ABSTRACT
The purpose of this work was to develop a primary solution standard for iridium (Ir) that is directly traceable to the International System of Units (SI). The candidate starting material was ammonium hexachloroiridate hydrate, ((NH4)3IrCl6·3H2O), the Ir salt. The SI traceability of the Ir salt was established by the gravimetric reduction (GR) of the salt to the metal under H2. GR traces the results of the analysis directly to the SI base unit of mass, the kg. The GR was also performed on high-purity Ir metal powder, an independent source of Ir, used as a comparison material for the salt. A method for dissolving the Ir metal was developed by modifying information found in the literature. Trace metallic impurities (TMI) analysis was performed on the Ir salt using ICP-OES and ICP-MS. Inert gas fusion (IGF) analysis provided data for the O, N, and H content of the gravimetrically reduced and unreduced Ir metals. The combined results of the TMI and IGF analyses provided the purity data, a required component for the claim to SI traceability. Solution standards were gravimetrically prepared from the candidate SI traceable Ir salt. Solution standards for comparison were prepared from the dissolved, unreduced high-purity Ir metal powder. These solutions were compared by a high-precision ICP-OES method. Agreement in the results between these Ir solutions, with uncertainty estimates calculated by error budget analysis, confirmed the accuracy of the Ir assay in the candidate SI traceable Ir salt, (NH4)3IrCl6·3H2O, thus confirming the concentrations and uncertainties for the primary SI traceable Ir solution standards made from the (NH4)3IrCl6·3H2O.
ABSTRACT
The purpose of this work was to develop an accurate osmium (Os) solution standard that is traceable to the International System of Units, the SI. A gravimetric reduction (GR) method was developed to accurately assay the Os in ammonium hexachloroosmate salt, (NH4)2OsCl6, the chosen starting material for the Os solution standard. This GR method was also applied to -200 mesh high-purity Os metal powder, which served as an independent source of Os for comparison. An alkali fusion method was developed to create water-soluble salts from the Os metal GR products of both the (NH4)2OsCl6 and -200 mesh high-purity Os metal powder. Quantitatively prepared Os solutions from each of these water-soluble salts were compared by inductively coupled plasma spectrometry, ICP-OES. The purities of the Os starting materials were determined by quantitatively performed trace metallic impurities analysis, by ICP-OES and ICP-MS; the O, N, and H impurities were determined by inert gas fusion analysis. The percent purities of the starting materials were applied as corrections to the Os assay results obtained by GR. The agreement between these Os solutions, corrected for random and systematic errors by error budget analysis, confirmed the accuracy of the Os assay in the (NH4)2OsCl6. The SI traceability of the Os assay in the (NH4)2OsCl6 salt was established through the GR procedure and the purity analysis of this material. An SI traceable Os solution standard was gravimetrically prepared from this batch of (NH4)2OsCl6, based on the accurate Os assay and the percent purity of the starting material.
