Determining Aromatics in Finished Gasoline Using the Agilent 6820 GC System

Significance of the Topic

The accurate determination of aromatic compounds in finished gasoline is critical for regulatory compliance, environmental protection, and product quality assurance. Benzene and other aromatics are known carcinogens, and their levels are strictly limited by global fuel standards. Reliable quantitation of these compounds ensures safe and clean fuel production and helps laboratories meet stringent quality and environmental regulations.

Objectives and Study Overview

This work presents a streamlined gas chromatographic (GC) method based on the Agilent 6820 GC system equipped with a 10-port switch valve, two flame ionization detectors (FID), and Cerity NDS software. The method follows ASTM D5580 procedures and aims to quantify benzene, toluene, ethylbenzene, o-xylene, p/m-xylene, C9+ heavier aromatics, and total aromatic content in finished gasoline through two complementary chromatographic runs.

Methodology

The analysis utilizes a micropacked polar precolumn containing TCEP (1,2,3-tris(2-cyanoethoxy)propane) for preseparation of aromatics from nonaromatics within the same boiling range, followed by a nonpolar HP-1 capillary column for final separation. Two runs are performed:

• Run 1 isolates benzene, toluene, and the internal standard (2-hexanone) on the HP-1 column after selective backflush of nonaromatics.
• Run 2 targets ethylbenzene, xylenes, C9+ aromatics, and total aromatics, using timed valve switches to divert early eluting nonaromatics and heavier aromatics appropriately.

Precise valve switch times (T1–T4) are calibrated to prevent loss or contamination of analytes. Calibration is conducted with multi-component standards, yielding linearity with R² > 0.999 and minimal intercepts. Repeatability tests demonstrate compliance with or superiority to ASTM D5580 criteria.

Used Instrumentation

• Agilent 6820 Gas Chromatograph with 10-port switch valve
• Split/Splitless inlet
• Flame Ionization Detectors (two FIDs)
• TCEP micropacked precolumn (56 cm × 1/16″ OD × 0.38 mm ID, 20% TCEP)
• HP-1 capillary column (30 m × 0.53 mm, 5 µm)
• Cerity NDS software for instrument control and data analysis

Main Results and Discussion

Calibration curves for each aromatic compound exhibit excellent linearity (R² > 0.999) and y-intercepts that satisfy ASTM D5580 requirements. The method shows high repeatability (differences between runs fall within the specified mass-percent ranges). Valve switching optimization prevents coelution and loss of target analytes, ensuring accurate quantitation across the entire range of aromatic compounds.

Benefits and Practical Applications

• Comprehensive coverage of key aromatics and total aromatic content in a single workflow.
• ASTM D5580 compliance with demonstrated linearity and repeatability.
• Efficient two-run approach reduces analysis time compared to separate single-column methods.
• Easy method control and data processing via Cerity NDS software.
• Applicability to regulatory testing, quality control, and environmental monitoring laboratories.

Future Trends and Potential Applications

Advancements in microcolumn and fast GC technologies may further reduce analysis time and solvent consumption. Integration with mass spectrometric detection could enhance selectivity for complex matrices. Automation of valve switch optimization and data evaluation through advanced software and machine learning will improve throughput and consistency. Portable or field-deployable GC systems may extend routine aromatic analysis to on-site monitoring in remote locations.

Conclusion

The two-column Agilent 6820 GC method with dual FIDs and switch valve control offers a robust, accurate, and ASTM-compliant solution for determining benzene, toluene, ethylbenzene, xylenes, heavier aromatics, and total aromatics in finished gasoline. Its high linearity, repeatability, and streamlined operation make it well suited for analytical laboratories focused on fuel quality and environmental compliance.

References

• GB 17930-1999 Unleaded Gasoline for Motor Vehicles. The People’s Republic of China National Standard.
• S. Ito, Analysis of Aromatic Hydrocarbons in Gasoline and Naphtha with the Agilent 6820 Series GC and a Single Polar Column, Agilent Technologies, publication 5988-9261.
• C. Yang et al., Test Methods of Petrochemical (RIPP test method), 1990, 233.
• ASTM D5769-98 Determination of Benzene, Toluene, and Total Aromatics in Finished Gasoline by GC/MS.
• ASTM D3606-99 Determination of Benzene and Toluene in Finished Motor and Aviation Gasoline by GC.
• ASTM D5580-02 Determination of Benzene, Toluene, Ethylbenzene, Xylenes, C9+ Aromatics, and Total Aromatics in Finished Gasoline by GC.
• ASTM D4815 Determination of MTBE, TAME, DIPE, Tertiary-Amyl Alcohol, and C1–C4 Alcohols in Gasoline by GC.
• J. D. McCurry, Running ASTM Methods D4815 and D5580 on a Single Agilent 6890N GC with Nitrogen Carrier Gas, Agilent Technologies 5988-9153EN.