Choline derivative ionic liquids-based aqueous two-phase systems: Phase diagrams and partition of purine alkaloids

Searching for environmentally friendly aqueous two-phase systems is imperative for the sustainable development of separation technologies. In this work, five kinds of environmentally benign choline derivative ionic liquids were synthesized and used for the formation of aqueous two-phase systems with K3PO4, K3C6H5O7 or K2CO3. In order to understand the phase formation processes of these aqueous two-phase systems and their possible application in extraction, phase diagrams and partition coefficients of purine alkaloids were determined at T = 298.2 K, and the effects of structure of the ionic liquids, nature of the purine alkaloids, composition and temperature of the systems on the partitioning behaviour of purine alkaloids were investigated systematically. It was shown that caffeine, theobromine and 2,6-amino purine could be extracted effectively into the ionic liquid-rich phase of the aqueous two-phase systems, and the partition coefficients were as high as 4.5–42 under the optimized conditions. The partitioning was found to decrease with the increase of the ratio of H2O weight fraction (in the ionic liquid-rich phase and in the salt-rich phase) and hydrophobicity of both the purine alkaloids and the ionic liquids, but not sensitive to the change of temperature.