Many molecules of farmacological interest could not have been studied for the classical electrochemical technical due to the great complexity that they present when they are submitted to voltammetric processes. An electrochemical method for quantifying betalactam antibiotic (amoxicillin) is described. Cyclic voltammetry at the water/nitrobenzene interface in a four-electrode system is used. The zwitterion compound was ionized to the necessary electrochemical form by pH adjustment. The ionized antibiotic is studied by voltammetric transfer since water to nitrobenzene using the method of the interface between two immiscible electrolyte solutions (ITIES).