UREA TRANSPORT THROUGH SUPPORTED LIQUID MEMBRANES USING SYNTHETIC CARRIERS

Urea can be transported through a supported liquid membrane (Accurel/N POE) by carriers such as metallomacrocycles and polyaza (cleft-type) r eceptors. The urea flux is increased by a factor 4-8 using polyaza rec eptors and by a factor 10-15 using metallomacrocycles containing a sal ophene unit in which a uranyl cation is incorporated. These carriers h ave a high hydrophobicity and do not significantly leak from the membr ane phase into the aqueous phases. The structure of the receptors and the type and number of binding sites have a pronounced influence on th e transport rate. The lower urea fluxes found for the polyaza (cleft-t ype) carriers are most likely caused by a weaker complexation (only H- bond interactions). No transport is observed for carriers which form i ntramolecular H-bonds. Although lower fluxes are obtained than with a commercial haemodialysis membrane (Cuprophan), the selectivity of tran sport may be much higher using carrier-mediated transport.