Hydrocarbons, C6 - C9 - Reference method for monitoring systems for analysis of hydrocarbons in environmental air

Importance of the Topic

Monitoring volatile organic compounds (VOCs) in environmental air is crucial for assessing pollution sources, ensuring compliance with air quality regulations, and protecting human health. Accurate detection of C6 to C9 hydrocarbons supports both routine environmental monitoring and industrial safety programs.

Objectives and Study Overview

This application note describes a reference method for automated systems based on thermal desorption and gas chromatography with flame ionization detection (GC-FID). The main goal is to achieve reliable separation and quantification of a standard mixture of C6 to C9 hydrocarbons using an Agilent CP-Sil 5 CB capillary column with cyclohexene as an internal standard.

Applied Methodology

The method employs split injection of a 10 microliter sample in carbon disulfide onto a GC system. Helium is used as carrier gas and a temperature program ramps from 35 degrees Celsius to 120 degrees Celsius in stages to resolve compounds ranging from light olefins to heavier aromatics and alkanes. Detection is performed with an FID at 200 degrees Celsius.

Used Instrumentation

• Gas chromatograph equipped with split injector
• Agilent CP-Sil 5 CB capillary column, 0.25 mm by 25 m, film thickness 0.4 micrometer
• Flame ionization detector operating at 200 degrees Celsius
• Helium carrier gas
• Sample solvent: carbon disulfide

Main Results and Discussion

The separation of 24 target compounds including aliphatics, aromatics, and chlorinated solvents was achieved without coelution with the internal standard. Retention times followed expected volatility and structural trends. Key findings include baseline separation of isomeric xylenes and clear resolution between linear and branched hydrocarbons, demonstrating the column selectivity and temperature programming efficiency.

Benefits and Practical Applications

• Robust and reproducible analysis suitable for continuous air monitoring
• Wide dynamic range for environmental and industrial samples
• Simple sample preparation using thermal desorption or solvent extraction
• Compliance with regulatory requirements for VOC emissions

Future Trends and Potential Applications

Advancements may include coupling this method with mass spectrometry for improved compound identification, integrating real time sampling modules for on site monitoring, and applying machine learning algorithms for data interpretation. Miniaturized and portable GC systems could expand field applications.

Conclusion

The presented reference method offers effective separation and quantification of C6 to C9 hydrocarbons in environmental air. With its reliable performance and clear chromatographic resolution, it is recommended for laboratory and field monitoring systems.