地质样品中高精度铬同位素分析纯化技术研究进展

A Review on the Progress of Purification Techniques for High Precision Determination of Cr Isotopes in Geological Samples

随着多接收器热电离质谱仪(MC-TIMS)和多接收器电感耦合等离子体质谱仪(MC-ICP-MS)的发展,高精度铬(Cr)同位素测试已成为可能。铬同位素在地球、环境、农业生态和宇宙化学等科学领域中已显示出良好的应用潜力。然而,样品的纯化分离、干扰和仪器质量分馏的校正,依然是制约铬同位素高精度测试的重要因素。本文在近年来铬同位素分析技术最新进展的基础上,结合本课题组已有的研究,对陨石、地质和环境等各类样品中铬同位素的分离纯化方法、MC-ICP-MS测试中干扰与质量歧视校正等进行了详细综述。本文认为,阴阳离子树脂交换联用与过硫酸钾等强氧化剂的结合,可以进行低铬高基质样品的有效纯化,是一种较为普适性的纯化方法。使用铬同位素双稀释剂校正质量歧视效应,在MC-ICP-MS的中高分辨与静态测量模式下,不仅可以有效分开多原子离子的干扰,而且也可以进行高精度铬同位素分析,其δ53/52Cr的分析精度与TIMS相当,可以达到0.04‰(2SD),且最低测试浓度可低至10ng,能够实现超微量铬的同位素分析。

BACKGROUND: With the development of Multi-collector Thermal Ionization Mass Spectrometry(MC-TIMS) and Multi-collector Inductively Coupled Plasma-Mass Spectrometry(MC-ICP-MS), Cr isotopes had been successfully measured at a high resolution. Chromium isotopes have shown good application potential in the fields of environmental geochemistry, agroecology and cosmochemistry. However, sample purification and interference correction are still the main factors that suppress the high-resolution measurement of Cr isotopes. The development of a high-recovery, universal and efficient separation and purification method is an urgent problem to be solved.OBJECTIVES: To discuss the purification of Cr isotopes in geological and environmental samples, interference and mass discrimination correction during measurement of MC-ICP-MS.METHODS: This study compared and analyzed the current chemical separation and purification methods and main instrumental analysis techniques commonly used for chromium isotopes(e.g. MC-ICP-MS), and discussed the current mainstream quality discrimination correction methods. The combination of anion and cation exchange resin with strong oxidants such as K2S2O8 can effectively separate Cr from low Cr samples with high matrix contents, which is a more universal purification method. Medium-high resolution and static measurement mode was used during MC-ICP-MS analysis and Cr isotopes double spike method to correct mass discrimination effect.RESULTS: The analytical precision of δ53/52Cr was 0.04‰(2 SD), similar to that of TIMS. Moreover, the minimum analytical sample was 10 ng, thus isotope analysis of ultra-micro chromium can be achieved.CONCLUSIONS: The proposed method cannot only separate the polyatomic ion interference, but can also perform high-precision Cr isotope analysis. It is necessary to reduce the process blank, remove the interfering elements and completely separate the different forms of chromium.