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 such as phosphine (PH3) and sulfur hexafluoride (SF6) is critical due to their widespread industrial use (fumigation, arc quenching, semiconductor processing) and high toxicity at trace concentrations. Reliable detection at sub-nanogram levels is essential for occupational hygiene and environmental monitoring.

Objectives and study overview

This work evaluates a commercial cryotrapping–GC–ICP-MS setup (TDS G–CIS coupled to Agilent 7500 ICP-MS) for preconcentration, separation, and simultaneous multielement detection of highly volatile metalloid compounds. PH3 and SF6 serve as model analytes to optimize trapping temperature, carrier-gas flow, and method performance.

Methodology and Instrumentation

• Cryotrapping unit (TDS G): silanized glass-wool tubes; desorption at 200 °C; valve/transfer line at 150 °C.
• Cooled injection system (CIS): programmable from –180 to +150 °C (optimum –170 °C), heated at 12 °C/s for transfer to GC.
• Gas chromatography: MXT silcosteel column (30 m × 0.53 mm, 5 µm PDMS), helium at 10 mL/min, isothermal 80 °C, splitless.
• ICP-MS: Agilent 7500, 1250 W, Ar cooling gas 15 L/min, nebulizer 0.95 L/min, dwell 20 ms per mass, monitoring 31P, 34S; xenon as internal standard.
• Sampling: cryogenic trapping at –175 °C with pre-dried ambient air (0.2 L/min); storage at –190 °C prior to analysis.

Main Results and Discussion

• Optimal CIS trapping temperature: –170 °C ensures quantitative retention of PH3 and SF6; temperatures above –150 °C lead to significant losses.
• Carrier-gas flow (40–200 mL/min) had negligible effect on trapping efficiency (RSD < 10 %).
• Calibration linearity: R² > 0.99 for PH3 (0.14–2.88 ng) and SF6 (5.8–116.4 ng).
• Absolute detection limits: 3 pg for PH3 (31P) and 1 ng for SF6 (34S, 4.2 % abundance) based on 3σ criterion.
• Recoveries ranged from 90 % to 120 % across manual and TDS modes, demonstrating robust quantitative performance.
• Water vapor in sampled air can clog transfer lines; efficient drying limits icing and allows larger sample volumes.

Benefits and Practical Applications

This commercial cryotrapping–GC–ICP-MS platform streamlines sample handling, minimizes transfer artifacts, and delivers ultra-trace sensitivity for fumigants, insulating gases, and other volatile metalloid species in workplace and environmental air.

Future Trends and Possibilities

• Application to additional hydride-forming elements (As, Sb, Se, Sn) in geochemical and environmental studies.
• Field-deployable automated sampling units integrating cryotrap and GC-ICP-MS for on-site monitoring.
• Advanced humidity and interferent removal to extend sample throughput and system robustness.
• Coupling with isotope-ratio mass spectrometry for source apportionment and tracer studies.

Conclusion

The integrated TDS G–CIS–GC–ICP-MS system provides highly sensitive, reproducible, and user-friendly analysis of volatile metalloid species. Optimized trapping temperature and gas handling ensure reliable trace-level detection suitable for industrial hygiene and environmental surveillance.

References

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