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Negative ion source for chlorine isotope ratio measurements
Andrzej Pelc1, Stanislaw Halas
1Mass Spectrometry Laboratory, Institute of Physics, Maria Curie-Skłodowska University, 20-031 Lublin, Poland. andrzej.pelc@poczta.umcs.lublin.pl
Rapid Communications in Mass Spectrometry : RCM
|November 21, 2008
Summary
A new negative chlorine ion source offers superior precision and sensitivity for isotope ratio measurements. The molybdenum-rhenium (MoRe) alloy filament provides optimal performance, simplifying sample analysis.
Area of Science:
- Analytical Chemistry
- Mass Spectrometry
- Isotope Geochemistry
Background:
- Chlorine isotope ratio measurements are crucial for various scientific disciplines.
- Existing positive ionization sources have limitations in precision and sensitivity.
- Surface ionization offers a potential alternative for generating chlorine ions.
Purpose of the Study:
- To design and construct a novel negative chlorine ion source.
- To evaluate different filament materials for optimal performance in direct surface ionization.
- To assess the capabilities of the new source for chlorine isotope ratio measurements.
Main Methods:
- Direct surface ionization of chloromethane gas on heated metal filaments.
- Testing of four filament alloys: W99Th1, W75Re25, Hf97.5Zr2.5, and Mo52.5Re47.5.
- Comparison of negative ion source performance against a previous positive ionization source.
Main Results:
- The MoRe alloy demonstrated the optimal signal-to-noise ratio among tested materials.
- The negative ion source achieved higher precision (typically 0.005 permil) and sensitivity compared to the positive ionization source.
- Analysis of negative ions eliminated the need for isotope ratio corrections and allowed for less purified samples.
Conclusions:
- The developed negative chlorine ion source, utilizing a MoRe filament, significantly enhances chlorine isotope ratio measurements.
- The source's high sensitivity and precision, coupled with simplified analysis, make it a valuable tool for geochemical and analytical studies.
- Direct surface ionization of chloromethane provides a robust method for generating intense negative chlorine ion currents.
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