Precise measurement of 41K/39K ratios by HR-MC-ICP-MS under a dry and hot plasma setting
Precise measurement of 41K/39K ratios by HR-MC-ICP-MS under a dry and hot plasma setting
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在干燥和热等离子体设置下通过高分辨率多接收器电感耦合等离子体质谱精确测量 41K/39K 比率
DOI：
10.1002/rcm.9289
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发表时间：
2022
影响因子：
2
通讯作者：
Weiqiang Li
中科院分区：
文献类型：
--
作者：
Shichao An;Xianglong Luo;Weiqiang Li
稳定的K同位素地球化学正在成为各种应用的重要工具。基于无碰撞电池的多收集器电感耦合等离子体质谱（MC - ICP - MS）的K同位素分析方法的发展将为许多现有的MC - ICP - MS实验室带来K同位素的研究能力。方法在Nu 1700蓝宝石高分辨率多集电极电感耦合等离子体质谱仪上，在不使用“冷等离子体”和碰撞电池的情况下，对稳定K同位素进行分析。使用传统的干热等离子体设置进行分析，以保持高K灵敏度和信号稳定性，并采用高质量分辨率提供39K+的无干扰肩，用于41k /39K比率的同位素测量。ICP中产生的40Ar+离子束在Daly探测器的离子导轨中被中和。结果在此操作条件下，对于1ppm及以上的K溶液，在41k /39K条件下，外部重现性<±0.1‰（2个标准偏差）。试验考察了总钾负荷、钾浓度和酸的量浓度错配、基质效应以及40ar +和40ar1h +尾矿对钾同位素分析的影响。我们发现样品与标准K的浓度错配会影响K同位素分析的准确性，每1%的K含量错配会影响δ41K的0.007‰。相比之下，hno3的量浓度不匹配或HCl的存在对K同位素分析的精度和准确度的影响可以忽略不计。此外，当Na/K、Mg/K、Ca/K、Rb/K、V/K和Cr/K比值低于3%时，K同位素分析结果仍然准确。结论本文报道的高精度K同位素分析方法对于研究地质、宇宙化学和生物样品中的K同位素变化是可靠的。用本方法测得的6个国际土工标准的f41K值与其他实验室用不同分析方法测得的数据一致。
RationaleStable K isotope geochemistry is becoming an important tool for various applications. Developments in analytical methods for K isotopes based on multicollector inductively coupled plasma mass spectrometry (MC‐ICP‐MS) without collision cell will bring research capability of K isotopes to many existing MC‐ICP‐MS labs.MethodsStable K isotopes were analyzed without applications of “cold plasma” and collision cell on a Nu 1700 Sapphire high‐resolution multicollector inductively coupled plasma mass spectrometer. A conventional dry and hot plasma setting is used for analysis to maintain high K sensitivity and signal stability, and high mass resolution was applied to provide interference‐free shoulders of39K+for isotopic measurement of41K/39K ratios.40Ar+ion beam generated in ICP was neutralized in the ion guide rail for the Daly detector.ResultsUnder such operating conditions, an external reproducibility of <±0.1‰ (2 standard deviation) for41K/39K is achieved for K solutions of 1 ppm or above. Tests were carried out to evaluate the influence of total K loading, K concentration and acid molarity mismatch, matrix effects, and40Ar+and40Ar1H+tailing on K isotope analysis. We found that the accuracy of K isotope analysis can be compromised by concentration mismatch of sample and standard K, by 0.007‰ in δ41K per 1% mismatch of K content. By contrast, mismatch of HNO3molarity or existence of HCl in HNO3exerts negligible influences on the analytical precision and accuracy of K isotope analysis. Furthermore, K isotope analytical results remain accurate when Na/K, Mg/K, Ca/K, Rb/K, V/K, and Cr/K ratios are below 3%.ConclusionsThe high‐precision K isotope analytical method reported here is robust for studies on K isotopic variations in geological, cosmochemical, and biological samples. The f41K values of six international geostandards measured using our method are consistent with data measured using different analytical methods from other laboratories.