Segmented electrostatic trap with inductive, frequency based, mass-to-charge ion determination

Abstract

We propose a new type of mass analyser - an electrostatic ion trap utilising a quadro-logarithmic trapping potential comprising concentric ring electrodes and inductive mass-charge detection in which packets of ions oscillating in a harmonic potential are arranged to be spatially focused as they pass the detection electrodes. Image-current detection is performed by two thin wire electrodes at the centre of the device. The combination of maximised ion velocity and ion focussing improves the signal-to-noise characteristic, allowing the device to operate at high resolution with short transient times. In order to fully exploit the sharp, localized features in the resulting transients, we utilise a Bayesian signal processing algorithm to fully exploit the sharp, localised features in the resulting transients, and to avoid the strong harmonics that would be produced by Fourier transform methods. The geometry of the mass analyser and possible ion introduction methods are described and results from an in-silico model are presented. The properties of ion motion in an ideal quadro-logarithmic potential are reviewed and integration of ion trajectories in the perturbed field created by the device is performed. The detection electronics and the signal processing approach are described and simulated. The potential instrument resolution and detection limits are presented. A simulated mass-to-charge doublet of 100 Th and separation 3 mTh can be resolved in 3.1 μs when there are 250 ions of each species. This corresponds to a simulated resolving power of 33,000 in 3.1 ms.