Calibration of ion effective temperatures achieved by resonant activation in a quadrupole ion trap.

The present paper describes a calibration of the ion effective temperatures as a function of the resonant activation amplitude in a quadrupole ion trap mass spectrometer. MS/MS experiments are performed on leucine enkephalin (M + H)+, bradykinin (M + H)+, (M + 2H)2+, and (M + 3H)3+, and ubiquitin (M + 11H)11+. For each amplitude, the effective temperature is calculated as the temperature that would give the same dissociation rate constant as the one observed and is calculated using published Arrhenius parameters. The effective temperature is found to be linearly dependent on the activation amplitude on the range investigated. The dependence of the slope and of the intercept of the T(eff) = f (amplitude) functions on the parent ion m/z is examined and an equation is derived to calibrate the ion effective temperature between 365 and 600 K. Below 365 K, a deviation from linearity is expected. Above 600 K, the validity of the equation will depend on whether the rapid energy exchange limit is still reached. Calculating backward, the Arrhenius parameters from the measured dissociation rates using this calibration show excellent agreement with the published values. The calibration can therefore be used to determine Arrhenius activation parameters from dissociation kinetics under resonant activation in quadrupole ion trap mass spectrometers.