Towards increasing the performance of FTICR-MS with signal detection at frequency multiples: Signal theory and numerical study

In Fourier transform mass spectrometry, detection of the signal at the cyclotron frequency multiples using multi-electrode ion traps, called nX-ICR cells, yields high resolution mass spectra at proportionally increased acquisition speed, and facilitates applications in omics and complex mixture analysis. In this approach, the mass-analyzer performance depends crucially on the trajectory of the ion motion during detection. For example, the ion orbital radius is one of the main factors affecting detection sensitivity nonlinearly, whereas high orbital radius during detection could significantly reduce the time of the ion coherent motion deteriorating both resolution and sensitivity. To address this issue and ensure optimal performance, a detailed description of the signal induced in the detection circuit of the nX-ICR cell for different ion motion trajectories and cell parameters is needed. In this study, we consider a simplified analytical model for image current induced on the electrodes of a model nX-ICR cell. The proposed formalism establishes the relationships between the cell parameters (e.g., detection circuit input resistance, temperature, frequency bandwidth, number of electrodes), and ion trajectory, and parameters of the acquired signal. These relationships reveal the key factors affecting the sensitivity of nX-ICR cell and intensities of undesirable peaks at the frequency multiples in the mass spectra.