MATRIX VAPORS AND PHYSICAL INTERFERENCE EFFECTS IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY .2. SIDE-HEATED TUBES

A model for vapour losses in a transverse heated graphite atomizer (TH GA) was developed, taking into account diffusion and convection. The l atter includes an upward directed flow at the tube ends and an axial f low from the tube outside towards the injection port. The validity of the model was proved by experimental results, generated by using (i) v arious temperature and gas-flow conditions during atomization and (ii) standard and modified, end-capped, THGA-tubes. By adding end-caps wit h an aperture of 3 mm diameter to the THGA-tubes, diffusional losses t hrough the tube ends were limited. As a result we eliminated interfere nce effects due to analyte trapping on the surface of matrix particles , formed in cooler zones at the ends of the tube. For standard THGA-tu bes, using recommended conditions, this interference could decrease th e analyte signal by 10-20% in the presence of mug masses of matrices l ike Ag, Cu, Pd etc. In addition, the sensitivity was increased 1.7 tim es by using end-capped tubes.