Precise determination of rare earth elements, thorium and uranium in chondritic meteorites by inductively coupled plasma mass spectrometry - A comparative study with radiochemical neutron activation analysis

摘要

An inductively coupled plasma mass spectrometry (ICP-MS) procedure for determining trace amounts of rare earth elements (REEs), Th and U in chondritic meteorites (chondrites) is presented. As chondrites have low contents of these elements (10(-2) to 10(-4) x crustal rock averages), the procedure was designed to be performed in as small a scale as possible in order to reduce the procedural blank. Serious matrix effects (ion suppression) may be caused by high Fe contents (20-35 wt.%), which could be eliminated by applying appropriate internal standards (Rh for Y, In and Tl for lanthanides, and Bi for Th and U) and dilution factors (10(4) for Y and 10(3) for the rest of elements). Radiochemical neutron activation analysis (RNAA) was also applied for determining 10 REEs (La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb and Lu) in chondrites. It is found that both ICP-MS and RNAA have comparable detection limits for REEs. ICP-MS, however, has the great advantage that all REEs (including Y), Th and U can be determined with similar precision. Three Antarctic chondrites for which some anomalous REE abundances had been reported by RNAA, were also analyzed by ICP-MS but no anomalies were found, which implies the Limitation of RNAA data in discussing the REE abundances in detail.