Oxide interference can be problematic for trace element and isotopic analyses using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Yet, the oxide production mechanism remains poorly understood. Here, we determined the oxide production rates (MO⁺/M⁺ ratios) of 15 rare earth elements (REEs), Th, and U by LA-ICP-MS analyses of synthetic and natural phosphates as well as NIST SRM 610 glass and natural zircon. We found two contrasting oxide production behaviors against the Ar sample gas flow rate, depending on the MO⁺ dissociation energy (D₀(MO⁺)): the MO⁺/M⁺ ratios of elements with D₀(MO⁺) ≥7 eV increased with the gas flow rate from 0.85 to 1.00 L min⁻¹, whereas those with D₀(MO⁺) <7 eV were nearly constant. Moreover, while there is a generally positive relationship between log(MO⁺/M⁺) and D₀(MO⁺) among all elements, only the former showed a linear correlation whose slope increased with the gas flow rate. These results indicate that oxide production is a combined result of the following two processes: (i) the equilibrium reaction of MO⁺ ↔ M⁺ + O within the plasma and (ii) the bonding of M⁺ and O through collisions followed by radiative transition in the interface region. Oxide production through the first process was significant relative to the second process only when the elements had D₀(MO⁺) ≥7 eV and the gas flow rate was high enough to decrease the plasma temperature to ∼8000 K. We further demonstrate the significance of middle-REE oxide interference on heavy-REEs during LA-ICP-MS analyses of monazites from pegmatites and garnet-bearing metamorphic rocks.

中文翻译：

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通过对REE-Th-U磷酸盐的综合分析来揭示LA-ICP-MS中氧化物生成的机理和影响

对于使用激光烧蚀电感耦合等离子体质谱法（LA-ICP-MS）进行的痕量元素和同位素分析，氧化物干扰可能会成问题。然而，氧化物的产生机理仍然知之甚少。在这里，我们通过合成和天然磷酸盐以及NIST SRM 610玻璃和天然磷酸盐的LA-ICP-MS分析，确定了15种稀土元素（REE），Th和U的氧化物生产率（MO ⁺ / M ⁺比率）锆石。根据MO ⁺离解能（D ₀（MO ⁺）），我们发现了两种与Ar样品气体流速相对的氧化物生产行为：D ₀元素的MO ⁺ / M ⁺比（MO ⁺）≥7eV随着气体流量从0.85升至1.00 L min ^-1而增加，而D ₀（MO ⁺）<7 eV的气体几乎恒定。此外，虽然所有元素之间的log（MO ⁺ / M ⁺）与D ₀（MO ⁺）之间通常存在正相关关系，但只有前者呈线性关系，其斜率随气体流速的增加而增加。这些结果表明，氧化物的产生是以下两个过程的综合结果：（i）等离子体中MO ⁺ ↔M ⁺ + O的平衡反应，以及（ii）M ⁺的键合和O通过碰撞，随后在界面区域发生辐射跃迁。仅当元素的D ₀（MO ⁺）≥7eV并且气体流速高到足以使等离子体温度降至8000 K时，相对于第二步而言，通过第一步工艺产生的氧化物才有意义。 LA-ICP-MS分析伟晶岩和含石榴石的变质岩中独居石对中等稀土氧化物干扰重稀土元素的影响。