An effective high throughput screening technique is described for the rapid analysis of solid-supported libraries to identify selective chelating agents for metals, focusing on those possibly present in radioactive dispersal devices. Micro X-ray Fluorescence (MXRF) is the method of choice. MXRF is a rapid and sensitive technique which allows the measurement of metal-chelator complexes without significant sample preparation. For this study we have employed commercial peptide libraries and have examined factors such as side-chain charge, oligopeptide length, hydrophobicity, and aromaticity in relation to metal binding. MXRF provides a rapid and quantitative means for screening chelator-ion binding. Initial experiments carried out successfully identified sequences that are selective for Co under certain binding conditions containing possible interferences (e.g. Ca, Fe, Al, Cs, Ir), which could be encountered in our application.