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Thermo Fisher Scientific

Low sensitivity and high column bleed


Unit is experiencing low sensitivity and high column bleed.


  • TSQ Series
  • ISQ Series


If low sensitivity is observed check the following:

  1. Run an Air/Water scan and check that the isn’t an air leak. m/z 18 should be bigger than m/z 28. See picture 1 for an example.


Figure 1: ISQ Manual Tune

  1. Change to full scan and check background spectrum for any possible contaminates. m/z 207 is quote a common contaminate from a bleeding column.
  2. Turn on Cal Gas (FC43) and see if the m/z 207 peak can still be seen. If so, this could a that the column is the issue.
  3. If not contaminate peak is observed, run a tune and diagnostics following your normal protocols to see if sensitivity returns.
  4. Remove and clean the Ion Source.
  5. Remove the column from the MS and blank off the MS and allow to pump down below 80 mTorr.
  6. Insert the clean source and wait for 30 minutes.
  7. Check Air/Water spectrum to ensure system leak tight.
  8. Check background and Cal Gas spectrum for presence of contaminate ions such as m/z 207. (Hyrocarbons from the cleaning process may be visible.
  9. Tune the instrument using Smart Tune or running a Default tune followed by Daily Tune and run diagnostics.
  10. If sensitivity restored in this state, condition or replace existing column and then reintroduce in to the MS.
  11. If contaminates still present on conditioned column remove and replace it.
  12. If new column installed and contaminates still present complete injector maintenance as detailed in the Trace 1300 Series GC manual. Also reclean the Ion Source or raise the temperature to 300C – 350C to burn off any contaminate.
  13. If sensitivity still down contact Service Desk for additional support.
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