Metal Ion Separations in Polyethylene Glycol-Based Aqueous Biphasic Systems

Abstract

Aqueous biphasic systems of two dissimilar polymers, or of a water-soluble polymer and an inorganic salt, can be used to selectively partition metal ions. While these systems are well known for separating biomaterials, only a handful of papers have appeared investigating their utility for separating metal ions. The few results that have appeared in the literature have utilized salt solutions of polyethylene glycol (PEG) and fall into two categories: 1) partitioning of the metal ion to the PEG-rich phase by the addition of a water-soluble extractant which coordinates the metal ion and 2) addition of an inorganic anion which produces a metal complex that partitions to the PEG-rich phase. In addition the authors have recently added a third category: 3) partitioning of a metal ion directly from the salt-rich to the PEG-rich phase without an added component. It appears that a separations strategy can be developed for metal ions from all areas of the periodic table under a wide variety of conditions. This review covers papers published concerning metal ion separations in aqueous biphasic systems and unpublished work of the authors. The incredible potential of this area for future research is discussed.