Precise thermal ionization mass spectrometric measurements of ~(142)Nd/~(144)Nd and ~(143)Nd/~(144)Nd isotopic ratios of Nd separated from geological standards by chromatographic methods

摘要

A chromatographic separation technique for ~(142)Nd/~(144)Nd and ~(143)Nd/~(144)Nd isotope ratio measurements is established and applied to the analyses of geological standards of basaltic compositions (BCR-2, BIR-1) using Isoprobe-T TIMS. The instrument was tested for reliability and reproducibility to measure Nd isotope composition using the synthetic standard JNdi-1. The techniques were also applied to a carbonatite lava sample, OL-6, Oldoinyo Lengai, to check the validity of method for carbonatite matrix. The isotope ratios of ~(143)Nd/~(144)Nd for synthetic Nd standard JNdi-1, geological standards BCR-2, BIR-1, and carbonatite lava sample OL-6 obtained by these methods are in good agreement with previously published data. The ~(143)Nd/~(144)Nd values for JNdi-1 and BCR-2 have an external precision of ±13ppm and ±15ppm (2σ), respectively. The JNdi-1 and BCR-2 data for ~(142)Nd/~(144)Nd has an external precision of ±12ppm and ±8ppm (2σ), respectively. The ~(142)Nd/~(144)Nd composition of the two geological standards BCR-2 and BIR-1 are indistinguishable from synthetic mono-element standard JNdi-1, and they all fall within the 12ppm (2σ) envelope of external precision. The external reproducibility is sufficient to distinguish and resolve 20ppm anomalies in ~(142)Nd/~(144)Nd values.