Bohlin Madeleine S, Misra Sambuddha, Lloyd Nicholas, Elderfield Henry, Bickle Mike J
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK.
Centre for Earth Sciences, Indian Institute of Science, Bangalore, 560012, India.
Rapid Commun Mass Spectrom. 2018 Jan 30;32(2):93-104. doi: 10.1002/rcm.8020.
Li and Mg isotopes are increasingly used as a combined tool within the geosciences. However, established methods require separate sample purification protocols utilising several column separation procedures. This study presents a single-step cation-exchange method for quantitative separation of trace levels of Li and Mg from multiple sample matrices.
The column method utilises the macro-porous AGMP-50 resin and a high-aspect ratio column, allowing quantitative separation of Li and Mg from natural waters, sediments, rocks and carbonate matrices following the same elution protocol. High-precision isotope determination was conducted by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) on the Thermo Scientific™ NEPTUNE Plus™ fitted with 10 Ω amplifiers which allow accurate and precise measurements at ion beams ≤0.51 V.
Sub-nanogram Li samples (0.3-0.5 ng) were regularly separated (yielding Mg masses of 1-70 μg) using the presented column method. The total sample consumption during isotopic analysis is <0.5 ng Li and <115 ng Mg with long-term external 2σ precisions of ±0.39‰ for δ Li and ±0.07‰ for δ Mg. The results for geological reference standards and seawater analysed by our method are in excellent agreement with published values despite the order of magnitude lower sample consumption.
The possibility of eluting small sample masses and the low analytical sample consumption make this method ideal for samples of limited mass or low Li concentration, such as foraminifera, mineral separates or dilute river waters.
锂和镁同位素越来越多地被用作地球科学中的一种组合工具。然而，既定方法需要利用多种柱分离程序的单独样品纯化方案。本研究提出了一种单步阳离子交换方法，用于从多种样品基质中定量分离痕量水平的锂和镁。
柱法使用大孔AGMP - 50树脂和高纵横比柱，按照相同的洗脱方案，可从天然水、沉积物、岩石和碳酸盐基质中定量分离锂和镁。通过配备10Ω放大器的赛默飞世尔科技™NEPTUNE Plus™多接收电感耦合等离子体质谱仪（MC - ICPMS）进行高精度同位素测定，该放大器可在离子束≤0.51 V时进行准确精确的测量。
使用所提出的柱法可常规分离亚纳克级锂样品（0.3 - 0.5 ng）（产生1 - 70μg的镁质量）。同位素分析期间的总样品消耗量为<0.5 ng锂和<115 ng镁，δLi的长期外部2σ精度为±0.39‰，δMg的长期外部2σ精度为±0.07‰。尽管样品消耗量低了几个数量级，但我们的方法分析地质参考标准物质和海水的结果与已发表的值非常吻合。
洗脱少量样品的可能性以及低分析样品消耗量使得该方法非常适合质量有限或锂浓度低的样品，如浮游有孔虫、矿物分离物或稀释河水。
