the speed and thus the time required to pass a given
distance depends on the mass. This is exploited directly
by time-of-flight mass spectrometers for the purpose of
separating masses. In sector field mass spectrometers,
the ions describe a circular path in the homogeneous
magnetic field caused by the Lorentz force which acts
on the moving ions perpendicularly to the speed and
perpendicularly to the magnetic field.