Resolving 18 PAHs, Including Benzofluoranthenes, Using the Unique Selectivity of a 50% Phenyl Methylpolysiloxane-Phased GC Column

Importance of the Topic

The analysis of polycyclic aromatic hydrocarbons (PAHs) is critical in environmental monitoring, food safety and industrial quality control. Achieving clear separation of isobaric and isomeric PAHs ensures accurate identification and quantification, which is essential for regulatory compliance and risk assessment.

Study Objectives and Overview

This application note demonstrates the ability of a 50% phenyl methylpolysiloxane stationary phase (TraceGOLD TG-17SilMS) to resolve 18 priority PAHs, including the challenging benzofluoranthene isobaric trio (benzo[b]-, benzo[j]- and benzo[k]fluoranthene). A comparison is made with a conventional 5% diphenyl/95% dimethyl polysiloxane phase.

Methodology and Instrumentation

• Sample Preparation: A 16-PAH standard mix (US EPA Method 610) spiked with benzo[j]fluoranthene and benzo[e]pyrene at 10 µg/mL in hexane.
• Chromatographic Columns: TraceGOLD TG-17SilMS (30 m×0.25 mm×0.25 µm) and equivalent 5SilMS column of same dimensions.
• GC-MS System: TRACE GC Ultra with TriPlus RSH autosampler and ISQ single-quadrupole MS.
• Carrier Gas and Flow: Helium, constant flow at 1.2 mL/min.
• Oven Program TG-17SilMS: 90 °C (1 min)→30 °C/min→250 °C→4 °C/min→330 °C (5 min).
• Oven Program 5SilMS: 90 °C (1 min)→25 °C/min→280 °C→4 °C/min→320 °C (2 min).
• Injection: Split 25:1, 1 µL volume, injector at 250 °C.
• MS Conditions: Electron impact ionization at 70 eV, source 250 °C, transfer line 300 °C, scan range 40–450 amu.

Results and Discussion

The TG-17SilMS column achieved baseline separation of all 18 PAHs, notably resolving benzo[j]-fluoranthene from the co-eluting benzo[b]- and benzo[k]-fluoranthenes observed on the 5SilMS phase. Key observations:

• The unique selectivity of the 50% phenyl phase separates critical isobaric pairs.
• High-temperature low bleed performance allows analysis of heavy PAHs with late elution without baseline drift.
• Non-isobaric critical pair (indeno[1,2,3-cd]pyrene and dibenzo[a,h]anthracene) is easily distinguished by MS detection.

Benefits and Practical Applications

The enhanced resolving power of the TG-17SilMS column provides:

• Reliable quantification of priority and regulated PAHs in environmental and food matrices.
• Reduction of false positives from co-eluting isobaric compounds.
• Improved throughput by eliminating the need for extended method optimization.

Future Trends and Potential Applications

Advances in stationary phase chemistry and MS detectors will further improve PAH analysis. Emerging trends include:

• Integration with high-resolution MS to distinguish structurally similar PAHs by accurate mass.
• Development of faster temperature programming profiles for high-throughput screening.
• Application of novel phases for mixed polarity analytes and complex environmental samples.

Conclusion

The TraceGOLD TG-17SilMS column delivers unique selectivity and low bleed characteristics, enabling baseline separation of complex PAH mixtures, including challenging isobaric components. Its performance surpasses conventional 5SilMS phases, supporting robust GC-MS analysis in regulatory and research settings.

References

• Khan A. I. Application Note 20740: Resolving 18 PAHs, Including Benzofluoranthenes, Using the Unique Selectivity of a 50% Phenyl Methylpolysiloxane-Phased GC Column. Thermo Fisher Scientific, 2013.