Potential-driven peptide extractions across supported liquid membranes: Investigation of principal operational parameters

Fundamental experiments on electromembrane extraction were performed to increase the basic knowledge about the current and the mass transfer of target peptides and background electrolyte ions. Three peptides (angiotensin 2, bradykinin, and enkephalin) were extracted from 500 mu L aqueous donor solution (1 mM HCl, positive electrode), through a 200 mu m supported liquid membrane (SLM) of 1-octanol/di-isobutylketon/di-(2-ethylhexyl) phosphate (55:35:10 w/w/w) sustained in the pores of a porous hollow fiber, and into 25 mu L aqueous acceptor solution (50 mM HCl, negative electrode) present inside the lumen of the fiber by the application of an electrical potential (50 V) and agitation (1050 rpm). Recoveries were typically in the range of 55-65% after 5 min of extraction and were principally determined by the chemical composition of the SLM and by the applied voltage. The electrical current in the system was measured during the extraction and was close to 350 mu A. The current arose to some extent from mass transfer of the target peptides, but the major contribution was due to a background current from di-(2-ethylhexyl) phosphate in the SLM and from mass transfer of background electrolytes. Operation at relatively low background current was important to maintain a stable system.