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Proper guard column Inlet Installation (between analytical column and inlet)/Leak check

BChristle

Hi

I am pretty new to GCMS, so may need extra details on how to do things you suggest

I attached a picture of the set up of our gc system, so I can explain better. We recently installed a guard column using 30 cm piece of FS Deactivated 0.250 mm(Agilent PN 160-2255-30) . We reused the column nut shown in a separate picture because we did not have a new one. We installed it without a ferrule (which I am not sure if a ferrule is needed or not as it seems to have a ferrule inside (or at least it looks like it. I measured 5 mm of the column end sticking out and inserted and tightened it into the inlet. We had issues with a leak afterwards with N2 values varying from 22 to 16% and  O2 values varying from 7 to 5%. I tightened fittings, replaced inlet and septum. Nothing helped. Mass spec does not seem to be an issue. 

When I read the installation instructions and it seems a ferrule is needed. I removed the column again and reinstalled it with a Graphite Vespel Ferrule P/N 290VA191 from Thermofisher  (did not have any ferrules of that type/size from agilent. But

For the analytical column (which is Restek RTX-5MS, 0.25 mmID, 0.25 um df (PN :12623) I use these Agilent ferrules G3188-27501 (for 0.1-0.25 mm). Unfortunately I ran out of these while failing to do proper trimming after tightening the ferrule and used G3188-27505 (for 0.35-0.32 mm) for one of the analytical column connections. I'm seeing the same issues. Now the values are even higher N2 250%, O2 80%.

I tried to follow this video for leak check https://www.youtube.com/watch?v=hwPNejGBuqk , but there is no option for septum purge flow. When I set the purge flow to 50 and the column flow to 7, the total flow is 59.5. I don't understand why the total flow should be less than 10. Isn't the total flow all flows added up? Then in my case it should be 57.

Feedback, guidance, suggestions would be great.

  • 0 in reply to BChristle

    You want the GC conditions to match what you'll use when running samples.  If you tune it one way and run it a different way, the tune is not as...tuned.

    What matters:  Column flow,  QQQ collision cell flows, and Transferline, Source, and Quad temperatures.

    Always run the column(s) in Constant Flow mode.  The tuning absolutely changes with column flow changes.

    It takes a good hour or so for the system to become stable after temperature changes.

    It takes at least 15 to 20 minutes or so for a QQQ to become stable after Collision Cell flow changes.

    Never run with a leak of any consequence. If the leak is before the column the oxygen will break the spine of the stationary phase cross-linking and kill the column. If the leak is after the column, the air will interfere with the molecules and then ions of interest and also oxidize the hot metal pieces inside.  A leak reduces the lifetime of the filaments, quad(s), and electron multiplier.

  • 0 in reply to paulsalverda

    Thank you Paul. Just saw this now. I would not know how to change the collison cell flows. Is that controlled by the voltage in my MS? What is QQQ? Triple Quadrupole?

  • 0 in reply to BChristle

    Sorry! I added QQQ/Triple Quad information on this reply to you. On your 5975 system ignore the note above and use this revised one: 

    You want the GC conditions to match what you'll use when running samples.  If you tune it one way and run it a different way, the tune is not as...tuned.

    What matters:  Column flow and the Transferline, Source, and Quad temperatures.

    Always run the column(s) in Constant Flow mode.  The tuning absolutely changes with column flow changes.

    It takes a good hour or so for the system to become stable after temperature changes.

    Never run with a leak of any consequence. If the leak is before the column the oxygen will break the spine of the stationary phase cross-linking and kill the column. If the leak is after the column, the air will interfere with the molecules and then ions of interest and also oxidize the hot metal pieces inside.  A leak reduces the lifetime of the filaments, quad(s), and electron multiplier.

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