Chapter 8 - Microextraction With Supported Liquid Membranes

Abstract

This chapter discusses microextraction based on supported liquid membranes (SLMs), with special emphasis on two- and three-phase hollow-fiber liquid-phase microextraction (HF-LPME), solvent bar microextraction (SBME), 96-well LPME (parallel artificial liquid membrane extraction), and electromembrane extraction (EME). In two-phase HF-LPME, analytes are extracted from aqueous sample, into an organic SLM immobilized in the pores in the wall of a porous hollow fiber and further into a μL volume of organic solvent (acceptor) located in the lumen of said hollow fiber. After extraction, the acceptor is typically analyzed directly by gas chromatography (GC). SBME is similar to two-phase HF-LPME, except that the hollow fiber with SLM and acceptor is moving freely in the sample. Three-phase HF-LPME is similar to two-phase HF-LPME, except that the acceptor is aqueous. After extraction, this can be injected directly into liquid chromatography (LC). Three-phase extractions can also be performed in commercial 96-well plates and is termed 96-well LPME. In both two- and three-phase HF-LPME and SBME, partition serves as driving force for extraction, and mass transfer across the SLM is by passive diffusion. Alternatively, an electric field can be applied across the SLM, and extraction is then by electrokinetic migration. This is termed electromembrane extraction (EME). Both LPME and EME can be performed using hollow fibers, in microfluidic devices or in commercially available 96-well plates. This chapter gives an overview of the historical development, extraction principles, method optimization, technical formats, and selected applications.