Tandem mass spectrometry: dissociation of ions by collisional activation

This review presents a brief historical introduction to the development of tandem mass spectrometry and its principal applications. It is placed in the context of the general principles underlying mass spectrometry, particularly the relationships between internal energy and fragmentation kinetics. The center-of-mass framework is presented as a convenient means of applying conservation of momentum to the energy transfer problem in tandem mass spectrometry as a means of deducing energy transfer in the collisional activation step and kinetic energy release as activated ions dissociate into fragment ions and neutrals. The principles of molecular beam methods are summarized and illustrative examples are given for which definitive information on reaction dynamics is available. The importance of scattering-very little appreciated in early discussions of tandem mass spectrometry-is shown to be the natural consequence of impulsive collisions, which appears to be a general mechanism for energy exchange in collisional activation. It is shown that the average energy transferred in single collisions is much less than the theoretical maximum given by the center-of-mass collision energy and the Massey criterion is presented as a simplistic rationale for understanding the essentially exponential decline in the energy transfer function above and below the relative velocity at which the probability for energy transfer is maximized. The issues of energy transfer in collisions of large molecular ions with low-mass neutrals are reviewed and a general description of energy transfer in multiple collisions is presented. It is shown that the center-of-mass and Massey criterion limitations are pragmatically overcome by multiple collision activation in ion traps. Surface-induced dissociation is presented as a viable alternative to multiple collision activation which is especially attractive for activation of large molecular ions. Finally, a few of the emerging dynamics principles governing energy transfer and dissociation of peptides are summarized. Copyright 2000 John Wiley & Sons, Ltd.