Abstract: A large amplitude sine wave is applied as the excitation potential to a amperometric measurement to produce a current output that is a phase shifted sine wave containing faradaic information at many frequencies. A current obtained from a conventional potentiostat coupled to the electrode is coupled to a lock-in amplifier that monitors the signal at one frequency at a specified phase angle. Since most of the background remains at the fundamental frequency, a higher harmonic of the fundamental frequency of the sinusoidal sweep frequency is monitored. By locking in on the higher harmonic components, the faradaic signal is therefore distinguished from the background signal. The background is diminished thereby allowing signal recognition at low analyte concentrations and increasing the signal-to-noise ratio.