MECHANISMS CONTROLLING THE DIRECT SOLID SAMPLING OF SILICON FROM GOLD SAMPLES BY ATOMIC-ABSORPTION SPECTROMETRY WITH ELECTROTHERMAL ATOMIZATION .1. ANALYTE MIGRATION TO THE SOLID-SURFACE

The results of electrothermal atomic absorption spectrometry (ETAAS) investigations of Si vaporization from solid gold samples indicate that Si is released only after melting of the gold matrix, and the migration of Si to the surface is assisted by the formation of convection cells in the melt. This convection is driven by the thermal gradients in the sample. Diffusion alone, in either the solid or the melt, is too slow to account for the relatively short time for total Si release before a significant portion of the gold matrix is depleted. Silicon that is carried by the induced convection to the surface is readily vaporized. It is shown that the liquidus lines of the binary phase diagrams associated with a gold solvent can be used to predict the existence of analyte carryover in the gold, Consequently, these diagrams offer a means of identifying, a priori, candidate elements that may be determined by solid sampling ETAAS in gold, via aqueous solution calibration.