pH Effect on the Formation of Deep-Eutectic-Solvent-Based Aqueous Two-Phase Systems

Deep eutectic solvents (DES) are an emerging type of green solvents that have been used in aqueous two-phase systems (ATPS). However, its application in ATPS can present some limitations, due to the nonstoichiometric partition between the two aqueous phases of the hydrogen-bond acceptor (HBA) and the hydrogen-bond donor (HBD) that compose the DES. In this context, pseudoternary DES-based ATPS, in which DES' components stoichiometry is maintained, appear as potential liquid–liquid systems to the extraction and separation of biomolecules. Here the pH influence on the phase equilibrium and DES' components partition on ATPS composed of DES, constituted by tetrabutylammonium chloride + ethanol/ n-propanol, and potassium citrate/citrate buffer was evaluated at 298 K and pH 9, 7, and 5. In addition the partition coefficients of gallic acid, caffeine, and L-tryptophan were also determined, allowing inferences to be made on the potential application of these systems. The results suggest that the change on the pH impacts the chemical speciation of the potassium citrate salt, and consequently its ability to form an ATPS, allowing the stoichiometric partition of DES' components and the formation of a pseudoternary system and the tuning of biomolecules partition behavior to be controled.