A theoretical investigation of the kinetic energy of ions trapped in a radio-frequency hexapole ion trap

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Eur. J. Mass Spectrom. 8, 181 - 189 (2002)

A theoretical investigation of the kinetic energy of ions trapped in a radio-frequency hexapole ion trap

Liam A. McDonnell, Anastassios E. Giannakopulos and Peter J. Derrick^*
Institute of Mass Spectrometry and Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
Youri O. Tsybin and Per Håkansson
Ion Physics Division, Ångström Laboratory, Uppsala University, Box 534, SE-751 21, Uppsala, Sweden

ABSTRACT:

The kinetic energy dependence of ions trapped in a radio-frequency (RF) hexapole ion trap has been calculated as a function of space charge, mean free path, mass, RF potential and charge. The average kinetic energy of the ions was found to increase with increasing space charge, mean free path and the ion charge state. For a trapped ion in a given coulombic field, the mass of the ion and the amplitude of the applied RF potential did not affect the average kinetic energy. The consequences for multipole-storage-assisted dissociation (MSAD), in which ions are accumulated for prolonged periods of time in the multipole ion trap of an electrospray ion source, are discussed. As a result of radial stratification inside the ion trap, MSAD can lead to the preferential excitation of ions with larger m/z values. Such discrimination would have negative consequences for the detection of labile non-covalent adducts, which are normally detected at higher m/z values than their constituent species.

Keywords: Fourier-transform ion cyclotron resonance (FT-ICR), ion optical modelling, hexapole ion trap

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