Trace Level Gases via GC/MS and a Unique Valve Switching Concept

Significance of the Topic

This application note addresses the critical need for accurate, low-level quantification of permanent gases and carbon dioxide in environmental and industrial settings. Monitoring trace concentrations of neon, nitrogen, oxygen, carbon monoxide, argon, methane and CO2 is essential for air quality assessment, process control and compliance with regulatory standards.

Objectives and Study Overview

The primary goal of the study is to demonstrate a novel valve-switching configuration in a GC/MS system that achieves baseline separation and sensitive detection of five permanent gases and CO2 within a 16-minute run time. This approach aims to simplify hardware requirements while maintaining high throughput and sub-ppm detection limits.

Methodology

The technique employs two packed capillary PLOT columns—PoraPLOT Q and Molsieve 5 Å—interfaced via a 10-port Valco injection valve. In the first valve position, all permanent gases elute as a single composite peak from the PoraPLOT Q column while CO2 remains retained. Upon switching to the second position, CO2 is directed to the mass spectrometer, and the permanent gas mixture is routed through the Molsieve column for individual separation before passing back through the PoraPLOT Q column to the detector. Precise valve timing prevents CO2 adsorption on the Molsieve phase and eliminates flow reversal, ensuring a single transfer line to the MS.

Instrumentation Used

• Gas chromatograph with Valco 10-port injection valve at 30 °C
• Column 1: Agilent J&W PoraPLOT Q, 0.53 mm × 25 m, df=20 μm
• Column 2: Agilent CP-Molsieve 5 Å, 0.53 mm × 25 m, df=50 μm
• Carrier gas: Helium at 30 kPa (0.3 bar)
• Transfer line: 0.25 mm × 10 m fused silica, methyl-deactivated
• Detector: Mass spectrometer
• Sample loop: 250 μL volume, analyte concentration ≈100 ppb in helium

Key Results and Discussion

The described configuration achieved complete separation of five permanent gases—neon, nitrogen, oxygen, carbon monoxide and argon—within a single co-elution peak followed by resolved CO2 detection. Total cycle time was 16 minutes. The additional passage of the permanent gases through the PoraPLOT Q column after separation resulted in only a minor sensitivity decrease. System integrity was maintained by enclosing all fittings in a helium-purged housing to prevent leaks and contamination.

Benefits and Practical Applications

This method offers a streamlined workflow for simultaneous determination of permanent gases and CO2 at sub-ppm levels without complex flow reversals or multiple transfer lines. It is particularly suited for environmental monitoring laboratories, industrial QA/QC processes and research applications requiring reliable trace gas analysis.

Future Trends and Applications

Advances may include integration with automated sampling interfaces, microfluidic GC platforms and enhanced column materials to further reduce runtimes and improve detection limits. Coupling this valve-switching strategy with real-time data processing algorithms could enable on-line monitoring in remote or field environments.

Conclusion

The unique valve-switching concept in a dual-column GC/MS setup provides a robust, efficient and sensitive solution for trace-level analysis of permanent gases and CO2. Its simple hardware requirements and fast run times make it an attractive choice for diverse analytical applications.

Reference

• Agilent Technologies, Inc. Trace Level Gases via GC/MS and a Unique Valve Switching Concept. Application Note, December 17, 2018.