Determination of Total FAME and Linolenic Acid Methyl Ester in Pure Biodiesel (B100) by GC in Compliance with EN 14103

Significance of the Topic

Biodiesel purity and fatty acid distribution directly influence fuel performance and engine safety. Accurate quantification of total fatty acid methyl esters (FAME) and linolenic acid methyl ester is critical for determining cetane number and ensuring compliance with industry standards ASTM D6751 and EN 14214.

Objectives and Study Overview

This study aims to apply EN 14103 to measure the total FAME content and linolenic acid methyl ester in B100 biodiesel. By using gas chromatography with a programmable temperature vaporizing injector and backflush capability, the method ensures precise ester determination and contaminant removal.

Methodology

• Sample Preparation: Approximately 250 mg of biodiesel is weighed and diluted with 5 mL internal standard solution (10 mg/mL methyl heptadecanoate).
• PTV Backflush: Heavy glyceride fractions are vented after 3 min to prevent column contamination while allowing complete transfer of FAMEs.
• Temperature Program: Start at 120 °C (0.5 min), ramp to 220 °C at 30 °C/min, then to 250 °C at 10 °C/min, hold 5 min.
• Injection: 1 µL in split mode, split flow 100 mL/min.
• Carrier Gas: Helium at 2 mL/min constant flow.
• Detection: Flame ionization detector at 280 °C.

Instrumentation

• Gas Chromatograph: Thermo Scientific TRACE GC Ultra with PTV inlet and backflush accessory.
• Autosampler: TriPlus liquid autosampler.
• Column: TRACE TR-BIODIESEL(F), 30 m × 0.25 mm ID, 0.25 µm film thickness.
• Software: Thermo Scientific Chrom-Card data system.
• Internal Standard: Methyl heptadecanoate (C17:0).

Main Results and Discussion

Both a reference rapeseed biodiesel and an unknown sample achieved total FAME >96.5% m/m and linolenic acid methyl ester <12% m/m, satisfying EN 14214 criteria. Repeatability tests (n=10) yielded %RSD of 0.35 for total FAME and 0.19 for linolenic acid, well below the maximum allowable %RSD, demonstrating robust precision and stable retention times (~0.05% RSD).

Benefits and Practical Applications

• High analytical precision and compliance with EN 14103.
• Extended column lifetime through PTV backflush, eliminating heavy contaminant buildup.
• Simultaneous profiling of FAME composition (C14–C24) and quantification of free methanol (via liquid or headspace injection).
• Suitable for routine quality control in biodiesel production and blending operations.

Future Trends and Potential Uses

Advancements may include coupling GC to mass spectrometry for enhanced structural insights, miniaturized PTV designs for high-throughput labs, automated on-line sampling directly from production lines, and expanded method adaptation to second-generation biofuels and alternative ester distributions.

Conclusion

The described TRACE GC Ultra method with PTV backflush and FID detection delivers a reliable, repeatable, and standards-compliant protocol for assessing total FAME and linolenic acid methyl ester in pure biodiesel, ensuring fuel quality and regulatory adherence.

References

• ASTM D6751: Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels.
• EN 14214: Automotive fuels – Fatty Acid Methyl Esters (FAME) for diesel engines – Requirements and test methods.
• EN 14103: Fat and oil derivatives – FAME – Determination of ester and linolenic acid methyl esters content.
• EN 14105 / ASTM D6584: FAME – Determination of free and total glycerol content.
• EN 14110: FAME – Determination of methanol content.
• Thermo Scientific AN10192: Free and Total Glycerin in B-100 Biodiesel via ASTM D6584.
• Thermo Scientific AN10215: Free and Total Glycerin in Pure Biodiesel by GC / EN 14105.
• Thermo Scientific AN10216: Methanol Content in Pure Biodiesel by Headspace-GC / EN 14110.