I would never use ferrite beads on the ADC inputs to a microcontroller, for one simple reason: I never, never, NEVER connect any microcontroller pin, input or output, analog or digital, directly to the outside world (i.e., off-board). Doing so invites all manner of trouble, in the form of susceptibility to external interference as well as damage from ESD. In the case of ADC inputs, I always precede these by a buffer amplifier of some sort, at a minimum, as well as whatever input protection and filtering is appropriate for the operating environment. But ferrite beads? Never.
Ferrite beads are most appropriate for the power sections of circuits. Read the following: