Analysis of Sulfur Compounds Using On-line and Off‑line TD–GC

Importance of the Topic

Sulfur compounds are responsible for pungent odors even at extremely low concentrations, impacting air quality, industrial emissions, environmental monitoring, health and safety, and product quality in food, flavor, and fragrance sectors.

Study Objectives and Overview

This study evaluates the compatibility and performance of Markes International’s thermal desorption (TD) technology for trace-level sulfur compound analysis. Both on-line (real-time) and off-line (sorbent tube) TD–GC methods are assessed using standard mixtures and real-world samples, including compliance monitoring under Korean odor regulations and analysis of landfill gas emissions.

Methodology and Instrumentation

The on-line configuration employs a UNITY–Air Server connected to a gas chromatograph with a pulsed flame photometric detector (PFPD). Critical parameters include:

• Sampling flow: 50 mL/min, 100–500 mL volume
• Trap temperatures: –15 °C (low) to 250 °C (high)
• Inert flow path materials: PTFE, quartz, inert-coated stainless steel

The off-line approach uses inert-coated Tenax TA/UniCarb sorbent tubes and a UNITY thermal desorber linked to GC–MS. Key conditions include:

• Prepurge and desorb cycles at 200–300 °C
• Trap materials: U-T6SUL porous polymer/carbon molecular sieve
• Carrier gas: helium at controlled flow
• GC temperature program: 60 °C to 220 °C ramping at 10 °C/min

Main Results and Discussion

On-line TD–GC–PFPD data show:

• Detection limits: 0.15 ppb for H2S, CH3SH, DMS; 0.10 ppb for DMDS
• Excellent linearity (r > 0.997) over 0–100 ppb
• Reproducibility RSD < 1.8% for most compounds; H2S RSD ≈ 4% at 20 ppb
• Recovery > 93% across 0–80% relative humidity

Field data from Korean odor monitoring networks confirmed:

• Peak area precision < 4.3% RSD for H2S across multiple sites
• Retention time stability < 0.1% RSD
• Recovery > 87% for H2S under routine conditions

Off-line landfill gas analysis demonstrated trace detection of priority sulfur species with minimal breakthrough and consistent quantitation.

Benefits and Practical Applications

The TD–GC methods deliver:

• High sensitivity and selectivity for reduced sulfur compounds
• Robust inert flow paths to prevent analyte degradation
• Adaptability for real-time monitoring, compliance testing, and field sampling
• Simplified workflow for laboratories in environmental, industrial, and product testing

Future Trends and Possibilities

Emerging developments include:

• Integration with advanced mass spectrometry for structural confirmation
• Portable and on-site TD–GC systems for rapid assessments
• Automated data analytics and AI-driven odor profiling
• Expanded sorbent chemistries for ultra-volatile and polar sulfur species

Conclusion

Markes’ thermal desorption technology, with fully inert flow paths and specialized focusing traps, offers reliable, sensitive, and reproducible analysis of trace sulfur compounds. Both on-line and off-line TD–GC configurations meet regulatory requirements and support diverse applications in environmental monitoring and quality control.

References

1. Kim K-H. Insights into the gas chromatographic determination of reduced sulfur compounds in air. Environ Sci Technol. 2005;39:6765–6769.
2. Kim K-H, Ju D-W, Joo S-W. Evaluation of recovery rates for thermal desorption systems in atmospheric reduced sulfur analysis. Talanta. 2005;67:955–959.
3. Song K-P et al. QA/QC study for reduced sulfur compounds using cryofocusing TD–GC/PFPD. Korean J Odor Res Eng. 2007;6:33–39.
4. LFTGN 04. Monitoring trace components in landfill gas. UK Env Agency; 2009.
5. EC Directive 1999/31/EC on landfill of waste.