Analyses of Polychlorinated Biphenyl (PCB) Mixtures and Individual Congeners by GC

Significance of the Topic

The persistence and toxicity of polychlorinated biphenyls (PCBs) in water, soil, sediments and biota pose a major environmental challenge. Effective monitoring of PCB mixtures and individual congeners is critical for compliance with regulatory guidelines, risk assessment and remediation efforts. Gas chromatography (GC) coupled with selective detectors remains a cornerstone for congener-specific analysis and identification of commercial Aroclor mixtures.

Objectives and Overview of the Study

This bulletin presents a comprehensive survey of GC column packings, operating conditions and sample preparation techniques for PCB analysis. It reviews methods for identifying, resolving and quantifying both complex Aroclor mixtures and individual PCB congeners under regulatory and research-driven protocols. Applications span transformer oil, wastewater, sediments and biological matrices.

Methodology and Instrumentation

Sample Preparation and Extraction

• Simple matrices (oil) often require dilution with organic solvent.
• Complex matrices (wastewater, sediment, tissue) use liquid–liquid extraction, solid-phase extraction and solid-phase microextraction (SPME).
• SPME uses a polydimethylsiloxane fiber to concentrate PCBs from headspace or liquid samples, with rapid solvent-free preparation.

Chromatographic Conditions

• Packed columns: 2 m glass columns with 1.5% SP-2250/1.95% SP-2401 or 3% SP-2100 on SUPELCOPORT support meet EPA Method 608 for routine monitoring and Aroclor identification.
• Capillary columns: SPB-5, SPB-608, PTE-5 and SPB-Octyl phases provide enhanced resolution of congeners and degraded mixtures.
• Temperature programs range from isothermal runs to gradient ramps (e.g., 30 °C to 300 °C) optimized for homolog elution.

Detection Techniques

• Electron capture detection (ECD) offers high sensitivity for PCBs at low-pg to ppt levels.
• Mass spectrometry (MS) allows selective ion monitoring (e.g., m/z 326 for pentachloro-, m/z 360 for hexachloro-biphenyls), resolving coeluting homologs.

Main Results and Discussion

Aroclor Pattern Recognition

• Packed columns generate characteristic chromatograms for Aroclor 1016 through 1260; chlorine content correlates with later-eluting peaks.
• SP-2250/SP-2401 columns spread peaks for easier pattern matching, while SP-2100 packings shorten run times but compress patterns.

Congener-Specific Resolution

• Capillary columns separate individual congeners in complex or degraded mixtures, enabling retention-time based identification.
• SPB-Octyl offers unique selectivity for coplanar, dioxin-like congeners due to hydrocarbon shape selectivity and high boiling point discrimination.
• Ortho-substitution classes (non-ortho, mono-ortho, di-ortho, tri-ortho, tetra-ortho) elute in distinct zones on SPB-Octyl, facilitating toxic equivalency analysis.

Solid-Phase Microextraction Performance

• SPME achieves detection limits below 5 ppt with 20–60 min extraction from sediment headspace.
• Extracted PCB profiles closely match Aroclor standards despite aging or weathering effects.

Benefits and Practical Applications

• Compliance with EPA 608 and SW-846 protocols for routine wastewater and oil screening.
• Rapid, solvent-free SPME simplifies trace-level analysis in environmental samples.
• Capillary phases enable congener-specific quantification for toxicological and ecological studies.
• SPB-Octyl columns enhance selectivity for dioxin-like congeners, critical for risk assessments.

Future Trends and Potential Uses

• Integration of high-resolution GC with tandem MS for ultra-trace congener detection.
• Development of customized stationary phases targeting emerging halogenated pollutants.
• Automation of SPME and on-fiber derivatization for high-throughput environmental monitoring.
• Application of congener-specific data to refine toxic equivalency factors and exposure models.

Conclusion

The selection of GC column, detector and sample preparation strategy critically influences the successful analysis of PCB mixtures and congeners. Packed columns remain suitable for routine Aroclor screening, while capillaries, particularly SPB-Octyl, deliver the selectivity needed for coplanar and toxic PCB congeners. Solid-phase microextraction further streamlines trace-level detection in diverse matrices, supporting regulatory compliance and environmental research.

Reference

1. US EPA Method 608, Monitoring Organochlorine Pesticides and PCBs in Wastewater (1979).
2. EPA Test Method 600/4-81-045, Determination of PCBs in Transformer and Waste Oil (1982).
3. Ballschmiter K., et al., Journal of High Resolution Chromatography 15:260–270 (1992).
4. Ahlborg U.G., et al., Chemosphere 28:1049–1067 (1994).
5. Brown J.F. Jr., Environmental Science & Technology 28:2295–2305 (1994).
6. McFarland V.A. and Clarke J.U., Environmental Health Perspectives 81:225–239 (1989).