¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China

In this study, a high-precision method for the determination of Sm and Nd concentrations and Nd isotopic composition in highly depleted ultramafic rocks without a preconcentration step is presented. The samples were first digested using the conventional HF + HNO₃ + HClO₄ method, followed by the complete digestion of chromite in the samples using HClO₄ at 190–200 °C and then complete dissolution of fluoride formed during the HF decomposition step using H₃BO₃. These steps ensured the complete digestion of the ultramafic rocks. The rare earth elements (REEs) were separated from the sample matrix using conventional cation-exchange chromatography; subsequently, Sm and Nd were separated using the LN columns. Neodymium isotopes were determined as NdO⁺, whereas Sm isotopes were measured as Sm⁺, both with very high sensitivity using single W filaments with TaF₅ as an ion emitter. Several highly depleted ultramafic rock reference materials including USGS DTS-1, DTS-2, DTS-2b, PCC-1 and GSJ JP-1, which contain extremely low amounts of Sm and Nd (down to sub ng g^-1 level), were analysed, and high-precision Sm and Nd concentration and Nd isotope data were obtained. This is the first report of the Sm-Nd isotopic compositions of these ultramafic rock reference materials except for PCC-1.