Transport Study of Metal Cations Through a Bulk Liquid Membrane Using Benzo-18-crown-6 as an Ionophore.

Abstract

The transport experiments of Cr³⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and
Pb²⁺ metal cations were carried out by benzo-18-crown-6 (B18C6) using
chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE), dichlorometh-ane
(DCM), nitrobenzene (NB), chloroform-nitrobenzene (CHCl₃-NB) and
chloroform-dichloromethane (CHCl₃-DCM) binary mixed solvents as
liquid membranes. The aqueous source phase consisted of a buffer solution
(CH₃COOH/CH₃COONa) at pH = 5 and containing an equimolar mixture
of these 7 metal cations. The organic phase contained the macrocycle
ligand, benzo-18-crown-6 (B18C6) as an ionophore and the receiving
phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3.
The obtained results show that benzo-18-crown-6 is a highly selective
ionophore for Pb²⁺ cation. The sequence of transport efficiency for Pb²⁺
cation in organic solvents was found to be : DCM > NB > 1,2-DCE >
CHCl₃. The influence of the stearic acid, palmitic acid and oleic acid in
the membrane phase on the ion transport was investigated.  A non-linear
behaviour was observed for variation of the transport rate of Pb²⁺ cation
vs. the composition of CHCl₃-NB and CHCl₃-DCM binary mixtures.