Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Acetonitrile as adjuvant to tune polyethylene glycol + K 3 PO 4 aqueous two- phase systems and its effect on phenolic compounds partition Regina Luana Santos de França do Rosário a , Ranyere L. Souza a,b , Fabiane Oliveira Farias c , Marcos R. Mafra c , Cleide M.F. Soares a,b , Helena Passos d , João A.P. Coutinho d , Álvaro Silva Lima a,b, ⁎ a Tiradentes University, Avenida Murilo Dantas 300, 49032-490 Aracaju, Sergipe, Brazil b Institute of Technology and Research, Avenida Murilo Dantas 300, 49032-490 Aracaju, Sergipe, Brazil c Departament of Chemical Engineering, Federal University of Paraná, Polytechnic Center, Avenida Coronel Francisco H. dos Santos, s/n, Jardim das Américas, 81531-990 Curitiba, Paraná, Brazil d CICECO – Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal ARTICLE INFO Keywords: Liquid-liquid systems Organic solvents Kamlet-Taft parameters Extraction Phenolic compounds ABSTRACT Aqueous two-phase systems (ATPS) have been proposed as platforms for the purification of biomolecules, and the application of adjuvants to tune the properties of ATPS phases and their ability to extract and separate biological products investigated. This work addresses, for the first time, the use of acetonitrile (ACN) as adjuvant in ATPS composed of polyethylene glycol (PEG) of different molecular weights (from 400 to 20,000 g·mol -1 ) and potassium phosphate. The effect of ACN concentration (at 0.25, 2.5, 5 and 7.5 wt%) in the liquid-liquid equilibrium is here studied by measuring the phase diagrams, the composition of the phases in equilibrium and their Kamlet-Taft parameters. The results obtained demonstrate that the ACN presence increases the biphasic region of PEG-K 3 PO 4 ATPS and its distribution between the coexisting phases is dependent on its concentration and ATPS composition. The difference in the dipolarity/polarizability of the coexisting phases is significantly affected by the presence of ACN in the ternary mixture. The partition of two phenolic compounds – proto- catechuic acid and gallic acid – was studied, showing that ACN improves the partition of these molecules to the salt-rich phase, and that the system selectivity can be significantly improved by changing the concentration of the phase forming compounds. 1. Introduction The separation and purification stages of biotechnological processes requires high energy and chemical consumption, which produce an important impact in the final product cost. Liquid-liquid extraction appears as a cost-effective separation technique due to its technological simplicity, easy scale-up, low cost, and high efficiency in the separation of a large range of compounds or materials. However, the liquid-liquid extraction of biomolecules is typically carried out by using volatile organic solvents due to their immiscibility with aqueous media where biomolecules are present [1]. These are often poorly biocompatible media and may lead to the denaturation of proteins and other com- pounds. Aqueous two-phase systems (ATPSs) have been widely studied as benign liquid-liquid systems to separate and purify biological products. These systems consist of two immiscible aqueous phases that can be formed by the mixture of two polymers or a polymer with a salt [2,3]. Polyethylene glycol (PEG) is one of the most studied phase-forming compounds in literature. This polymer presents high biodegradability, low toxicity, large water miscibility, and low cost, and is widely used in industrial processes [4,5]. However, the hydrophilic, and poor tailoring nature of PEG is a limitation on the application of these systems to the extraction of several biomolecules. The use of additives to minimize some of the limitations associated to the application of PEG-based ATPS, was proposed for the first time in the 90s [6,7]. In these studies [6,7], authors used small amounts of sodium chloride to increase the hydrophobicity difference between the coexisting phases of polymer- polymer and polymer-salt ATPS, influencing the partition coefficient of different proteins. Since then, several works were reported suggesting the use of salts, ionic liquids, and polymers, as additives in different types of ATPS [4,8–10]. Nowadays these additives are known as ad- juvants: compounds able to fine-tune the intrinsic properties of the https://doi.org/10.1016/j.seppur.2019.04.062 Received 5 February 2019; Received in revised form 17 April 2019; Accepted 18 April 2019 ⁎ Corresponding author at: Tiradentes University, Avenida Murilo Dantas 300, 49032-490 Aracaju, Sergipe, Brazil. E-mail address: alvaro_lima@unit.br (Á.S. Lima). Separation and Purification Technology 223 (2019) 41–48 Available online 20 April 2019 1383-5866/ © 2019 Published by Elsevier B.V. T