TechTip 5: When to replace a gas cylinder

Published: 5th September 2011 | © Anthias Consulting Ltd

Knowing where your gas cylinders are located and regularly checking the contents is very important for any analytical scientist when troubleshooting an instrument. People responsible for the cylinders go on holiday or leave and the first the instrument operators knows about it is when they run out of gas and then it is a major panic!

Unfortunately, many problems have already occurred by then.

  • In gas chromatography, analytical column stationary phases are damaged at high temperatures when exposed to oxygen and if there is no clean, pure carrier gas purging through them then it will be air and contaminants getting in, oxidising or hydrolysing the stationary phase.
  • Mass spectrometers with a vacuum usually don’t shut down when there is no gas, therefore air and contaminants will be sucked in.
  • Spectroscopy instruments, like ICP-OES need a continuous purge of clean gas through them otherwise damage can occur resulting in a need for replacement.
  • Instruments with a plasma can result in damage to the torch and beyond when the gas runs out.
  • Plus, there is the down time when no samples can be analysed, maybe the gas ran out mid-way through a run requiring re-analysis of those samples and maybe standards too.

Looking further back down the line, the impurities within cylinders are held on the cylinder walls by pressure. When the gas is running out the pressure reduces and the impurities are likely to mix with the remaining gas and enter the gas plumbing. If you’re a scuba diver and have run out of air, you know that the last 10-20 bar of gas tastes horrible, well this can enter your analytical instrument too!

  • Cylinders with Built-In Purifiers (BIP) should trap contaminants before they enter your plumbing.
  • If you have traps or purifiers (as you should) between the cylinder and the instrument, then these should remove the contaminants as long as they aren’t saturated, but you will need to replace them sooner than expected.

If you don’t use traps or purifiers, the contaminants will enter the analytical system and may take some time to purge through or require physical maintenance of the instrument to take it back to full operational sensitivity. Severe contamination may require replacement of parts.

Solution:

  • Always replace gas cylinders before they run out of gas, at 30 bar consider replacement and certainly before they reach 20 bar.
  • Ensure each cylinder is regularly checked for remaining gas, this could be weekly or daily depending on the number of instruments using them.
  • Finally, every analytical scientist should know the source of their gas (cylinder or generator), where it is located and what to do if it is running out or has a problem. If a solution can’t be found there and then, shut down the instruments in a controlled manner before the gas runs out!

To learn more about gases and plumbing for GC & GC-MS, attend:

We also offer an onsite Hands-on Gas Supply & Plumbing Health Check – find out more.

For LC: LC-MS only and maintenance which includes:

For Elemental analysis training, check out our range of course here: Elemental Analysis training

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