esters and of linolenic acid methyl ester are parameters of the specification for FAME; in studies at the Oil and Gas Institute rapeseed esters (RME) from various producers had 98.6–98.8 % (m/m) of esters and 8.3–8.5 % (m/m) of linolenic acid methyl ester (according to PN-EN 14103:2012).
Method principle
The determination of the mass percentage of the total fatty acid methyl esters and of the mass percentage of linolenic acid methyl ester in the sample by gas chromatography with internal calibration (nonadecanoic acid methyl ester, FAME C19:0). About 250 mg of the homogenised FAME sample and about 100 mg of the standard (accuracy ± 0.1 mg) are diluted with 10 ml of toluene and 1 µl is analysed on a capillary column with a polyethylene glycol phase (for example 30 m × 0.25 mm × 0.25 µm) with a FID; all the peaks from hexanoic acid methyl ester (C6:0) to nervonic acid methyl ester (C24:1) are integrated. Other stationary phases have to be checked first — on a 70 % cyanopropyl polysilphenylene-siloxane (BPX70) C19:0 co-elutes with linoleic acid methyl ester (C18:2). The purity of the standard is checked for each batch by GC under the conditions of EN 14105 (a 15 m high-temperature column programmed to 400 °C) and taken into account in the calculations.
Applications
- Quality control of FAME (biodiesel) — an ester content above 90 % (m/m)
- Determination of linolenic acid methyl ester (the limit 1–15 % m/m) in rapeseed and other esters
- Assessment of FAME blending components for B7–B10 diesel fuels (studies at the Oil and Gas Institute)
- Determination of the profile of the fatty acid methyl esters (Annex C)
- Verification of the FAME feedstock (FAME from animal fats, used frying oils, fish oils — additional peaks)
Key parameters
| Parameter | Value |
|---|---|
| Range | Esters > 90 % (m/m); C18:3 1–15 % (m/m); FAME C6–C24; the precision established for 95 % and 100 % of esters |
| Internal standard | Nonadecanoic acid methyl ester C19:0, GC purity ≥ 99.0 % (m/m), water < 0.2 % (m/m) (Karl Fischer) |
| Test portions | ≈ 250 mg of FAME + ≈ 100 mg of C19:0 (± 0.1 mg) in 10 ml of toluene; the samples and the standard ≥ 3 h at ambient temperature before weighing |
| Column | Polyethylene glycol (Carbowax 20M), 30 m × 0.25 mm, film 0.25 µm |
| Example conditions | 60 °C (2 min) → 10 °C/min to 200 °C → 5 °C/min to 240 °C (7 min); injector and detector 250 °C; 1 µl; split 100 ml/min; H2 70 kPa, flow 1–2 ml/min |
| Integration | All the peaks from C6:0 to C24:1, with C24:0 and C24:1 visible |
Standard
- Standard number
- PN-EN 14103:2020-06
- Title (PL)
- Produkty przetwarzania olejów i tłuszczów — Estry metylowe kwasów tłuszczowych (FAME) — Oznaczanie zawartości estrów i estru metylowego kwasu linolenowego
- Title (EN)
- Fat and oil derivatives — Fatty Acid Methyl Esters (FAME) — Determination of ester and linolenic acid methyl ester contents
Step-by-step procedure
-
Check of the purity of the standard
For each new batch of C19:0 prepare a solution of about 1 mg/ml in toluene and analyse 1 µl on the 15 m high-temperature column (50 °C 1 min → 15 °C/min to 180 °C → 7 °C/min to 230 °C → 10 °C/min to 370 °C, 15 min; detector 380 °C; H2 80 kPa); analyse 1 µl of toluene as well. Calculate the purity P from all the peaks apart from the solvent and take it into account in the calculations.
-
Conditioning
Leave the standard and the FAME samples in closed containers for at least 3 h at ambient temperature before weighing, so as to limit the uptake of water.
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Preparation of the solution
Weigh accurately about 250 mg (± 0.1 mg) of the homogenised FAME sample into a 10 ml tube and about 100 mg (± 0.1 mg) of C19:0; dilute with 10 ml of toluene. For FAME from an unidentified feedstock prepare a solution without the standard as well, to check for the presence of natural C19:0 or of co-eluting substances (their area is to be subtracted from the area of the standard).
-
GC analysis
Inject 1 µl of the solution onto the polyethylene glycol column under conditions chosen to suit the column and the carrier gas (example: 60 °C 2 min → 10 °C/min to 200 °C → 5 °C/min to 240 °C, 7 min; injector and detector 250 °C; split 100 ml/min; a flow of ≥ 1 ml/min at the maximum temperature).
