Analysis of Fatty Acid Methyl Esters (FAMEs) in Jet Fuel by GC-TOFMS

Significance of the topic

Bio-derived contaminants in petroleum-derived aviation fuels, specifically fatty acid methyl esters (FAMEs) from biodiesel, pose a real risk to thermal stability and engine performance when transferred via shared storage or transport infrastructure. Regulatory screening thresholds (commonly 5 mg/kg) and standardized methods such as IP 585 exist to ensure flight-safety and fuel integrity. Rapid, reliable analytical approaches that combine identification and quantification in a single injection improve laboratory throughput and reduce the risk of false negatives arising from coeluting hydrocarbon matrix interferences.

Objectives and study overview

This application note evaluates a GC–time-of-flight mass spectrometry (GC–TOFMS) implementation of Method IP 585 to screen and quantify C16–C18 FAMEs in jet fuel. Goals were to demonstrate: calibration across method-specified ranges, selectivity in a complex jet-fuel matrix, and practical quantification/identification using full mass-range TOFMS data rather than separate SIM and scan acquisitions on a quadrupole instrument.

Methodology

Sample preparation followed IP 585 Section 7. FAME calibration standards (C16:0 through C18:3) were prepared in dodecane at 0–100 ppm (w/w). Methyl heptadecanoate-d33 was used as an internal standard at 10 ppm.

GC–TOFMS analytical details (based on IP 585 Section 8) included:

• Instrument: LECO Pegasus HT (LECO Pegasus TOFMS coupled to an Agilent 6890 GC and GERSTEL MPS2 autosampler).
• Injection: 1 µL splitless, inlet 260 °C; inlet purge 100 mL/min after 2 min.
• Carrier gas: He at 1.0 mL/min.
• Column: Stabilwax, 60 m × 0.25 mm × 0.50 µm.
• Oven program: 5 min at 150 °C, ramp 12 °C/min to 200 °C (hold 17 min), ramp 3 °C/min to 252 °C (hold 6.5 min).
• TOFMS: mass range 33–500 m/z, acquisition rate 10 spectra/s, source temperature 250 °C, acquisition delay 10 min.
• Data system: LECO ChromaTOF (v4.50) for automated peak finding, library matching (NIST), deconvolution, and calibration application.

Calibration approach

Two calibration regions were produced per IP 585: a low-level calibration (0–10 ppm using 0, 2, 4, 6, 8, 10 ppm standards) and a high-level calibration (0–100 ppm using 0, 20, 40, 60, 80, 100 ppm standards). Peak areas (area ratios to internal standard) were computed automatically and linear calibration equations fitted. Required linearity (R2 ≥ 0.985) was met with:

• Low-level R2: 0.9858–0.9927.
• High-level R2: 0.9966–0.9980.

Main results and discussion

Key findings from the study:

• Linearity and calibration: Both low- and high-range calibrations exceeded IP 585 linearity requirements. Calibration slopes were consistent across analytes with predictable response factors when normalized to the d33 internal standard.
• Matrix behavior: Using the chosen column and oven program, bulk jet-fuel constituents eluted prior to the FAME window, though some naphthas coeluted in the FAME region. To minimize hydrocarbon interference, quantification employed selected high m/z ions characteristic of each FAME (the same ions recommended by IP 585) while TOF full-scan data supported library-based identification and deconvolution.
• Sensitivity and identification: The JP8 reference fuel contained no detectable FAMEs. When JP8 was spiked with roughly 10 ppm of each FAME, all targets were detected and quantified (reported concentrations near nominal spike levels). Signal-to-noise ratios for spiked analytes and the internal standard demonstrated robust detectability in the jet-fuel matrix.
• Advantages of TOFMS: Full mass-range acquisition allowed simultaneous use of selected quantification ions and spectral matching from the same injection, avoiding the need for separate SIM and scan runs required by some quadrupole systems.

Benefits and practical applications of the method

The GC–TOFMS implementation provides several practical advantages for routine screening of aviation fuels:

• Single-injection workflow combining quantification and identification, improving sample throughput.
• Improved selectivity through high-m/z ion selection and software deconvolution reduces false positives from hydrocarbon coelution.
• Full spectra enable retrospective data mining and library-based confirmation without re-running samples.
• Automated calibration and data processing streamline compliance with IP 585 performance criteria.

Instrumentation used

Instruments and consumables explicitly used in this evaluation included:

• LECO Pegasus HT system (LECO Pegasus TOFMS).
• Agilent 6890 gas chromatograph.
• GERSTEL MPS2 autosampler.
• Stabilwax column (60 m × 0.25 mm × 0.50 µm, Restek).
• Standards: C16–C18 FAMEs and methyl heptadecanoate-d33 (Sigma-Aldrich).
• Data software: LECO ChromaTOF v4.50 with calibration feature and NIST spectral library matching.

Future trends and potential applications

Anticipated directions and opportunities for improving FAME screening in jet fuels include:

• Adoption of higher-resolution and multidimensional separations (GC×GC–TOFMS or HRMS) to further resolve coelutions and lower detection limits.
• Expanded and curated spectral libraries for better identification of minor FAME homologs and oxidized derivatives.
• Implementation of isotope-labeled internal standards for each analyte class to improve accuracy and correct matrix effects.
• Inline or field-deployable screening tools for rapid contamination checks at transfer points and storage facilities.
• Integration with laboratory information management systems (LIMS) for automated compliance reporting against regulatory thresholds.

Conclusions

The GC–TOFMS approach described meets the analytical requirements of Method IP 585 for quantifying and identifying C16–C18 FAME contaminants in jet fuel. Full mass-range TOF acquisition allows simultaneous identification and quantification from a single injection, delivers calibration linearity exceeding method criteria, and provides robust performance in a complex fuel matrix when combined with high-m/z quantification and deconvolution. This workflow offers an efficient alternative to dual-mode quadrupole workflows while maintaining compliance with method performance requirements.

References

1. IP 585:2010 Determination of Fatty Acid Methyl Esters (FAME), Derived From Bio-Diesel Fuel, In Aviation Turbine Fuel – GC–MS With Selective Ion Monitoring/Scan Detection Method.
2. LECO Corporation. Analysis of Fatty Acid Methyl Esters (FAMEs) in Jet Fuel by GC–TOFMS. Application note, Form No. 203-821-431, 2012.
3. Sigma-Aldrich. FAME analytical standards and isotopically labeled internal standards (product documentation).