Parallel flow microfluidic contactors employing systems of two aqueous phases for the separation of antibiotics, their intermediates or other solutes are investigated in this report. A mathematical model of these contactors with either co-current or counter-current flow arrangements is formulated. As both aqueous phases are electrically conductive, dc electric field applied perpendicularly to their interface is considered as a tool to enhance the efficiency of separation of charged reaction components. Six dimensionless parameters of the contactor were identified. Three of them, namely the Peclet number, the electric Peclet number, and the ratio of electric conductivities of the phases, were selected as the parameters allowing for the control of the separation process. Regions of 90% separation efficiency were identified in the three-dimensional parameter space. Dimensionless expressions approximating the boundaries of these regions were suggested. The reported findings can help to design and control highly efficient parallel flow microfluidic separators.