Mechanisms of action of platinum group modifiers in electrothermal atomic absorption spectrometry

Data on mechanisms of action of chemical modifiers based on Pd, Pt, Rh, Ru and Ir in electrothermal atomic absorption spectrometry (ETAAS) are critically discussed. In a very simplified form, the sequence of processes affording thermal stabilization of analytes by platinum group metal (PGM) modifiers appears to be the following: low-temperature stabilization of volatile analyte species is reached as a result of their chemisorption on the surface of the modifiers and/or on the graphite surface. At higher temperatures reached in the pyrolysis stage, reduction by the graphite (or thermal dissociation) of analyte species catalyzed by PGM modifiers occurs. The elemental analytes so formed interact with elemental PGM modifiers via formation of the corresponding solid solutions and/or stoichiometric compounds. According to existing knowledge, under correctly optimized conditions, analyte–PGM modifier compounds decompose completely during the atomization stage. Consequently, from the viewpoint of minimization of analyte losses, the processes of formation of these compounds during the pyrolysis stage are most critical. Existing theories can not explain the significant differences in the efficiency of Pd, Pt, Rh, Ru and Ir when used as modifiers in ETAAS.