DETERMINATION OF NOBLE-METALS BY CARBON FURNACE ATOMIC-ABSORPTION SPECTROMETRY .1. ATOM FORMATION PROCESSES

Evidence is presented to support the theory that the formation of atoms of noble metals during carbon furnace atomisation proceeds via direct evaporation of the metal. The evidence includes (i) thermogravimetric investigation of noble metal salts and their aqueous solutions in an argon atmosphere, (ii) X-ray diffraction studies of the residues formed on heating aqueous solutions of some noble metal salts in a carbon furnace atomiser and in the microfurnace of a thermobalance, (iii) measurements of the appearance temperatures of noble metals in a carbon furnace atomiser using aqueous solutions and vacuum-deposited metal films and (iv) activation energies, Ea, and vapour pressure data relating to noble metals at elevated temperatures. Experimental conditions giving the best sensitivity for the determination of seven noble metals (osmium was not detected) in the Perkin-Elmer HGA-74 carbon furnace atomiser are presented. On the basis of a 20-μl sample volume these gave sensitivities (1% absorption) of 0.019, 0.0058, 0.0045, 0.00021, 0.038, 0.023 and 0.00089 μg ml-1 for ruthenium, rhodium, palladium, silver, iridium, platinum and gold, respectively.