Autosampling in Purge & Trap Analysis

Importance of the topic

The reliable detection and quantification of trace volatile organic compounds in water and the structural characterization of polymer additives are critical in environmental monitoring, industrial quality control, and materials research. Automated purge and trap sampling minimizes manual intervention and enhances reproducibility, while hyphenated GPC–IR techniques provide detailed chemical identification within complex polymer mixtures.

Objectives and Study Overview

This application note describes two complementary analytical approaches. The first evaluates the performance of the CDS Model 380 autosampling purge & trap system coupled to a capillary GC–FID for priority pollutants in water. The second illustrates how GPC–IR hyphenated technology (DiscovIR-GPC) separates and identifies polymer components and additives in a silver-ink paste formulation.

Used Methodology and Instrumentation

• Purge & Trap GC–FID setup
  • CDS Model 380 autosampler with 15-vessel sample concentrator
  • Trap material: Tenax TA, 25 cm
  • Purge: Helium at 40 mL/min, 11 min
  • Trap dry: 35 °C, 3 min; desorption: 200 °C, 5 min
  • Cryofocusing: –100 °C, 10 min; GC start at 200 °C
  • Gas chromatograph: Varian 3700; program: 35 °C for 4 min then 6 °C/min to 200 °C; detector: FID
  • Capillary columns: 0.75 mm wide-bore and 0.25 mm narrow-bore with optional cryogenic refocusing
  
• GPC–IR hyphenated technology
  • Instrument: DiscovIR-GPC system
  • Application: Separation of polymer A (aliphatic polyester resin), polymer B (aliphatic polyurethane), and additive C (latent cross-linker HDI trimer)
  • IR detection across full FTIR range for structural fingerprinting
  

Main Results and Discussion

• Purge & Trap GC–FID
  • Reproducibility: average RSD < 5 % for ten replicate runs at 100 ppb
  • Sensitivity: aromatic compounds detected at < 10 ppt using narrow-bore column with cryofocusing
  • Representative chromatogram: 20 ppb target analytes in a 5 mL water sample
  
• GPC–IR analysis
  • Effective separation of polymer fractions and additives in silver-ink paste
  • Characteristic IR bands allowed unambiguous identification of additive C as HDI trimer and polymers A and B by their unique fingerprint regions
  

Benefits and Practical Applications

• Automated purge & trap sampling enables high throughput, unattended analysis and consistent results for environmental water testing and regulatory compliance.
• Cryogenic refocusing and narrow-bore capillaries dramatically improve sensitivity in the low ppb to ppt range.
• GPC–IR hyphenation delivers both molecular weight distribution and structural information, facilitating formulation development and quality assurance in polymer and ink industries.

Future Trends and Applications

• Integration of mass spectrometric detectors with purge & trap systems for enhanced selectivity and identification.
• Miniaturization of autosamplers and columns for field-deployable monitoring devices.
• Advanced chemometric interpretation of hyphenated GPC–IR data for comprehensive polymer characterization and real-time process control.

Conclusion

Automated purge & trap GC–FID and hyphenated GPC–IR techniques together address critical analytical needs: achieving trace-level sensitivity and robust reproducibility for water pollutant analysis, while providing molecular-level insights into complex polymer formulations. These methods support both compliance testing and R&D in industrial and environmental laboratories.

Reference

• Washall J. and Wampler T., “Purge and Trap Analysis of Aqueous Samples with Cryofocusing,” Amer. Lab., 20(7), 70–74 (1986).
• Wampler T., Bowe W., Higgins J., and Levy E., “Systems Approach to Automated Cryofocusing in Purge and Trap,” Amer. Lab., 17(8), 82–87 (1988).