Ion 44 baseline

Hi! We are actually having some issues with my GC-MS. Some months ago started appearing an annoying ion during all the TIC, the m/z = 44. Some threads comment that could be some air leak. we have checked all the possible parts of the chromatograph and seems not to be that. Also, the autotunes are apparently correct and they do not show me any leak. 

On the other hand, ions 18 (water), 28 (nitrogen) and 32 (oxigen) are very high. I'll attach to this post some screenshots with a blank TIC. The peaks of the blank TIC are due to the m/z = 28 (nitrogen). We want to solve this problem because some peaks appear under the baseline and it is quite annoying.

 

Thank you for your attention!

attachments.zip

Top Replies

  • hello ,

     

    1) to see when/how the unwanted peaks come:

                   please create an extracted TIC once: Chromatogram > Extract ion chromatogram > type in all masses (18, 28...)

    EXAMPLE:

      

    now we can see if…

Parents
  • I sometimes get lair eaks from the big O ring that seals the analyzer to the mass spec.  So I try and wipe the seal down with methanol before I turn it on.  Also I have had leaks around the vent valve and we have had to put in a new O ring. 

  • hello

     

    * vent "valve" O-ring is a consumable, however:
       ~ it ages quickly when dirt particles are pressed in
       ~ normally this O-ring lasts for several years, if it is defective this can also be an indicator: screw is tightened too tight.
          This screw should be hand-tightened + max 1/2 turn

     

    * the large analyzer O-ring:
       i avoid cleaning the O-ring with solvent
       if my fingers are halfway clean: then i wipe the O-ring with my finger: particels away & regrease the O-ring.
       if the O-ring should have no more grease: use very thin high vaccum grease

     

    * leaks on these O-rings can be found very quickly with duster or coolant sprays.

     

    regards, M

Reply
  • hello

     

    * vent "valve" O-ring is a consumable, however:
       ~ it ages quickly when dirt particles are pressed in
       ~ normally this O-ring lasts for several years, if it is defective this can also be an indicator: screw is tightened too tight.
          This screw should be hand-tightened + max 1/2 turn

     

    * the large analyzer O-ring:
       i avoid cleaning the O-ring with solvent
       if my fingers are halfway clean: then i wipe the O-ring with my finger: particels away & regrease the O-ring.
       if the O-ring should have no more grease: use very thin high vaccum grease

     

    * leaks on these O-rings can be found very quickly with duster or coolant sprays.

     

    regards, M

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