Frossard Paul, Ball James M J, Schönbächler Maria
Institute for Geochemistry and Petrology, ETH Zürich Zürich Switzerland
J Anal At Spectrom. 2024 Nov 18;40(1):146-161. doi: 10.1039/d4ja00301b. eCollection 2025 Jan 2.
This study presents a new procedure for high-precision Sm isotope analysis by thermal ionisation mass spectrometry (TIMS) for geological samples. A four-step chemical separation scheme results in sharp separation of Sm and Nd from the same sample aliquot. The first step utilises anion exchange resin to remove Fe from the sample solution. Two different liquid-liquid extraction resins are then used to isolate rare-earth elements (TRU-Spec) and purify Sm from Nd (DGA). Fractionation occurs on the DGA resin due to the nuclear field shift effect, but this is negligible if yields greater than 70% are achieved. Different analytical setups were tested to ascertain their ionisation efficiencies on TIMS. The effect of activators composed of Pt and Ta was tested on single Re filaments but the conventional double Re filament assembly provided efficient ionisation and more stable ion beams. The determination of nucleosynthetic isotope variations requires high precision for all Sm isotope ratios. We aimed to improve the precision on the scarce Sm isotope (3% of all Sm). Static, multistatic and dynamic methods were tested. Isotope ratios were normalised to both Sm/Sm and Sm/Sm for comparison. The dynamic methods failed to provide better precision on ratios involving Sm, whereas the multistatic method yielded improved precisions between 13 and 22 ppm (twice the standard deviation, 2 SD) on the Sm/Sm ratio. Synthetic standards have variable Sm isotope compositions, thus requiring systematic and precise characterisation against terrestrial samples. Analyses conducted using this new procedure yielded high-precision values which were consistent with literature data for an array of terrestrial rock standards and the meteorite Allende.
本研究提出了一种通过热电离质谱法（TIMS）对地质样品进行高精度钐同位素分析的新方法。一个四步化学分离方案可实现从同一样品等分试样中清晰分离钐和钕。第一步利用阴离子交换树脂从样品溶液中去除铁。然后使用两种不同的液 - 液萃取树脂分离稀土元素（TRU - Spec）并从钕中纯化钐（DGA）。由于核场位移效应，在DGA树脂上会发生分馏，但如果产率大于70%，这种分馏可以忽略不计。测试了不同的分析装置以确定它们在TIMS上的电离效率。测试了由铂和钽组成的活化剂对单铼灯丝的影响，但传统的双铼灯丝组件提供了高效的电离和更稳定的离子束。对于所有钐同位素比值，核合成同位素变化的测定都需要高精度。我们旨在提高稀有钐同位素（占所有钐的3%）的精度。测试了静态、多静态和动态方法。将同位素比值归一化为Sm/Sm和Sm/Sm进行比较。动态方法未能在涉及钐的比值上提供更好的精度，而多静态方法在Sm/Sm比值上的精度提高到了13至22 ppm（两倍标准偏差，2SD）。合成标准品具有可变的钐同位素组成，因此需要针对地球样品进行系统且精确的表征。使用这种新方法进行的分析产生了高精度值，这些值与一系列地球岩石标准品和陨石阿伦德的文献数据一致。
