Control of ion kinetic energy in ion cyclotron resonance spectrometry: Very‐low‐energy collision‐induced dissociation

A novel means of effecting collision‐induced dissociation of molecular ions for use in conjuction with Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometry is reported. Using an electronic circuit external to the ICR hardware and software, ions are continuously acceperated and decelerated over a period of hundreds of milliseconds by rledpreatedly shifting the phase of the radio frequency excitation driving signal by 180°. At low kinetic energies, a succession of collisions which transfer small amounts of energy favors the lowest energy fragmentation pathway and allows ions with large activation energies to fragmentation of n‐butylbenzene cation and by extremely large secondary isotope effects in the dissociation of t‐butoxide‐d 6 anion.