Vortex-assisted liquid-liquid microextraction revisited

In 2010, we proposed vortex-assisted liquid-liquid microextraction (VALLME) that used vortex agitation to disperse microliters of a water-immiscible solvent into an aqueous sample. After extraction, the two phases were separated by centrifugation and the extracting solvent was collected and used for analysis. The seemingly easy steps of VALLME involve complex and poorly understood processes that require consideration of solvent drop breakup and coalescence plus the problem of interphase analyte mass transfer. The overall aim of this review is to transfer knowledge from other disciplines and improve current understanding of VALLME. Initially, the fundamental hydrodynamic and interfacial science concepts of emulsion formation and phase separation applying to VALLME are presented. Building on this knowledge, the effects of several experimental parameters on VALLME are discussed. Advancing the current (and limited) knowledge on the fundamentals behind VALLME is critical to allow cognitive control and full exploitation of the method. (C) 2018 Elsevier B.V. All rights reserved.