Abstract
Fourier transform ion cyclotron resonance (FT-ICR) is the observation of an image current induced by a well defined ion packet, consequently the high resolution and high sensitivity arise from the ability to produce coherent ion motion from an initially random ensemble of ions. A coherent packet of ions is defined by an ensemble of ions which can be approximated by a rotating monopole. To meet this requirement the ion ensemble must be spatially defined. Spatial definition is a combination of radial distribution (i.e., energy distribution) and radial dispersion (i.e., phase relationship). Signal intensity and mass resolution are dependent upon the spatial distribution of the ensemble and the length of time the packet is observed. Therefore, the current limitation to mass analysis of high molecular weight biomolecules is attributed to the loss of the coherent ion packet. For example, the external ion source systems (e.g., the tandem quadrupole FT-ICR and electrostatic ion guide system) are attractive for analytical FT-ICR applications; however, the issues concerning injecting ions from an external ion source are not yet resolved. In order to address the problems incurred in FT-ICR at high mass, it is important to define the factors affecting ion trap ping and ion detection in a systematic manner. T h e mechanism for the production of a coherent ion packet is acceleration by a resonant oscillating electric field. Ion injection from an external source results in an ion ensemble having significant translational energy distribution. Ions having initially high translational energies experience a strong magnetic field force. The force of the magnetic field complicates phase synchronization and results in a spatially disperse packet of ions following excitation. The impact of the spatial definition of the ion ensemble is two-fold: first, loss of spatial definition results in signal loss (i.e., loss of sensitivity) and second, spatially disperse ions lose coherence (i.e., loss of mass resolution) in inhomogeneous ExB fields. Radially inhomogeneous ExB fields cause variations in the orbital frequencies and phase angles of the trapped ions...
Hanson, Curtiss Dwight (1989). The effect of translational energy on trapping and detection in fourier transform ion cyclotron resonance mass spectrometry. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1028975.