Comparative efficacy of platinum group metal modifiers in electrothermal atomic absorption spectrometry

Data relating to the comparative efficacy of chemical modifiers based on Pd, Pt, Rh, Ru and Ir (platinum group metals, PGMs) for electrothermal atomic absorption spectrometry (ET-AAS) are critically discussed. Often, the differences claimed are moderate or completely absent. However, superiority of one PGM modifier over its analogues is sometimes pronounced. Some differences are caused not by the properties of the PGMs themselves but by the properties of their complex chlorides. Their stability constants are significantly higher for Pt and Ir compared to those for Pd, Rh and Ru. Therefore, the latter chlorides transform more easily to the active forms of the modifiers (elemental metals and their oxides) at relatively low temperatures, and this ultimately determines their superiority over Pt and Ir modifiers. Specific interactions in an “analyte–modifier–sample matrix–graphite” system are the second main reason for differences in efficacy of the PGM modifiers. These interactions may significantly influence the matrix interferences or the analysis conditions. Exact mechanisms of the processes often cannot be explained on the basis of current knowledge in inorganic chemistry and material science. Keeping in mind these peculiarities is especially important when working with permanent PGM modifiers (because of their rather large masses used), when attempting multielement ET-AAS analysis and during investigation of fundamental processes involving PGM modifiers.