A CRITICAL-EVALUATION OF 2 SAMPLE PREPARATION TECHNIQUES FOR LOW-LEVEL DETERMINATION OF SOME GEOLOGICALLY INCOMPATIBLE ELEMENTS BY INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

The accurate measurement of low levels of highly incompatible elements is an essential requirement for many geochemical studies. The elements of interest vary, depending on the rock suite under investigation, but frequently include the heavier elements, e.g. Pb, Zr, Hf, U, Th, Nb, Ta and the REE. Some of these elements are partitioned into resistant mineral phases, which can most easily be brought into solution using a fusion technique. This work describes a method for the determination of low levels (< 1 μg g-1 in the rock) of incompatible elements using inductively coupled plasma-mass spectrometry (ICP-MS). Twenty-three standard reference materials were prepared using both an open acid digestion and a lithium metaborate fusion. Calibration of the ICP-MS instrument was achieved using simple aqueous solutions and analysis times were short, typically < 1 min. per analysis. The accuracy of the data is dependent on the particular element of interest. Y, Th, U and the REE can be measured with good accuracy (typically better than ± 5%) in a range of silicate and carbonate matrices, both in samples brought into solution by acid digestion and fusion. Data for Zr, Hf, Ta, Nb and Pb are more complex to interpret. Pb is lost from fused samples while some other elements display inaccurate data, probably due to dissolution problems with resistant mineral phases. © 1990.