4 Replies Latest reply on Oct 26, 2018 1:57 AM by yitnazewdie

7000C GC MS with exraction source sensitivity become low

yitnazewdie Aug 30, 2018 4:42 AM

One of our customer GC MS/7890B 7000C with extractor source was working well.

But after stopping for a certain period & trying again now the sensitivity was decreased & not comes to the previous one.

we made cleaning of ion source 3 times while changing the extractor with new one & change the detector.But there is no sensitivity improvement as previous one.

Even the sensitivity of tune with inert source mode was better than with extractor mode one.

what will be the probable cause of decreasing in sensitivity like this?

For more information please look on attached tune file of the previous one & present one.

Best regards

Re: 7000C GC MS with exraction source sensitivity become low

paulsalverda Sep 6, 2018 10:19 AM (in response to yitnazewdie)

The tunes are all acceptable. The total abundances and relative abundances are within the normal ranges.
The polarity of Q1 was changed between the two tunes from 2015 and the new ones.

What specifically do you think is less sensitive?
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- Re: 7000C GC MS with exraction source sensitivity become low
  
  yitnazewdie Oct 26, 2018 7:57 AM (in response to paulsalverda)
  
  Dear paulsalverda
  
  Tahnks so much for your reply
  
  The abundance(number of ion count) for extraction source was not what
  was suppose to be.
  For comparison The previous ion count for mass 69 was 21772768.0 where
  as now it become 2645672.
  
  So that is what I mean that there is an indication of sensitivity loss
  on analysis using extraction source.
  
  With many thanks & best regards
  
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  - Re: 7000C GC MS with exraction source sensitivity become low
    
    paulsalverda Sep 11, 2018 10:08 AM (in response to yitnazewdie)
    
    Yitna, The raw height counts in the tune report are not an indication of the system sensitivity as the multiplier is adjusted during tune. The range is dependent on the instrument, source type, detector type, and software version. The lowest Electron Multiplier voltage that will begin function when the system is new, or the EM is new, will often create very high tune abundance numbers.
    
    For the extractor source:
    
    M/z 69 is typically around an abundance of 1.2M on MS1 and 2.7M on MS2. Anything less than 200K would be alarming.
    
    M/z 264 is typically around an abundance of 300K on MS1 and 625K on MS2. Anything less than 50K would be alarming.
    
    M/z 502 is typically around an abundance of 75K on MS1 and 60K on MS2. Anything less than 5K would be alarming.
    Your current tunes look great to me. Use gain in your methods, as described in these documents, and your sample responses will be stable as the tunes change with use, 'dirtiness', and system age.
    
    Read:
    https://www.agilent.com/cs/library/technicaloverviews/public/5989-7654EN.pdf
    https://www.agilent.com/cs/library/technicaloverviews/public/5991-2105EN.pdf
    
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    - Re: 7000C GC MS with exraction source sensitivity become low
      
      yitnazewdie Oct 26, 2018 1:57 AM (in response to paulsalverda)
      
      Thank you so much Paulsalverda for your help
      
      I agree with you that The raw height counts in the tune report are not an indication of the system sensitivity.
      But for the sake of customer satisfaction we are trying to replace tunning solution with fresh one even if it was not expired one.In addition to this we did ion source cleaning again
      Then the result with new fresh tunning solution become satisfactory. i.e.Ion count for mass 69 became 17752768 which was 2645672 before
      
      Yitna zewdie
      
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