7010 GC/MS air/water leak at MS interface

Hello,

I confirmed I have a leak at the MS interface of a 7010 GC/MS TQ. Roughly 22% H2O and 22% Nitrogen and 6% oxygen. I tried two different self tightening nuts and also the older model MS interface nut while using a no hole ferrule and still can observe the leak. Is it possible MS interface itself is damaged and is this part replaceable? Are there no-hole ferrule that would fit the newer self tightening nuts, if so what is the part number?

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  • The HES ion source does not work properly without the helium carrier gas flowing into it between 0.8 and 1.4 ml/min or so. The ion ratios will be very far off with a no-hole ferrule installed, so that is only useful for gross leak checking.  The no hole ferrule for the self tightening nuts is: 5190-0454.

    Column nuts do not need to be tightened very much to stop any air. You're only sealing against atmosphere - 14.7psi - and the sealing surfaces are very small.  Vent. Remove the column from the MS, wipe off the threads with a solvent-dampened cloth to remove any ferrule residue or metal residue from the nuts. Inspect the end of the transferline tip where the ferrule seals. Is it clean, smooth, flat, and not scratched?  Is the transferline bent from previous overtightening? 

    If it's fine, use a new ferrule and install the column. Put the column through the nut, through the ferrule in the right direction, cone end into the nut, then install the column into the MS. Open the analyzer door so that you can access the column inside. Push the column all the way through the transferline until some inches show through by the source. Cut the end of the column, then WIPE that part of the column with a solvent-wet lint-free cloth.  Pull the column back into the GC oven until the end is flush with the ceramic transferline tip. Tighten the column nut only until you cannot move the column any more.  Once the ferrule has grabbed and the column can't be moved any more, tighten the nut -- a tiny little bit, like five degrees or so, hardly any.  The spring washers inside the self-tightening nut will compress and hold the ferrule, sealing the column properly.

    Some say that the column needs to stick out past the ceramic tip seal one or two millimeters for the HES source. That's fine, but not a requirement for most applications. I did some tests myself and found that I still saw great looking peaks with the column pulled back into the interface even five or six millimeters. The peaks are coming out of your column into the vacuum really, really fast and one millimeter or two millimeters will make very little difference as long as it's not installed too far into the MS.

    22% H2O. With that much water, there will always be some air showing.  How long did you wait before that test? You need to wait at least an hour or two after pumping down before doing any useful testing on a GCMS.  The water should be down to a lower level after pumping for four to six hours, for sure after pumping overnight.

  • Thank you for the feed back. After trying different types of MS columns nuts, one of the old fashioned nuts gave me an air/water check with results which near the limits. Made sure their is Helium gas flowing through the column, N2 is turned off in the collision cell and waited couple days to before testing after pumping down. My next step is to vent and inspect the transfer line tip/threading.

    Abundance:
    PFTBA:  1054714.5
    Water: 41491.5
    Oxygen: 27467.5
    Nitrogen  102371.4

    Ratios:
    H2O: 3.93% 
    O2: 2.60%
    N2: 9.71%

  • Hope, problem will solve...

  • Hi chemist123,

    Were you able to resolve the issues fully? 

    Regards

    James

  • We're working on getting the MS transfer-line replaced. 

  • The transferline is a brazement -- not welded but brazed together and tested under vacuum.  They don't break. The threads and ferrule sealing surface get damaged or bent by overzealous wrench-users, using the wrong ferrule, or putting the ferrule on backwards. The transferline is held onto the mass spectrometer manifold by three screws and the seal there is an O ring.  The undisturbed O ring very rarely leaks. 

    Please let us know the final solution!

  • We ended up replacing the transferline, the O-ring and the gasket to the ci (I think that is what it's called) and now the air/water checks look better and I do not see any leaks when spraying with an air can near the transfer line area between the MS and GC. Hard to say if it was the O-ring or threads, but it's leak free now!

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