Determination of Total Aromatic Hydrocarbons and Total Saturates with the Agilent 1260 Infinity Binary LC System with RI Detection According to ASTM D7419

Importance of the Topic

Analysis of lube oil composition is essential for performance evaluation and quality control in industrial applications. Determining the levels of aromatic and saturate hydrocarbons supports formulation stability and compatibility in lubrication and blending processes.

Objectives and Study Overview

This work presents a modernized version of the standard test method for measuring total aromatics and total saturates in lube base stocks. The main goals are to reduce analysis time and solvent usage by employing smaller diameter columns while maintaining compliance with the original ASTM standard criteria.

Methodology and Instrumentation

The method uses a binary HPLC system with refractive index detection operating at 35 degrees C for the column compartment and 20 degrees C for the detector. A dual column setup comprises a silica gel column and a cyano column connected in series. Heptane is used as the mobile phase at a flow rate of 1 mL per minute. A two position six port valve enables backflush to isolate and elute aromatic components after saturates have passed through the silica column. Calibration is performed with hexadecane and octadecylbenzene standards over concentration ranges from 0.1 percent to 50 percent and 0.1 percent to 30 percent respectively. Sample injections of 2 microliters are used to match the scaled down column geometry.

Results and Discussion

The system performance standard shows sharp single bands for hexadecane and octadecylbenzene at retention times near eight and ten minutes. Calibration curves demonstrate linearity with correlation coefficients above 0.996 down to 0.1 percent. Method precision yields retention time relative standard deviations below 0.1 percent and area RSD below 0.2 percent. The detection limit for aromatic hydrocarbons is approximately one microgram per milliliter at a signal to noise ratio of three.

Benefits and Practical Applications

The reduced internal diameter columns deliver equivalent analytical performance to the original method while cutting solvent consumption by more than two thirds and run time by over fifty percent. This scaled down approach lowers operational costs and increases sample throughput for quality control laboratories handling lube base stocks and hydrocarbon mixtures.

Future Trends and Applications

Ongoing developments may include integrating higher sensitivity detectors and longer life guard columns to further improve method robustness. Additional applications could extend to tracking poly aromatic hydrocarbon content in environmental samples or monitoring aromatic profiles in fuels and petrochemical streams.

Conclusion

The modified chromatographic method meets key ASTM criteria for total aromatics and saturates analysis while offering faster cycle times and lower solvent usage. The approach is a cost effective alternative to conventional setups and retains high precision and sensitivity.

Reference

• ASTM D7419 13 Standard Test Method for Determination of Total Aromatics and Total Saturates in Lube Basestocks by HPLC with Refractive Index Detection
• Agilent Application Note 5991 3170EN Determination of Aromatic Hydrocarbons in Petroleum Middle Distillates by HPLC RID
• Agilent Application Note 5991 3172EN Determination of Aromatic Hydrocarbons in Aviation Fuel by HPLC RID