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Atmospheric Pressure Ion Source Development: Experimental Validation of Simulated Ion Trajectories within Complex Flow and Electrical Fields

  • Walter WissdorfEmail author
  • Matthias Lorenz
  • Thorsten Pöhler
  • Herwart Hönen
  • Thorsten Benter
Research Article

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.

Key words

CFD SIMION SDS DIA APLI 

Notes

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.

Supplementary material

13361_2013_646_Fig7_ESM.jpg (160 kb)
Figure S1

Effects of dry-gas volume flow variation in experimental acquired DIA. Capillary voltage 500 V; spray shield voltage 50 V; the dry gas flow is given in the insets. The maximum signal level (brightest contour) is given above each plot. The spatial axes are in mm (JPEG 160 kb)

13361_2013_646_MOESM1_ESM.tif (313 kb)
High resolution image (TIFF 313 kb)
13361_2013_646_Fig8_ESM.jpg (270 kb)
Figure S2

Geometry variations. DIA simulations with different positions of the capillary cap (given in the inset in the plots) in the horizontal direction. The base position (0 mm) was used for the simulations shown in Figures 3 and 4. The dry gas flow (DG) is given on the left side. Capillary voltage 1000 V; spray shield voltage 50 V; ion depletion probability 10–5 (JPEG 269 kb)

13361_2013_646_MOESM2_ESM.tif (527 kb)
High resolution image (TIFF 527 kb)
13361_2013_646_MOESM3_ESM.png (1.4 mb)
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)
13361_2013_646_MOESM4_ESM.jpg (46.4 mb)
Low resolution image (JPEG 46 mb)
13361_2013_646_MOESM5_ESM.jpg (87.6 mb)
Low resolution image (JPEG 87 mb)
13361_2013_646_Fig9_ESM.jpg (1.8 mb)
Figure S4

Full set of performed DIA simulations (projections) for three different positions of the inlet capillary cap (“geometry”). The base position (geometry: 0 mm) was used for the simulations shown in Figures 3 and 4. “Sp.-Sh.” is the spray shield voltage, “cap” the inlet capillary voltage, and “dry gas” the dry gas volume flow. The ion depletion reaction probability was set to 10–5 (JPEG 1884 kb)

13361_2013_646_Fig10_ESM.jpg (1.7 mb)
Figure S5

Full set of performed DIA simulations (3D volume renderings) for three different positions of the inlet capillary cap (“geometry”). The simulation raw result data set was the same as in S2. DIA simulations with different positions of the capillary cap (given in the inset in the plots) in the horizontal direction. The base position (geometry: 0 mm) was used for the simulations shown in Figures 3 and 4. “Sp.-Sh.” is the spray shield voltage, “cap” the inlet capillary voltage, and “dry gas” the dry gas volume flow. The ion depletion reaction probability was set to 10–5. The origin of the coordinate system is marked by the tip of the black cone on the left side of the simulation domain (JPEG 1761 kb)

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Copyright information

© American Society for Mass Spectrometry 2013

Authors and Affiliations

  • Walter Wissdorf
    • 1
    Email author
  • Matthias Lorenz
    • 2
  • Thorsten Pöhler
    • 3
  • Herwart Hönen
    • 3
  • Thorsten Benter
    • 1
  1. 1.Institute for Pure an Applied Mass Spectrometry, Physical and Theoretical ChemistryUniversity of WuppertalWuppertalGermany
  2. 2.Chemical Sciences DivisionOak Ridge National LaboratoryOak RidgeUSA
  3. 3.Institute of Jet Propulsion and TurbomachineryRWTH Aachen UniversityAachenGermany

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