Analysis of Free and Total Glycerol in B-100 Biodiesel Methyl Esters Using Agilent Select Biodiesel for Glycerides

Significance of the topic

Monitoring free and total glycerol, as well as mono-, di-, and triglycerides in biodiesel is essential for product quality, engine performance and compliance with international standards. Precise quantification of these impurities helps prevent engine deposits, filter clogging and corrosion, ensuring reliable fuel performance in variable climatic conditions.

Study objectives and overview

The application note demonstrates an analytical workflow based on ASTM D6584 for determination of free and bound glycerol in B-100 fatty acid methyl esters (FAME). Key aims include:

• Quantifying free glycerol and bound glycerol (mono-, di-, triglycerides) in biodiesel samples.
• Validating method performance, linearity and repeatability using spiked and commercial biodiesel.

Methodology and instrumentation

Sample derivatization and GC-FID analysis were performed as follows:

• Derivatization with N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) in the presence of pyridine.
• On-column injection of 1 µL sample into an Agilent Select Biodiesel for Glycerides UltiMetal capillary column (0.32 mm × 10 m, 0.1 µm, with retention gap).
• Oven temperature program from 50 °C to 380 °C (ramp rates of 15, 7 and 30 °C/min) to achieve baseline separation.
• Helium carrier gas (3 mL/min) and flame ionization detection at 380 °C.
• Internal standards: 1,2,4-butanetriol and 1,2,3-tricaproylglycerol.

Main results and discussion

Calibration curves for glycerol, monoolein, diolein and triolein exhibited excellent linearity (r2 ≥ 0.9994). The method’s detection ranges are 0.005–0.05 % (m/m) for free glycerol and 0.05–0.5 % for total glycerol. Repeatability tests (n=21 injections) showed retention time RSD of 0.022 min and concentration RSD below 3 % for glycerol, within ASTM tolerance. Chromatograms demonstrated clear peak resolution and low column bleed up to 380 °C.

Benefits and practical applications

• High robustness and longevity of the UltiMetal column under extreme temperature conditions.
• Pre-installed retention gap reduces risk of column coupling errors and enhances reproducibility.
• Compatible with various feedstocks (rapeseed, sunflower, soybean) except lauric oils due to peak overlap.
• Ensures compliance with ASTM D6751 and EN-14105 specifications for biodiesel blends.

Future trends and potential applications

• Integration with automated sample preparation and online derivatization to increase throughput.
• Application of alternative derivatization reagents or detectors (e.g., mass spectrometry) for improved sensitivity and selectivity.
• Extension of method to emerging feedstocks and advanced bio-lubricants.
• Data-driven optimization of temperature programs using digital twins or AI-based modeling.

Conclusion

The described GC-FID method on the Agilent Select Biodiesel for Glycerides UltiMetal column delivers accurate, repeatable quantification of glycerol derivatives in biodiesel. It meets industry standards for free and total glycerol content and offers a robust solution for routine quality control in biodiesel production and blending operations.

References

1. ASTM D6584–07. Test Method for Free and Total Glycerine in B-100 Biodiesel Methyl Esters by Gas Chromatography.
2. Knothe G. (2006) Analyzing Biodiesel: Standards and other Methods. JAOCS 83, 823–833.
3. ASTM D6751–06a. Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels.