GAS SOURCES:
Gas types commonly used in gas chromatography include: Helium, Hydrogen, Nitrogen, Air, Argon
Sources of gas include: Gas cylinders (most common), Gas generators, Piped-in gas
Gas cylinders should never be allowed to run dry or run out, due to increased contaminant concentration in the gas that can contaminate the GC system and column. There are commercially available Low Gas Alarm devices that alert you when your cylinder is running low, so that you avoid downtime and contamination. These devices are available in standalone (at cylinder) and wireless (remote) monitoring configurations. These devices are low cost alternatives to the possible high costs of damages to GC system and column which can occur when gases suddenly run out in cylinder
KEEPING GASES PURE:
Impurities in gases can be measured in the “parts per billion” – you won’t see them, but they have serious effects on your chromatography. Impurities in your gas can:
- Degrade your column
- Interfere with your analysis
- and sometimes block those capillary gas lines supplying gases to your inlet and detectors
A number of gas purifiers or traps are commercially available to help reduce the load of impurities in the gas reaching your GC system:
- In-line gas filters: These connect directly in to your gas line.
System Purifiers: These consist of a manifold which ties into your gas line, and purifiers are in the form of changeable cartridges
Gas Filter System with manifold
Single component Purifiers: These remove gas contaminants of only one type (usually air, water or hydrocarbons)
Combination traps ; These are often large capacity and have several sorbents in one cartridge to trap various contaminants
HOW TO USE GAS PURIFIERS:
- Always install traps in a vertical position.
- Metal or glass body traps are best
- There should be no O-rings in the gas flow path
- When changing the in-line purifiers, always purge the air from the regulator by repeating these steps five times:
1) Turn the regulator knob fully counter clockwise.
2) Open the Cylinder Main Valve, pressurizing the primary side of the regulator
3) Turn OFF the Cylinder Main Valve
4) Turn the Regulator Knob clockwise, slowly bleeding off the gas pressure
For single component filters, It is important to always place them in the “MHO” order from the gas source to the GC, as follows:
1) First is Moisture traps, which remove residual water from the carrier gas.
2) Second is Hydrocarbon traps, which remove hydrocarbons.
3) Final is Oxygen traps, which remove oxygen from the gas, which can rapidly degrade the GC column (indicated by increased column bleed)
SUMMARY
Good Gas Management Practices Include the following:
- Use gas purifiers (or traps) to remove contaminants from your gas source, usually air, water and hydrocarbons
- Do not use plastic, rubber or Teflon tubing in the gas path.
- Only use materials that have been cleaned for chromatographic use.
- Minimize connections, so that you minimize the opportunities for system leaks
- It’s important to check for leaks in the system whenever you change a cylinder or purifier. Use electronic gas leak detectors which have audible and visual alerts for leaks as small as 0.01 ml/min. Liquid leak detectors or soapy solutions are not recommended because they can contaminate the system.
- Keep a log book to keep track of when traps are installed and when replacement is due.
- Purge your system with carrier gas and then check for leaks whenever you open your gas lines: change cylinders, traps, or columns.
- To purge the system: pressurize the injection port, confirm column flow and then purge the column with the carrier gas for five minutes before heating the oven.
Important Tips to remember:
- Never let your cylinder gas run to empty
- Maintain your purifiers and gas lines regularly
- Keep purifiers vertically oriented.
Reference
http://www.agilent.com/chem/lowgas
http://www.agilent.com/chem/renewable
http://www.agilent.com/chem/purifierselection
http://www.agilent.com/chem/leakdetector
http://www.agilent.com/chem/flowmeter