Liquid-phase microextraction of hydrophilic drugs by carrier-mediated transport

Basic studies on carrier-mediated transport as a mechanism to extract polar drugs by hollow fibre-based liquid-phase microextraction are presented for the first time. Hydrophilic alkaline drugs with log P (octanol/water partition coefficient) values less than 1 were selected as model substances. Sodium octanoate served as carrier and was added to the sample solution at pH 7 to form hydrophobic ion-pair complexes with the analytes. The ion-pair complexes were extracted into octanol as liquid membrane immobilised in the pores of the hollow fibre. Further extraction into an aqueous acceptor phase inside the lumen of the hollow fibre was facilitated by counter transport of protons from the acceptor solution to the sample solution. Protons from the acceptor solution released the analytes at the liquid membrane–acceptor interface and neutralized the carrier. The acceptor phase was analysed by capillary electrophoresis. The studies show that high extraction recoveries of ionic hydrophilic drugs can be obtained at a sample–acceptor volume ratio of 10. Linear calibration graphs and clean electropherograms indicate that carrier-mediated transport is a promising technique in microextraction of polar drugs from biological matrices.