Cyclic voltammetry with harmonic lock-in detection: Applications to flow streams

The second harmonic frequency is monitored using a conventional lock-in amplifier in a continuous scan cyclic voltammetric experiment. The background charging current is predominantly composed of odd harmonic frequencies, while the analyte Faradaic signal is composed of both odd and even harmonic frequencies. By 'locking-in' on the second harmonic frequency one can isolate the Faradaic current from the charging current in the frequency domain. Model compounds (hexaammineruthenium(III) chloride, ferrocene) at carbon and gold microelectrodes as well as carbohydrates at copper microelectrodes were examined in flow injection analysis experiments. Limits of detection an order of magnitude lower than DC amperometry were observed.