Ion internal temperature and ion trap collisional activation: protonated leucine enkephalin

Protonated leucine enkephalin has been used as a prototypical high-mass ion to yield a quantitative estimate of the relationship between the amplitude of the resonance excitation voltage used in an ion trap collisional activa tion experiment, and the internal temperature to which an ion can be elevat ed over the bath gas temperature. The approach involves the measurement of the ion dissociation rate as a function of resonance excitation voltage, an d the correlation of dissociation rate with ion internal temperature. The r elatively high ion trap dissociation rates observed under typical resonance excitation conditions preclude the direct application of the Arrhenius equ ation to derive internal temperatures. An empirical determination of the re lationship between ion internal temperature and dissociation rate over the rate range of interest here was made via the systematic variation of bath g as temperature. The data suggest a very nearly linear relationship between ion internal temperature and resonance excitation voltage, at least under c onditions in which ion ejection is minimal. It is shown that protonated leu cine enkephalin ions can be elevated by about 357 K over the bath gas tempe rature using a monopolar resonance excitation voltage of 540 mV p - p(q(z) = 0.163) without significant ion ejection. It is also demonstrated that ion internal temperature can be readily increased by increasing the bath gas t emperature, by accelerating the ions in the presence of a room temperature bath gas (i.e. conventional ion trap collisional activation), or by a combi nation of the two approaches. (C) 1999 Elsevier Science B.V.