New Method of Tangential Ion Injection into Electrostatic Orbitrap with Simulation

The key monopoly technique of electrostatic orbitrap mass spectrometer is to inject ions from the C-trap into Orbitrap. In this work, a new method of ion injection with an O-shaped ion trap was presented. The O-trap was located on the outer orbit of electrostatic Orbitrap. Firstly, ions were introduced tangentially into O-trap for circular motion, and then by controlling the voltage between the O-trap and Orbitrap electrodes, ions could be directly transferred from the circular O-trap down to an elliptical orbit with a lower potential. Ions travelled downward along the elliptical orbit, and eventually down-injected into the static circle Orbitrap. The method allowed the ion flue ionized by ion source to enter continuously into the circular O-trap and to repulse into static Ob-trap, avoiding the long-distance transmission of ions from the C-trap. The ions inject volume therefore increased with more ions being injected. The equation of ion motion trajectory had been derived and the energy equation of the applied pulse was established to alter ion orbital. According to the equation, for the elliptical motion after the descent, its long axis (2a) was determined by the geometric dimensions of the electrostatic Orbitrap and the outer O-trap, and its length of the short axis (2b with a²=b²+c², c is the focal length of ellipse) was related to the strength and duration of the pulse voltage. The variable-orbit pulse voltage ΔU was determined only by the differential voltage applied to the respective internal and external electrodes of Orbitrap and O-trap. Meanwhile, the method of ion introduction was also simulated in this study. The simulation results showed that the angle of incidence was equal when multiple ions were tangent inward at each point of the outer O-trap due to the symmetry of the electrostatic ion trap device. Thus, no obvious effect was found for multi-ion and multi-position injection on ion trajectory, but the tangential ion injection was very critical, and any deviation from tangent injection would greatly reduce the ion lifetime. Because the deviation from the tangential introduction would cause the ions to deviate from the circular orbit and make the elliptical motion, the ions would be lost by hitting the internal and external electrodes of the orbit. The new O-trap ensures continuous tangential injection of ions into Orbitrap, such that allows more ions to be introduced into the electrostatic ion trap for analysis with low less.