Analysis of Aromatic Hydrocarbons in Fuels by ASTM D6379 and D6591 on a Single HPLC Platform

Importance of the topic

Determining aromatic hydrocarbon content in fuels is essential for predicting combustion behavior, meeting environmental regulations, and ensuring fuel quality across aviation and diesel applications. Traditional methods such as ASTM D1319 face reagent availability challenges, prompting the adoption of high-performance liquid chromatography (HPLC) techniques that offer faster, more precise quantitation.

Objectives and study overview

This work evaluates the application of two isocratic HPLC methods—ASTM D6379 for kerosene and middle distillates and ASTM D6591 for diesel fuel—on a single Shimadzu Prominence system. The goals are to demonstrate method performance, resolution of aromatic classes, calibration linearity, and repeatability, while optimizing run times and solvent consumption.

Methodology and instrumentation used

The two assays employ heptane as the mobile phase and polar amino and cyano-bonded columns:

• ASTM D6379: Series connection of Shim-pack GIST NH2 (4.6×250 mm, 5 µm) and CN (4.6×150 mm, 5 µm) columns, 1.0 mL/min flow, 1 µL injection, 15 min run.
• ASTM D6591: Single Shim-pack GIST NH2 (4.6×250 mm, 3 µm) column, 0.8 mL/min flow, 3 µL injection, 28 min run with back-flush at 9.24 min.

Both methods use a Shimadzu Prominence HPLC platform featuring an LC-20AD pump, DGU-20A5R degasser, SIL-20AC autosampler, CTO-20A oven with 6-port valve, and RID-20A refractive index detector. Guard columns ensure column protection.

Main results and discussion

System resolution standards showed clear separation of cyclohexane (saturates), o-xylene (mono-aromatics), and 1-methylnaphthalene (di-aromatics) with resolution >8.9, exceeding ASTM and IP requirements. Calibration curves for key components demonstrated excellent linearity (r2 >0.9999). Precision tests yielded retention time RSDs <0.5% and peak area RSDs <0.3%. Real sample injections of Jet A and pump diesel confirmed method robustness, with diesel sample retention time RSDs <0.035% and peak area RSDs ~1%.

Benefits and practical applications

• Modernizes assays formerly reliant on column chromatography (ASTM D1319) by offering faster run times and reduced reagent use.
• Enables simultaneous quantitation of mono-, di-, and higher polyaromatics in a single system.
• Delivers high resolution and reproducibility suitable for QA/QC labs in fuel production, distribution, and regulatory monitoring.

Future trends and potential applications

Advances may include integration with mass spectrometric detection for structural confirmation, adoption of green solvents to enhance sustainability, automated sample preparation, and miniaturized HPLC formats for field-based screening of fuel quality.

Conclusion

The implementation of ASTM D6379 and D6591 on a single HPLC platform provides a robust, precise, and efficient approach for aromatic analysis in middle distillates and diesel fuels. The method meets or exceeds regulatory performance criteria and offers practical benefits in laboratory throughput and resource use.

References

• ASTM D1319-18, Standard Test Method for Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator Adsorption, ASTM International, 2018.
• ASTM D6591-18, Standard Test Method for Determination of Aromatic Hydrocarbon Types in Middle Distillates—High Performance Liquid Chromatography Method with Refractive Index Detection, ASTM International, 2018.
• ASTM D6379-11, Standard Test Method for Determination of Aromatic Hydrocarbon Types in Aviation Fuels and Petroleum Distillates—High Performance Liquid Chromatography Method with Refractive Index Detection, ASTM International, 2011.