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

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 lo w 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 p ossible in order to reduce the procedural blank. Serious matrix effect s (ion suppression) may be caused by high Fe contents (20-35 wt.%), wh ich could be eliminated by applying appropriate internal standards (Rh for Y, In and Tl for lanthanides, and Bi for Th and U) and dilution f actors (10(4) for Y and 10(3) for the rest of elements). Radiochemical neutron activation analysis (RNAA) was also applied for determining 1 0 REEs (La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb and Lu) in chondrites. It i s found that both ICP-MS and RNAA have comparable detection limits for REEs. ICP-MS, however, has the great advantage that all REEs (includi ng Y), Th and U can be determined with similar precision. Three Antarc tic chondrites for which some anomalous REE abundances had been report ed by RNAA, were also analyzed by ICP-MS but no anomalies were found, which implies the Limitation of RNAA data in discussing the REE abunda nces in detail.