Defining the Retention Times of 209 PCB Congeners Using GCxGC-TOFMS

Importance of the Topic

Polychlorinated biphenyls (PCBs) remain among the most persistent and toxic environmental contaminants. Their structural similarity and isomeric diversity challenge conventional analytical methods, making accurate congener identification critical for environmental monitoring and human health risk assessment.

Goals and Study Overview

This study aimed to establish a comprehensive retention map for all 209 PCB congeners by determining their primary (tr’) and secondary (tr’’) retention times using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS). A secondary objective was to evaluate the performance of ChromaTOF software and its ion ratio calculation in resolving critical congener pairs.

Methodology

Individual PCB congeners were prepared at 20 µg/mL, and critical pair mixtures at 10 µg/mL. Separation was performed on a GCxGC system with an RTX-PCB primary column and an RTX-17 secondary column. The temperature program covered 70°C to 275°C on the primary oven with a 15°C offset for the secondary, using a 4 s modulation period. TOFMS data were acquired at 100 spectra/s over 45–550 m/z.

Instrumental Setup

• GC: Agilent 6890 with LECO thermal modulator
• Primary column: RTX-PCB (40 m × 0.18 mm × 0.18 µm)
• Secondary column: RTX-17 (1 m × 0.10 mm × 0.10 µm)
• Mass spectrometer: LECO Pegasus 4D TOFMS
• Software: ChromaTOF 4.22 and Microsoft Excel for data review

Key Results and Discussion

The retention map showed a general increase in both tr’ and tr’’ with the number of chlorines, although significant overlap occurred across congener classes. Critical pair analysis demonstrated that secondary retention times and ion ratios improved the correct identification of congeners that coelute in the first dimension. While mass spectra alone often misassigned isomers, combining retention time data with ion ratio-based classification elevated correct hits to the top rank.

Benefits and Practical Applications

By providing a detailed two-dimensional retention library and leveraging ion ratio metrics, this approach reduces candidate congeners to one or two possibilities, enhancing confidence in PCB analysis. It supports environmental laboratories, regulatory compliance testing, and QA/QC protocols.

Future Trends and Applications

Advances may include integrating high-resolution mass spectrometry, automated library searches with machine learning, and expanding GCxGC-TOFMS retention libraries to other isomeric pollutant classes. Portable GCxGC devices and real-time monitoring platforms could further streamline contaminant surveillance.

Conclusion

This work establishes a robust GCxGC-TOFMS retention time database for all 209 PCB congeners and demonstrates the value of combining retention dimensions with ion ratio classification for reliable isomer differentiation.

Reference

1. Safe S. Polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs): biochemistry, toxicology, and mechanism of action. Crit Rev Toxicol, 1984, 13(4):319–395.
2. LECO Corporation. GCxGC-TOFMS application note on PCB separation. 2020.