ELECTROLYTIC HYDRIDE GENERATION ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY - IN-SITU TRAPPING OF AS ON DIFFERENT PRE-CONDITIONED END-HEATED GRAPHITE TUBES

An automated analytical system for the determination of As combining a n electrolytic hydride generator and a graphite furnace atomic absorpt ion spectrometer has been developed. To investigate the trapping effic iency of permanent modifiers, the end-heated graphite tubes have been impregnated with Ir and mixed Pd/Ir pre-reduced modifiers, respectivel y, or pre-coated with Ir by electron beam evaporation under high vacuu m. Furthermore, the influence of the modifier mass on the shape of the absorption signal has been studied and the performance of the modifie r has been discussed. Using the pre-coated graphite tube the calculate d detection limit (3s criteria) for As was 3 pg and 15 ng/L (200 mu L sample volume, two preconcentration steps) for the absolute mass and t he concentration, respectively. The long-term stability of the permane nt modifiers and their physical and or chemical changes during the lif etime of the tube have been observed.