Precise measurement of stable neodymium isotopes of geological materials by using MC-ICP-MS

Abstract

A method has been developed to determine high-precision stable Nd isotopic compositions in geological samples by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using sample-standard-bracketing (SSB) mode. Nd was pre-concentrated and purified through a two-column ion-exchange chromatographic procedure. The recovery for Nd is generally better than 96%, and the interferences, such as Ce and Sm can be efficiently removed, allowing negligible influence on the stable Nd isotopic composition during mass spectrometry measurement. The internal precision for the stable Nd isotopic compositions, ε¹⁴²Nd, ε¹⁴⁵Nd, ε¹⁴⁶Nd and ε¹⁴⁸Nd were generally better than ±0.2 (2 SEM), and the external precision was generally better than ±0.2 (1 SD) for ε¹⁴²Nd, ε¹⁴⁵Nd and ε¹⁴⁶Nd, and better than ±0.5 (1 SD) for ε¹⁴⁸Nd based on the long-term results of the Nd standard solutions, such as La Jolla, Nd-GIG and NIST 3135a. Both the internal and external precisions are comparable to those by double-spike method. The averages of our measured ε¹⁴²Nd, ε¹⁴⁵Nd, ε¹⁴⁶Nd and ε¹⁴⁸Nd results of La Jolla are identical to those by the double-spike method within analytical error. Thus, our method can provide comparable results with the double-spike method, but does not bring any inconvenience of calibrating double spikes, and the efficiency is greatly improved. This provides a more convenient way for studying stable Nd isotopes in geological processes. By using this method, the stable Nd isotopic compositions for a series of international rock standard references were measured.