Ce and Nd stable isotope purification and determination of geological samples by MC-ICP-MS

Abstract

The combined study of Ce and Nd stable isotopes is promising because Ce and Nd behave similarly in geological processes and distinctively in redox reactions. However, the sequential purification of Ce and Nd from other REEs is particularly challenging because of their similar physicochemical properties. In this contribution, we present a novel two-stage ion-exchange chromatography method to purify Ce and then Nd using Bio-Rad AG50W-X12 (200–400 mesh) and Eichrom TODGA resin (50–100 μm). The yields of Ce and Nd are both typically more than 99.3% after measurements of natural materials. The potential influence of the HCl content and rock type were thoroughly evaluated. Stable Ce and Nd isotopic ratios were measured by MC-ICPMS and calibrated with Sm and Eu internal standards, respectively. The long-term external reproducibility was better than ±0.04‰ (2SD) for δ^142/140Ce and ±0.03‰ (2SD) for δ^146/144Nd. The stable Ce and Nd isotopic ratios of ten commercially accessible geological rocks were measured here. The δ^142/140Ce values of four geological rocks were presented for the first time. Other results are in good accordance with reported values within analytical uncertainties. The similarity in the degree of Ce and Nd isotopic fractionation may be induced by diagenetic processes, whereas the difference may be accused by redox reactions. In addition, our method using a single sample aliquot can help to minimize the consumptions and heterogeneities of the samples. This procedure for a two-stage isolation of Ce and Nd and high-precision analysis of their isotopic ratios has important advantages in the study of Ce and Nd isotope geochemistry.