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Mass Spectrometer Question

  1. Apr 18, 2008 #1
    Not sure where exactly this should go, as it's a hardware question rather than a homework problem or question about the theory behind it, so, sorry if it's the wrong place.

    But, I've been working on getting an old HP 5971A mass GC-MS up and running over the past semester, and there's a part of the ion source I don't understand the function of.

    It's a quadrupole machine, and apparently there's a ceramic disk between the quadrupole and the ion source. The front nose of the ion source fits through a hole in the disk to point down the quadrupole.

    I watched a video explaining how to clean the machine, and in the video it explicitly notes the disk should be able to move freely to keep alignment between the ion source and quadrupole. What I don't understand is how disk moves. The one in the machine I was working on was actually stuck in place apparently when I first replaced the source after cleaning it. After some fiddling, the professor I work with and I got the disk to turn some, but it still sticks.

    I don't see any mechanism that could make the disk move, and it has a groove around its edge that little screws are pointed into apparently to keep it in place. As noted, the nose of the ion source goes through a hole at the center of the ceramic disk, so the only motion I can see the disk being able to make is rotating around that hole, but...I don't understand how it does this, or why it needs to.

    Anyone happen to know? No one I know has yet been able to explain it to me.
  2. jcsd
  3. Apr 21, 2008 #2


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    It probably is moveable only during servicing. The fact that it can move easily indicates that the plate is installed with the hole 'normal' to the axis of the ion source. Moving freely indicates that it isn't cocked or wedged into place before fixing its position with the adjustment screws.
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