Analysis of Soil Samles using the HTD

Importance of the Topic

Thermal desorption combined with gas chromatography–infrared spectroscopy (GC-IR) offers a solvent-free route for rapid screening of semivolatile organic pollutants in complex environmental matrices such as soils and sludges. By eliminating labor-intensive extraction steps, this approach accelerates routine environmental monitoring and improves laboratory throughput while preserving analytical accuracy.

Objectives and Overview of the Study

This application note demonstrates the performance of a high-temperature desorption (HTD) system paired with a GC-IR platform for direct analysis of soil samples contaminated by diesel fuel. The study aims to:

• Streamline sample preparation by direct thermal desorption of 5–200 mg samples
• Optimize desorption heating profiles to avoid secondary reactions
• Obtain infrared spectral identification of volatile and semivolatile analytes

Methodology and Instrumentation

A 5 mg soil aliquot was loaded into a 25 mm × 6 mm quartz tube and held in place with glass wool. The tube was inserted into a platinum heating coil controlled by a Pyroprobe 2000 temperature controller. Desorption program: initial 3 s burst to 1000 °C, then 50 s at 200 °C, delivering analytes directly into the GC injection interface without trapping. The GC-IR instrument, featuring full-range FTIR detection, acquired spectral data for each separated compound immediately as the GC run began.

Instrument Configuration

• CDS High Temperature Desorber (HTD) with platinum coil
• CDS Analytical Pyroprobe 2000 temperature controller
• Gas chromatograph equipped with megabore capillary column (30 m × 0.53 mm, SE-54)
• Hyphenated GC–IR detector providing full FTIR range for compound identification
• Helium carrier gas flow at 7 mL/min

Main Results and Discussion

Comparison of contaminated versus blank soil showed clear chromatographic peaks corresponding to diesel components. Direct desorption yielded reproducible recoveries of semivolatile organics with no solvent background. Infrared spectra enabled confirmation of key functional groups and identification of a latent HDI cross-linker additive (Component C) that remains blocked at room temperature but deblocks during thermal curing to form reactive isocyanate cross-links.

Benefits and Practical Applications

The described HTD–GC–IR workflow:

• Reduces sample preparation time by eliminating solvent extraction
• Minimizes risk of artifact generation through controlled heating rates
• Provides simultaneous chromatographic separation and IR spectral identification
• Is suitable for environmental monitoring, QA/QC of industrial sludges, and screening of polymer additives in formulated inks

Future Trends and Potential Uses

Advances in automated cryofocusing and multi-step temperature programming will broaden the applicability of thermal desorption methods. Integration with high-resolution mass spectrometry and enhanced IR imaging may enable even finer structural characterization of complex matrices. Emerging needs include on-site portable GC-IR systems for rapid field screening and expanded use in polymer science for real-time monitoring of curing processes.

Conclusion

The CDS HTD coupled with GC-IR represents a powerful, efficient tool for direct thermal desorption analysis of soil samples. It delivers rapid, solvent-free results, precise temperature control to avoid byproducts, and definitive spectral identification of target analytes, positioning it as a valuable asset in environmental and industrial laboratories.

References

• Wampler W., Bowe J., Higgins J. Systems approach to automated cryofocusing in purge and trap, headspace and pyrolytic analysis. American Laboratory, 17(8), 1985.
• Kristunas J. CDS Application Note #155.