Analysis and Evaluation of Imperfect Harmonic Potential in Orbitrap

Orbitrap mass analyzer is renowned for its capability to confine charged particles stably and precisely determine their mass-to-charge ratios via a unique electrostatic field generated by spindle-shaped electrodes. However, practical imperfections such as electrode axial truncation, outer electrode splitting, and the incorporation of ion inlets can significantly degrade the instrument’s mass resolving power. This study proposed a method for analyzing the mass resolution of Orbitrap. By combining finite element-based electromagnetic field simulations with higher-order resonance term coefficient analysis, a systematic study was conducted on the mass resolution of Orbitrap under varying axial truncation lengths, outer electrode splitting sizes, and ion injection inlet dimensions. Finite element simulations were employed to construct two distinct models: the standard Orbitrap and the high-field type. This study focused on three primary parameters: the axial truncation length, the outer electrode splitting size, and the size of the ion injection inlet. The results indicated that the high-field Orbitrap consistently exhibits superior resolving power compared to the standard Orbitrap. This is due to the stronger electric field in the high-field model, which can effectively compensate for imperfect electric fields, resulting in smaller higher-order resonance terms and, consequently, higher mass resolution. The effect of a finite axial electrode length on resolution is negligible when the length is within a certain threshold, beyond which deviations may disrupt the electrostatic field. Additionally, as the degree of outer electrode splitting increases, the resolving power decreases significantly due to the resulting imperfect electric field, which distorts ion trajectories and degrades mass accuracy. Furthermore, the presence of an ion injection inlet introduces an asymmetry in the axial electric field, leading to additional resolution loss. This asymmetry disrupts the ideal field distribution necessary for stable ion motion, further highlighting the importance of precise electrode design in optimizing Orbitrap performance. This study is of great significance for both the theoretical research and practical optimization of Orbitrap mass spectrometers. Optimizing electrode dimensions and configurations, particularly by adopting a strong-field approach and minimizing external electrode splitting, can substantially improve instrument performance. Although the finite element models offer valuable insights into the influence of electrode variations, the study acknowledges certain limitations. The simulations are based on idealized operating conditions and do not fully capture real-world factors such as mechanical tolerances. In summary, this work provides a concise yet comprehensive analysis of how electrode structural parameters impact the resolving power of Orbitrap analyzers. The insights gained offer practical guidance for the future design and optimization of high-performance mass spectrometric instruments, contributing to advances in various scientific disciplines.