Analysis of Total Aromatic Content in Motor Gasoline by ASTM D5769 Using an Agilent 8850/5977C GC/MSD System

Importance of the Topic

Motor gasoline’s aromatic fraction directly impacts fuel octane rating, emissions profile and regulatory compliance. Accurate quantification of benzene, toluene and total aromatics is essential for quality control in petroleum refining and ensuring environmental and safety standards are met. ASTM D5769 offers a robust GC/MS approach that combines chromatographic separation with mass-selective detection to meet stringent aromatic measurement requirements in under ten minutes.

Objectives and Study Overview

This study evaluates the performance of the Agilent 8850 GC coupled with the Agilent 5977C GC/MSD for rapid determination of individual and total aromatic compounds in motor gasoline according to ASTM D5769. Key goals include assessing linearity across a wide concentration range, precision and accuracy against gravimetric standards, and real-world cross-laboratory sample validation.

Methodology and Instrumentation

The system was configured per ASTM D5769 Condition 3 with two custom modifications: a 9 mm extraction lens in the MSD source to extend linear dynamic range and a 0.3 µL injection on a 40 m × 0.18 mm, 0.4 µm DB-1 column with hydrogen carrier gas. The electron multiplier gain factor was adjusted (0.3) to attenuate high-abundance signals while preserving sensitivity for trace components. Calibration standards spanning 500 to 149 000 ppm of 24 aromatic species were prepared gravimetrically, and performance checked with deuterated internal standards and a reformulated gasoline (RFG) sample from an interlaboratory cross-check program.

Results and Discussion

Chromatographic separation delivered baseline resolution of critical coelutions, with m- and p-xylene and 1,4-diethylbenzene/n-butylbenzene pairs reported as composite peaks per method allowances. Calibration linearity exceeded R2 > 0.9999 for all 24 target analytes, including toluene (R2 = 0.99996) up to 16.3 % m/m. Optimizing the MSD gain factor produced signal-to-noise ratios above 50 for 100 ppm 1,4-diethylbenzene, well above the method requirement of 5. Daily quality control on a multicomponent standard achieved < 3.5 % deviation for all analytes (±5 % requirement) and resolution between 1,3,5-trimethylbenzene and 1-methyl-2-ethylbenzene of R = 4.77 (requirement R ≥ 2). Analysis of an RFG sample returned total aromatics of 14.46 vol % versus an accepted reference of 14.82 vol % (Z-score –0.63), demonstrating excellent agreement.

Benefits and Practical Applications

This GC/MSD configuration offers:

• A nine-minute runtime for high sample throughput.
• Compact footprint—2/3 size of standard benchtop GC/MS systems.
• Wide dynamic range to measure trace and bulk aromatics in a single run.
• Robust precision and accuracy meeting stringent ASTM criteria.

Applications include refinery QA/QC, fuel certification labs and environmental monitoring.

Future Trends and Opportunities

Advances in extraction lens design and automated gain control will further enhance linear range and ease of method transfer across instruments. Integration with real-time data analysis and remote diagnostics could enable continuous online monitoring of aromatic content in process streams. Expanding the method to wider hydrocarbon matrices and coupling with high-resolution MS are promising directions.

Conclusion

The Agilent 8850 GC with the 5977C GC/MSD achieves rapid, accurate and precise measurement of individual and total aromatics in gasoline per ASTM D5769. Customization of the extraction lens and electron multiplier gain delivered exceptional linearity and sensitivity across a broad concentration range, streamlining fuel analysis workflows.

Reference

ASTM D5769-22, Standard Test Method for Determination of Benzene, Toluene, and Total Aromatics in Finished Gasolines by Gas Chromatography/Mass Spectrometry, ASTM International, 2022
McCurry J. D. A High Performance and Cost-Effective GC/MS Solution for Measuring Aromatics in Gasoline Using ASTM Method D5769. Agilent Technologies application note, May 2020