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High-precision potassium isotopic measurements by collision cell equipped MC-ICPMS
Chemical Geology ( IF 3.6 ) Pub Date : 2021-04-24 , DOI: 10.1016/j.chemgeo.2021.120281
Heng Chen , Naomi J. Saunders , Matthew Jerram , Alex N. Halliday

We report techniques for measuring 41K/39K ratios using a Nu Instruments Sapphire double-focusing multi-collector ICPMS, equipped with a hexapole collision/reaction gas cell. Large Ar-hydride spectral interferences, as well as the 40Ar+ ion beam from the Ar-plasma, are effectively eliminated through a series of reactions with H2 gas in the collision/reaction cell. This allows the 39K+ and 41K+ ion beams to be measured directly and without offsetting peak centers. With optimized operating conditions, 41K/39K can be routinely obtained with an external reproducibility of 0.07 per mil (2 standard deviations), facilitating resolution of small K isotopic variations among terrestrial samples. The signal intensity can be further increased (1200 V/ppm for 39K) by utilizing a desolvating nebulizer (Apex Omega) for introducing samples, making measurements of low-K samples possible. We evaluate the effects of matrix elements, mismatch of K concentration, and mismatch of acid molarity on the accuracy of sample-standard bracketing measurements. A relatively straightforward method for accurate determination of K isotopic ratios is likely to accelerate development and utilization of a wide range of potassium studies, such as into its global geochemical cycle.



中文翻译:

配备碰撞池的MC-ICPMS进行高精度钾同位素测量

我们报告了使用配备六极碰撞/反应气室的Nu Instruments蓝宝石双聚焦多收集器ICPMS测量41 K / 39 K比率的技术。通过在碰撞/反应池中与H 2气体进行一系列反应,有效消除了较大的氢化物光谱干扰以及来自Ar等离子体的40 Ar +离子束。这样就可以直接测量39 K +41 K +离子束,而不会偏移峰中心。在优化的工作条件下,41 K / 39可以常规获得K,外部重现性为每密耳0.07(2个标准差),这有助于解决陆地样品之间较小的K同位素变化。通过使用去溶剂化雾化器(Apex Omega)引入样品,可以进一步提高信号强度(对于39 K为1200 V / ppm ),从而可以进行低K样品的测量。我们评估了基质元素,钾浓度的不匹配以及酸摩尔浓度的不匹配对样品标准方括号测量的准确性的影响。准确测定K同位素比的相对简单的方法可能会加快钾的广泛研究的开发和利用,例如进入其全球地球化学循环。

更新日期:2021-05-09
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