School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK.
GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148, Kiel, Germany.
Rapid Commun Mass Spectrom. 2020 Jun 15;34(11):e8762. doi: 10.1002/rcm.8762.
To detect the small changes in past pH the boron isotope ratio of coral carbonates, expressed as the δ B value, needs to be both precise and accurate (2sd <<1‰). Boron measurements by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) require the boron to be carefully purified before analysis, which is time consuming, and requires specialist training. Here, we use the prepFAST-MC method that enables the automatic extraction of B (up to 25 ng load) from a CaCO matrix.
Samples were purified using the prepFAST-MC automated system with a ~25-μL column of Amberlite IRA743 resin. Boron isotope measurements were performed by MC-ICPMS. The effects of matrix load, speed of sample loading onto the column, and blank contamination were tested to evaluate the effects on the purification process. The optimised protocol was tested on various standards and samples of aragonite corals.
The blank contribution for the approach is ~60 pg and is negligible given our sample size (<0.2% sample size). Efficiency of matrix removal is demonstrated with the addition of up to 1.6 mg of dissolved low-B calcium carbonate to NIST SRM 951 with no impact on the accuracy of δ B values. The Japanese Geological Survey Porites reference material JCp-1, boric acid standard NIST SRM 951, and seawater, all processed on the prepFAST-MC system, give δ B values within error of literature values (δ B = 24.31 ± 0.20‰ (2sd, n = 20); δ B = -0.02 ± 0.15‰ (2sd, n = 13) and δ B = 39.50 ± 0.06‰ (2sd, n = 2)). Results obtained from the coral Siderastrea siderea purified with the prepFAST-MC system show an average offset from the manual ion-exchange protocols of Δδ B = 0.01 ± 0.28‰ (2sd, n = 12).
Our study demonstrates the capacity of the prepFAST-MC method to generate accurate and reproducible δ B values for a range of materials, without fractionation, with efficient matrix removal and with negligible blank contribution.
为了检测过去 pH 值的微小变化，需要对珊瑚碳酸盐中的硼同位素比值（表示为 δB 值）进行精确和准确的测量（2sd << 1‰）。多接收电感耦合等离子体质谱仪（MC-ICPMS）的硼测量需要在分析前仔细纯化硼，这既耗时又需要专业培训。在这里，我们使用 prepFAST-MC 方法，该方法能够自动从 CaCO 基质中提取 B（最高 25ng 负载）。
样品使用 prepFAST-MC 自动化系统进行纯化，使用 ~25μL 的 Amberlite IRA743 树脂柱。硼同位素测量由 MC-ICPMS 进行。测试了基质负载、样品加载到柱上的速度和空白污染的影响，以评估对纯化过程的影响。优化后的方案在各种标准和棘皮动物珊瑚样品上进行了测试。
该方法的空白贡献约为 60pg，考虑到我们的样品量（<0.2%的样品量），可以忽略不计。通过向 NIST SRM 951 中添加高达 1.6mg 的低 B 溶解碳酸钙，可以证明基质去除效率高，并且不会影响 δB 值的准确性。在 prepFAST-MC 系统上处理的日本地质调查局 Porites 参考物质 JCp-1、硼酸标准物质 NIST SRM 951 和海水的 δB 值均在文献值的误差范围内（δB = 24.31 ± 0.20‰（2sd，n = 20）；δB = -0.02 ± 0.15‰（2sd，n = 13）和 δB = 39.50 ± 0.06‰（2sd，n = 2））。用 prepFAST-MC 系统纯化的 Siderastrea siderea 珊瑚的结果显示，与手动离子交换方案相比，平均偏移量为 ΔδB = 0.01 ± 0.28‰（2sd，n = 12）。
我们的研究表明，prepFAST-MC 方法能够生成准确且可重复的 δB 值，适用于一系列材料，无分馏，具有高效的基质去除和可忽略不计的空白贡献。
