GC-IRMS: Tracing pollutants in soil and sediment using carbon isotope fingerprint

Importance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that persist in air, soils and sediments. Many PAHs exhibit toxic, carcinogenic or mutagenic properties, making accurate source identification essential for risk assessment, pollution control and environmental forensics.

Objectives and Study Overview

This application brief demonstrates the use of compound-specific carbon isotope analysis (13C) by gas chromatography–isotope ratio mass spectrometry (GC-IRMS) to distinguish pyrogenic versus petrogenic PAH inputs. A sediment sample from a freshwater lake was examined alongside a standard mixture to illustrate carbon isotope fingerprinting on local and regional scales.

Methodology

• A 1 µL aliquot of sediment extract was injected in splitless mode with 1.4 mL/min helium flow
• Separation was performed on a Thermo Scientific™ TraceGOLD™ TG-5MS GC column coupled to a TRACE™ 1310 GC
• Eluting compounds were oxidized or pyrolyzed in the GC IsoLink™ II conversion interface to CO2 for carbon isotope analysis
• Evolved gases were transferred via ConFlo IV to a DELTA V isotope ratio mass spectrometer for δ13C measurement

Used Instrumentation

• Thermo Scientific™ TRACE™ 1310 Gas Chromatograph
• Thermo Scientific™ GC IsoLink II Conversion Interface
• Thermo Scientific™ ConFlo IV Universal Interface
• Thermo Scientific™ DELTA V Isotope Ratio Mass Spectrometer
• Thermo Scientific™ TraceGOLD™ TG-5MS Capillary Column

Main Results and Discussion

• Standard mixture δ13C values: perylene –24.3 ‰; friedelin –28.8 ‰
• Sediment sample δ13C values: perylene –27.8 ‰; friedelin –30.8 ‰
• Coal-derived PAHs typically fall between –23 and –25 ‰, while diesel particulates show more depleted values around –28 to –31 ‰
• The more negative δ13C in the sample indicates a predominantly pyrogenic origin, consistent with incomplete combustion sources such as biomass or fossil fuel burning

Benefits and Practical Implications

• Enables unambiguous differentiation of PAH sources in soil and sediment matrices
• Supports environmental forensics, pollution monitoring and regulatory compliance
• Offers high separation efficiency and full automation for routine laboratory workflows

Future Trends and Opportunities

• Integration of multi-isotope (C, H, N, O) fingerprinting for enhanced source resolution
• Development of miniaturized and high-throughput CSIA platforms
• Combining isotope data with chemometric and machine learning approaches for predictive source apportionment

Conclusion

Compound-specific δ13C analysis by GC-IRMS with the GC IsoLink II platform provides a reliable, high-precision method to trace PAH origins and distinguish between pyrogenic and petrogenic inputs. This approach enhances pollutant source identification and supports a wide range of environmental and industrial applications.

Reference

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