A Solution for Determination of High-Concentration Aromatic Compounds in Finished Gasolines Satisfying ASTM D5769 Using a New Benchtop GC-TOFMS

Importance of the Topic

Reliable quantification of aromatic compounds such as benzene, toluene and related poly­aromatics in finished gasoline is critical for regulatory compliance, environmental monitoring and product quality control. The widely applied ASTM D5769 standard prescribes GC-MS analysis but often encounters ion source saturation when high concentrations of aromatics are present, leading to non-linear calibration and compromised accuracy.

Study Objectives and Overview

This study demonstrates the application of a benchtop time-of-flight mass spectrometer (GC-TOFMS) to meet and exceed all key ASTM D5769 performance criteria: sensitivity at 0.01 % mass for 1,4-diethylbenzene, specified ion‐abundance ratios, and calibration linearity across a broad concentration range. After method validation, a commercial 93-octane gasoline sample was analyzed to illustrate real-world performance.

Methodology

A calibration strategy was developed for 23 target and structurally similar aromatic analytes using triplicate injections to assess precision. Sensitivity checks at 0.01 % mass confirmed signal-to-noise ratios exceeding 100. Ion-ratio verification was performed for trimethylbenzene isomers to comply with Section 9.2.5 of ASTM D5769. A standard gasoline matrix (93-octane) was then analyzed with automated deconvolution and peak finding to determine both calibrated and semi‐quantified uncalibrated analytes.

Used Instrumentation

• Gas Chromatograph: Agilent 7890 with Agilent 7693 autosampler
• Injection: 0.1 µL, split 1200:1 at 260 °C
• Column: Rxi-1ms, 30 m×0.25 mm×1.00 µm film
• Carrier Gas: Helium at 1.0 mL/min constant flow
• Oven Program: 55 °C (1 min) → 70 °C @ 20 °C/min (4 min) → 220 °C @ 30 °C/min (5 min)
• Transfer Line: 280 °C
• Mass Spectrometer: LECO Pegasus BT GC-TOFMS, 35–550 m/z, 10 spectra/s, ion source at 250 °C

Main Results and Discussion

Calibration curves for all ASTM D5769 analytes exhibited R² values ≥ 0.9998. Sensitivity testing for 0.01 % mass 1,4-diethylbenzene yielded an average S/N > 100. Ion-ratio checks passed tolerance windows for key masses of trimethylbenzene.
Analysis of the 93-octane sample produced the following volume % results:

• Benzene: 0.20 %
• Toluene: 1.44 %
• Ethylbenzene: 0.20 %
• 1,2-Dimethylbenzene: 0.31 %
• 1,3,5-Trimethylbenzene: 0.11 %
• Naphthalene: 1.98 %
• Total Aromatics: 10.75 %

All three primary criteria—sensitivity, ion abundance ratios, and calibration linearity—were met, confirming robust performance even at high aromatic concentrations.

Benefits and Practical Applications

The benchtop GC-TOFMS approach provides:

• Resilience against ion source saturation, ensuring linear response up to high analyte levels
• High throughput with rapid deconvolution and automated peak finding
• Simultaneous quantification of multiple aromatic species in a single run
• Compliance with ASTM D5769 for quality assurance and regulatory reporting

Future Trends and Opportunities

Emerging developments may include integration of advanced chemometric algorithms for enhanced peak deconvolution, real-time monitoring of aromatic emissions, miniaturized field-deployable TOFMS units, and application of machine learning for automated compound identification. Expansion to biodiesel blends, alternative fuels and other complex matrices is anticipated.

Conclusion

The LECO Pegasus BT GC-TOFMS method reliably satisfies ASTM D5769 requirements, delivering superior sensitivity, precise ion-ratio control and excellent linearity for high-concentration aromatics in finished gasoline. This solution enhances confidence in aromatic quantification for industrial, environmental and regulatory laboratories.