COMPARISON OF DIFFERENT PLASMA EXCITATION AND CALIBRATION METHODS IN THE ANALYSIS OF GEOLOGICAL-MATERIALS BY OPTICAL-EMISSION SPECTROMETRY

A comparative study has been made of different dissolution and calibration methods for analyses by optical emission spectrometry (OES) utilizing inductively coupled plasma (ICP) and capacitively coupled microwave plasma (MWP) as excitation sources. The test substances were geological standard rocks, in which SiO2, Al2O3, TiOz, Fe203, MnO, MgO, CaO, Na2O, Ba, some traces were determined. The results show that analyses by MWP-OES are severely disturbed by matrix effects; only in the presence of large quantities of ionization buffers e.g., [Sr(NO3)2] can MWP-OES yield rock analyses of very good quality. No buffers are needed for analyses by ICP-OES, for which the matrix effects are remarkably low. ICP-OES may suffer from annoying nebulizer disturbances when concentrated solutions are used but, with properly diluted solutions, all major and many trace elements can routinely be analyzed in 50-mg rock samples. MWP-OES on the other hand is poorly suited for trace element determinations. © 1979, American Chemical Society. All rights reserved.