Fast Trace Analysis in Ultra High Purity Helium using Parallel PLOT Columns and a Single PDHID Detector

Significance of the topic

Ultra high purity helium is essential in many industrial and research applications. Traces of permanent gases (H₂, O₂, N₂, CO, CH₄) and CO₂ degrade performance in semiconductor manufacturing, gas chromatography carrier gas, and other sensitive processes. Fast and accurate detection of these impurities at sub-ppm levels is critical to ensure product quality and process reliability.

Objectives and Study Overview

This application note describes a rapid gas chromatographic method for simultaneously quantifying low-level permanent gases and CO₂ in helium. The goal was to achieve complete separation and detection within 120 seconds using a single detector and a dual-column, parallel configuration, thereby simplifying analysis and reducing cycle time.

Methodology and Instrumentation

A SCION 456-GC system was configured with two parallel columns connected to one injector and one detector.

• Injector: Gas sampling valve with 1:15 mini gas splitter
• Column 1: SCION Molsieve 5A, 10 m × 0.32 mm × 30 µm
• Column 2: SCION PLOT Q, 30 m × 0.32 mm × 10 µm
• Oven: 60 °C isothermal
• Carrier gas: Helium 99.99999%, 12 psi
• Detector: Pulsed Discharge Helium Ionization Detector (PDHID) at 120 °C, range 12

Key Results and Discussion

The parallel column setup achieved baseline separation of H₂, O₂, N₂, CO, CH₄, and CO₂ within 120 seconds. The lowest detection limit was approximately 50 ppb for all analytes. Repeatability was excellent, with relative standard deviations (RSD) below 1.0% for individual columns and 0.66% for summed methane over 20 injections. Peak shapes were sharp and free of tailing, even for CO, due to the inert nature of the molsieve column.

Benefits and Practical Applications

This method offers several advantages for high-purity helium analysis:

• Rapid cycle time reduces sample throughput constraints.
• Single-detector, dual-column design minimizes instrument complexity.
• High sensitivity and low detection limits support stringent quality control.
• Robust peak shapes ensure reliable quantification of all permanent gases.

Future Trends and Potential Applications

Potential developments include:

• Automated, on-line sampling integration for real-time purity monitoring.
• Extension of the parallel column concept to other carrier gases (e.g., hydrogen, nitrogen).
• Miniaturized GC systems for field or point-of-use high-purity gas analysis.
• Coupling with advanced detectors (e.g., mass spectrometry) for broader impurity profiling.

Conclusion

The SCION 456-GC equipped with parallel PLOT and molsieve columns and a PDHID offers a fast, sensitive, and reliable solution for trace analysis of permanent gases and CO₂ in ultra high purity helium. The method achieves complete separation and detection within two minutes and demonstrates outstanding repeatability, making it ideal for stringent industrial quality control applications.

References

• SCION Instruments. Fast Trace Analysis in Ultra High Purity Helium using Parallel PLOT Columns and a Single PDHID Detector. Application Note AN0007.