Analytical microextraction with supported liquid membranes

This chapter focuses on microextraction using supported liquid membranes (SLMs) and discusses two- and three-phase hollow-fiber liquid-phase microextraction, solvent bar microextraction, 96-well liquid-phase microextraction (parallel artificial liquid membrane extraction), and electromembrane extraction. These techniques all rely on mass transfer across an SLM, which is a microliter volume of organic solvent held by capillary forces in the pores of porous polymeric membrane. The organic solvent is immiscible with water, such as 1-octanol. The polymeric membrane is either a hollow-fiber membrane or a flat membrane and is hydrophobic such as polypropylene or polyvinylidene fluoride. Extraction can be in two-phase systems, from aqueous sample, across organic SLM and into organic acceptor; or in three-phase systems from aqueous sample, across organic SLM and into aqueous acceptor. The volume of acceptor is typically 2-50µL and preconcentration is feasible. Extraction can be by passive diffusion or by migration in an electrical field sustained across the SLM. In the following, we discuss the different principles, along with practical examples and method development.