Detection and Quantitation of Carbonyl Sulfide, Using SIFT-MS

Importance of the topic

Carbonyl sulfide (COS) is a volatile sulfur compound with potential use as a fumigant, especially in cases where pests develop resistance to conventional treatments. Rapid, accurate monitoring of COS concentrations is critical for ensuring effective pest control and environmental safety.

Study objectives and overview

This report assesses the capability of Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) to detect and quantify COS in gas samples. Key performance metrics, including linear range, limit of detection (LOD), and limit of quantitation (LOQ), are established.

Methodology

• Sample preparation: COS was synthesized by reacting ammonium thiocyanate with sulfuric acid, dried over calcium chloride, purified via freeze–thaw cycles, and diluted in dry nitrogen.
• SIFT-MS analysis modes:
  • Full Scan Mode (FSM): Acquired mass spectra from m/z 15–200 using H3O+, NO+, and O2+ reagent ions to verify sample purity and identify product ions.
  • Selected Ion Mode (SIM): Monitored COS-specific product ions for quantitative analysis in parts per billion by volume (ppb).

Used instrumentation

• Syft Technologies Voice200® SIFT-MS system.
• Reagent ions employed: H3O+, NO+, and O2+.

Key results and discussion

• FSM confirmed that COS reacts solely with O2+ to produce a COS+ ion at m/z 60; no reaction was observed with H3O+ or NO+.
• SIM calibration demonstrated excellent linearity (R^2 = 0.999) over four orders of magnitude.
• LOD of 1.8 ppb and LOQ of 3.1 ppb were achieved with a 5 s sampling interval, with isobaric interferences (e.g., acetic acid, propanol isomers) identified as limiting factors.
• Natural atmospheric COS levels (~0.5 ppb) are below the LOD, while occupational exposure limits (100 ppm) are orders of magnitude higher, underscoring the method’s suitability for fumigation monitoring.

Benefits and practical applications

• Real-time, direct analysis without the need for chromatographic separation.
• High specificity and reduced interferences through the use of multiple reagent ions.
• Rapid throughput ideal for shipping container screening and industrial fumigation quality control.

Future trends and opportunities

• Integration of SIFT-MS into multi-analyte monitoring platforms for comprehensive fumigant profiling.
• Development of portable SIFT-MS instruments for on-site environmental and safety assessments.
• Advances in reagent ion chemistry to further improve detection limits and mitigate interferences.

Conclusion

The Syft Voice200® SIFT-MS technique offers a robust, sensitive, and rapid approach for COS detection. It provides a linear response across a wide concentration range with sub-ppb detection capabilities, making it a valuable tool for real-time fumigation monitoring.

References

• Wright T. Carbonyl Sulfide: Progress in Research and Commercialization of a New Commodity Fumigant. Stored Grain Research Laboratory, CSIRO Entomology; 1992.
• Adams WT, Smith D, Paulson SE. Gas-phase reaction kinetics for sulfur-containing compounds. Journal of Chemical Physics. 1980;72:288–297.
• Skoog DA. Principles of Instrumental Analysis. 3rd ed. Philadelphia: Saunders College Publishing; 1985.
• Material Safety Data Sheet: Carbonyl Sulfide. Oxford University; accessed December 2009.