Sequential separation of multi-isotopes from limited samples through a two-step column chromatography approach†

Abstract

Calcium (Ca), strontium (Sr), barium (Ba), cerium (Ce), and neodymium (Nd) isotopes have broad applications in the Earth and planetary sciences. Usually, only one specific element is separated using an individual separation procedure, which requires substantial sample quantities. However, this poses challenges for limited samples, such as extraterrestrial materials (meteorites or returned samples). Herein, we developed a two-step, three-column method to separate multi-isotopes—Ca, Sr, Ba, Ce, and Nd—from a single geological sample solution. In the first step, AG 50W-X8 (200–400 mesh) resin was used to separate the sample solution into two sub-solutions: (1) major elements + Sr and (2) rare-earth elements (REE) + Ba. In the second step, Ca and Sr were sequentially separated from the former solution using AG 50W-X12 (200–400 mesh) resin, while Ba, Ce and Nd were sequentially separated from the latter solution using DGA (50–100 μm) resin. The recovered yields of all the target elements were over 99.5%, with low whole-procedure blanks. To verify the reliability of this analytical technique, five international rock standards, including NOD-A-1 (manganese nodules), AGV-2 (andesite), BHVO-2 (basalt), GSP-2 (granodiorite), COQ-1 (carbonatite), and two simulated lunar soil samples (CUG-1A and CUG-1B), were analyzed. Results show that only 1–2 mg of samples is sufficient to achieve simultaneous and accurate measurements of Ca, Sr, Ba, Ce and Nd, offering comprehensive isotope data with minimal sample consumption. This approach will be particularly valuable for studying limited and precious samples, thus providing important technological support for the development of the earth sciences and planetary sciences.