Simultaneous determination of neodymium and samarium in silicate rocks and minerals by isotope dilution inductively coupled plasma mass spectrometry: Results on twenty geochemical reference samples

A series of experiments was performed to test the feasibility and the advantages of the determination of Nd and Sm in igneous rocks and minerals by isotope dilution (ID) carried out by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). The main advantage of this method, compared to isotope dilution analyses using thermal ionization mass spectrometers (TIMS), is the high sample throughput. This mainly arises (i) from the direct measurement of the solutions obtained from the acid attack on rock powders using a HF + HNO3 mixture without any chemical separation procedure, (ii) from the sampling of rock solutions at atmospheric pressure and (iii) from the short time of analysis (about 10 min/sample). In comparison with conventional ICP-MS, the proposed method, is less sensitive to all the possible causes of signal drift and does not need matrix-matched standards. Results obtained for international and in-house igneous rock standards, in a very wide range of Nd and Sm concentrations and Sm/Nd ratios, compared also with TIMS/ID and ICP-MS data, indicate an accuracy generally better than 5% and a precision about one order of magnitude better than external calibration ICP-MS. (C) 1997 Elsevier Science B.V.