Aqueous biphasic systems (ABS) are efficient and environmentally friendly separation processes, which allow the recovery of diverse biomolecules. However, the common ABS based in polyethylene glycol (PEG) present a limited range of applicability, due to the low polarity difference between the phases. To overcome this limitation, the use of ionic liquids (ILs) as adjuvants in ABS were proposed. In this work , ILs were used in small amounts (5wt%) in ABS composed of potassium citrate buffer pH 7.0 + water + PEG 400 aiming at controlling their phase behaviour and the partition coefficients of antioxidants (gallic acid, vanillic acid and eugenol). The results obtained indicate that the addition of ILs to the typical PEG/ salt ABS can increase the biphasic region and the partition of antioxidants.