Determination of Benzene and Toluene in Gasoline by ASTM D3606 on an Agilent 8890 GC with Capillary Columns

Significance of the Topic

The accurate determination of benzene and toluene in gasoline is critical for environmental compliance and quality control, especially following stringent regulatory limits on benzene content in fuels.

Study Aims and Overview

This study applied ASTM D3606 Method A using an Agilent 8890 gas chromatograph equipped with capillary columns, a midcolumn backflush and a monitor channel. It compared performance using helium and hydrogen carrier gases and assessed method robustness and regulatory compliance.

Instrumentation

• Agilent 8890 Gas Chromatograph
• Columns: HP-1ms Ultra Inert (30 m × 250 µm, 0.5 µm), DB-WAXetr (60 m × 320 µm, 1.0 µm), fused silica guard segment (0.57 m × 100 µm)
• Two flame ionization detectors (FID)
• Two-way splitter with pneumatic switching device for backflush

Methodology

A seven-level calibration (benzene 0.06–5% v/v, toluene 0.5–20% v/v) used methyl isobutyl ketone as internal standard. Samples of gasoline were spiked with IS. The backflush timing was optimized by monitoring baseline return after toluene elution. Method translation tools adjusted column flows to replace helium with hydrogen while preserving retention times.

Main Results and Discussion

• Resolution (ethanol/benzene > 15), (benzene/IS > 21), (IS/toluene > 17), exceeding ASTM criteria.
• Calibration linearity R² > 0.999 for both gases; S/N for benzene > 190:1.
• Repeatability and sample analyses passed 95% confidence intervals for both carrier gases.
• Hydrogen carrier delivered comparable chromatograms and retention times to helium, with similar peak shapes.

Benefits and Practical Applications of the Method

• Reduced run times and gas consumption using capillary columns and hydrogen carrier.
• Improved column longevity and maintenance efficiency via backflush.
• Compliance with regulatory limits for benzene in automotive fuels.
• Feasible monitoring for QA/QC in fuel production and environmental laboratories.

Future Trends and Potential Applications

• Extending backflush configurations to other complex fuel matrices.
• Integration of advanced software for automated method translation across carrier gases and column geometries.
• Use of alternative green carrier gases and detector technologies to further optimize throughput and sustainability.
• Application of machine learning algorithms for predictive retention modeling and method development.

Conclusion

The described capillary column method with midcolumn backflush reliably quantifies benzene and toluene in gasoline, meeting ASTM D3606 requirements. Hydrogen serves as an effective carrier gas alternative to helium, offering cost and efficiency benefits.

Reference

1. Federal Register, Vol. 72, No. 37, February 26, 2007. Control of Hazardous Air Pollutants from Mobile Sources, U.S. EPA.
2. ASTM Standard D3606-17. Determination of Benzene and Toluene in Spark Ignition Fuels by GC, ASTM International.
3. Fitz B. Using the PSD for Backflushing on the Agilent 8890 GC System, Agilent Technologies Application Note, 2018.