Numerical simulation of Monte Carlo ion transport at atmospheric pressure within improved air amplifier geometry

Abstract

A computational fluid dynamics (CFD) software package ANSYS Fluent was employed for simulation of ion transport at atmospheric pressure between a nano-electrospray ionization (nano-ESI) emitter and the mass spectrometer (MS) sampling inlet tube inside an improved air amplifier device incorporating a radiofrequency ion funnel. The flow field, electric field and the ion trajectory calculations were carried out in separate steps. Parallelized user-defined functions were written to accommodate the additional static and transient electric fields and the elastic ion-gas collisions with the Monte Carlo hard-sphere simulation abilities within Fluent’s environment. The ion transmission efficiency from a nano-ESI emitter to the MS sampling inlet was evaluated for different air amplifier and ion funnel operating conditions by tracking 250 sample reserpine ions. Results show that the high velocity gas stream and the external electric field cause a rapid acceleration of the ion beam and its dispersion along the centreline of the air amplifier which leads to reduction of the space-charge effect and the beam divergence. The radiofrequency potential applied to the ion funnel contributed to additional ion focusing.