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Space charge evaluation in a plasma-source mass spectrograph
T W Burgoyne1, G M Hieftje, R A Hites
1Department of Chemistry, Indiana University, Bloomington 47405, USA.
Analytical Chemistry
|February 1, 1997
Summary
Space charge effects in inductively coupled plasma mass spectrometry (ICP-MS) are problematic. This study reveals that second vacuum-stage acceleration significantly influences ion beam distribution, mitigating these interferences in mass spectrographs.
Area of Science:
- Analytical Chemistry
- Mass Spectrometry
- Atomic Spectroscopy
Background:
- Space charge effects in inductively coupled plasma mass spectrometry (ICP-MS) cause matrix interferences.
- These effects are reportedly less significant in sector-field instruments due to high accelerating potentials.
- The role of accelerating potentials in mitigating space charge in plasma-source mass spectrographs requires further investigation.
Purpose of the Study:
- To investigate the significance of space charge effects in a plasma-source mass spectrograph operating at moderate accelerating potentials.
- To examine the influence of second vacuum-stage acceleration on ion beam characteristics and elemental distribution.
- To compare findings with sector-field instruments and the attributed role of high accelerating potentials.
Main Methods:
- Utilized a plasma-source mass spectrograph with a graphite disk placed behind the skimmer.
- Introduced a multielement solution into an inductively coupled plasma for 17 hours.
- Analyzed the graphite disk using spatially resolved laser ablation ICP time-of-flight MS.
- Varied the accelerating potential (800 V and 4000 V) to observe its effect on ion beam width.
Main Results:
- Second vacuum-stage acceleration was identified as a critical factor in governing elemental distribution within the ion beam.
- At 800 V, the ion beam width at m/z 208 was one-third of its width at m/z 7, indicating mass-dependent broadening.
- At 4000 V, the ion beam width showed no variation with mass, suggesting effective suppression of space charge effects.
Conclusions:
- Second vacuum-stage acceleration is crucial for controlling ion beam distribution and minimizing space charge effects in ICP-MS.
- Higher accelerating potentials effectively eliminate mass-dependent ion beam broadening caused by space charge.
- The findings support the hypothesis that accelerating potentials play a key role in the reduced space charge effects observed in sector-field instruments.