m/z-selective infrared multiphoton dissociation in a Penning trap using sidekick trapping and an rf-tickle pulse

We present a novel scheme for performing m/z-selective infrared multiphoton dissociation (IRMPD) in a Penning trap. Ions are injected into the trapped ion cell of a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer and trapped using the 'sidekick' approach. Because this mode of ion trapping can result in an ion cloud precessing about the central axis of the cell with a significant magnetron radius, the effectiveness of conventional on-axis IRMPD schemes can be adversely affected. Here we demonstrate that the non-zero magnetron radius of the ion ensemble can be exploited with rf-tickle pulses which excite, either in an m/z-selective or broadband mode, the cyclotron frequency of the orbiting ions such that their flight path intercepts the on-axis laser beam resulting in effective IRMPD. This approach has potential utility in the tandem mass spectrometric characterization of complex mixtures, suggests new approaches for two-dimensional FTICR studies and, most importantly, represents a straightforward approach to improve the effectiveness of IRMPD for ions captured using sidekick trapping protocols. Copyright (C) 2001 John Wiley & Sons, Ltd.