Demonstration of a nested electrostatic linear ion trap for flexibility in selecting analyzer figures-of-merit

Abstract

An electrostatic linear ion trap (ELIT) is used to trap ions between two ion mirrors with image current detection by central detection electrode. Transformation of the time-domain signal to the frequency-domain via Fourier transform (FT) yields an ion frequency spectrum that can be converted to a mass-to-charge (m/z) scale. Injection of ions into an ELIT from an external ion source leads to a time-of-flight ion separation that ultimately determines the range of m/z over which ions can be collected from a given ion injection step. The m/z range is determined both by the length of the ELIT and by the distance of the ELIT entrance from the ion source. A longer ELIT leads to a wider m/z range while a shorter ELIT, under equivalent conditions, leads to higher resolving power due to increased ion frequencies. Hence, there is an inherent trade-off between the two important analyzer figures-of-merit: m/z range and resolving power, based on the length of the ELIT. In this work, we demonstrate a nested ELIT arrangement, referred to herein as an NELIT, that allows for the selection of one of two possible ELIT lengths within a single array of plates while employing a common detection electrode. While a range of ELIT lengths are possible, in principle, the geometry described herein leads to an effective length ratio of 2.40 for the two traps in the NELIT.