Communication. Selective removal of plasma matrix ions in plasma source mass spectrometry
Communication. Selective removal of plasma matrix ions in plasma source mass spectrometry
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沟通。
DOI：
10.1039/ja9961100317
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发表时间：
1996
影响因子：
3.4
通讯作者：
D. Koppenaal
中科院分区：
文献类型：
--
作者：
G. Eiden;C. Barinaga;D. Koppenaal
报道了一种选择性去除等离子体源中的Ar离子和其他等离子体基质离子的新方法。该方法包括对等离子体进行采样，并将采样的等离子体和分析离子与氢气反应。在三台仪器上对反应进行了研究：在等离子体源离子陷阱(PSIT)质谱仪的离子陷阱中，在传统的电感耦合等离子体质谱仪和第二个PSIT质谱仪的后撇子区。在离子陷阱中，Ar+和H2之间的反应几乎以碰撞速度进行，而大多数其他原子离子的反应速度要慢四到五个数量级。对于中等的氢气压力和离子陷阱中的反应时间[10-4托(1托=133.322帕)和10毫秒]，Ar+信号减少了六个数量级。我们研究了氢与33个不同原子离子的反应；唯一明显反应的离子是N+、O+、Cl+和Ar+。Ar+的减少是通过一系列快速反应发生的，导致Ar+的电荷转移，形成低m/z离子H2+和H3+，并迅速从离子陷阱中喷射出来。净效果是通过化学方法选择性地去除Ar+，而不是像共振离子喷射方法那样，仅仅依靠其质量与电荷比。在传统的电感耦合等离子体质谱实验中，反应时间很短，在初步实验和未优化的实验中，Ar+的降幅仅为40倍左右。然而，该反应仍然是选择性的：氢的简单散射仅以Ar+反应损失速率的5%降低了45Sc+信号。在常规的电感耦合等离子体质谱实验中直接观察到H2+和H3+的产生，表明后撇油区的化学成分与离子陷阱中观察到的化学成分是一致的。我们讨论了在传统的电感耦合等离子体质谱中实现离子陷阱中观察到的Ar+还原幅度的方法，从而可能允许更大的分析物离子传输效率和减少空间电荷效应。
We report a new method for selective removal of argon ions and other plasma matrix ions in plasma source MS. The method consists of sampling the plasma and reacting the sampled plasma and analyte ions with hydrogen gas. Reactions have been studied in three instruments: in the ion trap of a plasma source ion trap (PSIT) mass spectrometer and in the post-skimmer region of both a conventional ICP mass spectrometer and a second PSIT. In the ion trap, the reaction between Ar+ and H2 proceeds at nearly the collisional rate whereas reaction of most other atomic ions is four to five orders of magnitude slower. For modest H2 pressures and reaction times in the ion trap [10–4 Torr (1 Torr = 133.322 Pa) and 10 ms], the Ar+ signal is reduced by six orders of magnitude. We have examined reactions of H2 with 33 different atomic ions; the only ions for which a reaction was evident were N+, O+, Cl+, and Ar+. The decrease in Ar+ occurs by a sequence of fast reactions resulting in charge transfer from Ar+ to form the low m/z ions H2+ and H3+, which are rapidly ejected from the ion trap. The net effect is the selective removal of Ar+ chemically, not by virtue of its mass-to-charge ratio only, as in resonant ion ejection methods. In the conventional ICP-MS experiments the reaction time is short, limiting the decrease in Ar+ to about 40-fold in preliminary and unoptimized experiments. However, the reaction is still selective: simple scattering by H2 reduces the 45Sc+ signal at only 5% of the rate of reactive loss of Ar+. Production of H2+ and H3+ is observed directly in the conventional ICP-MS experiments, indicating that the chemistry in the post-skimmer region is consistent with that observed in the ion trap. We discuss methods by which the magnitude of Ar+ reduction observed in the ion trap might be realized in conventional ICP-MS, thus possibly allowing a greater analyte ion transmission efficiency and reduced space-charge effects.