Aqueous biphasic formation, volumetric and compressibility behaviour in tetrabutylammonium bromide-inorganic salts aqueous systems

Abstract

Phase diagrams for several (salt+salt) aqueous biphasic systems containing tetrabutylammonium bromide and inorganic salts NaH2PO4, Na2HPO4, Na3PO4, Na2CO3, K3Cit and Na2SO4 were determined at T=(298.15, 308.15 and 318.15)K. The salting-out strength of the investigated kosmotropic salts on the tetrabutylammonium bromide (chaotropic salt) in aqueous solutions follows the well established Hofmeister series, as in the case of (polymer+salt) aqueous biphasic systems. In order to obtain further evidence about the salting-out effect in these systems, volumetric and compressibility behaviour of tetrabutylammonium bromide aqueous solutions were also determined in the absence and presence of the investigated inorganic salts at different temperature. It was found that there is a relation between the relative concentration of various salts to form two-phase system with tetrabutylammonium bromide and the apparent molar volume or isentropic compressibility of transfer of tetrabutylammonium bromide from water to aqueous solution of the investigated salts.