Abstract: A time-of-flight method and apparatus of analysis comprising a first step of continuously scanning the surface of a solid sample to be analyzed with a primary particles beam to liberate secondary particles from the sample and to thereby ionize the secondary particles. A second step forms a secondary particles beam and makes it travel through a path which is long enough for secondary particles with different energy levels or different masses to have substantially different times of flight. Then, the secondary particles are discriminated by deflecting them at an angle which is variable periodically as a function of time, with the same period as that of the scanning by the primary particles beam, but with a fixed phase shift such that the secondary particles have a given time of flight and are deflected in a pre-determined direction, irrespective of the point on the sample from which these secondary particles have been liberated.