Meeting the requirements of ASTM D 6591-06 (IP548/06) Using Agilent 1200 Series HPLC Systems

Importance of the Topic

The aromatic content of diesel fuel directly influences ignition quality, engine performance and longevity. ASTM D 6591-06 (IP548/06) provides a standardized high-performance liquid chromatography (HPLC) approach for quantifying mono-, di-, tri+ and polycyclic aromatics in middle distillates. Reliable determination of these compound classes supports quality control in refineries, fuel suppliers and engine manufacturers.

Objectives and Study Overview

This work demonstrates how an Agilent 1200 Series HPLC system meets the requirements of ASTM D 6591-06. It covers:

• Separation of aromatic and non-aromatic hydrocarbon classes boiling between 150 °C and 400 °C.
• Performance qualification with system performance solution (SPS).
• Calibration linearity and precision for aromatic markers.
• Analysis of representative diesel and diesel/biodiesel blend samples.

Methodology and Instrumentation

The method uses normal-phase HPLC on an amino-bonded silica column with programmed backflush to group eluting saturates, mono-, di- and tri+ aromatics. Detection is by refractive index, responding equally to aromatic and non-aromatic species.

Instrumentation Used

• LC System: Agilent 1200 Series
• Binary Pump G1312B (normal-phase seals p/n 0905-1420)
• Autosampler G1367C with needle wash
• Thermostatted Column Compartment G1316C with 6-port switching valve
• Refractive Index Detector G1362A
• Software: Agilent ChemStation B.04.02
• Column: ZORBAX NH2, 4.6 × 250 mm, 5 μm (p/n 880952-708)
• Mobile Phase: HPLC-grade n-heptane at 1 mL/min
• Injection Volume: 10 μL, Column Oven: 20 °C

Main Results and Discussion

• System Qualification: Resolution between cyclohexane and o-xylene exceeded the method requirement (R = 8.8 vs. min. 5).
• Calibration: Three aromatic standards (o-xylene, 1-methyl-naphthalene, phenanthrene) yielded linearity R² > 0.9999, intercepts < 0.01 g/100 mL.
• Precision: Retention time RSD ≤ 0.07 %, area RSD ≤ 1.2 % across calibration levels.
• Sample Analysis: Retail ultra-low sulfur diesel showed ~29–30 g/100 mL monoaromatics, ~5 g/100 mL diaromatics, < 1 g/100 mL tri+ aromatics with RSD < 3 %.
• Biodiesel Interference: A mislabeled pump sample gave anomalous tri+ aromatics (~4 g/100 mL) due to FAME; re-analysis by the biodiesel-compatible IP391/07 method resolved FAME and yielded expected low tri+ values.

Benefits and Practical Applications

This HPLC-RI method:

• Provides reliable group quantification without UV-active standards.
• Supports routine QC of diesel, bio-blend and middle distillates.
• Enables rapid troubleshooting of mislabeling or contamination by FAME.

Future Trends and Potential Applications

Increasing biofuel use and tighter fuel specifications will drive:

• Adaptation of normal-phase HPLC methods for broader biodiesel blends.
• Advanced detection schemes (e.g. evaporative light scattering) for polar contaminants.
• Automation of backflush and group integration for higher throughput.

Conclusion

The Agilent 1200 Series HPLC system meets or exceeds ASTM D 6591-06 requirements for aromatic hydrocarbon group analysis in middle distillates. Careful sample identification and method selection ensure accurate results, particularly for fuels containing fatty acid methyl esters.

Reference

1. Woodman M., Sierocinska M. Meeting the Requirements of EN12916:2006 (IP391/07) Using Agilent 1200 Series HPLC Systems. Agilent Application Note 5990-4789EN, 2009.
2. ASTM D 6591-06 Standard Test Method for Determination of Aromatic Hydrocarbon Types in Middle Distillates by HPLC with Refractive Index Detection. 2006.
3. Gratzfeld-Huesgen A. Analysis of Aromatic Hydrocarbons in Middle Distillates with HPLC using IP Standard Method 391/95. Agilent Application Note 5965-9044E, 1997.