ExB ion traps, such as Fourier transform Ion Cyclotron Resonance mass spectrometers (FY:ICR), mass analyze sample ions based on differences in their cyclotron frequencies in a homogeneous magnetic field. The high resolution mass measurements of FT-ICR are based on the relationship between the frequency of the cyclotron orbit and the mass-to-charge (m/q) ratio of an ion. Both the orbit and the frequency/mass relationship result from the radial forces on the ion. Ions trapped by inhomogeneous electric fields experience different magnitudes of the radial electric fields at different positions resulting in a positionally dependent frequency. Such differences in orbital frequencies for ions of a single m/q ratio result in line broadening and loss of resolution
