Ce–Nd separation by solid-phase micro-extraction and its application to high-precision 142Nd/144Nd measurements using TIMS in geological materials

Abstract

In view of the low initial abundance of 146Sm, 142Nd anomalies are expected to be extremely small (less than 40 ppm), and their detection requires ultra-precise 142Nd/144Nd measurements. A rapid solid-phase micro-extraction (SPME) technique, using HEHEHP resin as sorbent, is established to completely separate Ce from rare earth element (REE) mixtures. This technique is applied to ultra-high-precision 142Nd/144Nd measurements in geological materials. In contrast to the traditional liquid–liquid micro-extraction (LLME) technique, the benefits of the SPME tandem column are high Nd recovery, low residual Ce (Ce/Nd < 10−6), and easy operability. In addition, a single HEHEHP resin column, replacing the traditional two-column scheme (AG 50W + HDEHP resins), is used to further purify Nd by removing Na salt and Sm isobaric interferences. All mean values of 140Ce/144Nd of geological samples after separation never exceed 0.000010 even though the Ce/Nd ratio of geological materials is >3.0. Thus, 142Ce interferences on 142Nd never exceed 1.3 ppm. Ultra-high-precision thermal ionization mass spectrometry analyses of silicate standards show that the internal precision of all runs are better than 4 ppm (2 RSE) for 142Nd/144Nd values. 142Nd/144Nd values for JNdi-1, JR-3, and BCR-2 have external precisions of ±4.8, ±4.4, and ±3.9 ppm (2 RSD), respectively. The external reproducibility is sufficient to distinguish and resolve 5 ppm anomalies in 142Nd/144Nd values.