Desorption of PCBs from Soil Using the HTD

Significance of the Topic

This application note illustrates two complementary analytical approaches for rapid screening in environmental and materials chemistry. The first method focuses on direct thermal desorption of polychlorinated biphenyls (PCBs) from soil, eliminating lengthy solvent extractions. The second employs hyphenated GPC–FTIR to unravel complex polymer mixtures within silver conductive ink formulations. Both techniques enhance throughput, reduce solvent use, and provide deeper molecular insight.

Objectives and Overview of the Study

The study comprises two parts:

• Develop and validate a high‐temperature desorption (HTD) protocol for quantitative recovery of Arochlor 1221 from spiked soil samples.
• Demonstrate the capability of GPC–FTIR hyphenation to separate and identify polymeric components and latent crosslinkers in a silver ink paste.

Methodology and Instrumentation

• Thermal Desorption (PCBs): Samples of soil (30 mg) spiked with Arochlor 1221 (27 ppm in methanol) were loaded into quartz tubes (25 mm × 6 mm i.d.) and inserted into the CDS Analytical HTD, controlled by the Pyroprobe 2000 temperature controller. A temperature program consisting of an initial 150 °C start, rapid ramp to 300 °C (60 °C/min, hold 10 min) and a second ramp to 450 °C (20 °C/sec, hold 3 min) desorbed volatiles into an HP 5890 GC–FID with a 30 m × 0.53 mm SE-54 column and helium carrier (10 mL/min).
• GPC–FTIR (Polymer Analysis): A Discover-IR–GPC system hyphenated to a full‐range FTIR detector was used. The ink paste was dissolved and fractionated on a size‐exclusion column. Eluting fractions were directed in a heated transfer line into the FTIR flow cell, capturing infrared spectra for each polymer fraction.

Main Results and Discussion

• PCB Desorption: A comparison of GC/FID chromatograms from inert glass wool versus soil matrices showed efficient desorption of Arochlor 1221 from soil with an average recovery of 98 %. Complex soil organics generated additional peaks but did not interfere with target analyte quantification.
• Polymer Characterization: GPC–FTIR resolved three major polymer fractions in the silver ink paste:
  • Polymer A: An aliphatic polyester resin (high molecular weight, broad distribution) providing flexibility and adhesion.
  • Polymer B: An aliphatic polyurethane elastomer (medium molecular weight, narrow distribution) conferring elasticity.
  • Additive C: A ketoxime-blocked HDI trimer latent crosslinker that deblocks at elevated temperature to form an isocyanate and crosslink with the polyurethane network.
  Component D, identified as a latent crosslinking agent Desmodur LS-2800, completes the 3D network, enhancing mechanical stability and electrical connectivity of silver particles.

Practical Benefits and Applications

• Environmental Monitoring: The HTD–GC approach offers rapid onsite screening of PCB contamination with minimal sample preparation and no solvents.
• Materials Development: GPC–FTIR provides formulators with direct infrared fingerprinting of polymer components, aiding quality control, intellectual property protection, and competitive benchmarking.

Future Trends and Potential Applications

• Integration of HTD with mass spectrometry or tandem detectors for enhanced selectivity in environmental forensics.
• Automation and miniaturization of thermal desorption modules for field deployable systems.
• Expansion of hyphenated GPC–IR to include chemometric analysis, enabling rapid screening of complex polymer blends and nanocomposites.
• Application of real‐time FTIR flow cells to monitor polymer curing and ageing directly during manufacturing processes.

Conclusion

The combined use of high‐temperature thermal desorption and hyphenated GPC–FTIR permits fast, solvent‐free analysis of both volatile contaminants in environmental matrices and complex polymer formulations in industrial materials. These approaches streamline workflows, improve data quality, and open new avenues for rapid screening and detailed molecular characterization.

Reference

No formal literature references provided in the original text.