Comparison of Standard Liquid Extraction and Direct Thermal Desorption GC/MS Techniques for the Analysis of Charcoal Filters used for Indoor Air Purification in a PCB Contaminated Building

Importance of the topic

Indoor air contamination by polychlorinated biphenyls (PCBs) poses chronic health risks at trace levels. Activated carbon filters are widely implemented to reduce PCB concentrations and ensure air quality in contaminated buildings. Reliable quantification of PCBs adsorbed on these filters is essential for monitoring filter performance and guiding remediation strategies.

Objectives and study overview

This study compares conventional liquid extraction followed by gas chromatography–mass spectrometry (GC/MS) against direct thermal desorption (TD) GC/MS for analyzing PCBs trapped on multi-stage air charcoal filters. The goal is to assess method reliability, sensitivity, processing time, and overall suitability for routine monitoring.

Methodology

Liquid extraction: Filter samples from five filter stages (particle filtration and five layers of NANOSORB™ foam loaded with activated carbon) were weighed, hot-extracted with toluene, concentrated, and injected splitless into an HP 5890 GC with HP 5972 MS. GC conditions: DB-5 column (30 m × 0.25 mm, 0.25 µm), He carrier at 70 kPa, injector at 260 °C, oven ramp 80 °C to 280 °C.
Thermal desorption: Equivalent filter pieces were thermally desorbed in a Gerstel TDS 2 system, cryo-focused in a CIS 3 cooled injection system at –50 °C, then transferred to an HP 6890 GC with HP 5972 MS. Conditions: DB-5 column (60 m × 0.25 mm, 0.25 µm), He at 1 mL/min, TDS ramp 20 °C to 350 °C, CIS ramp –50 °C to 350 °C, oven 60 °C to 300 °C.

Instrumentation

• Gas chromatographs: HP 5890 Series II, HP 6890
• Mass selective detectors: HP 5972 MS
• Thermal desorber: Gerstel TDS 2
• Cooled injection system: Gerstel CIS 3
• Columns: J&W DB-5 capillary columns

Main results and discussion

Recovery for TD was approximately 25%, comparable or superior to liquid extraction. Selected ion monitoring (SIM) chromatograms across filter layers revealed similar PCB congener distribution for both methods. Thermal desorption yielded higher total PCB mass per layer, indicating improved extraction efficiency. Layer-by-layer analysis showed major retention in the first layer with decreasing concentrations downstream.

Benefits and practical applications

• Eliminates solvent use and reduces sample preparation time
• Maintains sensitivity and precision for trace-level PCB quantification
• Facilitates rapid, high-throughput monitoring of air filter performance in remediation projects

Future trends and potential applications

Integration of automated TD–GC/MS workflows for on-site monitoring, expansion to other semi-volatile organic pollutants, and development of enhanced cryo-focusing techniques to boost recovery rates and lower detection limits.

Conclusion

Direct thermal desorption GC/MS offers a robust, efficient alternative to standard liquid extraction for PCB analysis in charcoal filters. It achieves comparable or improved recovery, streamlines workflow, and supports accurate monitoring of indoor air remediation efforts.

References

1. Kames J, Törnblom J. Indoor Air - An Integrated Approach. Elsevier Science; 1992:285-288.
2. Ludewig S, Kruse H, Wassermann O. Gesundh. Wes. 1993;55:431-439.
3. Bundesgesundheitsblatt. 1990.