7010B GC-MS TQD high vacuum turns off on its own


I am using a 7010B GC-MS TQD and when I perform the air/water check in the morning everything looks good i.e H2O, O2, N2 reading all below 5%. But when I perform a 2nd and 3rd air water check the water readings jump to around 13% H2O and I notice the high vac is set to off. How come did high vac is shutting off on its own? I realize it is suppose to be around 10e-5 Torr for the high vac and around 100 mTorr for the rough vac.

  • Hi

    Chances of leak from side door or somewhere else...

  • i just realized it is because i forgot to turn the collision cell gas back on. Would this be the cause?

  • Why do a second or third water check? If it's fine once, it's fine.   The PFTBA takes time to stabilize.  When the PFTBA valve first opens there is quite a large amount of PFTBA molecules bouncing around through the very small restrictor in the valve into the manifold. This rapidly decreases to some sort of stability, but does not get really stable for a long time, some many minutes.  If the valve is closed, and then opened again to do, for example, another air/water check, the amount of PFTBA molecules will be less than they were the first time.  The raw air/water abundances will be the same, but the raw PFTBA abundance will be less, which may fake you out into thinking that the air/water got larger.

    It is possible that turning the collision cell gases on while the gauge is on may cause it to turn off from that burst of flow and the requisite increase in pressure.

    It takes about 15 to 20 minutes for the collision cell to become stable after flow changes, especially after having the CC flows off and then turning them on. 

    Don't tune every day!  Print a report, which uses the current tune file parameters and acquires new tune ion peaks and spectra.  Manually evaluate the report and if it looks fine, run.  You may have to use the Advanced Tune options to do a MS1 and an MS2  Mass Axis calibration, but that is frequently all that is truly necessary.   Look in the acquisition help: Home > Tuning > Tune Reports > Run a check tune report

    An automatic tune is not like searching for the very tip of a needle, it’s more like landing somewhere around the top of a wide bell curve.  Most applications don’t need a system at the exact cutting edge perfect tune.  They could be detuned by 10% to 25% and not miss anything at all.  Stability is much more important for most applications than ultimate sensitivity.  Every time you tune, it changes the response of the instrument.

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