High-throughput synthetic and screening methods have been used to prepare and evaluate caesium, cobalt and strontium selective sequestering agents derived from aza-crown ethers. Storage phosphor autoradiography was the screening method used to determine potential lead compounds. The most effective complexants for Cs+ have a very high selectivity over potassium ions and will bind picomolar quantities of Cs+ in the presence of mM K+. The binding and selectivity of these compounds with 60Co and ...