The present work involves an attempt to demonstrate the application of potential difference, existing across the interface of the aqueous two-phase system (ATPS), as a tool for the prediction of the phase equilibrium. The contribution due to long-range interaction for the potential difference and its variation with the composition is studied for the polyethylene glycol (PEG) 2000-Sodium Citrate-Water-based ATPS (Merck, Germany). The developed correlation for the potential difference with concentration shows a satisfactory prediction of the phase equilibrium for the present system. © 2014 Taylor and Francis Group, LLC.