Liquid-liquid-liquid microextraction for sample preparation of biological fluids prior to capillary electrophoresis

Methamphetamine as a model compound was extracted from 2.5-mL aqueous sampl es adjusted to pH 13 (donor solution) through a thin phase of 1-octanol ins ide the pores of a polypropylene hollow fiber and finally into a 25-mu L ac idic acceptor solution inside the hollow fiber. Following this liquid-liqui d-liquid microextraction (LLLME), the acceptor solutions were analyzed by c apillary zone electrophoresis (CE). Extractions were performed in simple di sposable devices each consisting of a conventional 4-mL sample vial, two ne edles for introduction and collection of the acceptor solution, and a 8-cm piece of a porous polypropylene hollow fiber. From 5 to 20 different sample s were extracted in parallel for 45 min, providing a high sample capacity. Methamphetamine was preconcentrated by a factor of 75 from aqueous standard solutions, human urine, and human plasma utilizing 10(-1) M HCl as the acc eptor phase and 10(-1) M NaOH in the donor solution. In addition to preconc entration, LLLME also served as a technique for sample cleanup since large molecules, acidic compounds, and neutral components were not extracted into the acceptor phase. Utilizing diphenhydramine hydrochloride as internal st andard, repetitive extractions varied less than 5.2% RSD (n = 6), while the calibration curve for methamphetamine was linear within the range 20 ng/mu L to 10 mu g/mL (r 0.9983), The detection limit of methamphetamine utilizi ng LLLME/CE was 5 ng/mL (S/N = 3) in both human urine and plasma.