Quantitative description of macrocycle-mediated cation separations in liquid membranes and on silica gel as a function of system parameters

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Abstract
Cation transport by both neutral and proton-ionizable macrocycles in liquid membranes is often d iffusion limited. Extraction constants, distribution coefficients, aqueous phase macrocycle-cation and anion-cation interaction constants and membrane geometry are the parameters in the diffusion limited t ransport equations. On the other hand, the behavior of cation solutions in silica gel columns containing bonded macrocycles can be described using homogeneous phase macrocycle- cation equilibrium constants and column geometry as modeling parameters. Examples from our recent work are given to show how separation processes can be designed from an understanding of these parameters. The separations of Sr(I1) from Ba(I1) and of Hg(II), Cd(I1) and Zn(I1) from each other using 18-crown-6 type macrocycles and the separation of Ag(1) from Pb(I1) using pyridono and triazolo type macrocycles are described. The influence of macrocycle, solvent, c ation and anion types on the parameters is examined in discussing these examples.

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