Determination of iridium at sub ng x g-1 levels in geological materials by RNAA

Radiochemical neutron activation method is presented for the determination of iridium in geological materials. The procedure consisted of thermal neutron irradiation of an 500 mg sample followed by sinterization with sodium peroxide, precipitation with tellurium and high resolution gamma-spectrometry with a hyper-pure Ge-detector. The procedure was evaluated by the analysis of the certified reference materials SARM-7 and W-1. The detection limit for the analytical conditions employed was 0.004 ng x g-1 Ir. The procedure was applied to the reference materials TDB-1 and WGB-1, which present provisional values for Ir concentration, and GXR-3, GXR-5 and GXR-6, which do not present any reported data for Ir contents. (author)