Abstract
Three-dimensionally (3D) resolved ion trajectory calculations within the complex viscous flow field of an atmospheric pressure ion source are presented. The model calculations are validated with spatially resolved measurements of the relative sensitivity distribution within the source enclosure, referred to as the distribution of ion acceptance (DIA) of the mass analyzer. In previous work, we have shown that the DIA shapes as well as the maximum signal strengths strongly depend on ion source operational parameters such as gas flows and temperatures, as well as electrical field gradients established by various source electrode potentials (e.g., capillary inlet port potential and spray shield potential). In all cases studied, distinct, reproducible, and, to some extent, surprising DIA patterns were observed. We have thus attempted to model selected experimental operational source modes (called operational points) using a validated computational flow dynamics derived 3D-velocity field as an input parameter set for SIMION/SDS, along with a suite of custom software for data analysis and parameter set processing. Despite the complexity of the system, the modeling results reproduce the experimentally derived DIA unexpectedly well. It is concluded that SIMION/SDS in combination with accurate computational fluid dynamics (CFD) input data and adequate analysis software is capable of successfully modeling operational points of an atmospheric pressure ion (API) source. This approach should be very useful in the computer-aided design of future API sources.
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Freely accessible at http://dia.ipams.uni-wuppertal.de
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Acknowledgments
Financial support of the German Research Foundation (DFG project BE BE2124/6-1) is gratefully acknowledged. W.W. acknowledges support through a graduate student research stipend from the Institute of Pure and Applied Mass Spectrometry, University of Wuppertal, Germany.
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The full set of fully rotatable DIA simulation results and a comprehensive experimental DIA dataset are available at http://dia.ipams.uni-wuppertal.de in a web-browser based viewer tool (DIA explorer).
Figure S3
Additional set of ion trajectory simulations. Additional set of ion trajectories resulting from SIMION/SDS and the relative neutral analyte concentration distribution from the CFD model for three different positions of the inlet capillary cap (“cap pos.”). The starting positions of the ions were uniformly distributed on a line, irrespective of the neutral analyte mixing ratio. The spray shield voltage was 50 V and the dry gas flow 3.8L/min. The parameter “D” represents the distance of the ion starting zone from the spray shield. The complex electrostatic and fluid dynamic forces acting on the ion motion are clearly observable. The experimental DIAs result from the convolution of the relative neutral concentration with the ion trajectories (PNG 1400 kb)
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Wissdorf, W., Lorenz, M., Pöhler, T. et al. Atmospheric Pressure Ion Source Development: Experimental Validation of Simulated Ion Trajectories within Complex Flow and Electrical Fields. J. Am. Soc. Mass Spectrom. 24, 1456–1466 (2013). https://doi.org/10.1007/s13361-013-0646-5
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DOI: https://doi.org/10.1007/s13361-013-0646-5