Multiple ion capture and separation in an electrostatic storage device

Abstract

The present study introduces new approaches for the capture/injection and selection of ions with large mass-to-charge (m/q) differences in an electrostatic ion beam trap (EIBT) or multi-reflection time-of-flight (MR-ToF) device. While no m/q-dependent storage criterion exists for devices of this nature, the process of injecting ions into the trap relies on a timed potential switching and is therefore mass-selective to some extent. To partially circumvent this restriction, the approach of sequential capture is presented, where additional ion species are captured while already-stored ones are unaffected by the switching pulses. Specifically, it is possible to perform a full in-trap lift capture pulse while a given, already-stored ion species is reflected in a mirror potential or passes through the lift electrode itself. Additionally, the technique of ion selection by means of transversal ejection from the trap is extended to allow ion species with large m/q differences to be retained. To this end, deflector functions with different frequencies are added with an AND logic and supplied to an in-trap deflector electrode. The combination of both techniques allows the simultaneous storage of size-selected ion species with an m/q ratio surpassing 4 : 1 at the present setup, where the single-pulse lift capture is restricted to a ratio of only 1.9.