Senior engineer LI Chaofeng and his team present a new method of directly determining ¹⁴³Nd/¹⁴⁴Nd isotope ratios using thermal ionization mass spectrometry (TIMS) for geological samples.

The key point is to well correct isobaric interferences of ¹⁴⁴Sm on ¹⁴⁴Nd for this method. The accurate intensity of 144Sm can be obtained using ¹⁴⁷Sm/¹⁴⁴Sm ratio of 4.87090 and mass discrimination factor of Sm (bSm), which is achieved using ¹⁴⁷Sm/¹⁴⁹Sm ratio of 1.08583 with Russell equation. Consequently, the real intensity of 144Nd was achieved, then also raw 146Nd/144Nd, 143Nd/144Nd ratios. Finally, ¹⁴³Nd/¹⁴⁴Nd ratio is normalized using ¹⁴⁶Nd/¹⁴⁴Nd ratio of 0.7219 following exponential law.

The accuracy of this method is validated by replicating TIMS measurements for thirteen international reference materials of silicate rock, spanning a wide range of Sm/Nd from 0.13 to 0.46 and bulk compositions. The measured ¹⁴³Nd/¹⁴⁴Nd ratios of the rock standards are in good agreement with the reported values of within error of ±0.004%. Our new method shortens the analytical procedure and significantly improves sample throughput which greatly contributes to those studies requiring a large dataset and quick analysis.

Fig. 1 Comparison of ¹⁴³Nd/¹⁴⁴Nd average value between purifed Nd fractions and REEs fractions. (Image by LI)

Li et al. Directly determining ¹⁴³Nd/¹⁴⁴Nd isotope ratios using thermal ionization mass spectrometry for geological samples without separation of Sm-Nd. Journal of Analytical Atomic Spectrometry. 2011, 26（10）: 2012–2022 （Download Here）