MODIFICATION BY PALLADIUM IN THE ANALYSIS OF SLURRIES BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY - A PHYSICAL-MECHANISM

The atomization of lead from sediment particles after introduction to the graphite furnace as a slurry is studied. Absorbance characteristics with and without the addition of a palladium/magnesium modifier mixture are compared, and scanning electron micrographs are presented to show the distribution of palladium and slurry particles in the graphite furnace during the heating cycle. The results are consistent with a physical mechanism of modification by palladium. When palladium is premixed with the slurry, prior to pipetting it into the furnace, palladium becomes absorbed on the slurry particles. The rate-limiting step leading to atomization is then diffusion of lead through the palladium layer. When palladium is pipetted into the furnace before the slurry, atomization proceeds via the release of lead from the slurry particle, followed by its collision with a palladium droplet, and subsequent rate-limiting diffusion out of the droplet.