Cooling time and pressure effects on competitive thermalization/activation processes by resonance excitation on ITMS

Abstract

AbstractThe classical n‐butylbenzene model is used to estimate the qualitative variation of the precursor ion internal energy by the resonant excitation method in an ion‐trap mass spectrometer. The kinetic energy thermalization process is confirmed by insertion of a cooling time (⩽10ms under our conditions). An initial internal energy relaxation process due to collisions between the molecular ion and neutral species of n‐butylbenzene is proposed. The larger amount of internal energy deposited in ions as the helium pressure is increased can be explained in terms of the number of collisions between the molecular ion and helium atoms, the competition between ion dissociation and ion ejection, the rate constant of dissociation and the secular axial frequency resolution of the isolated ions. Increased analyte pressure does not accelerate the ion relaxation process, probably due to the space charge effects. In summary, variation of helium pressure and cooling time permit optimization of ion internal energy deposition leading to enhanced sensitivity in MS/MS experiments.