Determination of Free and Total Glycerol in Biodiesel Samples by HPAE-PAD Chromatography

Importance of the topic

Accurate quantification of free and total glycerol in biodiesel is essential to maintain engine performance, prevent filter clogging, ensure compliance with ASTM regulatory limits, and support sustainable biofuel production.

Objectives and study overview

This work presents a high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) method for quantifying free glycerol and total glycerol (after base hydrolysis) in various biodiesel samples, including B100 and blends from multiple feedstocks.

Methodology and instrument setup

Sample preparation involved aqueous extraction for free glycerol and potassium hydroxide reflux hydrolysis for total glycerol. Chromatography was performed on a Thermo Scientific Dionex ICS-3000 system equipped with a CarboPac MA1 guard (4×50 mm) and analytical (4×250 mm) columns, using 100 mM NaOH eluent at 0.40 mL/min and 30 °C. Detection employed a gold working electrode with a four-potential carbohydrate waveform.

Main results and discussion

The method achieved baseline separation of glycerol within 11 min with symmetric peaks (As≈1.1), linear response from 0.05 to 10 mg/kg (r²=0.9998), an LOD of 0.5 µg/kg, and an LOQ of 2.4 µg/kg. Precision (n=7) yielded RSDs <1% for retention time and <3% for peak area. Spike recoveries ranged from 93.9% to 104.4% (free glycerol) and 92.1% to 100.0% (total glycerol). Free glycerol concentrations in biodiesel samples ranged from 0.02 to 12 mg/kg, and total glycerol from 0.064 to 200 mg/kg, all meeting ASTM D6751 specifications.

Benefits and practical applications

The described HPAE-PAD approach requires no derivatization, offering a sensitive, selective, and relatively rapid analysis suited for routine quality control in biodiesel production and regulatory compliance.

Future trends and possibilities

Further developments may include automated sample handling, on-line coupling with mass spectrometry for enhanced selectivity, miniaturized flow cells for reduced reagent consumption, and extension to other biofuel-related analytes.

Conclusion

The HPAE-PAD method with the CarboPac MA1 column and gold electrode provides a robust, precise, and accurate protocol for determining free and total glycerol in biodiesel, fulfilling industry and regulatory requirements.

Used instrumentation

• Thermo Scientific Dionex ICS-3000 HPAE-PAD system (DP/SP pump, AS autosampler, ED detector)
• Dionex CarboPac MA1 guard and analytical columns
• Gold working electrode with four-potential carbohydrate waveform
• Reflux distillation and hydrolysis apparatus for total glycerol

References

• UNEP-DTIE (2009) Towards Sustainable Production and Use of Resources: Assessing Biofuels
• Evans (2007) Liquid Transport Biofuels – Technology Status Report
• Meher et al. (2006) Technical Aspects of Biodiesel Production. Renewable and Sustainable Energy Reviews, 10, 248–268
• Ma & Hanna (1999) Biodiesel Production: a Review. Bioresource Technology, 70, 1–15
• McCormick & Westbrook (2007) Biodiesel and Biodiesel Blends. ASTM Standardization News