Simulation of ion beam and optimization of orthogonal tandem ion trap/reflector time-of-flight mass spectrometry

Abstract

The aim of the present work is to design an orthogonal coupling between a quadrupole ion trap and a reflector time-of-flight (reTOF) analyzer. According to the characteristics of the orthogonal ion injection in the reTOF analyzer, the incident ion beam properties have been determined. Different ion ejection modes from the trap cell, consistent with orthogonal-reflector time-of-flight mass spectrometry (O-reTOF/MS), have been investigated by simulations (SIMION 6.0) and experimental exploration. Especially, the following scanning modes have been studied: (1) dc scan applied to the ring electrode, (2) dc pulse applied to the ring electrode, and (3) dc pulse applied to the end-cap electrodes with switching off the drive rf voltage, under various storage conditions and for different m/z values. Distributions of ion velocities, kinetic energies, and ion ejection times, obtained by simulations and experiments, were compared using the ejection mode (2). Results from simulations of ions orthogonally injected into the reTOF/MS, show that the incident ion beam must be mono-energetic, with initial radial KE<2 eV to be efficiently deflected and detected. The simulations and experiments of original scanning from ion trap enlighten that dc ejection with rf voltage was not compatible with O-reTOF analysis (high energetic and noncontinuous ion beam). Appropriate dc ejection, with switching off the rf voltage, was consistent with O-reTOF analysis. For enhancing the duty cycle of the proposed system, the challenge is then to optimize ion ejection to get an ion beam as continuous as possible.