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Determination of Trace Elemental ratios from Marine Biogenic Carbonates.
  • Satya Chanakya I V,
  • Sambuddha Misra
Satya Chanakya I V
Indian Institute of Science Centre for Earth Sciences

Corresponding Author:[email protected]

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Sambuddha Misra
Indian Institute of Science Centre for Earth Sciences
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Abstract

An improved method for accurate and precise determination of metal to calcium ratio in mass limited calcium carbonate samples has been developed. We used an Agilent ®5800 ICP-OES for major elements (Na/Mg/Sr to Ca) and an Agilent ®8900 QQQ-ICP-MS for minor and trace elements (Li/B/Na/Mg/Al/Mn/Fe/Zn/Sr/Cd/Ba/U to Ca). Our method has a long-term precision of ≤1%(1s), determined by repeat analysis over different analytical sessions (n≥6) of multiple external standards spanning a large range of concentrations. We quasi-quantitatively eliminated potential matrix effect raising from high [Ca] by analyzing samples and standards at identical concentrations (∆[Ca] ≤ ±5%) during both ICP-OES and ICP-QQQ-MS sessions. ICP-OES analyses were done on 200µl of sample at 60 ppm [Ca], consuming ~30µg of CaCO 3 per analysis. Whereas trace element analyses by ICP-QQQ-MS required ~150µl of sample at 20 ppm [Ca], consuming ~7.5µg of CaCO 3 per analysis. Thus, the present method allows for high precision determination of TE/Ca in <40µg of CaCO 3. The sensitivity and stability of ICP-OES was optimized for selected elements (Na, Mg, Ca and Sr) by tuning for gas flows, plasma power, viewing height in order to select wavelengths which exhibits minimal interferences, high sensitivity and linearity. For choice of Ca lines, the focus was on the minimization of self-matrix effect. The optimization of ICP-QQQ-MS method focused on the selection of right isotope(s) for elements with minimal to no interferences, relatively high absolute abundance. We minimized instrumental drift by conditioning the cones with 20 ppm Ca. Furthermore, the present method allows for precise B/Ca determination sans the use of HF matrix. In summary, this paper presents an easily adopted method for determining element-to-calcium ratios, suitable for analyzing limited-mass carbonate samples including foraminifera and coral samples from culture experiments, and core-top/down-core samples using readily-available-instrumentation.