Chemical Characterization of Cobalt Crust from Afanasy-Nikitin Seamount in the Eastern Indian Ocean by Inductively Coupled Plasma Time-of-Flight Mass Spectrometry

Abstract

Analytical methodology was developed for the chemical characterization of cobalt crust samples collected from the Afanasy-Nikitin seamount in Eastern Equatorial Indian Ocean by inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS). Concentrations of geochemically significant groups of different trace elements such as large-ion-lithophile elements (e.g., Rb, Cs), high field strength elements (e.g., Ta, Nb, Hf and Zr), rare earth elements in addition to a few major and minor elements were determined in these samples. Samples (~50 mg) were digested in closed digestion vessels for 48 h before the expulsion of Si and the residues were taken in 5 % nitric acid. 103Rh was used as an internal standard. Matrix matching external calibrations were utilized in order to compensate for the spectroscopic and non-spectroscopic interferences. The detection limits obtained for various elements were in the range 1–0.01 ng/ml for majority of the elements analyzed. Accuracy for the determination of different elements is assessed by measuring them in a few cobalt crust samples, ferromanganese nodules and similar marine sediment reference materials. Also, there is a very good agreement between the data sets obtained by ICP-TOF-MS as well as the well established ICP-quadrupole MS on cobalt crust samples. The precisions obtained in this study are <5 % RSD for majority of the elements with comparable accuracy. The results are in agreement with certified and reference values wherever available for comparison. The geochemical characteristics of these rare marine sediments have been described.