ion gauge pressure fluctuation

Hello everyone

Does anybody help with ion gauge pressure fluctuations?

I am using GC 5890 and HP 5972A with the foreline pressure reading 37 mtorr with the column flow 1.32 ml/min and He gas flow at 55 psi. Ion gauge pressure showing fluctuation between 2.1*10-5 to 2.4*10-5.

Can anybody suggest the reason of the fluctuation in the pressure?

Thank you.

  • 5972?  Time to upgrade man!  You could have a small leak somewhere most likely the detector nut.  If the air/water check is fine I wouldn't worry about it as old as it is.

  • Thank you for the suggestion. Yes ,we are thinking to upgrade the instrument but before that we want it to be in working condition.by detector nut ,you mean seal at the analyzer ring or seal at the transfer line? 

  • Hello ,

     

    does the problem still exist?

     

    if so:

    a) when do these fluctuations occur?

       e.g. with altered column flows or peaks arriving in MS vacuum changes are normal


    For me 2 statements are important:
    1) is high vac. low enough?
    2) does the tune report look perfect? (if you want you can upload your current tune here)

     

     

     

    b) slight variations in the high vac value may be possible., e.g. last digit, a change of 1-2 higher or lower

     

    c) For leak search @MSD a spray is mandatory:

     (aero duster spray or) electronic freeze spray down to -45°C (watch for m/z 83) 

     typical spray (hopefully this will not be seen as advertising here ;-) ) 

     

    ferrules & seals are typically hand-tightened + maximum 1/8 (-1/4) turn. Now if I suspect a leak:

      * manual tune: watch m/z 83

      * briefly apply a spray of the freeze spray to the screw connection/seals (1-2s is sufficient)

                   now a seal can be identified as dirty or defective. i avoid tightening metal screws/nuts too much.

        Then ferrules are not stressed too much, because many users have already destroyed the MS transferline by preventive "over" tightening.

     

     

    regards, M.

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