hinz
Hazard to Others
Posts: 200
Registered: 29-10-2004
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Ion trap mass spectrometer with oil diffusion pump
I recently bought this nice Ion trap mass spectrometer,
http://pic20.picturetrail.com/VOL1206/4241286/13306106/20220...
it was quite cheap.  But unfortunately, the turbo-pump has chrashed.  Normally these mass spectrometers are used with turbo-pumps, but new or used
turbo-pumps are quite expencive at E-bay. If I would buy a new pump I wouldn't know how long it runs, before it jumps out of the ball bearings
aggain, I've heard this should happen not to infrequently with the smaller ones. There will be also problems with the electronics for the high
frequency used by the fast spinning three phase AC motor.
So I want to build an adapter for a oil diffusion pump, I will build a table and place the pump under the table, since those pumps are bigger and
won't fit inside the mass spectrometer anymore.
The only problem I see is that some vaporised oil might contaminate the ion multiplier. Does anyone know how strong those pumps contaminate the high
vacuum with vaporised oil? And how this contamination might be decreased, normally they do this with cold traps filled with liquid nitrogen to
condense the vapors, but I don't like to use LN2 for this.
I thought about taking a frigde compressor, filling the freon into a bottle and soldering a copper coling mantle instead of the cooling spirals of the
frigde. This mantle will then be pushed over the vacuum gauge from the pump to the spectrometer, simmilar to a liebig condensor. Then I would refill
the freon. The freon will be pressed through the small holes, cooling the mantle on expansion and be recompressed in the frigde pump. If this idea
should work, how should I design the cooling mantle, like on this drawing or somehow different?
http://pic20.picturetrail.com/VOL1206/4241286/13306106/20221...
I know, this project will take some time, but if I'll have success, I'll have a great analytical instrument be used for
sciencemadness, without the fear of an exploding turbo-pump and hence I will be able to use it for some time. Then I can really start doing organic
chemistry, because I can identify my products and don't have to believe that a reaction mechansm yields exactly this product and nothing else.
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12AX7
Post Harlot
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Registered: 8-3-2005
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Offhand, one (of many) is specified as microtorr at room temp. YMMV.
http://www.apiezon.com/oiltablevapour.htm
Baffles and bends and such will probably help cool down any incident oil molecules, allowing them to condense and drain. They can still evaporate
higher, but that depends if the vapor pressure is a concern to you.
Tim
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Chemist514
Hazard to Self
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Registered: 12-5-2006
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Probably the best source for amateur vac...
The Bell Jar http://www.belljar.net
They have much vacuum related info hope it helps some, best of luck on such a cool piece of equipment.
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