Fast GC/MS Analysis for Benzene and Total Aromatic Content of Motor Gasoline

Importance of the Topic

The aromatic composition of motor gasoline directly impacts engine performance, emissions, and regulatory compliance. Rapid and accurate measurement of benzene and total aromatics is essential for quality control, environmental monitoring, and adherence to fuel standards.

Objectives and Overview

This study assesses the performance of an Agilent Intuvo 9000 GC coupled with a 5977B GC/MSD under ASTM D5769 conditions. Key aims include evaluating precision, calibration linearity, chromatographic resolution, and total analysis time for quantifying benzene, toluene, and total aromatics in gasoline samples.

Methodology and Instrumentation Used

• Sample Preparation: Approximately 0.8 g of gasoline sample and 0.04 g of internal standard mixture weighed into a GC autosampler vial.
• Internal Standards: Benzene-d6, Ethylbenzene-d10, Naphthalene-d8; optional Toluene-d8 for extended calibration.
• Calibration: Multi-point mass-based calibration following ASTM D5769, including a high-level toluene standard at 20.01 wt% and extended range to demonstrate linearity.
• Gas Chromatograph: Agilent Intuvo 9000 GC (G3950A) with HP-RFG Intuvo column (20 m × 0.10 mm, 0.40 µm); split/splitless inlet at 250 °C, split ratio 4000:1, helium carrier gas.
• Oven Program: 50 °C (0.5 min), ramp 20 °C/min to 100 °C, ramp 5 °C/min to 120 °C, ramp 30 °C/min to 250 °C; total run time 11.3 min.
• Mass Spectrometer: Agilent 5977B GC/MSD in scan mode (m/z 28.5–300), 70 eV ionization, source at 230 °C, quadrupole at 150 °C.

Main Results and Discussion

• Precision: Repeatability assessed by 21 sequential injections yielded RSD ≤ 1 % for benzene, toluene, and total aromatics.
• Linearity: Calibration curves achieved R² ≥ 0.999 for most analytes; toluene exhibited R² = 0.997 over 1.55–20.01 wt %.
• Chromatographic Resolution: HP-RFG column delivered a resolution factor of 5.3 for challenging isomer pairs, surpassing the ASTM D5769 requirement of 2.0.
• Internal Standard Separation: Near-baseline separation between toluene and toluene-d8 confirmed, enabling the use of a fourth standard when necessary.
• Verification: Quality control checks and ASTM Reformulated Gasoline proficiency testing (#1706–#1810) demonstrated excellent agreement with gravimetric values and industry results, with all Z-scores within acceptable limits.

Benefits and Practical Applications

• High Throughput: 11.3-minute runtime increases laboratory productivity for routine fuel analysis.
• Robust Precision and Accuracy: Ensures reliable compliance with fuel specifications and environmental regulations.
• Wide Dynamic Range: Extended calibration range supports quantification from trace to high aromatic concentrations.
• Flexible Standardization: Option to include additional internal standards enhances method versatility.

Future Trends and Opportunities

• Advanced Column Phases: Novel stationary phases may further shorten run times and improve resolution.
• Automation and Data Integration: Full workflow automation and LIMS connectivity will streamline sample throughput and data management.
• Expanded Regulatory Scope: Application of this method to biofuels and alternative fuels as specifications evolve.
• AI-Driven Analytics: Implementation of chemometric and machine-learning tools for enhanced data interpretation and quality assurance.

Conclusion

The Agilent Intuvo 9000 GC coupled with the 5977B GC/MSD meets and exceeds ASTM D5769 requirements, delivering rapid, precise, and accurate analysis of benzene, toluene, and total aromatics in motor gasoline with an efficient 11.3-minute runtime.

Reference

• ASTM D5769-15, Standard Test Method for Determination of Benzene, Toluene, and Total Aromatics in Finished Gasolines by Gas Chromatography/Mass Spectrometry, ASTM International, West Conshohocken, PA, 2015.