# Gas consumption estimative for price evaluation

Hi all!

I have been looking for information regarding the realistic consumption in GC, but didn't find something truly solid, especially regarding the flow variation betwing injection and pre/post injection phases.

The central idea is to build a calculator, with ajustable parameters, where people can evaluate their investment in different sources of gases.

Considering the two scenarios below, what would be the total gas flow per day for:

1 - Split injection; split ratio 20:1; collumn flow 2 mL/min; make-up 35 mL/min - Working sequential 20-minute runs during 12 hours and beeing in standy by 12 hours.

2 - Splitless injection: collumn flow 2mL/min; make-up 35 mL/min - Working sequential 20-minute runs during 12 hours and beeing in standy by 12 hours.

Please consider using the gas saver mode to minimize waste as much as possible.

Are there any significant points to consider? Please fell free to be as judicious as you want. The more thorough, the better!

Thanks!

• Hi Garbriel,

This is a great topic.  I have learned a lot about this over the years, but I think there is always newer information available.

There are a few things I would consider in addition to what you posted above.

• Are the standby conditions expected to be the same as standard method conditions?  Creating a GC 'sleep' method, will result in consuming lesser amounts of all gases when idle.
• For the example scenarios, we are missing purge flow and a purge time inputs.  However, if we are willing to sacrifice a little in accuracy, we may assume that each helium inlet consumption is essentially the gas saver setpoint, given this option is enabled.  Gas saver is typically enabled ~2min into the run and does not disengage until just before the injection takes place, so in these scenarios, 10% of the analysis time will be affected, which is a bit over an hour.
• Sampler type could play a role in consumption.  Headspace samplers, purge and trap, thermal desorption and others require gas and add volume to the carrier flow path.

I'd like to share some of our learnings.  What tends to be the more unaccounted consumption of helium happens outside of the GC in the supply lines.  Resources on how to look for leaks outside the GC can be found here:  https://www.agilent.com/en/products/gas-chromatography/gc-systems/handle-the-helium-shortage.  There is also a usage calculator on that page for specific GC conditions.

Something I think is nice, newer Agilent GC mainframes (Intuvo 9000, 8860, and 8890) have a built-in diagnostic routine that trends daily consumption of all gases on that specific system.

Thanks for the post, and I hope to learn how others approach helium management!

Regards,

Abbey