Micro-electromembrane extraction through volatile free liquid membrane for the determination of β-lactam antibiotics in biological and environmental samples.

Micro-electromembrane extraction (μ-EME) was presented for the selective extraction of four main β-lactam antibiotics (penicillin, phenoxypenicillin, ampicillin, and amoxicillin) from complex samples. A volatile solvent (ethyl acetate or chloroform) was sandwiched between a plug of the complex sample and another plug of an aqueous acceptor solution in a transparent polymeric tube and formed the so-called free liquid membrane (FLM). The use of the FLM eliminated the evaporation of the solvent and enabled the μ-EME of the antibiotics, which was carried out by the application of DC voltage to the terminal aqueous solutions. The drugs in the complex sample were selectively transferred through the FLM to the acceptor solution, which was directly used for their determination by micellar electrokinetic chromatography with ultraviolet detection (MEKC-UV). The μ-EME was characterized by sub-μA electric currents, high elimination of matrix components, high stability of operational solutions, and suitability for extracting undiluted complex samples. The μ-EME/MEKC-UV method yielded good analytical repeatability (RSDs of peak areas ≤5%), extraction recoveries (40-84%), accuracy (92-105%) and linearity over one and a half order of magnitude (R2 ≥ 0.9998), and was applied to the determination of the four β-lactam antibiotics in human serum and waste water at clinically and environmentally relevant concentration levels. Further improvement in the method sensitivity was achieved by changing the μ-EME tube geometry (conical shape) and increasing the complex sample volume (100 μL). The analytes were enriched by factors of 7.6-11.5, the limits of detection dropped down to less than 18 ng/mL, and the modified μ-EME/MEKC-UV method enabled the trace determination of β-lactam antibiotics in complex samples.