how does the mass spectrum work?

Answer 1

A sample is ionized into ions in the gas phase. The ions are usually +1. The means of ionization might be a stream of high-energy electrons or the alpha particles from a little bit of californium-252.

The ions are accelerated by a an electric potential difference toward a target, which has one or many senors to detect them when they hit. In one version, a magnetic field deflects the beam of ions away from their straight line. The lighter ions are most deflected; the heavier ions less so. This effect spreads the ion beam out according to the masses of the ions, resulting in a mass spectrum. The ions all hit the target in different places, and the sensors record the numbers of them according to their masses.

In another version called time-of-flight, the electric potential itself separates the ions, because the lighter ones fly fastest and reach the target first. It's a little like a horse race, with the horses starting at the gate, getting spread out, and then detected one by one at the finish.