Chemical separation of Nd from geological samples for chronological studies using 146Sm–142Nd and 147Sm–143Nd systematics

• We developed a new three-step column chemistry procedure aimed at high-precision Nd isotope analysis for Sm–Nd chronology.
• Effective separation of Nd from Ce was achieved by oxidative extraction chromatography using Ln Resin with KBrO3.
• Nd and Sm abundances in samples were simultaneously determined with ID-ICP-MS using 145Nd- and 149Sm-enriched spikes.
• The validity of overall techniques developed in this study was confirmed by analyzing meteorite samples (eucrites).

Sm–Nd dating, which involves long-lived 147Sm–143Nd and short-lived 146Sm–142Nd systematics, has been widely used in the field of geosciences. To obtain precise and accurate ages of geological samples, the determination of highly precise Nd isotope ratios with nearly complete removal of Ce and Sm is indispensable to avoid mass spectral interference. In this study, we developed a three-step column chemistry procedure for separating Nd from geological samples that includes cation exchange chromatography for separating major elements from rare earth elements (REEs), oxidative extraction chromatography using Ln Resin coupled with HNO3 + KBrO3 for separating tetravalent Ce from the remaining REEs, and final purification of Nd using Ln Resin. This method enables high recovery of Nd (>91%) with effective separation of Nd from Ce and Sm (Ce/Nd < 1.2 × 10−5 and Sm/Nd < 5.2 × 10−6). In addition, we devised a new method for determining Sm/Nd ratios with the isotope dilution inductively coupled plasma mass spectrometry method using 145Nd- and 149Sm-enriched spikes coupled with a group separation of REEs using TRU Resin. Applying the techniques developed in this study, we determined the Sm–Nd whole-rock isochron age of basaltic eucrites, yielding 4577 − 88+ 55 Ma and 4558 ± 300 Ma for 146Sm–142Nd and 147Sm–143Nd systematics, respectively.

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