Linear response theory of ion excitation for Fourier transform mass spectrometry.

A linear relation between the voltage density or magnitude spectrum of an excitation waveform and the corresponding ion orbital radius is derived for Fourier transform mass spectrometry (FTMS). This provides a theoretical foundation for the stored waveform inverse Fourier transform excitation method. The result is also useful for the design of optimal excitation signals as well as for the estimation of the kinetic energy of ions after an excitation event in collision-induced dissociation experiments. When the linear relation is applied to two-dimensional FTMS excitation, an analytical expression for ion speed modulation is obtained.