Simulation of Space\nCharge Effects in Fourier Transform\nQuadrupole Ion Traps (FT-QITs)

We\npresent ion dynamics simulations regarding the effect of space\ncharge on the performance of Fourier transform quadrupole ion traps\n(FT-QITs) with special attention to signal stability, mass resolving\npower, and sensitivity. Ion trajectory simulations within an idealized\nQIT geometry are performed by applying a dedicated application (QITSim)\nusing an in-house developed open simulation framework (IDSimF). Image\ncurrent detection transients are generated by the application and\nare subsequently transformed into frequency spectra of ion secular\nmotion. Such frequency spectra are the basis for the calculation of\nmass spectra in FT-QIT instruments. The simulation results are used\nto assess the extent of space charge induced effects regarding the\nanalytical performance of FT-QIT systems. The simulation results for\ntwo Cl<sup>+</sup> and seven Xe<sup>+</sup> isotope ions exhibit diverse\nspace charge induced phenomena. Most prominently, complete isotope\nsignal fusion, quantitative individual signal suppression, and severe\nsignal distortions are observed even at low absolute numbers of trapped\nions. Furthermore, significant shifts of the secular oscillation frequencies\noccur, even when the signal shape appears to be mostly unaffected\nand when the frequency separation for trapped ions with different\nmasses is large. This significantly limits the applicability of FT-QIT\nsystems for high resolution mass spectrometry. An increase of the\nRF amplitude of the trapping field as well as increasing the extent\nof ion excitation partly mitigate these adverse space charge effects;\nnevertheless, the usable operational range of the simulated FT-QIT\nsystem for analytical applications remains rather narrow.