Column outlet pressure


Please could you suggest what impact setting the column outlet pressure to ambient instead of vacuum when connected to a MSD could have?


  • hello ,

    if you change the column outlet parameters, the calculation of the inlet-/column pressure changes & at the same time the column flow changes.


    * if it is set wrong:
       ~ the separation on the column is massively affected.
       ~ with an MSD there is an additional problem: a too high flow (if vacuum outlet = ambient) lowers the MSD sensitivity, as it is dependent on the vacuum.


    * However, there are MSD systems that have a CFT splitter, where the outlet pressure NOT is set to vacuum (and its correct)

    some infos can be found:

       other links could not be passed on


    regards, M.

  • Thank you M for your reply and the slides. A splitter is not being used so the parameter will be corrected

    Best Regards

  • Hello from Kazakhstan,

    Very interesting theme.

    I also have some issues with flow method correction and some questions. 

    1) We use Excel CFT calculator. So how much pressure we should put on calculator, when using SCD detector with FID? As calculator vacuum values change then tube values change. Which value will be better pressure on reactor about 0 psi(between 2-7torr) or we should put the pressure on the dual plasma burner about 7.7 psi(400torr)? 

    2) How do we get splitter pressure or column outlet pressure to the splitter? May it has a positive pressure than atmospheric? Total ID restrictors out of splitter  have to be matched with ID of the columns, means column ID 0.53mm = Restrictor1 ID 0.20mm + Restrictor2 ID 0.32mm?

    3) We left our columns uncalibrated, because it affects on peak's behavior. In some cases peaks lose their symmetry. Also service engineers during start-up new GC do not calibrate them, default GC parameters work better, or calculator is working incorrect?

    Regards, Bekbolat

Was this helpful?