ABSTRACT

The advent of the latest-generation of mass spectrometers enables the determination of isotope ratios for several elements with very high precision. However, many obscure processes deteriorate analytical uncertainties. We investigated a likely process, the secondary instrumental fractionation of Nd isotopes during thermal ionization mass spectrometry (TIMS) analysis, which cannot be ignored in recent geochemical applications. Multiple Nd isotope measurements of the standard JNdi-1 and nine terrestrial rocks standards reveal small but resolvable isotopic fluctuations. The variations are attributed to secondary instrumental fractionation induced by the accumulation of conductive materials (e.g., H₃PO₄) from samples, on the ion lens assemblage surface. The secondary instrumental fractionation observed in ¹⁴²Nd/¹⁴⁴Nd ratios is corrected using the simultaneously measured ¹⁵⁰Nd/¹⁴⁴Nd ratios. The correction improves the ¹⁴²Nd/¹⁴⁴Nd reproducibility by a factor of ~1.3. This second-order correction produces more precise and accurate isotopic ratios for terrestrial rocks with potentially variable ¹⁴²Nd/¹⁴⁴Nd ratios.