Boundary Effects and Collisional Activation in a Quadrupole Ion Trap

The effects of storing ions at different values of the stability parameters a(z) and q(z) were studied in a quadrupole ion trap, using helium or argon as buffer. A region was localized near the boundaries of the stability diagram in which the ions experience an increase in their kinetic energy. This is reflected in the occurrence both of fragmentation due to collisional activation and of a certain extent of ion loss due to unstable trajectories. The results of this excitation, referred to as 'boundary effects,' depend on the specific q(z) at which the ion storage is performed and on the buffer gas used, and point to a simpler means of obtaining tandem mass spectra with the ion trap without the need to apply resonant tickle voltages between the end-cap electrodes.