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

Importance of the Topic

The polymerization of ethylene and propylene relies on metallocene catalysts that are highly sensitive to trace impurities such as arsine, phosphine, hydrogen sulfide and carbonyl sulfide. Even low-level contamination can deactivate catalysts, reduce polymer quality and force unscheduled shutdowns. Therefore, detecting these reactive contaminants at sub-picogram and sub-ppb levels in olefin feed streams is critical for process optimization and cost control.

Objectives and Study Overview

This study evaluates a GC/MS system combining a High Efficiency Source (HES) and JetClean self-cleaning ion source to measure trace levels of arsine, phosphine, H2S and COS in polymer-grade ethylene and propylene. Key goals include:

• Establishing method detection limits and linearity.
• Demonstrating chromatographic resolution of active contaminants from abundant matrix peaks.
• Assessing long-term stability and repeatability during extended runs.

Methodology and Instrumentation

The analytical setup employs an Agilent 7890B GC with a 10-port valve and dual sample loops for sandwich injection of calibrant and matrix gases. The separation uses a 120 m × 0.32 mm × 8 µm Select Olefins column. The MSD is a 5977B with an HES operated in EI mode under SIM acquisition of ions 34, 60 and 76. Key features:

• G-Cal permeation tubes and two-stage dilution (5–50 ppb range) with back-pressure regulation at 2 psi.
• Continuous hydrogen flow (0.15 mL/min) into the source to mitigate column bleed effects.
• JetClean ion source for automated in-situ cleaning and consistent response.

Main Results and Discussion

Instrument detection limits (IDLs) ranged from 0.045 to 0.715 fg (0.43–29.9 ppb), with linearity coefficients (R2) above 0.9987. In polymer-grade ethylene at ~1.5 ppb, all four contaminants were baseline-resolved from matrix peaks. In propylene, COS co-eluted with propylene, but phosphine, H2S and arsine remained distinguishable. Long-term testing over 300 runs (4.5 days) in a helium matrix demonstrated repeatability below 5 % RSD for all calibrants. An inert flow path eliminated the need for extended conditioning when running aggressive analytes like H2S.

Benefits and Practical Applications

The combination of HES and JetClean delivers:

• Sub-picogram detection capability for critical catalyst poisons.
• Robust chromatographic separation in complex olefin matrices.
• Stable, low-maintenance operation over hundreds of injections.

These advantages enable real-time monitoring of feed gas quality and proactive catalyst management in polyolefin production.

Future Trends and Opportunities

Potential developments include integration of online sampling for continuous process surveillance, application of high-throughput multiplexed GC platforms, and incorporation of machine-learning algorithms for pattern detection in complex impurity profiles. Advances in source design and column materials may push detection limits further into the attogram range.

Conclusion

The validated GC/MS method using an HES and JetClean source achieves sub-picogram sensitivity, excellent resolution and long-term stability for detection of arsine, phosphine, hydrogen sulfide and carbonyl sulfide in ethylene and propylene. This approach supports improved catalyst protection and optimized polymerization processes.

Reference

Smith Henry A., Quimby B. D., Astiphan B. Using GC/MSD with High Efficiency Source and Hydrogen Cleaning to Detect Low Level Contaminants in Ethylene and Propylene; ASMS 2016, TP161.