Electrokinetic migration across artificial liquid membranes: Tuning the membrane chemistry to different types of drug substances

Twenty different basic drugs were electrokinetically extracted across a thin artificial organic liquid membrane with a 300 V d.c. electrical potential difference as the driving force. From a 300 μl aqueous sample (acidified corresponding to 10 mM HCl), the drugs were extracted for 5 min through a 200 μm artificial liquid membrane of a water immiscible organic solvent immobilized in the pores of a polypropylene hollow fiber, and into a 30 μl aqueous acceptor solution of 10 mM HCl inside the lumen of the hollow fiber. Hydrophobic basic drugs (log P > 1.7) were effectively isolated utilizing 2-nitrophenyl octyl ether (NPOE) as the artificial liquid membrane, with recoveries up to 83%. For more hydrophilic basic drugs (log P < 1.0), a mixture of NPOE and 25% (w/w) di-(2-ethylhexyl) phosphate (DEHP) was required to ensure efficient extraction, resulting in recoveries up to 75%. DEHP was expected to act as an ion-pair reagent ion-pairing the protonated hydrophilic drugs at the interface between the sample and the membrane, resulting in permeation of the interface.