Aqueous two-phase systems: Methods of binodal curve generation and applications

Aqueous two-phase system (ATPS) has been of interest to both industry and academia for the extraction and purification of biomolecules/bioactives. ATPSs are formed by two-phase forming components such as polymer-polymer, polymer-salt, surfactant-salt, etc. when dissolved in water above critical concentrations. The binodal curve distinguishes the single-phase region from the two-phase region. These compositions are usually expressed in weight or mole fractions. The binodal curve and tie-lines in the phase diagram are pivotal in the design of extraction experiments, phase separation, and determining the concentration of phase-forming components. An engineered choice of working on a tie-line determines the purity and yield of the extracted compound. Researchers have explored various approaches for the generation of binodal curves including, macroscale, microscale, thermodynamic, and computational methods. Although different methods have been used for the generation of the binodal curves, there is limited information that summarizes these methods comprehensively. This article aims to summarize the different techniques of binodal curve generation for ATPSs, outlining their merits and demerits, along with the applications of ATPSs. Comparison of different methods for the generation of binodal curves is slightly challenging as every method is distinct and unique. In the case of the convenient method, the macroscale approach could be the preferred one, whereas the microscale approach is advantageous for the rapid generation with low volumes of samples. Furthermore, thermodynamic modeling and computational approaches can be preferred for the generation of binodal curves when minimizing experimentation and sophisticated equipment is a priority.