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A study is reported of the variation of cation transport rate through a bulk chloroform liquid membrane containing a neutral macrocyclic carrier with cation concentration in the source salt solution phase and with anion type. The transport rate was found to vary as the square of the cation activity in regions of low cation activity for the four salts studied (KCI, KI, KSCN, and KNO3) using dibenzo-18-crown-6 (DBI8C6) as membrane carrier. However, at high source phase cation activity, transport for some of the salts is less than that expected from this relationship. A mechanism is described to explain these results. The rates of transport of Li+, Na+, K+, and Ba2+ salts by DB18C6 or 4-tert-butylbenzo-15-crown-5 were found to be strongly dependent on the anion present. The transport rates of K+ salts with DB18C6 ranged over eight orders of magnitude according to anion. Anions with smaller Gibbs free energies of hydration allowed faster cation transport.

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