SLOW HEATING METHODS IN TANDEM MASS-SPECTROMETRY

Several approaches to ion activation in tandem mass spectrometry have been developed in recent years for use in ion trapping instruments tha t allow for conditions to be reached wherein rates of ion activation a nd deactivation are comparable. These approaches are defined as slow h eating methods and include continuous-wave laser infrared multiphoton dissociation, dissociation driven by blackbody radiation, quadropole i on trap collisional activation and sustained off-resonance irradiation in ion cyclotron resonance mass spectrometry. In the Limiting case in which ion activation and deactivation rates are equal, a steady-state parent ion internal energy distribution is achieved and the kinetics of dissociation can be interpreted in analogy with thermal dissociatio n. This discussion describes the thermal analogy and the Limiting cond itions of rapid energy exchange and slow energy exchange along with th e possible ramifications for dissociation rates and product ion spectr a, The figures of merit that the various slow heating methods share as a class of activation methods are also discussed. The purpose of this perspective is to provide a frame-of-reference from which slow heatin g methods can be considered. Such methods are seeing increasing nse as the number of ion trapping instruments grows and have shown remarkabl e success with dissociation of high-mass ions. (C) 1997 by John Wiley & Sons, Ltd.