Alcohols and aromatics - Separation of aromatics and alcohol from gasoline

Importance of the Topic

Accurate separation of aromatic hydrocarbons and alcohols in gasoline is critical for regulatory compliance, quality control and performance optimization of fuels. Variations in aromatic content affect combustion properties, emissions and octane rating. Reliable analytical methods enable refineries and laboratories to monitor composition efficiently and ensure product consistency.

Objectives and Overview

This application note demonstrates a gas chromatography method using an Agilent TCEP capillary column for the simultaneous separation and quantification of 15 aromatic and alcohol compounds in gasoline. The goal is to achieve baseline resolution within a 28-minute run to support routine quality assessment and research applications.

Used Methodology and Instrumentation

This method employs the following configuration:

• Technique: Gas chromatography with capillary column
• Column: Agilent TCEP WCOT, fused silica, 0.22 mm × 50 m, film thickness 0.4 µm (Part no. CP7525)
• Temperature Program: Start at 95 °C, ramp to 120 °C at 2.5 °C/min
• Carrier Gas: Nitrogen at 90 kPa (0.9 bar), linear velocity ~12.2 cm/s
• Injector: Split mode, 50 mL/min split flow, injection volume 0.2 µL
• Detector: Flame ionization detector (FID), sensitivity 4 × 10⁻¹² Afs

Main Results and Discussion

The optimized method achieved baseline separation of 15 analytes—including aliphatic alcohols (methanol, isopropanol, tert-butanol, 1-butanol), benzene, toluene, ethylbenzene, xylenes (o-, m-, p-), mesitylene, cumene, m-propylbenzene and 2-ethyltoluene—within 28 minutes. Peak ordering corresponded to increasing boiling point and polarity. Resolution between critical pairs (e.g., xylene isomers and alcohols) was consistently above accepted thresholds, ensuring accurate quantification.

Benefits and Practical Applications

This rapid, high-resolution GC method supports:

• Quality control in fuel production and distribution
• Regulatory compliance for aromatic limits and alcohol content
• Research into fuel performance and emission characteristics
• Routine screening in analytical laboratories due to minimal sample preparation

Future Trends and Potential Applications

Advances likely include coupling TCEP columns with mass spectrometry for enhanced compound identification, faster temperature programming for reduced cycle time, micro-column technology for lower sample and carrier gas consumption, and integration with chemometric tools for automated data processing and predictive quality models.

Conclusion

The described GC-FID method on an Agilent TCEP column provides a robust, efficient solution for separating and quantifying key aromatics and alcohols in gasoline. Its fast runtime and strong resolution make it suitable for both routine quality control and research environments.

Reference

• Agilent Technologies, Inc. Application Note A00031, October 31, 2011.