PREPARATION AND CERTIFICATION OF A RHODIUM STANDARD REFERENCE MATERIAL SOLUTION

A dual-path approach has been developed for the production of an accurate rhodium solution standard. First, a water-soluble rhodium salt was assayed for rhodium by gravimetry. Second, a different water-soluble rhodium salt was synthesized from a known mass of high-purity rhodium metal. After rhodium solution standards were prepared from both salts, their rhodium concentrations were compared by inductively coupled plasma emission spectrometry. The rhodium concentrations of the two solutions were statistically indistinguishable. The agreement between both rhodium solution standards, each based on gravimetry, and subject to different random and systematic errors, confirmed the accuracy of their rhodium concentrations. Based on this work an accurate rhodium solution standard [NIST Standard Reference Material (SRM) 3144] was prepared by dissolving in water a weighed portion of an accurately assayed, homogeneous, water-soluble rhodium salt, which had been dried to constant weight.