A conceptual approach for FT-ICR cell harmonization utilizing external shim electrodes

摘要

Recent advances in superconducting magnet technology make possible the construction of magnets with higher magnetic fields and regions of improved homogeneity, setting the stage for major advances in performance of Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). In particular, combining these advances in superconducting magnets with the next generation of ICR ion detection cells, which incorporate harmonic trapping electric fields, will simultaneously improve resolving power, mass measurement accuracy, dynamic range and sensitivity of FT-ICR MS. Realizing these potential advances in FT-ICR performance depends critically on enhanced performance of the trapped ion cell, where analyte ions are confined for excitation and detection. To that end, we propose a focused conceptual approach for achieving cell harmonization that uses as a metric the spatial uniformity of the radial electric field divided by radius. This concept for cell harmonization is applied to two proof-of-principle examples for externally shimmed cell configurations developed using appropriate three-dimensional potential calculations. Both examples utilize external electrodes to generate the trapping potential that are electrically de-coupled from the detection and excitation electrodes. A nearly ideal 3D quadrupolar potential is achieved throughout the cell volume in these proof-of-principle designs that simultaneously simplify both mechanical construction and supply of electrical connections to FT-ICR cells.