The Determination of C2 to C5 Hydrocarbons in Finished Gasolines using the PerkinElmer Clarus 680 GC with Swafer Technology

Importance of the Topic

Determination of light C2–C5 hydrocarbons in finished gasoline is essential for regulatory compliance, quality control and performance evaluation. Conventional ASTM D2427-06 workflows rely on packed columns and mechanical valves but struggle with modern fuel blends containing ethanol and oxygenates. Adoption of advanced capillary columns and backflush technology can enhance selectivity, reduce analysis time and eliminate costly carrier gases.

Objectives and Study Overview

This work aimed to adapt ASTM D2427-06 for a modern gas chromatograph by integrating a Swafer S6 backflush device and capillary columns to:

• Efficiently separate C2–C5 saturated and unsaturated hydrocarbons from higher boilers and polar interferents.
• Shorten total run time from over one hour to under 20 minutes.
• Maintain or improve precision and quantitative accuracy relative to method requirements.

Methodology and Instrumentation

A two-column backflush approach was implemented on a PerkinElmer Clarus 680 GC equipped with a Swafer S6 device. Key elements included:

• Precolumn: 30 m × 0.25 mm × 0.5 µm Elite Wax PLOT for initial elution of C2–C5 fraction.
• Analytical column: 50 m × 0.32 mm alumina PLOT for high-resolution separation.
• Backflush protocol: reversed carrier flow in the precolumn at 1.72 min to purge heavy compounds through split vent.
• Carrier gas: hydrogen for higher linear velocity, eliminating helium supply constraints.
• Detector: flame ionization (FID) monitored for both columns via a mid-column restrictor.
• Oven program: 40 °C hold for 2 min, ramp at 10 °C/min to 180 °C, 5 min hold.

Main Results and Discussion

Calibration with a refinery gas standard and an external n-pentane solution demonstrated consistent response factors (±10 %). Combined precolumn/PLOT chromatograms showed complete elution of C2–C5 analytes within 20 min with no interference from aromatics, MTBE or ethanol. Precision studies (n=10) on real gasoline yielded relative standard deviations <1 % for major C4–C5 components, surpassing ASTM D2427-06 requirements. Analyses of four gasoline samples of varying vintage confirmed detection limits and quantitative fidelity across complex matrices. A crude oil test illustrated robustness: heavy components were fully excluded, preserving column integrity.

Benefits and Practical Applications

• Run time reduced more than threefold, boosting sample throughput to 20 injections per 8 h shift.
• Enhanced method ruggedness by clean backflush of high boilers, protecting the analytical column.
• Hydrogen carrier gas avoids helium shortages and reduces operating costs.
• Single FID monitoring both columns simplifies setup and QC verification of backflush timing.
• External calibration strategy accommodates incompatible internal standards on alumina PLOT.

Future Trends and Potential Applications

The approach can be adapted for methane quantification and extended to C6–C8 hydrocarbons by modifying backflush timing or temperature programming. Combining advanced software-controlled pressure ramps with capillary backflush opens new avenues for rapid screening of volatile organics in complex matrices such as biofuels, petrochemical streams and environmental samples. Further integration with mass spectrometric detectors may enhance structural identification of trace aliphatic isomers.

Conclusion

Integration of modern capillary PLOT columns with Swafer backflush technology on a Clarus 680 GC successfully modernizes ASTM D2427-06, delivering faster, more reliable C2–C5 hydrocarbon analysis in gasoline and related samples. The method meets stringent precision and accuracy targets, offers significant time and cost savings, and exhibits broad applicability to diverse matrices.