Developing a New GC×GC-TOFMS Method for Quantitation of Biofuel Components in Jet Fuel

Importance of the Topic

The integration of renewable biofuels into aviation fuel supplies reduces carbon footprint but introduces risks such as pipeline cross-contamination and altered freeze-point behavior. Accurate quantitation of biofuel components in jet fuel is critical for regulatory compliance, fuel quality assurance, and prevention of gelling or performance issues.

Objectives and Study Overview

This work aims to develop a robust two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) method employing a novel diverting flow modulator. The method focuses on the precise quantification of fatty acid methyl esters (FAMEs) and synthetic iso-paraffin (SIP) hydrocarbons, such as farnesane, overcoming coelution and sensitivity limitations of existing ASTM D7974 and IP 585 methods.

Methodology

The analytical strategy uses a 1 µL split injection of jet fuel samples onto a primary nonpolar column followed by a complementary secondary polar column. A diverting flow modulator alternates sample transfer and waste diversion each second (modulation period), ensuring at least three modulated slices per peak for quantitative reliability. Fast second-dimension separations yield peak widths below 50 ms, supporting high peak capacity.

Used Instrumentation

• Gas Chromatograph: LECO FLUX GC×GC system
• Primary Column: Rxi-5 ms (30 m × 0.25 mm × 0.25 µm)
• Secondary Column: Rxi-17Silms (0.77 m × 0.10 mm × 0.10 µm)
• Carrier Gas: Helium at 1.4 mL/min constant flow
• Modulator: Diverting flow modulator with 1 s cycle time
• Mass Spectrometer: LECO Pegasus BT TOFMS (m/z 50–550, 200 spectra/s)

Results and Discussion

Calibration for farnesane over 10–1000 µg/mL demonstrated excellent linearity (R² = 0.999). Six common FAME analytes were quantified from 0 to 10 mg/kg with R² > 0.995, using methyl heptadecanoate-d33 as internal standard. GC×GC contour plots show clear separation of target analytes from complex jet fuel matrix and aromatic interferences. Peak slicing met quantitative sampling requirements, and TOFMS spectra matched commercial libraries to identify non-target contaminants (e.g., sulfur- or nitrogen-substituted species).

Benefits and Practical Applications

This method enhances chromatographic resolution and specificity, reducing coelution artifacts and improving accuracy for low-level biofuel components. Regulators and refineries can implement this approach for routine QA/QC to monitor biofuel blending, ensure freeze-point specifications, and detect pipeline carryover.

Future Trends and Applications

Advances may include integration of chemometric deconvolution for complex mixtures, expansion to trace contaminant screening, and automation of GC×GC workflows. Miniaturized modulators and real-time data processing will further streamline high-throughput biofuel analysis.

Conclusion

The new GC×GC-TOFMS method with a diverting flow modulator delivers high-resolution separations and sensitive quantitation of FAMEs and SIP hydrocarbons in jet fuel. It addresses regulatory needs and offers a comprehensive tool for biofuel monitoring in complex petroleum matrices.