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Identification and integration
Choose the conditions so that the peaks of the esters of lignoceric acid (C24:0) and of nervonic acid (C24:1) are properly visible. Integrate all the peaks from C6:0 to C24:1; commercial solutions may be used for the identification. Take into account the additional peaks from ruminant fats (odd-numbered, branched) and the isomers from frying oils; small unknown peaks between C18:3 and C24:1 may indicate fish oil.
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Calculation
Calculate the ester content (9.1) and the linolenic acid methyl ester content (9.2) from the peak areas and the area of the internal standard, taking into account the purity of the standard and the theoretical FID correction factor; the result in % (m/m) (9.3).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Gas chromatograph | With a split injector or an equivalent, a programmable oven and a flame ionisation detector | — |
| Capillary column | A polyethylene glycol phase (Carbowax 20M), 30 m × 0.25 mm × 0.25 µm | — |
| High-temperature column for checking the purity of the standard | 15 m × 0.32 mm × 0.1 µm, 100 % dimethylpolysiloxane or 95 % dimethyl-5 % diphenylpolysiloxane, programmed to 400 °C, an on-column injector | — |
| Disposable 10 ml glass tubes with stoppers, a 10 ml pipette | For the preparation of the solution of the sample | — |
| Analytical balance | Accuracy ± 0.1 mg | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Toluene | 108-88-3 | Analytical grade, free of impurities eluting after the C6:0 methyl ester |
| Nonadecanoic acid methyl ester (FAME C19:0) | 1731-94-8 | GC purity ≥ 99.0 % (m/m), checked for each batch; keep it in a desiccator; water < 0.2 % (m/m) by Karl Fischer; do not use it at a purity below 99.0 % |
| Carrier gas: hydrogen or helium | — | Purity ≥ 99.9995 %, GC grade, dried, the oxygen removed by filters (< 0.1 mg/kg), free of organic impurities |
| Auxiliary gases: hydrogen and air | — | GC grade, free of organic impurities |
Health and safety (OHS)
- Toluene is flammable and harmful — prepare the solutions in a fume hood, nitrile gloves
- Hydrogen as the carrier gas and as the fuel of the FID — check the tightness, a hydrogen sensor in the laboratory
- The hot zones of the chromatograph (injector and detector at 250 °C, the HT column up to 400 °C) — care when changing columns
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 14103:2020-06 — “Fat and oil derivatives — Fatty Acid Methyl Esters (FAME) — Determination of ester and linolenic acid methyl ester contents”.
How does this method work?
The determination of the mass percentage of the total fatty acid methyl esters and of the mass percentage of linolenic acid methyl ester in the sample by gas chromatography with internal calibration (nonadecanoic acid methyl ester, FAME C19:0). About 250 mg of the homogenised FAME sample and about 100 mg of the standard (accuracy ± 0.
What is the measuring range and accuracy?
Range: Esters > 90 % (m/m); C18:3 1–15 % (m/m); FAME C6–C24; the precision established for 95 % and 100 % of esters; Internal standard: Nonadecanoic acid methyl ester C19:0, GC purity ≥ 99.0 % (m/m), water < 0.2 % (m/m) (Karl Fischer); Test portions: ≈ 250 mg of FAME + ≈ 100 mg of C19:0 (± 0.1 mg) in 10 ml of toluene; the samples and the standard ≥ 3 h at ambient temperature before weighing; Column: Polyethylene glycol (Carbowax 20M), 30 m × 0.25 mm, film 0.25 µm.
How long does the test take?
The times given for the individual stages add up to approximately 3 h. The procedure comprises 6 steps.
What equipment is required?
Gas chromatograph, Capillary column, High-temperature column for checking the purity of the standard, Disposable 10 ml glass tubes with stoppers, a 10 ml pipette, Analytical balance.
Where is this test used?
Quality control of FAME (biodiesel) — an ester content above 90 % (m/m); Determination of linolenic acid methyl ester (the limit 1–15 % m/m) in rapeseed and other esters; Assessment of FAME blending components for B7–B10 diesel fuels (studies at the Oil and Gas Institute); Determination of the profile of the fatty acid methyl esters (Annex C); Verification of the FAME feedstock (FAME from animal fats, used frying oils, fish oils — additional peaks).
What safety precautions apply?
Toluene is flammable and harmful — prepare the solutions in a fume hood, nitrile gloves; Hydrogen as the carrier gas and as the fuel of the FID — check the tightness, a hydrogen sensor in the laboratory; The hot zones of the chromatograph (injector and detector at 250 °C, the HT column up to 400 °C) — care when changing columns.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 14103.