ALKALI-CATION TRANSPORT THROUGH SUPPORTED LIQUID MEMBRANES MEDIATED BY SOLVENT-LINKED CARRIERS

Neutral macrocyclic alkali-cation receptors have been covalently linke d to one or more molecules of the membrane solvent 2-nitrophenyl n-oct yl ether (NPOE). These compounds are all highly lipophilic and soluble in NPOE. The flux of alkali-perchlorate salts through supported liqui d membranes (SLMs) has been optimized by variation of the carrier cont ent in the membrane and the temperature. With all carriers, the optimu m flux is reached at carrier contents of about 20% (w/w) in NPOE. Abov e this carrier content the flux decreases because of an increase in th e viscosity of the membrane solutions. Relatively low activation energ ies for transport indicate that the transport is diffusion-limited. Th e excellent compatibility between the carriers and the membrane solven t leads to very stable membranes (NPOE/Accurel(R)). The mechanism of a lkali perchlorate transport has been investigated by variation of the source-phase salt activity and the carrier concentration. Indications about ion pair formation and 2/1 carrier/cation complexation have been obtained from variation of the carrier concentration and transport se lectivity measurements.