COMPARISON OF THE ENERGETICS OF DESORPTION OF SOLUTION AND VAPOR-PHASE DEPOSITED ANALYTES IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

The energetics of atomisation of Pb, Cu, Ag and Au in pyrolytic graphite coated, uncoated electrographite and glassy carbon tubes was studied following deposition of the analyte as a solution (primary site) and as an aerosol vapour (secondary site). Arrhenius activation energies (Ea) for Pb and Cu were independent of tube type and mode of analyte deposition. An apparent first-order rate of release occurs from all tube types and from both primary- and secondary-deposition sites, suggesting that both elements desorb from the surface as individual atoms. Values of Ea for desorption of Ag and Au were independent of furnace tube type but dependent on the deposition mode, with fractional orders of desorption obtained throughout. Data for these elements suggest the formation of micro-droplets or caps (primary site) and islands (secondary site) with desorption occurring from the droplet surface or at the metal - graphite interface.