The principle of a potentiostatic device used to measure the differential capacity of a metal/solution interface is analysed to assess the Limitations of such a system for the case of large area electrodes and relatively high resistance electrolytes. It is shown that the error function Phi of the measurement device, defined as the ratio of the measured value to the true value, depends on the transfer function of the potentiostatic control system. The variation of this function with the frequency of voltage modulation applied to the electrochemical interface is studied for different configurations of the measurement device. The ohmic drop correction effect on the operation of the potentiostatic system is also analysed. Values of the differential capacity calculated using the expression for the Phi function agree with those measured with an electrochemical dummy cell. This study shows that the variation with frequency depends on the compatibility between the time constant RC of the electrochemical system investigated and the bandwidth B-omega of the potentiostat.