Numerical Simulation and Experimental Validation of the Three-Dimensional Flow Field and Relative Analyte Concentration Distribution in an Atmospheric Pressure Ion Source

Abstract

In this study, the validation and analysis of steady state numerical simulations of the gas flows within a multi-purpose ion source (MPIS) are presented. The experimental results were obtained with particle image velocimetry (PIV) measurements in a non-scaled MPIS. Twodimensional time-averaged velocity and turbulent kinetic energy distributions are presented for two dry gas volume flow rates. The numerical results of the validation simulations are in very good agreement with the experimental data. All significant flow features have been correctly predicted within the accuracy of the experiments. For technical reasons, the experiments were conducted at room temperature. Thus, numerical simulations of ionization conditions at two operating points of the MPIS are also presented. It is clearly shown that the dry gas volume flow rate has the most significant impact on the overall flow pattern within the APLI source; far less critical is the (larger) nebulization gas flow. In addition to the approximate solution of Reynolds-Averaged Navier-Stokes equations, a transport equation for the relative analyte concentration has been solved. The results yield information on the three-dimensional analyte distribution within the source. It becomes evident that for ion transport into the MS ion transfer capillary, electromagnetic forces are at least as important as fluid dynamic forces. However, only the fluid dynamics determines the three-dimensional distribution of analyte gas. Thus, local flow phenomena in close proximity to the spray shield are strongly impacting on the ionization efficiency.

Numerical modeling of capillary electrophoresis - electrospray mass spectrometry interface design

“…In commercial as well as in free CFD codes more turbulent models are implemented; however, their accuracy and robustness are still questionable. An especially interesting research article was published by Poehler et al (), dealing with numerical simulation of the gas flow within a multi‐purpose ion source. A time‐averaged velocity and turbulent kinetic energy distributions model, SST, and its validation were given.…”

“…The original graphic work is labeled. Reproduced with permission from Poehler et al (), © 2011 Springer.…”

“…As an intuitive point of the development, an external automation script was written in Python environment for the systematic alteration of voltages on the spray shield and capillary cap electrodes for automation purposes. Their CFD model was tested against experimental fluid dynamic measurements using particle image velocimetry technique (Poehler et al, ). The very good overall agreement between the experimental and numerical results reliably validated their model, even in complex cases.…”

Simulation of Ion Motion at Atmospheric Pressure: Particle Tracing Versus Electrokinetic Flow

“…The first paper in the series described in detail the procedures required for computational flow dynamics (CFD) simulations within complex geometries [13]. The present paper examines the interplay between viscous and electrical forces on ions moving at atmospheric pressure.…”

Capillary atmospheric pressure chemical ionization using liquid point electrodes

“…Due to its wide applicability, Atmospheric Pressure Chemical Ionization (APCI) has become one of the most commonly used gas‐phase ionization techniques in modern Atmospheric Pressure (AP) mass spectrometry. Nevertheless, the analytical application of conventional APCI sources involves some disadvantages including (1) the strong dependence of the source conditions on operational parameters and thus a general instability of the source operational point, and (2) observation of unexpected signals in the recorded mass spectra due to rapid ion transformation processes caused by e.g. the direct interaction of the analyte and the corona discharge area.…”