1996 Volume 12 Issue 1 Pages 7-12
Iridium has been analyzed at nanogram levels in a geological sample by isotope dilution mass spectrometry employing inductively coupled plasma mass spectrometry (ICP-MS). It is well known that platinum group elements form strong anionic complexes, thus anion exchange resin was used for the preconcentration of Ir from sample matrix. Separation of Ir from elements in a complex matrix is problematic, as Ir(IV) is more efficiently extracted on the anion exchange resin than is the lower oxidation state of Ir. The total Ir content in a solution was oxidized to Ir(IV) using chlorinated lime as the oxidizing agent in order to enhance extraction of Ir on anion exchange resin in HCl medium. Its stripping was carried out with a mixture of HCl and HClO4. Prior to extraction, the most important step in isotope dilution mass spectrometric analysis of Ir is to achieve complete isotopic homogenization of natural Ir with the enriched isotope 191Ir*. In this paper, we have described a method for the isotopic homogenization of Ir in solution by microwave digestion spanning over a period of 12h. The isotope ratio values obtained by ICP-MS are sufficiently precise and accurate; from them the concentration was computed. The method has been successfully applied to determine Ir in a Cretaceous-Tertiary boundary sample from Stevns Klint, Denmark.
