An improved separation scheme for Sr through fluoride coprecipitation combined with a cation-exchange resin from geological samples with high Rb/Sr ratios for high-precision determination of Sr isotope ratios,Journal of Analytical Atomic Spectrometry

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An improved separation scheme for Sr through fluoride coprecipitation combined with a cation-exchange resin from geological samples with high Rb/Sr ratios for high-precision determination of Sr isotope ratios
Journal of Analytical Atomic Spectrometry ( IF 3.1 ) Pub Date : 2020-03-06 , DOI: 10.1039/d0ja00035c
Wen-Gang Liu _{1,

2,

3,

4,

5} , Shuang Wei _{1,

2,

3,

4,

5} , Jian Zhang _{1,

2,

3,

4,

5} , Cong Ao _{1,

2,

3,

4,

5} , Fu-Tian Liu _{1,

2,

3,

4,

5} , Bin Cai _{6,

7,

8,

9} , Hong-Ying Zhou _{1,

2,

3,

4,

5} , Ji-Long Yang _{1,

2,

3,

4,

5} , Chao-Feng Li _{4,

10,

11,

12,

13}

Affiliation

A cation-exchange resin is commonly used to separate Sr from geological and environmental samples. AG50 resin is the most traditional cation-exchange resin and has the advantages of good reusability and low cost. Although AG50 resin can meet the demands of most conventional geological samples, eliminating ⁸⁷Rb isobaric interference from samples with high Rb/Sr ratios (>30) is difficult during one-step separation. Separating Sr twice using AG50 resin is the general approach to Rb removal. The two-step separation method is time consuming and leads to a low Sr yield. This study aimed to improve the sample throughput and overcome the problem of ⁸⁷Rb isobaric interference from imperfect separation. A new separation method involving hydrofluoric acid (HF acid) coprecipitation combined with a cation-exchange resin (i.e. AG50 resin) for samples with high Rb/Sr ratios was developed. HF acid was used as a coprecipitator to remove most Rb (>90%) and recover Sr before performing AG50 column chemistry. The reliability of this method was examined using the rhyolite standard JR-2, a typical sample with a high Rb/Sr ratio (Rb/Sr = 37.36). Results in the JR-2 case showed that approximately 92% of Rb and most of the matrix elements (K, Ti, Fe, Al, Mn and Na) could be removed effectively. Moreover, Sr recovery exceeded 91% during HF acid coprecipitation. After the removal of Rb by HF acid coprecipitation, the Sr fraction with high purity was easily obtained through one-step separation using the AG50 resin column. However, we found that the removal rates of Rb and some matrix elements (such as Al and Na) were strongly affected by the composition of Al–Ca–Mg in samples. Our separation method is more suitable for samples with high Rb/Sr ratios and low Ca and Mg contents. A series of silicate rock reference materials were selected to evaluate the applicability of our method, and the Sr isotopic results were consistent with previously reported values. Overall, this rapid, simple and low-cost method shows great potential for the separation of Sr from geological samples with high Rb/Sr ratios, such as alkaline feldspar granite, alkaline granite and alkaline rhyolite.

中文翻译：

一种改进的氟化物共沉淀与阳离子交换树脂从高Rb / Sr比的地质样品中分离Sr的方案，用于高精度测定Sr同位素比

阳离子交换树脂通常用于从地质和环境样品中分离Sr。AG50树脂是最传统的阳离子交换树脂，具有重用性好，成本低的优点。尽管AG50树脂可以满足大多数常规地质样品的要求，但是在一步分离过程中，很难从具有高Rb / Sr比（> 30）的样品中消除⁸⁷ Rb等压干扰。使用AG50树脂将Sr分离两次是去除Rb的常规方法。两步分离方法耗时且导致Sr收率低。这项研究旨在提高样品通量并克服⁸⁷不完全分离产生的Rb等压干扰。一种新的分离方法，涉及氢氟酸（HF酸）与阳离子交换树脂（即开发了用于高Rb / Sr比样品的AG50树脂）。在进行AG50色谱柱化学分析之前，将HF酸用作共沉淀剂以除去大部分Rb（> 90％）并回收Sr。使用流纹岩标准品JR-2（一种具有高Rb / Sr比（Rb / Sr = 37.36）的典型样品）检验了该方法的可靠性。在JR-2案例中的结果表明，可以有效地去除大约92％的Rb和大多数基质元素（K，Ti，Fe，Al，Mn和Na）。此外，在HF酸共沉淀过程中，Sr的回收率超过91％。在通过HF酸共沉淀除去Rb之后，使用AG50树脂柱通过一步分离容易地获得高纯度的Sr级分。但是，我们发现样品中Al-Ca-Mg的成分对Rb和某些基质元素（如Al和Na）的去除率有很大影响。我们的分离方法更适用于高Rb / Sr比以及低Ca和Mg含量的样品。选择了一系列硅酸盐岩参考物质来评估我们方法的适用性，并且Sr同位素结果与先前报道的值一致。总体而言，这种快速，简单且低成本的方法显示出从高Rb / Sr比的地质样品（例如碱性长石花岗岩，碱性花岗岩和碱性流纹岩）中分离Sr的巨大潜力。

更新日期：2020-03-06

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