PRODUCTION ORIENTED METHOD FOR THE DETERMINATION OF RARE-EARTH AND OTHER TRACE-ELEMENTS IN ROCKS BY ICP-MS

The rare earth elements along with Y, Sc, Co, Hf, Nb, Rb, Ta, Th, Ti, U, V and Zr have been determined in ten standard reference materials a nd ten granitoid samples by inductively coupled plasma mass spectromet ry (ICP-MS). Two digestion methods have been used: (a) dissolution wit h hydrofluoric-perchloric acid followed by fusion of the residue with lithium metaborate, (b) dissolution with hydrofluoric acid-perchloric acid followed by fusion with lithium metaborate-sodium perborate and a ddition of hydrogen peroxide. An evaluation of the two decomposition m ethods and a comparison of the ICP-MS and X-ray fluorescence results h ave been carried out. In comparing the two digestion methods, method(b ) gave more accurate results for Nb and Ta, and it has been applied to a rock geochemistry project covering whole Finland (about 7000 sample s). The statistical stability of the method has been monitored by freq uent analyses of reference material SDC-1 (Mica Schist, USGS).