IMPROVED COLORIMETRIC DETERMINATION OF NO BLE-METAL IONS IN MULTITUDINOUS SOLUTION USING SODIUM-BROMIDE OR SODIUM-IODIDE

An improved colorimetric method for the determination of noble metal i ons in a solution containing multiple components, such as ultra fine p articles formed by reduction of noble metal ions and surfactants was i nvestigated. Usually, it is difficult to determine concentrations of n oble metal ions in such solutions due to tile interference of surface plasmon absorption of metal particles, In the present method, the addi tion of sodium bromide for gold ions and sodium iodide for palladium a nd platinum ions induced aggregation of noble metal particles, which w ere easily removed by filtration. Sodium cations may contribute to the precipitation process by salting-out. In addition, coordination of br omide or iodide ions to metal ions via a ligand exchange reaction gave metal complexes having a relatively large absorption coefficient in t he visible region, which is suitable for colorimetry. The lower limits of determination were 5.08X10(-2) mM for gold, 1.32X10(-1) mM for pal ladium, and 5.82X10(-2) mM for platinum. It is possible to measure the reduction rates of noble metal ions under various conditions by this method.