Assay of Hydrocarbons in Soil using the 7400 Auto-Sampler

Importance of Topic

Accurate and efficient detection of volatile organic compounds in soil is essential for environmental monitoring, site remediation and regulatory compliance. Equally important is the ability to characterize complex polymer formulations and latent additives in advanced materials, supporting quality control and innovation in coatings and adhesives.

Objectives and Overview

This document presents two complementary applications. The first describes an automated method for quantifying hydrocarbons in soil using the CDS Model 7400 auto-sampler coupled to a Model 7000 Purge & Trap GC system. The second outlines a GPC-IR hyphenated approach for separating a polymer blend and identifying latent cross-linking additives by infrared spectroscopy.

Methodology and Instrumentation

The soil assay workflow

• Sample preparation: 5 g soil in 40 mL vial, automated addition of 5 mL water and internal standard, magnetic stirring.
• Purge conditions: helium at 35 mL/min, 40 °C for 11 min (up to 80 °C for less volatile analytes).
• Trap desorb and bake: 250 °C for 2 min, 260 °C for 10 min.
• Gas chromatograph: injector 300 °C, split 20:1, 30 m × 0.25 mm 5% phenyl column.

The polymer characterization workflow

• Gel permeation chromatography hyphenated to Fourier transform infrared detection (GPC-IR).
• Mass spectrometer detector covering m/z 35–550.
• Oven program: initial 40 °C (4 min), ramp 10 °C/min to 210 °C (1 min).

Main Results and Discussion

Soil hydrocarbon analysis produced well-resolved chromatograms of benzene, toluene, ethylbenzene and xylenes. Calibration of ethylbenzene yielded a linear response (R² = 0.998). Concentrations in the test soil were determined as benzene 10 ppb, ethylbenzene 15 ppb, toluene 87 ppb and total xylene 102 ppb. GPC-IR separated a polymer A (aliphatic polyester resin) and polymer B (aliphatic polyurethane) and detected additive C, identified as a blocked HDI trimer (CAS 93919-05-2). Infrared bands provided signature fingerprints to distinguish monomers, oligomers and cross-linkers.

Benefits and Practical Applications

• Fully automated sample handling improves throughput, reproducibility and safety for soil VOC analysis.
• Low detection limits and linear calibration ensure reliable quantitation at regulatory levels.
• GPC-IR delivers simultaneous molecular weight distribution and chemical identity, facilitating formulation development and failure analysis.

Future Trends and Opportunities

Integration of automated sampling with on-line data processing and advanced chemometric tools will further streamline environmental analyses. Portable purge-and-trap GC systems could enable field screening. In polymer analytics, coupling GPC with multidimensional detectors (e.g. MS, UV, light scattering) and real-time IR imaging promises deeper insight into polymer architecture and additive interactions.

Conclusion

The CDS 7400 auto-sampler with purge-and-trap GC and GPC-IR hyphenated techniques both demonstrate robust, high-throughput workflows for complex sample matrices. These approaches expand analytical capabilities in environmental chemistry and materials science.

References

None provided in original document.