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

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.

Parents
  • A ferrule of the proper size and composition is always required on all GC and GCMS column connections. In general, ferrules are one time use items.

    The split/splitless inlet with a 0.25mm id column/guard column installed on a GCMS system should use the short, graphite/vespel 5181-3323 ferrules. (5181-3323 | Agilent)  The column should stick out 4-6 mm past the end of the ferrule, although I like a mm or so higher.  A tiny bit higher is definitely better than a tiny bit too low.  The Self-Tightening column nut makes installation easier G3440-81011 (G3440-81011 | Agilent ) .

    The Purge Ultimate Union (PUU) connections with a 0.25 mm id column/guard column must use the Flexible Metal Ferrules, either G2855-28501 (G2855-28501 | Agilent )  or G3188-27501 ( G3188-27501 | Agilent) .   If  you tried a graphite or graphite/vespel ferrule on those connections, there is residue in the Purged Ultimate Union that will cause problems. The PUU will need to be cleaned out, for sure.

    The MS transferline connection with a 0.25mm id column can be done two ways.  The brass nut shown 05988-20066  (05988-20066 | Agilent)  requires the long, graphite/vespel 5062-3508 ferrules (5062-3508 | Agilent)  .  The Self-Tightening column nut makes installation easier G3440-81013 (G3440-81013 | Agilent ) and requires the short, graphite/vespel 5181-3323 ferrules as shown above for the inlet.

    For leak checking, set the inlet to SPLIT mode, Gas Saver OFF, Split flow 20 ml/min, column flow 1.2 ml/min.  On a 6890 the septum purge is fixed at 3 ml/min.  Make sure that your column configuration is correct. It should show two columns. Column 1 from inlet to AUX# (frequently Aux4, but could be others depending on plumbing), and then column 2 from AUX# to MSD.   Set column 1 flow to 1.1 ml/min and column 2 flow to 1.25 ml/min.   It is required that column 2 is 0.1 to 0.3 ml/min HIGHER than column 1.

    The maximum column flow into a 5975C GCMS depends on high vacuum pump type.  The max on a diffusion pump system is 2.0 ml/min. The max on a turbo pump system is 4.  Optimum helium column flow into any Agilent GCMS ion source is 0.8 to 1.4 ml/min.  

    Hope that helps.

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