Gel electro-membrane extraction: An overview on recent strategies for extraction efficiency enhancement

In gel electro-membrane extraction (G-EME), target analytes are extracted from a donor phase, across a biopolymer membrane, and into an acceptor phase under the influence of an electrical field. Biopolymer membranes used include agarose, agar, tragacanth, polyacrylamide, and chitosan. G-EME is completely solvent-free (except two-phase G-EME mode), and represents a highly interesting approach to future green analytical chemistry. This method has the potential for extracting polar analytes with poor partition into organic solvents. On the other hand, due to the absence of a water-organic solvent interface, low selectivity and high electro-endosmosis (EEO) are challenges in G-EME. Due to EEO, the volume of donor and acceptor phases tends to change during extraction. To address the latter problems and enhance extraction efficiency, different strategies have been applied, including gel modification, addition of gel additives, and extraction set-up modifications. This article reviews recent efforts in the development of G-EME, with a special focus on efficiency enhancement and EEO.