Controlled variation of boundary-activated ion fragmentation processes in a quadrupole ion trap

Fragmentation in a quadrupole ion trap of each of two isomeric molecular ions, obtained from 4-nitro-o-xylene and 4-nitro-m-xylene, has been investigated. It is demonstrated that the degree of fragmentation may be controlled by prolongation of both the duration for which the working point of the mass-selected species is held in the vicinity of a stability boundary and a prior collisional cooling period. The extent of fragmentation has been found to increase as the working point is held near the βz = 0 stability boundary while the relative abundances of fragment ions can be varied with the duration of the collisional cooling period. Under appropriate conditions for 4-nitro-o-xylene, >94% of the isolated ions can be fragmented; <5% of the ions are lost from the ion trap while 1% remain intact. As 99% of the charge of the fragmented ions is retained in the ion trap, the overall optimum efficiency of boundary-activated dissociation is >93%; the corresponding efficiency for 4-nitro-m-xylene is 74%. 50% of the selected ions can be fragmented in ≤3 ms. The results are compared with collision-activated dissociation studies carried out with a triple stage quadrupole–hexapole–quadrupole instrument. This technique of boundary-activated dissociation provides a general procedure which does not require careful tuning of the instrument as is required for the more commonly-used technique of resonance excitation.