Improved colorimetric determination of noble metal ions in multitudinous solution using sodium bromide or sodium iodide

Abstract

An improved colorimetric method for the determination of noble metal ions in a solution containing multiple components, such as ultra fine particles formed by reduction of noble metal ions and surfactants was investigated. Usually, it is difficult to determine concentrations of noble metal ions in such solutions due to the interference of surface plasmon absorption of metal particles. In the present method, the addition of sodium bromide for gold ions and sodium iodide for palladium and platinum ions induced aggregation of noble metal particles, which were easily removed by filtration. Sodium cations may contribute to the precipitation process by salting-out. In addition, coordination of bromide or iodide ions to metal ions via a ligand exchange reaction gave metal complexes having a relatively large absorption coefficient in the visible region, which is suitable for colorimetry. The lower limits of determination were 5.08×10^-2 mM for gold, 1.32×10^-1 mM for palladium, and 5.82×10^-2 mM for platinum. It is possible to measure the reduction rates of noble metal ions under various conditions by this method.