How exactly are ions in a Mass Spectrometer accelerated?

After a molecule is ionised, the ion is accelerated by an electric plate up to a certain kinetic energy by the attraction of the ion to the electric plate. However, after the ion has passed the electric plate, won't the plate still exert an attractive force on the ion? If so, by the attraction between the ion and the electric plate, the kinetic energy of the ion were attenuated, perhaps even to the point where there would not be a net gain in kinetic energy of the ion.

• – Tyberius May 17 '17 at 16:13

The ions are initially accelerated by a potential difference, which means there are different voltages between two metal plates separated by some distance. As a result the potential energy present due to the voltage between two plates is converted into kinetic energy of the ion. In energy terms if at the exit plate, leading into the spectrometer, the energy is $E_x=mv_x^2/2$ and initially the ion energy is $E_0=mv_0^2/2$ then $E_x = E_0 +W$ where $W$ is the work term, i.e. the kinetic energy added to the ion. This is $W=\pm qEd$ where q is the ion's charge, E field strength in volts/cm and d the separation of the two plates, i.e the distance over which the acceleration takes place. If W is positive the ion is accelerated, if not decelerated.