Ethanolic two-phase system formed by polypropylene glycol, ethylene glycol and/or ionic liquid (phase-forming or adjuvant) as a platform to phase separation and partitioning study

Abstract This work studied the phase separation in systems formed by polypropylene glycol (PPG) with different molecular weights (425, 725, 1000, 2000 g mol−1) + ethylene glycol + ethanol, PPG + imidazolium chloride-based ionic liquid (IL) + ethanol, and PPG + ethylene glycol + IL (as adjuvant) + ethanol, which are namely Ethanolic Two-Phase System (ETPS). Systems based on PPG with highest molecular weight (2000 g mol−1) or IL with shortest alkyl chain ([C2mim]Cl) present the widest biphasic area and consequently the easiest phase formation. Moreover, the addition of low amounts of IL (5 wt%) is favorable for the liquid–liquid demixing. These systems were used in the partitioning of curcumin (hydrophobic compound) and caffeic acid (hydrophilic compound) from saffron (Crocus sativus L.). Curcumin migrated to the PPG-rich phase (extraction efficiency, EE = 90.3%) while caffeic acid partitioned to the oppositive phase (EECA = 89.1%), representing a selective partitioning. In systems using IL as a constituent or adjuvant, the interactions between the IL and biocompounds propitiate the curcumin and caffeic acid migration for the same phase, interfering in the selectivity of the systems. However, IL-based ETPS showed a complete partition of the curcumin (EE = 100%) and the caffeic acid achieved an EE values of 98.0% for IL of longer alkyl chain length ([C6min]Cl). This protocol based on ETPS can thus be applied as an approach to extract and purify biomolecules with very low (or null) water solubility.