Gas types commonly used in gas chromatography are Helium, Hydrogen, Nitrogen, Air, Argon and commonly used gas sources include Gas cylinders (most common), Gas generators, Piped-in gas
Impurities in gases can be measured in the “parts per billion” – you won’t see them, but they still affect your chromatography. Impurities in your gas can:
- Degrade the column
- Interfere with your analysis
Always use gas purifiers and ensure you use the right purifier for your application.
Types of gas purifiers
- In-line Gas Purifier – fittings connect directly in to your gas line.
- System type, in which a manifold connects to your gas line, and purifiers are attached in the form of changeable cartridges
You also have:
- Single component Gas Purifier which removes gas contaminants of only one type (e.g. air, water or hydrocarbons) OR
- Combination Gas Purifiers which are often large in capacity, and can remove more than one contaminant in a gas stream
Important Notes about 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
PURGING THE REGULATOR:
Purge the air from the regulator when changing in-line gas purifiers, by repeating these steps five times:
- Turn the regulator knob fully counterclockwise.
- Open the Tank Main Valve, pressurizing the primary side of the regulator
- Turn OFF the Tank Main Valve
Turn the Regulator Knob clockwise, slowly bleeding off the gas pressure
It is important to place single-component traps in the following order from the gas source to the GC:
- First is Moisture traps remove residual water from the carrier gas.
- Hydrocarbon traps remove hydrocarbons.
- Finally, Oxygen traps remove oxygen from the gas, which can rapidly degrade the GC column
Gas purification needs differ based on the detector you are using:
- FID: need to filter out hydrocarbons
- ECD: need to filter out moisture, hydrocarbons and oxygen
- MS: it is best to use a combination trap, followed by indicating trap
GOOD GENERAL GAS MANAGEMENT PRACTICES:
- Use gas purifiers 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.
- Keep a log book to keep track of when traps are installed and replacement is due.
- Purge your GC 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.
Tips to remember:
- Never let your cylinder gas run to empty
- Maintain your purifiers and gas lines regularly
- Keep purifiers vertically oriented.
Written by Muyiwa Adebola