Thermodynamic Studies of <scp>l</scp>-Tryptophan and <scp>l</scp>-Threonine Partitioning in Aqueous Two-phase Systems Containing Deep Eutectic Solvents (Choline Chloride/PEG) and Potassium Salts
Mohammed Taghi Zafarani-Moattar, Hemayat Shekaari, Paria Ardi-Samberan
Abstract
Deep eutectic solvent (DES)-based liquid–liquid extraction is a good alternative to toxic and irreversible organic solvents for the separation of biological materials such as amino acids. In this work, DESs consisting of choline chloride and polyethylene glycol with two molar masses of 300 and 600 g·mol–1 were prepared. Then, the phase diagrams of aqueous two-phase systems (ABSs) containing the prepared DESs and potassium salts (K3PO4 and K2HPO4) were studied at T = 298.15, 308.15, and 318.15 K under ambient pressure (≈85 kPa). In addition, the performance of these ABSs was evaluated for the extraction of two amino acids, l-tryptophan and l-threonine, at 298.15 K. The effects of the salt and DES have been carefully considered in this investigation. Under appropriate conditions, the extraction efficiency of both amino acids reaches about 99.5% with an ABS containing a DES with a polymer molar mass of 300 g·mol–1 and K2HPO4. Finally, the observed partitioning behavior with these ABSs was justified considering the extent of interaction between the amino acids and DESs by comparing volumetric results for aqueous ternary systems containing DESs and amino acids with those for aqueous binary DES or salt systems. For this purpose, the values of apparent molar volumes (Vφ), standard partial molar volumes (Vφ0), and partial molar volumes of transfer (ΔtrVφ0) calculated from the measured density values for the aforementioned binary and ternary solutions were used.