WINDOWS VERSION OF THE ION-TRAP SIMULATION PROGRAM ITSIM - A POWERFULHEURISTIC AND PREDICTIVE TOOL IN ION-TRAP MASS-SPECTROMETRY

The multi-particle simulation program ITSIM version 4.0 takes advantag e of the enhanced performance of the Windows 95 and NT operating syste ms in areas such as memory management, user friendliness, flexibility of graphics and speed, to investigate the motion of ions in the quadru pole ion trap. New features and capabilities significantly broaden its applicability. The simulation program can provide help in understandi ng fundamental aspects of ion trap mass spectrometry and both precede experiments and assist in directing their course. It also has didactic value in elucidating and allowing visualization of ion behavior under a variety of experimental conditions. ITSIM 4.0 provides easy access to ion simulations for all users through a dramatically improved user interface, The program uses the improved Euler method to calculate ion trajectories as a numerical solution to the Mathieu differential equa tion. The Windows version can simultaneously simulate the trajectories of ions with a virtually unlimited number of different mass-to-charge ratios, up to a maximum of 600 000 ions, and hence allow realistic ma ss spectra, ion kinetic energy distributions, phase-of-ejection distri butions and other experimentally measurable properties to be simulated . The simulated data are used to obtain mass spectra from mass-selecti ve instability scans and by Fourier transformation of image currents i nduced by coherently moving ion clouds, Field inhomogeneities arising from exit holes, electrode misalignment, imperfect electrode surfaces or alternative trap geometries can be simulated with the program. Non- zero angle scattering in the hard-sphere collision model allows simula tions involving collisional cooling to be performed. Complete instrume nts, from an ion source through the ion trap mass analyzer to a detect or, can be simulated. Some typical applications of the simulation prog ram are presented and discussed. Such features as the mass-selective i nstability scan mode, mass-range extension via resonant ion ejection, r.f. and d.c. ion isolation and non-destructive detection are shown. C omparisons are made between the simulated and experimental results, fo r example in mass-selective photodissociation. Fourier transform exper iments and a novel six-electrode ion trap mass spectrometer illustrate cases in which simulations precede reduction to practice. (C) 1998 Jo hn Whey & Sons, Ltd.