A new measuring principle to study interfacial effects using a displacement current through a dielectric coating is presented. It enables the scanning of the electric response from the core of the interface up to the bulk by changing the frequency, In contrast to traditional impedance measurements, the interfacial effects appear at higher frequencies than the bulk and can be measured with a corresponding high sensitivity. The investigations of the Ag/AgCl interface can be consistently explained by a depletion of silver vacancies due to injection of silver ions from the silver electrode. The perpendicular interfacial impedance is discussed in a new approach by using the Sturm-Liouville form of transport equation. The computational results are analysed on the basis of perturbed defect density in the system.