To explore proper extractive solvents and to design an optimized separation process it is highly imperative to understand the molecular-based phenomena governing the solutes partitioning. Moreover, the development of new techniques for the biomolecules separation and purification, while maintaining their functional characteristics unchanged, is still ongoing. Therefore, in this work, the partition coefficients of vanillin, a compound with well-known organoleptic properties, were determined using improved ionic-liquid-based aqueous two-phase systems (ATPS). Three main parameters were evaluated through the vanillin partitioning process: the ionic liquid (IL) cation and anion structure, the temperature of equilibrium and the available concentration of vanillin in the global system. In all systems and conditions tested, vanillin preferentially migrates for the IL-rich phase. In addition, the three studied parameters largely influence the vanillin partitioning. In an attempt to elucidate the thermodynamics of the partitioning process, the standard molar thermodynamic functions of transfer of vanillin were also determined based on the temperature dependence data. These data indicate that the partition of vanillin results from an interplay between enthalpic and entropic contributions where both the IL anion and more complex cations play an essential role. Moreover, viscosities and densities of both aqueous phases were experimentally measured at the mass fraction compositions for which the partition coefficients were determined. The results gathered in this work indicate that IL-based ATPS can be further employed in the extraction and purification of vanillin from different matrices, as confirmed by the large partition coefficients obtained and improved low viscosity systems. (C) 2010 Elsevier B.V. All rights reserved.