Flow In saver gas

Hi, 

Which is the correct flow in saver gas for GC/MS? I have it at 20ml/min. 

  • Hi Carol,

    That is perfect. The gas saver defaults to that flow and the design of the saver feature was for 20/ml/min which allows enough total flow to operate properly.

    Regards

    James

  • Hi,

    Kindly go with below chart as per column n split flow.

  • It's not safe for your columns to set the gas saver less than 20 ml/min.   There can be back diffusion of air into the inlet and so into the liner and the column. If the inlet is hot, that oxygen can cause issues with the inertness of the liner. Columns can be damaged by as little as 50ppm oxygen.  The low inlet pressure because the column outlet is at vacuum in a mass spectrometer allow this to happen even easier. The oxygen in the column goes into the source and causes issues inside the hot MS.  20 ml/min is the safest absolute minimum and a bit higher may be a bit safer depending on other settings.   If you want to save helium there are other ways that are better than just trying to turn the flows down.

  • Is this necessary on a GC when it is sitting idle for long periods of time or can I turn off the gas saver and just run a 1.5 ml\min flow to the column?  Currently,  I have a split inlet with a flow of 1.5ml\min, septum purge of 1 ml\min and column flow of 1.5ml\min with a helium carrier gas.  This is strictly when the unit is in standby.  Sometimes we don't run samples for weeks, so want to conserve helium.  Also wondering if it is a straight forward scenario to even convert to high purity nitrogen when in standby mode?  Thx

  • I'd refer to Paul's comments above regarding diffusion of air into the inlet when the inlet total flow gets too low.  Switching to an alternate such as N2 is pretty straightforward.  Agilent even has a helium conservation module for 7890 and 8890 GCs to simplify and automate the process: https://www.agilent.com/en/product/gas-chromatography/gc-systems/helium-conservation-module-for-gc 

  • Hi Lance.  Would it be possible to touch base with you in regards to the nitrogen switch?  Is it just a matter of swapping out cylinders and modifying parameters slightly i.e pressures, flowrates?  Our GC unit sits idle for long duration, so an alternate carrier gas during these periods would be ideal.  We would probably just swap out cylinders manually as it isn't in the budget to look at an EPC as you have linked above, at this time.  Thanks.

  • You can swap out cylinders to do it, but that means a lot more tubing, etc. to purge when you want to run.  With the EPC unit, you would simply load the appropriate method to use it and the switch is done at the instrument.  Much less tubing to purge and quicker to have the system ready to run when you need it.

    If you're idling the system for a few weeks at a time, it may be simpler to shut the system down.  More details on how to safely do that can be found at  How to shut down an Agilent GC/MS for power fails up to long term storage 17Mar2020.pdf  

  • We have 13 GCs on 5-17 mL total flow when idle and they work just fine for environmental samples and surge events the CDC sends us. 552.3 instrument probably has 3500 injections with no maintenance and a 17 month old curve. Some mass specs with a concentrator for 524 or TO-15 will see water climb in sleep mode but it all blows out after the tune is off. If there is column damage it's still cheaper to toss a new one in than foot the helium bill in my opinion, I haven't seen abnormal wear yet 9 months in. Our CDC unit has been running like this for years.

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