Analysis of various polyaromatic hydrocarbons in diesel fuels using an HPLC-RID system

Significance of the Topic

Diesel fuel combustion releases polyaromatic hydrocarbons (PAHs) that contribute to particulate matter emissions and pose health risks due to carcinogenic properties. Monitoring PAH content improves air quality, meets regulatory requirements, and informs fuel refinement strategies.

Objectives and Study Overview

This work aimed to:

• Implement the ASTM D6591-19 HPLC-RID method on a Thermo Scientific Vanquish Core system.
• Evaluate its performance for measuring mono-, di-, tri- and polyaromatic hydrocarbons in diesel according to both ASTM and Chinese PRC NB/SH/T 0806-2022 standards.

Methodology and Instrumentation

Reagents and standards:

• HPLC-grade n-heptane as mobile phase.
• PAH standards including cyclohexane, o-xylene, 1-methylnaphthalene, phenanthrene and additional compounds for system performance checks.

Instrumentation:

• Vanquish Core HPLC with quaternary pump and normal-phase kit.
• Hypersil APS-2 Amino analytical column (250×4.6 mm, 3 µm) and guard column.
• Refractive Index Detector at 35 °C, data acquired by Chromeleon CDS 7.3.2.
• Automated backflush valve triggered post di-aromatic elution to sharpen tri-aromatic bands.

Chromatographic conditions:

• Mobile phase: n-heptane, flow rate 1.0 mL/min, run time 30 min.
• Backflush initiated at 6.3 min, total run time reduced without compromising separation.
• Injection volume 5 µL, detector range 500 µRIU, data collection rate 10 Hz.

Key Results and Discussion

• System performance verification with a standard solution showed baseline separation of seven target PAHs, resolution > 6 for critical pairs, and signal-to-noise ratios > 1000.
• Calibration curves for representative PAHs yielded r² > 0.99997 across four concentration levels, confirming excellent linearity.
• Analysis of a diesel reference sample matched theoretical PAH content (12.1 % MAH, 5.9 % DAH, 0.3 % T+AH) within method reproducibility and repeatability limits.
• The Hypersil APS-2 Amino column and backflush approach halved analysis time compared to the PRC standard without loss of performance.

Practical Benefits and Applications

By integrating a normal-phase HPLC-RID platform with automated backflush and data processing:

• Laboratories can meet both ASTM and PRC regulatory methods for diesel PAH profiling.
• Reduced cycle times and robust peak shapes increase sample throughput and lower operating costs.
• Automated integration in Chromeleon eliminates manual peak assignment, enhancing data reliability and efficiency.

Future Trends and Opportunities

• Coupling RID with mass spectrometric detectors could extend specificity and sensitivity for low-level PAHs.
• Method automation and AI-driven data analysis may further streamline high-throughput fuel monitoring.
• Adapting similar workflows to alternative fuels and bio-diesels can support sustainability assessments.

Conclusion

The Thermo Scientific Vanquish Core HPLC-RID workflow fully complies with ASTM D6591-19 and PRC NB/SH/T 0806-2022 requirements for diesel PAH analysis. Enhanced column performance, automated backflush, and software-driven integration deliver accurate, reproducible results in half the typical run time, supporting efficient fuel quality control in industrial laboratories.

References

1. ASTM D6591-19: Determination of Aromatic Hydrocarbon Types in Middle Distillates—HPLC-RID.
2. NB/SH/T 0806-2022: Determination of Aromatic Hydrocarbon Types in Middle Distillates—HPLC-RID.
3. IP391 Application Note: Backflush Calculation for PAH Analysis.