Determination of Free and Total Glycerin inPure Biodiesel (B100) by GC in Compliancewith EN 14105

Significance of the Topic

Biodiesel (B100) is a renewable alternative to conventional diesel, offering lower emissions and improved sustainability. Monitoring free and total glycerin content is essential to certify product quality, prevent engine deposits, and comply with international standards such as EN 14105 and EN 14214.

Objectives and Study Overview

This study presents a validated gas chromatographic method for determining free and total glycerin in pure biodiesel. It demonstrates the use of a TRACE GC Ultra system combined with a TriPlus autosampler to achieve accurate, precise, and reproducible results in full compliance with EN 14105 requirements.

Applied Instrumentation

• TRACE GC Ultra gas chromatograph with true cold on‐column injector
• TriPlus liquid autosampler
• Flame ionization detector (FID)
• Thermo Scientific TRACE TR-BIODIESEL(G) column (10 m × 0.32 mm, 0.1 μm film) with 1 m × 0.53 mm ID pre-column
• High-temperature purged metal tee connector

Methodology

Samples and calibration standards were derivatized with MSTFA in pyridine to convert glycerin and glycerides into volatile silylated derivatives. Two internal standards (1,2,4‐butanetriol for glycerin and tricaprin for glycerides) and a four‐component calibration series (glycerin, monoolein, diolein, triolein) were used to establish linearity. Automated injections of 1 µL were performed under the following conditions:

• Carrier gas: Helium at 3 mL/min ramping to 5 mL/min
• Oven program: 80 °C (1 min) to 180 °C @15 °C/min, to 230 °C @7 °C/min, to 365 °C @10 °C/min (4 min)
• FID temperature: 380 °C

Sample preparation involved weighing ~100 mg biodiesel, adding internal standards and MSTFA, reacting 15 min, diluting with n‐heptane, and injecting the upper phase.

Main Results and Discussion

Calibration curves exhibited excellent linearity (r² > 0.997) across four concentration levels. Typical biodiesel chromatograms showed clear separation of free glycerin, mono-, di- and tri-glycerides with no carryover observed in blank runs. Repeatability tests met EN 14105 criteria, with absolute differences within prescribed limits (e.g., free glycerin ±0.0018 % m/m).

Benefits and Practical Applications

• True cold on‐column injection prevents discrimination of heavy glycerides and preserves labile compounds.
• High‐temperature column and purged connections offer robust performance and long lifetime.
• Automated derivatization and injection workflow enhance throughput and reproducibility.
• Compliance with EN 14105 and compatibility with EN 14214 specifications ensures regulatory acceptance.

Future Trends and Opportunities

Advances may include adaptation for alternative feedstocks (e.g., waste oils), coupling with mass spectrometry for enhanced identification, inline derivatization modules, and integration into Process Analytical Technology (PAT) frameworks for real‐time monitoring.

Conclusion

The presented GC‐FID method on the TRACE GC Ultra system, with true cold on‐column injection and TriPlus autosampler, delivers reliable, precise, and compliant determination of free and total glycerin in pure biodiesel. Its robustness and automation support quality control in biodiesel production and blending operations.

References

1. ASTM D6751: Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels.
2. EN 14214: Automotive fuels – Fatty Acid Methyl Esters (FAME) for diesel engines – Requirements and test methods.
3. EN 14103: Determination of total FAMEs and linolenic methyl ester content.
4. Thermo Scientific Application Note AN10212: Determination of Total FAME and Linolenic Acid Methyl Ester in Pure Biodiesel (B100) by GC in Compliance with EN 14103.
5. EN 14105: Determination of free and total glycerol and mono-, di-, tri-glyceride content.
6. ASTM D6584: Test Method for Determination of Free and Total Glycerin in B-100 Biodiesel by GC.
7. Thermo Scientific Application Note AN10192: Determination of Free and Total Glycerin in B-100 Biodiesel via ASTM D6584.
8. EN 14110: Determination of residual methanol in FAME by GC.
9. Thermo Scientific Application Note AN10216: Determination of Methanol Content in Pure Biodiesel (B100) by Headspace-GC in Compliance with EN 14110.