Liquid−Liquid−Liquid Microextraction for Sample Preparation of Biological Fluids Prior to Capillary Electrophoresis

TLDR

Methamphetamine was extracted from aqueous samples (pH 13) through a 1‑octanol phase inside a polypropylene hollow fiber into a 25‑µL acidic acceptor, with the acceptor analyzed by capillary zone electrophoresis, using a disposable device comprising a 4‑mL vial, two needles, and an 8‑cm fiber, allowing parallel extraction of 5–20 samples in 45 min. LLLME preconcentrated methamphetamine by 75× from aqueous, urine, and plasma samples, provided cleanup by excluding large, acidic, and neutral species, achieved <5.2 % RSD with diphenhydramine internal standard, yielded a linear calibration from 20 ng µL⁻¹ to 10 µg mL⁻¹ (r = 0.9983), and reached a detection limit of 5 ng mL⁻¹ in urine and plasma.

Abstract

Methamphetamine as a model compound was extracted from 2.5-mL aqueous samples adjusted to pH 13 (donor solution) through a thin phase of 1-octanol inside the pores of a polypropylene hollow fiber and finally into a 25-microL acidic acceptor solution inside the hollow fiber. Following this liquid-liquid-liquid microextraction (LLLME), the acceptor solutions were analyzed by capillary zone electrophoresis (CE). Extractions were performed in simple disposable devices each consisting of a conventional 4-mL sample vial, two needles for introduction and collection of the acceptor solution, and a 8-cm piece of a porous polypropylene hollow fiber. From 5 to 20 different samples 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 acceptor phase and 10(-1) M NaOH in the donor solution. In addition to preconcentration, 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 standard, repetitive extractions varied less than 5.2% RSD (n = 6), while the calibration curve for methamphetamine was linear within the range 20 ng/microL to 10 micrograms/mL (r = 0.9983). The detection limit of methamphetamine utilizing LLLME/CE was 5 ng/mL (S/N = 3) in both human urine and plasma.