INVESTIGATIONS INTO THE ROLE OF MODIFIERS FOR ENTRAPMENT OF HYDRIDES IN FLOW-INJECTION HYDRIDE GENERATION ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY AS EXEMPLIFIED BY THE DETERMINATION OF GERMANIUM

Pd-conditioned graphite tubes, placed in the furnace of an AAS instrum ent, were used for entrapment of germane as generated in an associated flow-injection system. Two different approaches were tested with the ultimate aim of allowing multiple determinations, i.e., introduction o f the modifier as a Pd salt solution, and use of electrolytically pd p re-coated tubes. While the former treatment resulted in satisfactory a nalytical performance, although requiring separate regeneration of the tubes prior to each sampling sequence, the electrolytically pre-coate d tubes did not function satisfactorily. This in turn led to a closer investigation as to the function of Pd in entrapping hydrides and rele asing the analyte. Based on an evaluation of the behaviour of the two types of tubes, supplemented by scanning tunnelling microscopy studies of tubes with and without modifier and treated in different ways, it is shown that heating at 2600 degrees C results in a physical-chemical change of the modifier in the electrolytically coated tubes; however, this change leads only to a loss of the ability of the modifier to en trap the hydrides, while the stabilizing effect is maintained.