Designer based Fourier transformed voltammetry: A multi-frequency, variable amplitude, sinusoidal waveform

Abstract

Fourier transform methods allow custom-designed complex waveforms to be used in ac voltammetry. Commonly a single wave or sum of sine waves of variable angular frequency but constant amplitude superimposed onto a dc ramp are employed. In the present case, a custom-designed waveform consisting of a combination of eight sine waves is introduced, with the property that each sine wave within the composite waveform has the property where i represents the ith sine wave. Frequencies (and amplitudes) employed in a single experiment cover the range from 34.94 Hz (20 mV) to 1970.01 Hz (2.66 mV). Reversibility is readily detected via use of this designer waveform by noting a constant peak height Ip (wt) for all eight frequencies, whereas Ip (wt) values decrease in a characteristic manner with increasing frequency for a quasi-reversible process or when uncompensated resistance is present, as demonstrated experimentally and theoretically. Importantly, background charging current contributions do not increase to a level that makes measurement of faradaic current difficult at high frequencies and hence charging current is readily corrected for over the entire frequency range of interest.