Determination of Olefin Content in Gasoline According to ASTM D6550

Significance of the Topic

Olefins in gasoline are highly reactive hydrocarbons that contribute to photochemical smog and ground-level ozone. Regulatory bodies such as the California Air Resources Board set maximum olefin limits to protect air quality. Reliable, precise measurement of total olefin content is therefore essential for producers and compliance laboratories.

Objectives and Study Overview

This study evaluates the performance of an Agilent 1260 Infinity Analytical SFC System coupled with a proprietary SIM flame ionization detector for quantifying olefin levels in gasoline according to ASTM D6550. The approach focuses on achieving required retention time precision for time-based valve switching, robust area repeatability, and a validated calibration function.

Methodology and Instrumentation

A two-column supercritical fluid chromatography (SFC) arrangement is used to separate saturates, aromatics and olefins. In forward-flush mode, saturates elute first while aromatics and oxygenates are retained. A timed valve switch initiates backflush of the silica column to elute aromatics, followed by backflush of the silver-loaded column to release trapped olefins. Carbon dioxide serves as the mobile phase, and hexane is used to purge the backpressure regulator.

Instrumentation Used

• Agilent 1260 Infinity Binary SFC Pump
• Agilent 1260 Infinity SFC Control Module
• Agilent 1290 Infinity Thermostatted Column Compartments (two units with 2-position/6-port valves)
• SIM Scientific Instruments Flame Ionization Detector (FID)
• CTC Analytics HTC PAL autosampler with 4-port valve
• Pursuit XRs 5 Si column (4.6 × 250 mm) and ChromSpher 5 Lipids silver-loaded column (4.6 × 30 mm)

Main Results and Discussion

Performance Test Mixture injections confirmed olefin-aromatic resolution (RAO) of 6.2 (method requirement ≥ 3). Retention time RSD values for hexane, toluene, and 3-methyl-2-pentene were ≤ 0.13 % and area RSDs ≤ 1.26 %. Calibration over five concentration levels (1.25–20 mass %) yielded linearity of R² = 0.99997. A real gasoline sample measured in 20 replicates gave an olefin content of 12.8 mass % with RSD 1.54 % (0.2 mass % absolute), meeting the ASTM repeatability limit of 0.7 mass %.

Benefits and Practical Applications

• Meets stringent ASTM D6550 requirements for retention time and area precision
• Efficient separation via timed valve-switching and backflush modes
• High sensitivity and linear response for low‐to‐high olefin concentrations
• Applicable to compliance testing, quality control, and regulatory analysis

Future Trends and Opportunities

Advances in detector sensitivity and automation may further reduce detection limits and analysis time. Integration with online sampling and enhanced software control will support high-throughput screening. Expansion of SFC methods to renewable and bio‐derived fuel blends will address emerging regulatory needs and sustainability goals.

Conclusion

The combined SFC/FID setup provides a robust, accurate, and reproducible solution for olefin determination in gasoline, fully compliant with ASTM D6550. Its reliable performance and streamlined workflow make it ideal for routine regulatory and quality assurance laboratories.

References

1. California Air Resources Board. The California Reformulated Gasoline Regulations, Title 13, California Code of Regulations, Sections 2250–2273.5 (2008).
2. ASTM D6550-10 (2009). Standard Test Method for Determination of Olefin Content of Gasoline by Supercritical-Fluid Chromatography.
3. ASTM D5186-03 (2009). Standard Test Method for Determination of the Aromatic Content and Polynuclear Aromatic Content of Diesel Fuels and Aviation Turbine Fuels by Supercritical Fluid Chromatography.
4. Noll-Borchers M, Hölscher T, Naegele E, Becker M. Determination of Aromatic Content in Diesel Fuel According to ASTM D5186. Agilent Technologies Application Note 5991-5682EN (2015).