The Determination of Benzene and Toluene in Finished Gasolines Containing Ethanol Using the PerkinElmer Clarus 680 GC with Swafer Technology

Importance of the Topic

Gasoline is a complex matrix containing volatile organic compounds such as benzene and toluene. These compounds are regulated due to their toxicity and contribution to air pollution. Modern fuel formulations often include ethanol to improve combustion efficiency and reduce greenhouse gases. However, ethanol presence complicates chromatographic analysis by co-eluting with target analytes when using traditional packed-column methods. Developing a rapid, robust technique to quantify benzene and toluene in ethanol-blended gasoline is vital for quality control, regulatory compliance, and environmental monitoring.

Objectives and Study Overview

This study aimed to adapt ASTM D-3606 for finished gasoline containing ethanol by replacing packed columns with capillary columns and integrating backflush control via Swafer technology. Key goals included eliminating ethanol interference, improving chromatographic resolution, and cutting analysis time by up to 75%. A PerkinElmer Clarus 680 GC system was configured in a two-column backflush arrangement to evaluate method performance across a range of standard and real gasoline samples.

Methodology and Instrumentation

Instrumentation Used:

• PerkinElmer Clarus 680 gas chromatograph with a programmable split/splitless injector (PSS)
• Swafer S6 backflush module and utility software for pressure programming
• Flame ionization detector (FID) operated at 200 °C
• Capillary precolumn: 30 m × 0.25 mm × 0.25 µm PDMS (Elite-1)
• Analytical capillary column: 50 m × 0.25 mm × 0.4 µm TCEP
• Fused silica restrictor: 60 cm × 0.10 mm between precolumn and detector

Chromatographic Conditions:

• Oven held isothermal at 100 °C for 4 min with 0.5 min equilibration
• Carrier gas: hydrogen at 30 psig (inlet) and 20 psig (midpoint) for 1.61 min, then adjusted to 5 psig and 25 psig respectively for backflush
• Sample injection: 0.3 µL of gasoline solution containing 2-butanol internal standard (1 mL per 25 mL)

Results and Discussion

Chromatographic Performance:
Baseline separation of ethanol, benzene, 2-butanol (internal standard), and toluene was achieved within a 4 min runtime. Backflush programming efficiently removed matrix components from the precolumn, protecting the analytical column. Monitoring both precolumn and analytical column responses in a single run facilitated precise determination of the backflush point and provided QC records unavailable in the original ASTM method.
Linearity and Precision:
Seven calibration solutions (benzene 0.06–5 % v/v; toluene 0.5–20 % v/v) exhibited correlation coefficients (R2) of 0.9995 for benzene and 0.9992 for toluene. Quantitative repeatability over 100 injections of a gasoline sample yielded relative standard deviations (RSD) of 0.5 % for benzene and 1.6 % for toluene, surpassing D-3606 requirements. Retention time precision (RSD < 0.03 %) confirmed method robustness.
Carry-over Assessment:
Following a high-level standard (toluene 20 % v/v), solvent blank injections showed carry-over below 0.016 %, translating to an interference of 0.0026 % v/v—well below regulatory thresholds.

Benefits and Practical Use

The capillary-column Swafer GC method offers:

• Faster analysis: runtime reduced from ~8–16 min to 4 min, with a 5.4 min cycle enabling 88 samples per shift
• Enhanced selectivity: complete elimination of ethanol interference
• Improved data quality: stable baselines, minimal drift, and precise backflush control
• Cost savings: use of hydrogen carrier gas and reduced cycle times

Future Trends and Opportunities

Emerging developments include advanced column chemistries tailored for biofuel matrices, integration of automated pressure programming with real-time data analytics, and coupling with mass spectrometry for expanded analyte panels. Miniaturized backflush modules and multi-detector configurations may further increase throughput and method versatility in on-line monitoring and refinery process control.

Conclusion

This adapted ASTM D-3606 method employing capillary columns and Swafer backflush technology provides a rapid, reliable, and sensitive approach for quantifying benzene and toluene in ethanol-blended gasoline. It overcomes co-elution challenges, meets stringent precision and carry-over requirements, and significantly enhances sample throughput.

Reference

Tipler A. The Determination of Benzene and Toluene in Finished Gasolines Containing Ethanol Using ASTM D-3606 on PerkinElmer Clarus 680 GC. Application Note. PerkinElmer, Inc.; 2010.