Separation of Nd from geological samples by a single TODGA resin column for high precision Nd isotope analysis as NdO+ by TIMS

Abstract

Nd can be ionized to NdO⁺ about 5–10 fold more efficiently than to Nd⁺ by thermal ionization mass spectrometry (TIMS). However, with the NdO⁺ method, Ce and Pr must be separated from Nd as completely as possible to reduce CeO⁺ and PrO⁺ isobaric interferences on NdO⁺ (e.g.¹⁴¹Pr¹⁸O⁺ on ¹⁴³Nd¹⁶O⁺). With previously reported methods, it is difficult to achieve an efficient Pr–Nd separation although a perfect Sm–Nd separation can be achieved. In this study, a rapid, single column scheme for the separation of Nd and Sm from geological samples, based on TODGA resins (1 mL resin bed volume, 50–100 μm particle size), was developed. The total column separation time, including column cleaning steps, was about 8 h. With this method, not only Nd and Sm could be efficiently separated from the sample matrix, but also a perfect separation of Nd from Ce, Pr and Sm could be obtained. The recovery yield was greater than 90% for Nd and 95% for Sm. Furthermore, since only a single TODGA column separation step was involved, low procedural blanks (Sm < 5 pg; Nd < 10 pg) could be achieved. Therefore, the method is particularly useful for the separation of low levels of Nd from geological samples for isotope analysis as NdO⁺ by TIMS. Finally, several rock reference materials, including BCR-2, BHVO-2, BIR-1a and UB-N, with different column loads, were analyzed to verify the reliability of the chemical procedure, and the analytical results show good agreement with the recommended values for the ¹⁴³Nd/¹⁴⁴Nd isotopic ratios and Sm and Nd concentrations.