Biodiesel quality assessment: an automated approach for analysis of free and total glycerol content in biodiesel (B100), according to the EN 14105 and ASTM D6584 methods

Importance of the Topic

Biodiesel (B100) produced via transesterification requires stringent quality control to ensure safe and efficient engine performance. Residual free glycerol and glycerides can cause injector clogging, deposit formation, and reduced fuel stability. Conventional manual sample preparation for glycerol analysis is time-consuming, involves hazardous reagents, and is prone to human error. Automating these procedures enhances throughput, precision, and operator safety.

Study Objectives and Overview

This study demonstrates the application of the Thermo Scientific™ TriPlus™ RSH SMART robotic autosampler coupled with the TRACE™ 1610 GC-FID system for fully automated sample preparation and online analysis of free and total glycerol in biodiesel (B100). The goal is to validate compliance with EN 14105 and ASTM D6584 methods, evaluating calibration, derivatization, chromatographic performance, and overall robustness.

Instrumentation

• Automated sample preparation: TriPlus RSH SMART robotic autosampler with Advanced Tool Change (ATC), solvent and wash stations, vortex mixer, and 10 mL headspace vial configuration.
• Gas chromatography: TRACE 1610 GC equipped with iConnect PTV injector operating in simulated cold on-column mode and iConnect FID detector.
• Analytical column: TraceGOLD TG-BIOD, 15 m × 0.32 mm × 0.10 μm with guard, and PTV Silcosteel liner for on-column injection.

Methodology

Automated workflows were developed for both EN 14105 and ASTM D6584:

• Weigh 100 mg biodiesel sample into 10 mL vial.
• Add internal standards (1,2,4-butanetriol for glycerol; tricaprin or glyceride mix for ASTM and EN methods).
• Derivatize with MSTFA reagent, vortex, and incubate for 15 min.
• Quench with n-heptane, vortex, and automatically inject 0.5 μL into GC-FID.
• GC conditions: H₂ carrier, temperature ramp from 50 °C to 380 °C, total run time ≈ 32 min (ASTM) or ≈ 46 min (EN).

Results and Discussion

• Calibration curves for glycerol and glycerides showed excellent linearity (r² = 0.999), surpassing method requirements.
• Repeatability studies (n = 21 for ASTM; n = 10 for EN) demonstrated consistent quantitation with %RSD and repeatability values within specified limits.
• Carry-over tests across 30 consecutive samples confirmed negligible system contamination.
• Analysis of unknown biodiesel and certified reference materials yielded total glycerol contents below the maximum limits (0.24% m/m), validating method accuracy.

Benefits and Practical Applications

Automating biodiesel quality assessment offers:

• Unattended processing of up to 30 samples, freeing analyst time for data review.
• Improved data precision and traceability via SMART syringe identification and CDS integration.
• Reduced exposure to hazardous chemicals and minimized cross-contamination.
• Streamlined compliance with EN and ASTM standards for industrial and regulatory laboratories.

Future Trends and Opportunities

The integration of advanced robotics with chromatography systems will continue to evolve, enabling:

• Higher throughput platforms and multiplexed derivatization protocols.
• Enhanced data integrity and regulatory compliance through secure CDS solutions.
• Adaptation of the automated workflows to additional analytes and fuel matrices (e.g., blends B5–B20).
• Potential coupling with mass spectrometry for expanded impurity profiling.

Conclusion

The fully automated TriPlus RSH SMART autosampler and TRACE 1610 GC-FID workflow efficiently meets the analytical requirements of EN 14105 and ASTM D6584 for biodiesel glycerol assessment. It delivers high accuracy, reproducibility, and safety, making it an effective solution for routine quality control in biodiesel production.

Reference

1. ASTM D6584-21. Standard Test Method for Determination of Total Monoglycerides, Total Diglycerides, Total Triglycerides, and Free and Total Glycerin in B100.
2. EN 14105. Fat and Oil Derivatives – Determination of Free and Total Glycerol and Mono-, Di-, Triglyceride Contents, September 2021.
3. EN 14110. Fat and Oil Derivatives – Determination of Methanol Content, June 2020.
4. EN 14103. Fat and Oil Derivatives – Determination of Total FAMEs and Linolenic Acid Methyl Ester Content, December 2020.
5. Thermo Fisher Scientific. Application Note 001898: Biodiesel Quality Assessment by Headspace Sampling per EN 14110.
6. Thermo Fisher Scientific. Application Note 001899: Biodiesel Quality Assessment by GC-FID per EN 14103.
7. ASTM D6751-20a. Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels.
8. EN 14214:2012+A2:2019. Fatty Acid Methyl Esters (FAME) for Diesel Engines – Requirements and Test Methods.
9. Thermo Fisher Scientific. Guide EB000396: Automated Sample Preparation for GC and GC-MS.
10. Thermo Fisher Scientific. Brochure BR52235-EN: TriPlus RSH SMART Robotic Sampling System.