Precise determination of seawater calcium using isotope dilution inductively coupled plasma mass spectrometry

• Main Authors: Liu, Hou-Chun, You, Chen-Feng, Cai, Wei-Jun, Chung, Chuan-Hsiung, Huang, Kuo-Fang, Chen, Bao-Shan, Li, Yen, 李炎
• Format: Article in Journal/Newspaper
• Language: English
• Published: ROYAL SOC CHEMISTRY 2014
• Subjects: CARBON-CYCLE; COMPLEXOMETRIC TITRATION; OCEAN ACIDIFICATION; SYSTEM; CO2; FEEDBACKS; MAGNESIUM; PACIFIC; DIOXIDE; Arctic; Arctic Ocean; Pacific; Ocean acidification
• Online Access: http://dspace.xmu.edu.cn/handle/2288/88204

NSC, Taiwan We describe a method for rapid, precise and accurate determination of calcium ion (Ca2+) concentration in seawater using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). A 10 mu L aliquot of seawater was spiked with an appropriate Ca-43 enriched solution for Ca-44/Ca-43 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 mu L 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 Ca2+ values, possibly due to a contribution of interference from Mg2+ and Sr2+ 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 Ca2+ determination with small sample size, high throughput, excellent internal precision and external reproducibility.