Research on the Chemical Pretreatment for Mo Isotope Analysis of Special Geological Samples
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ABSTRACT
BACKGROUNDMo isotopes have been widely used in the field of geosciences. They can be used to trace the global cycle of Mo, paleoocean redox conditions, mineralization processes, and astronomical evolution. Before the analysis of Mo isotope by multi-collector inductivity coupled plasma-mass spectrometry (MC-ICP-MS), the samples must be pretreated to enrich Mo and remove the interference elements (Zr, Ru, Fe and Mn). According to the traditional anion-cation exchange resin double-column method, it is necessary to use a cation-exchange resin multiple times to separate Fe. The steps are more complicated and the Mo recovery will be reduced. According to the traditional anion-exchange resin single-column method, 1mol/L hydrofluoride acid-0.5mol/L hydrochloric acid medium will produce more CaF2 precipitation and affect the separation and purification results.OBJECTIVESTo develop a new method for managing Ca-bearing geological samples with high Fe content before Mo isotope analysis.METHODSFor such special geological samples, the same anionic resin column (AG1-X8, 100-200 mesh) was used to rinse the sample twice, the first time using 6mol/L hydrochloric acid, and the second time using 1mol/L hydrofluoride acid-0.1mol/L hydrochloric acid and 6mol/L hydrochloric acid.RESULTSResults showed that Mo recovery was better than 96%, and the removal of the interference elements was good, especially the Ru removal rate, which was higher than the previous methods by 12%, up to 100%. The results of experiments on actual samples also showed that the recovery of Mo and the removal of interfering elements meet the requirements, and the measured values of δ98/95Mo were consistent with those reported in the literature.CONCLUSIONSThe improved anion exchange resin single-column elution method is suitable for special samples with high Fe and Ca content, which reduces the analysis cost and is applicable to most geological samples.
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