Accurately Quantify PAHs Down to 5 pg On-Column

Importance of the Topic

Polycyclic aromatic hydrocarbons or PAHs are pervasive environmental contaminants formed by incomplete combustion of organic materials. Many PAHs are classified as carcinogenic or mutagenic and are regulated by agencies such as the US Environmental Protection Agency. Sensitive and accurate quantification of PAHs at trace levels is therefore critical for environmental monitoring and compliance.

Objectives and Overview of the Study

This study aims to evaluate the performance of the new Rxi-5Sil MS column in combination with gas chromatography mass spectrometry in single ion monitoring mode to quantify 16 priority PAHs at on-column amounts as low as 5 picograms. The study examines calibration linearity, sensitivity, resolution, and robustness under optimized conditions.

Methodology and Instrumentation

The analytical system employs gas chromatography coupled to a mass spectrometer operating in SIM mode. Key components and parameters include:

• Column: Rxi-5Sil MS, 30 meters length, 0.25 mm internal diameter, 0.25 μm film thickness
• Carrier gas: Helium at 1.4 mL per minute constant flow
• Injection: Pulsed splitless injection with 4 mm drilled Uniliner inlet liner with wool, inlet temperature 300 °C
• Temperature program: 50 °C hold 0.5 minute, ramp to 290 °C at 25 °C per minute, then to 320 °C at 5 °C per minute
• Mass spectrometer: Electron ionization, transfer line 290 °C, ion source 290 °C, quadrupole 180 °C, SIM acquisition

Main Results and Discussion

Under these conditions, all target analytes, including sixteen PAHs, two internal standards, and a surrogate, were resolved in under 16 minutes. The system achieved excellent sensitivity, detecting 5 pg on-column with clear baseline resolution. Calibration over a 0.005 to 10 μg/mL range showed linearity with an average relative standard deviation of 4.7%. Low column bleed and enhanced thermal stability of the stationary phase contributed to improved signal-to-noise ratios and lower detection limits.

Benefits and Practical Application

• Wide dynamic calibration range spanning 2,000-fold concentration levels
• High sensitivity suitable for trace level environmental compliance testing
• Robust peak shapes and reproducible performance for routine laboratory analysis
• Improved column lifespan and reliability due to silarylene polymer stability

Future Trends and Potential Applications

Advancements may include coupling this methodology with high-resolution mass spectrometry for untargeted screening, automation for high-throughput laboratories, miniaturized GC/MS systems for field analysis, and extension to emerging semivolatile organic pollutants beyond PAHs.

Conclusion

The Rxi-5Sil MS column paired with an optimized GC/MS SIM method offers a powerful and reliable approach for quantifying trace levels of PAHs in environmental samples, meeting stringent regulatory requirements and enhancing analytical throughput.