sym-Dibenzo-16-crown-5-oxyacetic acid and its analogues are selective for the extraction of Y3+ over Sr2+ from aqueous solutions into chloroform. The selectivity and the pH range of extraction are influenced by the structure of the ligand. The size of the macrocyclic cavity, the tether length of the lariat, the attachment of alkyl functional groups to the lariat, and the identity of the ionizable group can affect selectivity and extraction efficiency. When the carboxylic acid at the terminal end of the lariat is replaced by a hydroxamic acid, the selectivity for Y3+ over Sr2+ is significantly increased. Using these ionizable crown ethers as extractants, 90Y fractions of greater than 99.9% purity can be obtained in a single solvent extraction step from solutions of 90Sr.