THE EFFECT OF INTERNAL GAS-FLOW ON THE SPATIAL-DISTRIBUTION OF SODIUM ATOM WITHIN A GRAPHITE-FURNACE ATOMIZER

A laser-based vidicon imaging system has been used to obtain spatially and temporally resolved absorbance profiles of Na atoms within pyrolytic graphite coated and uncoated polycrystalline electrographite tubes under gas-stop and gas-flow conditions in graphite furnace atomic absorption spectroscopy. During the initial period of atomization, the spatial distribution of Na indicates that most of the atoms are localized near the bottom of the furnace under the influence of convective flow. This observation suggests that the free Na atoms, upon collisions with the furnace walls, are interacting strongly with the graphite surface. The strength of interaction appears to be stronger for uncoated graphite tubes. After the peak absorbance, the Na atom density is lower near the furnace wall than in the center of the furnace. The observed gradient is likely a result of the Na atoms undergoing a series of redeposition and revaporization reactions with the graphite surface during the course of atom removal.