Numerical Simulation of Flow Field and Ion Transport for Different Ion Source Sampling Interfaces of a Mass Spectrometer

Abstract

Understanding ion transport mechanisms in the flow expansion section of the first vacuum region of a mass spectrometer (MS) with an atmospheric pressure ionization source is essential for optimizing the MS sampling interface design. In this study, numerical simulations of three types of ions in two different MS interface designs have been carried out. In contrast to previously reported numerical studies, nonequilibrium gas dynamics due to rarefied gas effects has been considered in modeling the flow expansion and a realistic space charge effect has been considered in a continuous ion injection mode. Numerical simulations reveal that a flat plate interface has a higher peak buffer gas velocity but a narrower zone of silence compared to the conical interface. Shock wave structures are clearly captured, and the Knudsen number distribution is displayed. Simulation results show that in the axial direction the buffer gas effect is much stronger than the electric force effect in the current configuration. The conical interface leads to both a strong ion acceleration in the zone of silence and a strong ion deceleration downstream. In the radial direction, both the electric force and buffer gas drag force play an important role. The conical interface introduces a relatively stronger ion focusing effect from the radial buffer gas effect and a stronger ion dispersion from the radial electric force than the flat plate interface. The net effect for the current configuration is an increase in ion losses for the conical interface. Nanoelectrospray ionization experiments were carried out to validate the ion transmission efficiency.

IDSimF: An Open-Source Framework for the Simulation of Molecular Ion Dynamics in Mass Spectrometry and Ion Mobility Spectrometry

“…The research and development of mass spectrometric devices is based to a large extent on insights into the behavior of ions within such devices. Numerical modeling of ion paths in the systems can be used for optimization and verification of established MS devices, as well as aid in the development of novel ion optics and multipole geometries. − Within such devices, however, rather complex physical conditions and processes may be present, such as ion-neutral interactions in collision cells, space charge effects, varying pressure ranges and reactive chemical systems, e.g. proton-bound water clusters. ,− To accurately depict the effects of the environment on the ions, specialized software addressing the conditions present in mass and ion mobility spectrometry is required.…”

“…15 Additionally, space charge effects are often relevant and thus have to be taken into account, especially for simulations in ion traps. 16−20 SIMION offers the calculation of space charge effects but does this with an all-to-all algorithm, which has a runtime scaling of n ( ) 2 (n being the number of particles). 21 As such, space charge simulations with large amounts of particles become infeasible fast.…”

Genetic Algorithm Optimized Printed Circuit Board Ion Funnel Tandem Subambient Pressure Ionization with Nanoelectrospray (SPIN) for High Sensitivity Mass Spectrometry

“…On the one hand, the largest ion losses generally occur in the interface region of ESI-MS, where conductance-limiting apertures (e.g., capillary, sampling cone, or orifice inlet) can lead to severe ion losses. On the other hand, an unavoidable consequence is the presence of gas-phase collisions, charge repulsion, or a supersonic free jet effect, − which can lead to ion cloud expansion, reducing ion transmission to the low-pressure region, and thus low detection sensitivity.…”

Simulation study of three new quadrupole ion funnels to improve low‐mass ion transmission

“…Despite ESI's high ionization efficiency, up to 99% of the ions produced at atmospheric pressure are lost en route to the mass analyzer. 1,2 This ion loss mainly occurs because the free ions that are in the process of differential pumping, when moving from one vacuum chamber to the next, must pass through a low-diameter capillary or small orifice inlet, resulting in charge repulsion and supersonic free-jet expansion, [3][4][5] thus making ion transmission more difficult. Therefore, solving the problem of ion focusing and transport in the low vacuum range is crucial to achieving high-performance MS.…”