Using GC/MSD with High Efficiency Source and JetClean to detect low level contaminants in ethylene and propylene

Significance of the Topic

The precise detection of trace contaminants such as arsine, phosphine, hydrogen sulfide and carbonyl sulfide is critical for maintaining catalyst performance in ethylene and propylene polymerization processes. Sub-ppb level monitoring enables early mitigation of impurities that can deactivate metallocene catalysts and disrupt production.

Objectives and Study Overview

This study demonstrates a robust GC/MSD approach combining a High Efficiency Source and JetClean self-cleaning ion source to achieve sub-picogram sensitivity for key gaseous contaminants in olefin streams. The method aims to deliver high chromatographic resolution, inert sample pathways and stable long-term performance.

Methodology and Instrumentation

Samples of arsine, phosphine, H2S and COS were generated from G-Cal permeation tubes and diluted via a two-stage system (5 to 50 ppb) into a pressurized sample loop (2 psi). A dual-loop 10-port valve facilitated sandwich injections of calibrants and matrix gases (helium, polymer-grade ethylene or propylene) onto a 120 m × 0.32 mm × 8 µm thick-film Select Olefins column. An Agilent 7890B GC interfaced with a 5977B MSD operated in EI-SIM mode with hydrogen introduced into the source for bleed control.

Used Instrumentation

• Agilent 7890B Gas Chromatograph
• Agilent 5977B Mass Selective Detector with High Efficiency Source
• JetClean self-cleaning ion source
• 120 m × 0.32 mm × 8 µm Select Olefins capillary column
• 10-port valve with dual sample loops and back-pressure regulator
• G-Cal permeation tubes and two-stage gas dilutor

Main Results and Discussion

The method achieved sub-picogram detection limits (e.g., ~387 fg AsH3) and resolved phosphine from matrix peaks. Over 300 injections in 4.5 days at ~5 ppb in helium, RSDs remained below 5% for all analytes. The inert deactivated flow path prevented adsorption losses, while the JetClean source maintained stable sensitivity without manual cleaning.

Benefits and Practical Applications

• Early detection of catalyst-poisoning impurities to avoid unplanned shutdowns
• High precision and repeatability for quality control in olefin production
• Low maintenance through self-cleaning ion source technology
• Inert flow path ensures reliable measurements of active, reactive gases

Future Trends and Opportunities

Advancements may include integration with online process analyzers for real-time monitoring, further miniaturization of MS systems, automated calibration protocols, novel inert materials for flow paths and coupling with advanced data analytics for predictive maintenance.

Conclusion

The presented GC/MSD configuration with a High Efficiency Source, JetClean and inert thick-film column provides a sensitive, precise and stable platform for monitoring ultra-trace contaminants in ethylene and propylene streams, supporting improved catalyst longevity and process efficiency.