Satisfying ASTM Method D5769: A Solution for Determination of High-Concentration Aromatic Compounds in Finished Gasolines

Importance of the Topic

Analysis of aromatic hydrocarbons in finished gasoline is critical for regulatory compliance and fuel quality assessment. ASTM D5769 provides a GC-MS based protocol to measure benzene, toluene, and total aromatics with high accuracy. Ensuring linear response and avoiding ion source saturation are key challenges when quantifying high-concentration aromatics.

Objectives and Study Overview

This study evaluates LECO’s Pegasus BT GC-TOFMS for its ability to satisfy ASTM D5769 requirements. Calibration performance, sensitivity, ion ratio compliance, and analysis of a commercial 93-octane gasoline sample were assessed.

Methodology and Instrumentation

The analysis employed high-split, low-volume injections on an Agilent 7890 GC with an Agilent 7693 autosampler coupled to the Pegasus BT time-of-flight MS. Key conditions included:

• Injection: 0.1 µL split 1200:1 at 260 °C
• Column: Rxi-1ms, 30 m × 0.25 mm × 1 µm
• Oven Program: 55 °C (1 min) to 70 °C at 20 °C/min (4 min), then to 220 °C at 30 °C/min (5 min)
• Carrier Gas: Helium at 1.0 mL/min
• Transfer Line: 280 °C, Ion Source: 250 °C
• Mass Range: m/z 35–550, Acquisition Rate: 10 spectra/s
• Data Processing: ChromaTOF Target Analyte Find with Quantitation and Semi-Quantitation tools

Main Results and Discussion

• Sensitivity: 0.01 mass % 1,4-diethylbenzene S/N consistently >5, with averages exceeding 100 across replicates.
• Ion Ratios: Measured ion abundance ratios for 3 mass % 1,2,3-trimethylbenzene fell within ASTM-specified ranges.
• Linearity: All 23 calibrated aromatics achieved R2 values >0.99 (average 0.99987), demonstrating no detector saturation even at high analyte levels.
• Sample Analysis: A commercial 93-octane gasoline showed 0.20 % benzene, 1.44 % toluene, and 10.75 % total aromatics, consistent with expected industry ranges.

Practical Benefits and Applications

• Reliable quantification of regulatory and high-concentration aromatics supports quality control in refineries and testing laboratories.
• High throughput capability and broad dynamic range streamline fuel analysis workflows.

Future Trends and Potential Applications

• Integration with automated sample preparation and real-time monitoring platforms.
• Expansion of semi-quantitative approaches to emerging fuel additives and bio-blend components.
• Advancements in data analytics for improved deconvolution and reporting efficiency.

Conclusion

The Pegasus BT GC-TOFMS fulfills all ASTM D5769 criteria, offering robust sensitivity, accuracy, and linearity for high-concentration aromatic analysis in finished gasoline. Its performance enhances regulatory compliance and operational efficiency in petroleum testing laboratories.