DIRECT FLAME ATOMIC-ABSORPTION SPECTROPHOTOMETRIC DETERMINATION OF MAJOR OXIDES IN ROCK SAMPLES OF DIVERSE COMPOSITION USING MATRIX BUFFER

Abstract

The atomic absorption spectrophotometric (AAS) determination of Fe, Ca, and Mg in the widely used fluoboric-boric acid matrix (HBF4-H3BO3) is seriously interfered with by Si and Al. These interferences can be overcome by a matrix buffer (a mixture of KCl, tartaric acid, HCl, and H2SO4). Based on this, an AAS method involving HF-HClO4 (2:1 mixture) decomposition has been proposed and results are given for determination of Al, Fe, Ca, and Mg in 12 Japanese rocks along with three well-characterized USGS geochemical samples covering the range of compositions most often encountered in routine analysis. Alkali contents (%Na2O and %K2O) have been estimated using a reverse alkali buffer (i.e., KCl for Na2O and NaCl for K2O). A mixture of KCl, tartaric acid, and SrCl2 has been found to be an appropriate buffer for Mn. Statistical data for all estimations are presented, and precision values are comparable with those of conventional methods used for silicate analysis. For most of the samples the agreement between the observed value and the published data is extremely good. Deviations have been noted in some samples where values are of ''proposed'' status, indicating that more data are still required to upgrade the status of some elements from the proposed/conditional to the certified level. (C) 1994 Academic Press, Inc.