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

The atomic absorption spectrophotometric (AAS) determination of Fe, Ca , and Mg in the widely used fluoboric-boric acid matrix (HBF4-H3BO3) i s seriously interfered with by Si and Al. These interferences can be o vercome 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 determinatio n of Al, Fe, Ca, and Mg in 12 Japanese rocks along with three well-cha racterized USGS geochemical samples covering the range of compositions most often encountered in routine analysis. Alkali contents (%Na2O an d %K2O) have been estimated using a reverse alkali buffer (i.e., KCl f or 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 fo r all estimations are presented, and precision values are comparable w ith those of conventional methods used for silicate analysis. For most of the samples the agreement between the observed value and the publi shed data is extremely good. Deviations have been noted in some sample s where values are of ''proposed'' status, indicating that more data a re still required to upgrade the status of some elements from the prop osed/conditional to the certified level. (C) 1994 Academic Press, Inc.