Liquid-phase microextraction and capillary electrophoresis of acidic drugs.

Vial liquid-phase microextraction (LPME) combined with capillary electrophoresis (CE) was evaluated for the determination of the acidic drugs ibuprofen, naproxen, and ketoprofen present in water samples and in human urine. The 2.5 mL samples containing the drugs were filled into conventional vials and subsequently acidified by 250 microL of 1-10 M HCl. Porous hollow fibers of polypropylene containing 25 microL of an aqueous solution of 0.01-0.1 M NaOH (acceptor solution) and with dihexyl ether immobilized in the pores of the wall were placed into each of the samples. The acidic drugs were extracted from the acidified sample solutions into the dihexyl ether phase, in the pores of the hollow fiber, and further into the alkaline acceptor solution forced by high partition coefficients. The drugs were extracted almost quantitatively (75-100% extraction efficiency) from the 2.5 mL samples and into the 25 microL acceptor solutions, providing 75-100 times preconcentration. The acceptor solutions were collected for automated CE analysis, which enabled the drugs to be detected down to the 1 ng/mL level.