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Space-charge-dominated mass spectrometry ion sources: Modeling and sensitivity
M Busman1, J Sunner, C R Vogel
1Department of Chemistry, Montana State University, 59717, Bozeman, MT.
Journal of the American Society for Mass Spectrometry
|November 19, 2013
Summary
Sensitivity in unipolar ion sources like electrospray (ESP) and corona atmospheric pressure ionization (API) is governed by ion density and drift time. Space charge significantly impacts source voltage, electric fields, and ion residence time.
Area of Science:
- Analytical and computational physics
- Mass spectrometry instrumentation
Background:
- Space-charge-dominated (SCD) unipolar ion sources, including electrospray (ESP) and corona atmospheric pressure ionization (API), are crucial for various analytical techniques.
- Understanding the factors influencing their sensitivity is essential for optimizing performance.
Purpose of the Study:
- To theoretically investigate the key parameters determining the sensitivity of SCD unipolar ion sources.
- To analyze the impact of space charge on ion source performance and sensitivity.
Main Methods:
- Solving the "space-charge problem" using a system of differential equations.
- Employing the finite-element method for realistic "needle-in-can" geometries.
- Utilizing a geometry-independent treatment for calculating absolute sensitivities.
Main Results:
- Ion density and ion drift time near the sampling orifice are critical sensitivity determinants.
- Space charge significantly influences the minimum voltage required to overcome its effects in ESP and corona API sources.
- Electric field, ion density, and ion residence time are primarily governed by space charge.
Conclusions:
- Space charge is a dominant factor in SCD ion source sensitivity.
- Theoretical analysis provides insights into optimizing ion source design and operating conditions for enhanced sensitivity.
- The developed methods allow for accurate calculation of absolute sensitivities for corona API sources.
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