A Computer Simulation Study on Ion Optics Aiming at the Realization of Projection-Type Mass Spectrometry Imaging

The projection mode in mass spectrometry imaging (MSI) obtains ion images by retaining the spatial distribution of desorbed ions immediately after their generation as the ion images, then projecting them onto an ion detector of time-of-flight mass spectrometry. Compared to conventional MSI, projection-type MSI can deliver overwhelmingly higher spatial resolution. The mass resolution of projection-type MSI can be improved by a technique named post extraction differential acceleration (PEDA). To assess the feasibility of projection-type MSI with minimal modification of a commercially available laser desorption/ionization time-of-flight mass spectrometer, ion trajectory simulations were performed using the ion optics simulation program SIMION. Under boundary conditions that reproduce the ion acceleration region of the commercial mass spectrometer with a high fidelity, the trajectory simulation results were obtained for a huge number of combinations of ion masses, initial conditions, PEDA parameters, etc. The data analysis provided useful findings that can lead to the realization of projection-type MSI based on the modified commercial mass spectrometer, for instance, the imaging conditions for ion images in the commercial equipment, guidelines for optimizing PEDA parameters, and the effects of differences in PEDA high-voltage rising waveforms.