Applied Analytical Systems

Gas Management Best Practices in Gas Chromatography

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

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