Analysis of Volatile Metalloid Species in Gas Samples using a Commercial Cryotrapping System (TDS-G-CIS GC) Coupled to ICP-MS with PH3 and SF6 as Example Compounds

Importance of the Topic

The analysis of volatile metalloid species at trace levels is critical for industrial hygiene and environmental monitoring. Compounds such as phosphine and sulfur hexafluoride are employed in fumigation, electrical insulation and various manufacturing processes. Their high toxicity at sub-mg/m3 concentrations demands highly sensitive, robust analytical methods capable of preconcentration, separation and multielement detection.

Objectives and Study Overview

This study evaluates a commercial cryotrapping system integrated with a cooled injection GC inlet coupled to ICP-MS. Phosphine (PH3) and sulfur hexafluoride (SF6) serve as model analytes. Key aims include optimizing cryosampling temperature and carrier gas flow, assessing trapping efficiency, establishing calibration, and determining detection limits and reproducibility.

Methodology and Instrumentation

The analytical setup combines a Gerstel TDS G cryosampling unit, a cooled injection system (CIS), an Agilent 6850 capillary GC and an Agilent 7500 ICP-MS. Cryogenic trapping occurs in a silanized glass wool liner at temperatures down to –180°C. Samples are desorbed at 200°C and transferred to a MXT silcosteel column (30 m×0.53 mm, 5 µm PDMS) under isothermal GC conditions. ICP-MS parameters include 1250 W plasma power and isotope monitoring for 31P, 34S, with xenon as internal standard.

Main Results and Discussion

Optimal cryofocusing was achieved at –170°C with carrier flows between 40 and 200 mL/min showing negligible effect on trapping efficiency (RSD 3–6%). Calibration curves were linear (r2>0.99) over 0.1–3 ng PH3 and 6–120 ng SF6. Absolute detection limits were 3 pg for PH3 and 1 ng for SF6. Recoveries approached 100% under manual and TDS modes. Humidity in ambient air samples caused ice formation in transfer lines, necessitating upstream gas drying.

Benefits and Practical Applications

• On-line preconcentration of highly volatile species
• Simultaneous multielement detection via ICP-MS
• High sensitivity and reproducibility
• Streamlined sample handling compared to home-made cryofocusing

Future Trends and Possibilities

Advancements may focus on integrated moisture removal, extension to other volatile metalloids (As, Sb, Se hydrides), enhanced automation, miniaturized sampling modules and real-time field monitoring capability.

Conclusion

The commercial TDS G-CIS GC-ICP-MS system provides a robust, user-friendly platform for trace analysis of volatile metalloid species. It delivers excellent trapping efficiency, low detection limits and strong reproducibility, making it suitable for environmental and occupational exposure assessment.

Reference

• Feldmann J and Hirner AV. Int J Environ Anal Chem. 1995;60.
• Pavageau M-P et al. Environ Sci Technol. 2002;In press.
• Pécheyran C et al. Environ Sci Technol. 2000;34.
• Hirner AV et al. Org Geochem. 1998;29.
• Pécheyran C et al. Anal Chem. 1998;70.