Three-Part Total Purification System for Gas Chromatography

Importance of the Topic

High-purity gases are essential for reliable gas chromatography performance. Impurities such as oxygen, water, and hydrocarbons can degrade column stationary phases, shorten detector lifetimes, and raise baselines, compromising sensitivity and accuracy. Traditional reliance on certified gas cylinders increases operational costs and logistical burdens.

Objectives and Study Overview

This work introduces a three-part gas purification system designed to deliver ultrapure carrier and detector gases from less expensive, 99.995% source gases. The system comprises:

• A High Capacity Heated Gas Purifier
• An OMI Indicating Purifier
• A Molecular Sieve 5A Moisture Trap

The aim is to remove critical contaminants to sub-ppm and ppb levels, extend column and detector lifetimes, and reduce overall gas costs.

Methodology and Instrumentation

The three modules operate in series:

• High Capacity Gas Purifier: A metal tube within an oven houses reactive getter material that chemically binds oxygen, water, CO, and CO₂. Trapped species remain irreversibly bound, even when the oven is off.
• OMI Indicating Purifier: A glass-bodied cartridge packed with Nanochem® resin removes residual oxygen, water, sulfur, halogens, and oxidized species to 10–100 ppb. A color change in the resin provides a visual end-point for replacement.
• Molecular Sieve 5A Moisture Trap: A packed tube upstream of the high-capacity purifier reduces water to below 0.5 ppm for up to one year and also protects flame ionization detectors and pneumatic lines.

Main Results and Discussion

By combining gettering, adsorption, and molecular sieving, the system achieves:

• Water levels below 0.5 ppm
• Residual oxygen and other impurities at 10–100 ppb
• Detection limits in the parts-per-trillion range with ECD, Hall®, GC/MS, and GC/FTIR detectors

The modular approach allows bulk purification by the heated purifier and final polishing plus visual quality assurance by the OMI module. This arrangement also prevents back-diffusion of ambient moisture or oxygen into the GC inlet.

Benefits and Practical Applications

Key advantages include:

• Significant cost savings by using economical source gases instead of specialty certified cylinders
• Extended lifetime of columns and detectors due to continuous removal of corrosive contaminants
• Improved analytical sensitivity and reproducibility
• Flexibility to purify multiple GC systems in parallel

Future Trends and Opportunities

Emerging directions in gas purification may include:

• Integration of real-time impurity monitoring sensors for proactive maintenance
• Miniaturized cartridges for bench-top and portable GC systems
• Advanced sorbent materials targeting trace-level organic contaminants
• Automated switching systems for fuel-cell hydrogen and specialty carrier gases

Conclusion

The three-part purification system offers a cost-effective, robust solution for achieving ultra-high gas purity in GC applications. By combining reactive gettering, visual adsorption monitoring, and molecular sieving, laboratories can lower operating expenses, enhance instrument longevity, and achieve superior analytical performance.

Used Instrumentation

• Supelco High Capacity Gas Purifier (110 VAC/220 VAC, 1/8″ or 1/4″ fittings)
• OMI Indicating Purifier (OMI-2, OMI-4 series, glass body with 1/8″ fittings)
• Supelco Molecular Sieve 5A Moisture Trap (200 cc and 750 cc, various fittings)