Detailed Hydrocarbon Analysis in Spark Ignition Fuels by ASTMD 6730-1 with an Agilent Inert Flow Path

Importance of the Topic

Detailed hydrocarbon profiling of spark ignition fuels is fundamental to both refined fuel quality assurance and catalytic process protection. Oxygenated additives introduced to meet regulatory and performance targets can interact with active sites of chromatography systems, causing peak tailing, selectivity loss and inaccurate quantitation. Robust, inert gas chromatography setups that satisfy ASTM D6730-01 and CGSB CAN/CGSB 3.0 No.14.3 requirements are key enablers for accurate blend characterization, operational efficiency and product compliance.

Objectives and Study Overview

This application note demonstrates how an Agilent inert flow path—comprising a short phenyl-methyl siloxane tuning column coupled to PONA GC columns and SilTite connectors—achieves complete separation of hydrocarbon classes and oxygenates in a 31-component fuel test mixture. Key goals include verifying critical-pair resolution, peak symmetry with reactive alcohols, and run time improvement using hydrogen as carrier gas.

Methodology and Instrumentation

A test mixture reflecting spark ignition engine fuel composition was analyzed using ASTM D6730-01 protocol on an Agilent 6890N GC equipped with FID detection and a 7683B liquid autosampler. A 5 m phenyl methyl-siloxane tuning column preceded a 100 m PONA column (HP-1 or CP-Sil PONA CB). Hydrogen at 2 mL/min constant flow served as carrier. A temperature program from 30 °C to 275 °C with multiple ramps was applied to resolve components spanning C5 to C13 and common oxygenates.

Applied Instrumentation

• Gas chromatograph: Agilent 6890N Network GC with FID
• Automatic liquid sampler: Agilent 7683B (0.5 µL syringe, split 150:1)
• Tuning column: Agilent J&W HP-5ms (5 m trimmed section of 15 m × 0.25 mm × 1.0 µm)
• Analytical columns: Agilent J&W HP-1 PONA or CP-Sil PONA CB (100 m × 0.25 mm × 0.5 µm)
• Flow path connectors: Agilent Ultimate Union with SilTite ferrules
• Carrier gas: Hydrogen at 38 cm/s (2.0 mL/min)

Main Results and Discussion

Critical hydrocarbon pairs such as 2,3,3-trimethylpentane vs. toluene were baseline-separated on both PONA columns, with symmetry factors ranging from 0.71 to 1.44 and selectivity values exceeding 1.00. Light oxygenates (ethanol, t-butanol) exhibited sharp, symmetric peaks, confirming the inertness of the flow path. Using hydrogen reduced total analysis time by approximately 25% compared to helium, with identical separation performance.

Benefits and Practical Applications of the Method

• Exceptional inertness: Elimination of reactive sites ensures reliable integration of polar oxygenates.
• Complete resolution: Guaranteed separation of all critical hydrocarbon pairs as per ASTM D6730-01.
• Improved throughput: Hydrogen carrier gas delivers shorter runtimes without loss of resolution.
• Compliance: Meets or surpasses ASTM and Canadian CGSB standards for detailed hydrocarbon analysis.

Future Trends and Opportunities

With expected growth in higher ethanol blends (e.g., E15), laboratories will demand even more inert flow paths and flexible column configurations. Advances in micro-flow technologies, faster temperature ramps, and integrated data analytics will further accelerate turnaround and support real-time quality control in fuel production and distribution networks.

Conclusion

By combining a phenyl-methyl siloxane tuning column with long PONA capillaries, inert connectors and hydrogen carrier gas, Agilent provides a turnkey solution for detailed hydrocarbon analysis of modern spark ignition fuels. This configuration offers superior peak shape, robust selectivity, and faster throughput, ensuring accurate, standards-compliant characterization of complex gasoline blends.

References

• ASTM D6730-01 (2011), Standard Test Method for Determination of Individual Components in Spark Ignition Engine Fuels by High-Resolution Capillary GC.
• CAN/CGSB 3.0 No.14.3-99, Canadian General Standards Board Detailed Hydrocarbon Analysis Method.
• Majors, R.E., “Hydrogen as a Carrier Gas for GC and GC–MS,” Agilent Technologies.