If you have two solutions with different amounts of salt (or something else) dissolved in them, and you separate them by something that will let water through but not the salt, water will move towards the side with more salt in it. This is why and snails shrivel up if you poar salt on them.
To demonstrate approximately how a mass spectrometer works for an outreach project at the Museum of Science and Industry in Manchester I built a ball bearing deflector. It works by having a ramp, that you roll ball bearings down, and at the bottom they go past a magnet. The small ball bearings are deflected more than the large ones, a bit like the ions in a real mass spectrometer. Apparently it went down well.
I have built a couple of these, one that is very heavily interlocked and sealed inside a box, so it is safer.