Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan.
Analyst. 2014 Feb 21;139(4):734-41. doi: 10.1039/c3an01948a. Epub 2014 Jan 17.
We describe a method for rapid, precise and accurate determination of calcium ion (Ca(2+)) concentration in seawater using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). A 10 μL aliquot of seawater was spiked with an appropriate (43)Ca enriched solution for (44)Ca/(43)Ca ID-ICP-MS analyses, using an Element XR (Thermo Fisher Scientific), operated at low resolution in E-scan acquisition mode. A standard-sample bracketing technique was applied to correct for potential mass discrimination and ratio drift at every 5 samples. A precision of better than 0.05% for within-run and 0.10% for duplicate measurements of the IAPSO seawater standard was achieved using 10 μL solutions with a measuring time less than 3 minutes. Depth profiles of seawater samples collected from the Arctic Ocean basin were processed and compared with results obtained by the classic ethylene glycol tetra-acetic acid (EGTA) titration. Our new ID-ICP-MS data agreed closely with the conventional EGTA data, with the latter consistently displaying 1.5% excess Ca(2+) values, possibly due to a contribution of interference from Mg(2+) and Sr(2+) in the EGTA titration. The newly obtained Sr/Ca profiles reveal sensitive water mass mixing in the upper oceanic column to reflect ice melting in the Arctic region. This novel technique provides a tool for seawater Ca(2+) determination with small sample size, high throughput, excellent internal precision and external reproducibility.
我们描述了一种使用同位素稀释电感耦合等离子体质谱法（ID-ICP-MS）快速、精确、准确测定海水中钙离子（Ca(2+)）浓度的方法。取 10 μL 海水样品，加入适量的（43）Ca 富化溶液，用于（44）Ca/（43）Ca ID-ICP-MS 分析，使用 Element XR（Thermo Fisher Scientific），在 E-扫描采集模式下以低分辨率运行。采用标准-样品内插技术，每隔 5 个样品校正潜在的质量歧视和比值漂移。使用 10 μL 溶液，测量时间小于 3 分钟，对 IAPSO 海水标准品进行了重复性测量，其精密度优于 0.05%，对运行内的精密度优于 0.10%。从北冰洋盆地采集的海水样品的深度剖面经过处理，并与经典的乙二醇四乙酸（EGTA）滴定法得到的结果进行了比较。我们的新 ID-ICP-MS 数据与传统的 EGTA 数据非常吻合，后者始终显示 Ca(2+)值高出 1.5%，可能是由于 EGTA 滴定中 Mg(2+)和 Sr(2+)干扰的贡献。新获得的 Sr/Ca 剖面揭示了海洋上层水柱中敏感的水团混合，以反映北极地区冰融化的情况。这项新技术为海水 Ca(2+)测定提供了一种工具，具有小样品量、高通量、优异的内部精度和外部重现性。
