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

GAS PURITY:

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.

References

 http://www.agilent.com/chem/lowgas

http://www.agilent.com/chem/renewable

www.agilent.com/chem/purifierselection

 http://www.agilent.com/chem/leakdetector

Written by Muyiwa Adebola

[email protected]

www.aasnig.com