Collision induced ion ejection in an FTICR trapped-ion cell

A collision algorithm was used with SimIon to evaluate collision-mediated ion ejection mechanisms in the ICR MS experiment. These mechanisms were characterized based on kinetic energy, ion mass, applied trapping potential, and collision gas mass. It was found that there are three collision-based energy regimes for ion loss from a trapped-ion cell. The first region is characterized by low initial cyclotron kinetic energy, a radial ejection mode, and a very high collision ratio (>100 collisions per ejection). The second region is characterized by a medium to high initial cyclotron kinetic energy leading to axial ejection at low collision ratio (1 to 10 collisions per ejection). The third region is characterized by a high initial cyclotron kinetic energy, a radial ejection mode, and a collision ratio of unity. It was also determined that there is a radial cyclotron mode limit, approximately 40% of the cell radius, after which an ion is ejected after a single collision. This has important consequences on the damping of the FTICR signal, various cooling techniques, ion activation techniques, and the remeasurement experiment.