Analytical Sciences

Abstract − Analytical Sciences, 14(1), 109 (1998).

Liquid Membrane Transport of Amino Acids Mediated by Reverse Micelles
Marc HEBRANT and ChristianTONDRE
Laboratoire d'Etude desSyste`mes Organiques et Collo¨ z ux (LESOC), Unité Associée au C. N. R. S.,n o 406, InstitutNancéien de Chimie Moléculaire, Université HenriPoincaré-Nancy I, B. P. n o 239,54506 Vandoeuvre-les-Nancy Cedex, France
The potentialities of reverse micelles of AOT (bis(2-ethylhexyl) sodiumsulfosuccinate) for the selective transport oftryptophane (Trp) and p-iodophenylalanine (pIPhe) are investigatedusing two different experimental devices. Winsor IIsystems were obtained from mixtures of AOT/isooctane/water (0.1 M phosphatebuffer). The microemulsion phase wasused as a liquid membrane in which the reverse micelles play the part ofmobile carriers. In the first device there was adirect liquid-liquid contact between the different phases whereas in thesecond one semi-permeable membranes wereintroduced at the interfaces. The transfer rates measured for Trp and pIPheat different AOT concentrations show verydifferent behaviors, which are only moderately altered by the presence ofthe semi-permeable membranes. Single uptakeand release experiments, which were independently undertaken show that therate-determining step is the release of theamino acids. A transport mechanism assuming a competitive release by twoprocesses (droplet opening at the interfaceand ion pair association/dissociation) is proposed. The best separationbetween the two amino acids is obtained at verylow AOT concentrations.