Numerical simulation of flow field and ion transport for different ion source sampling interfaces of a mass spectrometer

Understanding ion transport mechanisms in the flow expansion region 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, non-equilibrium 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. The conical interface leads to both a strong i...