title: Precise determination of seawater calcium using isotope dilution inductively coupled plasma mass spectrometry.
abstract: 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.
authors.affiliation: Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan. cfy20@mail.ncku.edu.tw.
authors.forename: Hou-Chun
authors.initials: HC
authors.lastname: Liu
authors.forename: Chen-Feng
authors.initials: CF
authors.lastname: You
authors.forename: Wei-Jun
authors.initials: WJ
authors.lastname: Cai
authors.forename: Chuan-Hsiung
authors.initials: CH
authors.lastname: Chung
authors.forename: Kuo-Fang
authors.initials: KF
authors.lastname: Huang
authors.forename: Bao-Shan
authors.initials: BS
authors.lastname: Chen
authors.forename: Yen
authors.initials: Y
authors.lastname: Li