Cation effect on anion separations by aza-crown ligands in liquid membranes

New carriers have been prepared based on the aza-18-crown-6 structure to facilitate membrane transport of ions. One of these incorporates four aza-18-crown-6 molecules bonded to a resorcinarene ring. The other, aza-18-crown-6 bonded to an undecyl chain, was studied as a monomeric analog. These carriers have been included in dichloromethane bulk liquid membranes (BLMs) to assess cation influence on competitive transport among anions (ReO4−, NO3−, ClO4−). ReO4− was investigated as a non-radioactive analog of the pertechnetate anion, which is of interest in nuclear waste separations. The permeability values and selectivity for ReO4− and ClO4− were the greatest when neutral source and receiving phases were used with K+ as the co-transported cation. The carriers also showed selectivity for ReO4− and ClO4− over NO3− with K+ and Na+ as the co-transported cations using neutral and basic aqueous phase solutions. It was also found that some cations inhibit anion transport.