Space Charge Evaluation in a Plasma-Source Mass Spectrograph

Abstract

Space charge effects, and the matrix interferences they cause, are problems in inductively coupled plasma mass spectrometry (ICPMS). It has previously been observed that these deleterious space charge effects are not significantly present in sector-field instruments, a fact that has been attributed, but not demonstrated, to the high accelerating potentials they commonly employ. To examine the significance of space charge in our plasma-source mass spectrograph (which operates at only moderate accelerating potentials) and in other sector instruments, a graphite disk was placed approximately 7 cm behind the skimmer. An inductively coupled plasma was operated for 17 h while a 0.01 mM multielement solution was introduced. This disk was then analyzed by spatially resolved laser ablation ICP time-of-flight MS. Second vacuum-stage acceleration appears to be an important factor that governs the elemental distribution within the ion beam. The ion beam width at m/z 208 is one-third of its width at m/z 7 using an accelerating potential of 800 V; at an accelerating potential of 4000 V, the ion beam width does not vary with mass.

Laser-ablation sampling for inductively coupled plasma distance-of-flight mass spectrometry

“…With this approach, the isotope-ratio precision worsens to 9.7% RSD, and so demonstrates how simultaneous multi-element detection improves precision. The observed isotope ratio of 65 Cu : 63 Cu is 0.466, 0.02 above the expected isotope ratio of 0.446; 52 this discrepancy is most likely due to mass bias in ion sampling from the ICP, 53,54 and is consistent with our previous solution-sample-introduction ICP-DOFMS studies.…”

Influence of room temperature on magnesium isotope measurements by multi‐collector inductively coupled plasma mass spectrometry

“…Previous studies proposed that mass bias in ICP‐MS could originate in the sample introduction and transportation processes, and different processes occurring in the ICP . The space‐charge effect is often considered as a dominant factor in causing instrumental mass bias because of the preferential transmission of heavier ions . A previous study also implied that any factors affecting plasma stability could cause variation in the instrumental mass bias .…”

Emergence and impact of alternative sources and mass analyzers in plasma source mass spectrometry

“…Because a sector-field mass spectrometer produces spectral features that become closer and closer together at higher masses, isotopic peaks at the upper end of the atomic mass range were impossible to resolve when the electro-optic imaging detector (EOID) was used. [72][73][74] This performance limitation was underscored and clarified by David Solyom, a graduate student who assumed the project after Tom Burgoyne received his doctorate. [75][76][77] As importantly, Solyom showed that the instrument, when tuned properly and fitted with a single-channel detector, could achieve resolution that was more than adequate, even at the highest atomic masses.…”