Space charge effects on relative peak heights in fourier transform-ion cyclotron resonance spectra

Abstract

Ion trajectory calculations have confirmed that space charge interactions can be a source for mass discrimination seen in Fourier transform-ion cyclotron resonance (FT-ICR) spectra. As compared with the previously recognized mechanism of z-axis excitation, ion-ion repulsion is a mechanism which specifically affects relative peak heights of ions close in mass, and is most severe for low excitation radiofrequency (rf) amplitudes. In this mechanism, Coulomb repulsion significantly perturbs the motion of the ion clouds during excitation and alters the final cyclotron orbital radii. Under these conditions peak heights do not accurately reflect the true ion abundances in the FT-ICR spectrometer. Mass discrimination can be minimized by using low numbers of ions, low ion densities, and a short, high amplitude rf excitation waveform. Experimental observation of the relative peak heights of the m/z 91, 92, and 134 ions in n-butylbenzene gives quantitative confirmation of the results of the trajectory calculations. Chirp, SWIFT, and impulse excitation were modeled: impulse excitation was found to be most effective in minimizing the effects of space charge interactions.

Prediction of a Space Charge Induced Upper Molecular Mass Limit Towards Achieving Unit Mass Resolution in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Each cloud's center position in the xy plane is rl = rcl + rmj, the sum of the cyclotron and magnetron position vectors. In order to integrate Eqn (7), a choice must be made for the coordinate representation of the cyclotron and magnetron position vectors. Cartesian coordinates are used for the magnetron position.…”

A signal filtering method for improved quantification and noise discrimination in fourier transform ion cyclotron resonance mass spectrometry-based metabolomics data

“…When "drop-out" occurs, the total ion current (TIC) of the signal drops significantly (Ͻ50% of typical values), and the resulting spectrum shows elevated noise levels and is not representative of the sample composition [18]. Some of this noise can be reduced before the measurement, for example by optimization of the ICR detector cell parameters [15,19], or after the measurement, during the preprocessing stages [20]. The overall signal-to-noise ratio (SNR) in a mass spectrum can be improved by acquiring more scans [21]: the magnitude of additive white Gaussian noise (AWGN) increases as n 1⁄2 (where n is the number of scans acquired) and the signal increases as n, and therefore the overall SNR is in principle proportional to n 1⁄2 [22].…”

Realistic modeling of ion cloud motion in a Fourier transform ion cyclotron resonance cell by use of a particle‐in‐cell approach

“…Simple 2D simulation programs have been used by different groups to investigate various phenomena related to coulombic interactions in FTICR. 3,4,[29][30][31] The first attempt to implement coulombic interaction in realistic three-dimensional (3D) calculations of simulations involving a relatively small number of interacting particles was undertaken by the groups of Inoue and Nikolaev. They developed a 3D parallel code to integrate the equations of motion of up to 1024 interacting particles for 50 000 time-steps.…”