Reliable Analysis of Glycerin in Biodiesel Using a High-Temperature Non-metal GC Column

Importance of the Topic

Over the past decade biodiesel has become a key renewable fuel alternative derived from common feedstocks. Ensuring low glycerin content is critical to avoid clogged filters and pressure drops and thus maintain engine reliability and compliance with ASTM and DIN quality standards.

Objectives and Study Overview

This study evaluates a novel high temperature fused silica column, Zebron ZB-5HT Inferno, designed for stability up to 430 C, comparing its thermal lifetime and bleed performance against leading columns DB-5ht and VF-5ht at 400 C. The method follows ASTM D 6584 for free and total glycerin analysis in biodiesel.

Methodology

• Lifetime comparison: Columns exposed to 400 C for 100 hours in cycles of 2 h hold then 50 injections of pentadecane at 120 C
• Bleed profile: Measured FID signal during oven ramp from 120 to 400 C with null injection at 250 C
• Biodiesel analysis: Samples derivatized with MSTFA and analyzed by GC under ASTM D 6584 conditions

Used Instrumentation

• Zebron ZB-5HT Inferno capillary column 15 m × 0.32 mm × 0.10 μm
• High temperature guard column 2 m × 0.53 mm
• HP 6890 gas chromatograph with cool on column injector
• Flame ionization detector

Main Results and Discussion

The Zebron column maintained consistent pentadecane retention for 80 hours at 400 C, twice the lifetime of DB-5ht. The VF-5ht failed after 40 hours. Bleed levels of ZB-5HT remained below MS certification limits even at 360 C and were significantly lower than DB-5ht at 380 C and above. Calibration of reference compounds yielded r2 above 0.99 and peak shapes for glycerol and internal standards demonstrated low activity and reliable quantitation.

Benefits and Practical Application

• Extended column lifetime reduces analysis cost per sample
• Lower bleed enhances detection sensitivity and reliability at high temperatures
• Compatibility with standard diesel engines and compliance with ASTM D 6584 enables routine quality control in biodiesel production

Future Trends and Possibilities

Advances in high temperature column chemistry may lead to further increases in thermal stability and reduced maintenance. Integration with automated sample derivatization and high throughput platforms could streamline glycerin analysis and support growing biodiesel markets.

Conclusion

The Zebron ZB-5HT Inferno column offers superior thermal stability, lower bleed, and extended lifetime for high temperature GC analysis of free and total glycerin in biodiesel. Its performance under ASTM D 6584 conditions can lower operational costs and improve method robustness.

References

1. Van Gerpen J Shanks B Pruszko R Clements D Knothe G Biodiesel Analytical Methods National Renewable Energy Laboratory 2004
2. ASTM Standard D 6584 00 Test Method for Determination of Free and Total Glycerin in B100 Biodiesel Methyl Esters by Gas Chromatography ASTM International 2000