RUBIDIUM ATOM DISTRIBUTION AND NON-SPECTRAL INTERFERENCE EFFECTS IN TRANSVERSELY HEATED GRAPHITE ATOMIZERS EVALUATED BY WAVELENGTH MODULATED DIODE-LASER ABSORPTION SPECTROMETRY

Measurements of the distribution of Rb atoms both inside and outside t he graphite tube in a transversely heated graphite atomizer (THGA) hav e been performed using a diode laser based absorption technique with h igh detection power. Theoretical models of the signal generation proce ss and the distribution of local atomic densities outside a tube end h ave been developed in order to extract quantifiable data from the meas ured signals, The density of atoms 1.2 mm outside the end of the THGA tube could be estimated to 14% and 17% of that at the centre of the tu be for open and end-capped tubes, respectively. The atoms outside the tube accounted for about 6% of the total signal (for both tubes). Usin g the outside mode of measurement a good agreement between the theoret ically predicted and experimentally obtained fractions of atom losses through the injection port was obtained. Furthermore, the outside mode of measurement supports the existence of axial convective flows direc ted towards the tube centre in standard THGAs. The atoms residing outs ide the tube ends show significantly lower recoveries than those insid e the tube which provides a direct confirmation of enhanced non-spectr al interference effects caused by matrix vapours residing outside the tube ends. In addition, a spatially resolved study of the rubidium ato mic density in the THGA has been performed, A rather homogeneous atomi c distribution was found virtually over the whole atomization cycle, t he only exception being a 25% larger density close to the platform. (C ) 1998 Elsevier Science B.V. All rights reserved.