Comparison of collisional activation by the ‘boundary effect’ vs. ‘tickle’ excitation in an ion trap mass spectrometer

It has been shown previously that collisional activation in an ion trap mass spectrometer can be achieved by storing parent ions within a narrow zone extending close to the theoretical boundaries β_r = 0 or β_z = 0 of the stability diagram. This procedure can be used for obtaining collision-induced dissociation of selected parent ions without the need to apply a precisely tuned resonant ‘tickle’ potential between the end-cap electrodes. In this investigation a comparison was made between the two methods (‘tickle’ and ‘boundary’) of activation based on the efficiency of parent-to-daughter conversion and on the relative abundance of daughter ions for a model system (the m/z 91/92 ratio for n-butylbenzene). The data show that, under conditions of maximum efficiency, a comparable amount of internal energy is present in the ions after activation with the two methods. However, with the ‘tickle’ technique it is possible to increase the internal energy of the parent ions even further, although at the expense of the efficiency, whereas in the case of the “boundary” activation, the conditions for optimum efficiency almost coincide with those for maximum activation and a drastic loss of ions follows any attempt to overcome these limits. It is also found that at any given q_z value used for storing and activating parent ions the permitted mass difference between parent and fragment ions is greater with ‘boundary’ than with ‘tickle’ excitation.