Liquid-liquid equilibrium data for systems based on acetonitrile + polyvinylpyrrolidone (PVP) (10000, 29000 and 40000 g.mol(-1)) + water were experimentally measured at 298.15 +/- 1.00 K and 0.1 +/- 0.01 MPa. Merchuck's empirical equation was correlated with experimental binodal data, and the tie-lines and critical points (PCs) to complete the phase diagrams were determined. In both phases, the content of acetonitrile is high (> 50 wt%), as the top-phase is rich in water while the bottom phase is rich in PVP. The systems were used in the partitioning of three phenolic compounds (here used as standard biomolecules). Cyanidin-3-O-glucoside chloride migrated preferentially to the top phase while gallic acid and quercetin migrated to the PVP-rich phase. The system formed by acetonitrile (ACN) (62.05 wt%) + PVP-10000 (12.05 wt%) + H2O (25.90 wt%) was more selective for the separation of cyanidin-3-O-glucoside chloride from gallic acid (S-CYA/AGA = 65.41) and quercetin (S-CYA/QUE = 42.77).