Characterization of a supported liquid membrane for macrocycle-mediated selective cation transport

Macrocycle-mediated cation transport has been studied using aqueous phases separated by a liquid membrane supported on a microporous polypropylene film. A macrocycle-containing organic phase was incorporated into the pores of the film. In this system, phenylhexane was found to be superior to chloroform, toluene and 1,2-dichlorobenzene as a membrane solvent in maintaining membrane integrity due to its lower water solubility and higher boiling point. Transport experiments using a bis (1-hydroxyheptyl) derivative of dicyclohexano-18-crown-6 (DC18C6) as carrier gave the selectivity sequecnes K + > Rb + > Cs + >Na + > Li + and Sr 2+ > Ba 2+ > Ca 2+. Furthermore, the addition of t-butyl or hydroxyheptyl side-chains to DC18C6 improved cation transport over that observed with DC18C6 due to the decreased distribution of the ligand from the membrane to the adjacent water phases. Cation flux was found to be independent of the rate of stirring of the water phases and to be a direct function of carrier concentration in the membrane.