Factors influencing the transport of tryptophan hydrochloride through supported liquid membranes containing macrocyclic carriers

Commercially available PTFE membranes were used as a support for liquid membranes in amino acid transport. Using tryptophan as a model amino acid, the influence of the type of organic liquid, kind of macrocyclic carrier and counter-ion on transport efficiency was examined. These studies show the strong influence of the kind of the counter-ion co-transported with amino acid cation, and the type of macrocyclic carrier used on the transport efficiency. The transport efficiency depends also on the pH of the source phase and on the nature of the organic liquid used as a membrane solvent. Liquid membranes supported on commercial porous-PTFE-membranes with hydrophobic solvents are stable for more than two months, while those with more hydrophilic solvents, for more than 30 days. The use of dodecylbenzenesulfonic acid as a counter-ion results in the highest flux of tryptophan, but in this case, the stability of membranes appeared to be five times lower.