ANALYSIS OF PROPYLENE IMPURITIES USING SELECT LOW SULFUR COLUMN AND SINGLE TUNE WITH GC-ICP-MS QQQ ORS

Importance of the Topic

The accurate measurement of trace impurities in high-purity propylene is critical for polymerization processes, influencing catalyst lifetime, product clarity, and odor. Quantitation at part-per-billion levels allows manufacturers to maintain consistent product quality and predict catalyst performance.

Objectives and Study Overview

This study evaluates a streamlined approach using a single GC column and one tune method to detect key gaseous contaminants—phosphine (PH₃), arsine (AsH₃), hydrogen sulfide (H₂S), and carbonyl sulfide (COS)—in propylene. The goal is to replace multi-column, multi-mode protocols with a unified, efficient analysis.

Methodology and Instrumentation

• Gas Chromatograph: Agilent 7890B with a 60 m × 0.32 mm Select Low Sulfur column; helium carrier at 20 psig; isothermal oven at 35 °C; 400 µL split injection (~5:1).
• Mass Spectrometer: Agilent 8800 ICP-QQQ in MS/MS mass-shift mode using oxygen as cell gas. Monitored transitions: S (m/z 32→48), P (31→47), As (75→91).
• Sample Preparation: Dynamic dilution of 10 ppmv gas standards (PH₃, AsH₃ in H₂; H₂S, COS in Ar) via a fixed restrictor system.
• Injection and Matrix Management: 10-port gas sampling valve for simultaneous sample and standard addition; high-flow Deans switch vents bulk propylene while maintaining ~800 mL/min Ar makeup gas to protect the torch.

Main Results and Discussion

• Chromatographic Separation: The Select Low Sulfur column resolved all analytes from the propylene matrix, overcoming coelution issues seen with conventional columns.
• Detection Limits: Achieved 3× S/N detection limits of 0.05 ppbv for AsH₃, 0.15 ppbv for PH₃, 1.9 ppbv for COS, and 2.5 ppbv for H₂S.
• Matrix Effects: Propylene displaces carrier gas, shifting retention times. Standard additions via the 10-port valve ensure accurate analyte identification and optimized vent timing.
• Interference Suppression: Oxygen in the Octopole Reaction System effectively removes OO⁺ interferences at m/z 32 and minimizes background, allowing a single tune mode.

Benefits and Practical Applications

This unified GC-ICP-QQQ method simplifies routine monitoring of sulfur-, phosphorus-, and arsenic-based contaminants in propylene. It increases laboratory throughput by eliminating column and tune changes, providing reliable sub-ppb quantitation essential for catalyst life prediction and QA/QC in petrochemical production.

Future Trends and Possibilities

Advancements may include the use of mega-bore columns with un-split injections for enhanced sensitivity, integration of automated, real-time sampling interfaces for process monitoring, and adaptation of this approach to other industrial gases requiring ultra-trace analysis.

Conclusion

The combination of the Agilent Select Low Sulfur column with GC-ICP-QQQ in a single oxygen MS/MS mode delivers a robust, sensitive, and interference-resistant platform for simultaneous ppb-level quantitation of PH₃, AsH₃, H₂S, and COS in propylene.