Effective ion internal temperatures achieved via boundary activation in the quadrupole ion trap: protonated leucine enkephalin

Abstract

The dissociation rate of protonated leucine enkephalin in a quadrupole ion trap was measured as a function of the proximity to which the ions are brought to a stability boundary. A bath gas temperature of 480 K was used so that a dissociation rate could be readily measured even when the parent ions were remote from a stability boundary. Changes in the dissociation rate as a function of d.c. potential applied to the ring electrode of the ion trap, used to bring ions close to a stability boundary, could then be attributed to the ‘boundary activation’ process. A relationship between dissociation rate and parent ion effective internal temperature, derived from a study involving conventional ion trap resonance excitation, was used to estimate effective ion internal temperatures achieved under the boundary activation conditions used here. Effective ion internal temperatures 170 K above the bath gas temperature could readily be achieved using boundary activation. However, the efficiency of the overall boundary activation experiment was compromised by an initial rapid parent ion loss that occurred upon application of the d.c. potential. After correction for this initial ion loss, dissociation rates and relatively low ion ejection rates could be measured. Effective ion internal temperatures achieved with boundary activation are similar to those observed previously using conventional resonance excitation. However, the generally poorer efficiencies associated with boundary activation that are observed with resonance excitation at high dissociation rates suggests that higher ion internal temperatures can be achieved with conventional resonance excitation. Copyright © 1999 John Wiley & Sons, Ltd.