GC-IRMS: δ13C Analysis of PAHs in Soil and Sediment Samples using High Resolution GC Coupled with Isotope Ratio MS

Importance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are persistent, bioaccumulative pollutants with structure-dependent toxicity that often resist conventional analysis. Compound-specific stable isotope analysis (CSIA) via GC-IRMS provides precise δ13C signatures to trace pollutant origin and transformation where standard GC/MS quantitation is insufficient.

Objectives and Study Overview

This study evaluates a novel GC-IRMS interface (GC IsoLink) for simultaneous 13C/12C and 15N/14N determination in PAHs from soils and sediments. Performance was assessed using a certified alkane reference (C16–C30) and complex environmental samples.

Methodology

An organic extract is separated by high-resolution gas chromatography on a 30 m TG-5MS column under constant helium flow. Eluents pass through a capillary microreactor (NiO/CuO) at 950–1100 °C, converting compounds to CO2 and N2. A ConFlo IV interface delivers reference and sample gases into an isotope ratio mass spectrometer for δ13C and 15N analysis.

Instrumentation Used

• Thermo Scientific GC IsoLink CNH with NiO/CuO combustion reactor
• ConFlo IV interface
• Thermo Scientific TG-5MS column (30 m × 0.25 mm × 0.25 µm)
• Isotope Ratio Mass Spectrometer (IRMS)

Main Results and Discussion

Analysis of the Schimmelmann B2 alkane mixture yielded δ13C values within ±0.5‰ of certified references and precision of 0.1–0.3‰. Peak shapes and resolution were preserved after conversion. Sediment samples exhibited more negative δ13C values (–28 to –31‰) compared to coal-derived PAHs (–24 to –25‰), indicating source differentiation and potential biodegradation effects.

Benefits and Practical Applications

The streamlined single-reactor design simplifies multi-isotope workflows and maintains chromatographic integrity. High-precision δ13C measurements enable reliable source apportionment of PAHs in environmental forensics, monitoring pollutant degradation, and QA/QC in industrial analyses.

Future Trends and Applications

Advances may include integrated multi-isotope (2H, 18O) analysis, coupling with comprehensive GC×GC for enhanced separation, real-time field deployable IRMS, and broader use in metabolomics and provenance studies.

Conclusion

The GC IsoLink GC-IRMS system with high-temperature NiO/CuO reactor achieves precise δ13C and 15N analysis of PAHs while preserving chromatographic resolution. Its flexibility and robustness make it a valuable tool for environmental forensics and pollutant monitoring.

References

• Dieter Juchelka. GC-IRMS: δ13C Analysis of PAHs in Soil and Sediment Samples. Thermo Fisher Scientific Application Note 30268.