ION CYCLOTRON RESONANCE MEASURING CELLS WITH HARMONIC TRAPPING POTENTIAL

摘要

The invention relates to devices and methods for the acquisition of mass spectra with very high mass resolution in ion cyclotron resonance mass spectrometers and methods to produce the devices. The invention presents cylindrical ICR measuring cells with special electrode geometries to generate harmonic trapping potentials for orbiting ions up to the walls of the cell. Only a single DC trapping voltage has to be applied to create the harmonic trapping potential distribution. The sheath of the cylindrical cell is divided by longitudinal gaps into a multitude of sheath electrodes, which either have to carry layers with resistance profiles able to generate parabolic voltage profiles along the sheath electrodes, or which form sheath electrodes of varying width by parabolic gaps, able to create complicated potential distributions which are harmonic on average for orbiting ions. Orbiting ions of a given mass m/z can oscillate harmonically in axial direction with exactly the same oscillation frequency, independent of the radius of their orbit and of their axial oscillation amplitude. Ideally, the cylinders are closed by endcaps with rotationally hyperbolic form, divided into partial electrodes like in infinity cells. The ions can then be excited to their cyclotron motions by dipolar excitation fields also uniformly filling the ICR cell up to the endcaps. The ion clouds orbiting on their cyclotron trajectory are kept together for much longer periods than was possible hitherto, even if they orbit near the sheath electrodes. The image currents thus give rise to minute-long transients, from which mass spectra with ultrahigh mass resolution can be obtained.