The Analysis of Polychlorinated Dibenzo-p-dioxins and Polychlorinated Dibenzofurans Using GCxGC-TOFMS

Importance of the Topic

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic by-products of combustion and industrial activities. Their environmental persistence and health risks demand sensitive and reliable analytical methods for monitoring trace levels in environmental and biological samples.

Objectives and Study Overview

This study evaluated comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) as a practical alternative to regulatory GC-HRMS for quantifying the 17 toxic PCDD/F congeners:

• Assess chromatographic separation and sensitivity for native and 13C-labelled standards
• Compare quantitative performance against EPA Method 1613-compliant GC-HRMS data
• Test real-world samples (fly ash, sediments, test matrix) for ng TEQ/kg equivalence

Methodology and Instrumentation

Sample preparation followed EPA-style extraction and cleanup protocols. Calibration used five standard mixtures with 17 native and 16 13C-labelled congeners plus recovery standards. Data processing employed isotope dilution in ChromaTOF software for automated deconvolution and quantitation.

Instrumentation Used

• GCxGC-TOFMS: LECO Pegasus 4D Time-of-Flight Mass Spectrometer, 50 Hz acquisition, mass range 160–500 u
• Primary column: Rxi-5SilMS (30 m × 0.25 mm ID, 0.25 µm film)
• Secondary column: Rtx-200 (1.5 m × 0.18 mm ID, 0.2 µm film)
• Temperature programs optimized for high-boiling congeners, modulation period 4 s, splitless injection at 250 °C

Main Results and Discussion

Calibration curves for 2,3,7,8-TeCDF (318 m/z labelled, 306 m/z native) showed R² = 0.99975 down to 0.5 pg/µL. Selected-ion GCxGC chromatograms displayed clear separation of tetra- through octachloro congeners. Four real-world samples analyzed by GCxGC-TOFMS produced ng TEQ/kg values in close agreement with GC-HRMS (within 5–10 %), confirming quantitative reliability. The enhanced peak capacity and software-driven deconvolution minimized coelution and improved detectability at low pg/µL levels.

Benefits and Practical Applications

• Comparable quantitative performance to GC-HRMS at environmental levels
• Higher chromatography peak capacity reduces interferences
• Automated deconvolution simplifies data processing for complex matrices
• Potentially lower cost and faster throughput for environmental screening

Future Trends and Applications

Advances may include integration with automated sample preparation, expansion to other persistent organic pollutants, higher-throughput instrumentation, and coupling with high-resolution TOFMS detectors to further lower detection limits and streamline regulatory workflows.

Conclusion

GCxGC-TOFMS is a robust, sensitive, and practical screening tool for PCDD/F analysis in environmental matrices. It delivers quantitative results comparable to GC-HRMS while offering higher chromatographic resolution, efficient data handling, and potential throughput advantages.

References

• P. Gorst-Allman, Data Processing with isotopes as internal standards, LECO Africa Website, Application Notes section.