Detailed Analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in Creosote Oil on Rxi®-PAH

Significance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are priority pollutants due to their toxicity, persistence and widespread occurrence in industrial products such as creosote oil. Reliable identification and quantification of PAHs is essential for environmental monitoring, regulatory compliance and risk assessment in industrial and laboratory settings.

Objectives and Study Overview

This study aims to develop and demonstrate a comprehensive gas chromatography–mass spectrometry (GC–MS) method for the separation and detection of 25 priority PAH compounds present in a creosote oil standard. The work evaluates chromatographic resolution, mass spectral identification and reproducibility using a high-performance Rxi®-PAH column.

Methodology and Instrumentation

The analytical procedure employs a 60 m × 0.25 mm ID, 0.10 µm Rxi®-PAH capillary column. A creosote oil standard at 50,000 µg/mL in dichloromethane is injected in split mode (1 µL, split ratio 40:1). The GC oven is programmed from 40 °C (1.6 min hold) to 210 °C at 24 °C/min, then to 295 °C at 1.9 °C/min, and to 350 °C at 3.7 °C/min (6 min hold). Helium carrier gas is maintained at 1.95 mL/min. The MS detector scans 35–450 amu at 3.5 scans/s (3.4–25 min) and 1.8 scans/s thereafter, with electron ionization at 70 eV.

Instrumentation Used

• GC–MS System: Agilent 7890B GC coupled to 5977A MSD
• Column: Rxi®-PAH, 60 m × 0.25 mm ID, 0.10 µm (Restek cat. #49317)
• Sample: Creosote oil standard (Restek cat. #31838)
• Injector: Premium 4 mm precision liner with wool, 275 °C
• Transfer line: 330 °C; Source: 350 °C; Quadrupole: 200 °C

Main Results and Discussion

The method achieves baseline separation of 25 PAH isomers within a 40-minute runtime. Retention times increase with molecular weight and ring condensation, while mass spectral peaks at characteristic m/z values (e.g., 228, 252, 276, 300, 302) confirm compound identities. Key isomer pairs such as chrysene/triphenylene and dibenz[a,h]anthracene/dibenzo[a,j]anthracene are well resolved, demonstrating the column’s selectivity.

Benefits and Practical Applications

• High resolution and reproducibility for regulatory compliance
• Robust detection of high-molecular-weight PAHs in complex matrices
• Rapid profiling for environmental monitoring and quality control

Future Trends and Opportunities

Advances may include multidimensional GC–MS for enhanced separation of coeluting isomers, high-resolution accurate-mass detection for greater confidence in identification, and faster analytical cycles using advanced stationary phases or micro-flow systems. Automated data processing and real-time monitoring will further streamline PAH analysis.

Conclusion

This validated GC–MS method on an Rxi®-PAH column offers a reliable, high-throughput approach for comprehensive PAH analysis in creosote oil. Its performance supports environmental laboratories and industrial quality control in meeting stringent analytical requirements.