Infoscience

Journal article

Morphological and spectroscopic investigation of the behavior of permanent iridium modifier deposited on pyrolytic graphite coated and zirconium treated platforms in electrothermal atomic absorption spectrometry

To better characterize a permanent modifier based on iridium deposited on zirconium or tungsten treated platforms of transversely heated graphite atomizer, and to gain addnl. information about its chem. behavior directed to an eventual further optimization, expts. were carried out, both by surface techniques such as SEM, XPS or ESCA and x-ray fluorescence (XRF) and by electrothermal at. absorption spectrometry on the iridium release from unmodified and various other modified pyrolytic graphite platforms. Special attention was paid to the influence of the amt. of iridium, zirconium carbide coating of the platform surface and the presence of citric acid on the iridium vaporization during pyrolysis and atomization. The processes of iridium losses during pyrolysis and atomization and peak max. alignment depend on the amt. of the iridium deposited on the pyrolytic graphite coated platforms in the presence of nitric acid. A fractional order of release which suggests an atom vaporization from the surface or edges of the iridium islands was estd. In the presence of citric acid, mass independence and zero order of the atom release were found. The zirconium treatment of the platform results in change of the spatial distribution of iridium and hence its vaporization. Vaporization temps. ?2100 Deg, and 1st order of the process of atom generation were obtained. While it was possible to study the iridium atomization from uncoated and zirconium coated surfaces, evidencing a different order for the release process, the same was not possible for the tungsten coated platforms due to an over stabilization that brought the iridium atomization temp. out of the working range of the instrument used. The different chem. behavior of tungsten and zirconium was also confirmed by XPS studies. With tungsten, evidence of both W-C and W-O bonding was found, while zirconium on the contrary shows only Zr-O bonding and no evidence of carbide bonding. The SEM revealed a highly dispersed distribution of spot-like features whose smallest av. diam. was of the order of 0.1 mm. The XRF asserted the confinement of iridium in these features and a strict assocn. with zirconium in the case of zirconium treated surfaces. It is worth mentioning that such structure was preserved also after 400 thermal cycles simulating an atomization step at 1900 Deg despite a quite evident deterioration of the graphite surface, thus confirming the excellent durability of this modifier. [on SciFinder (R)]

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