Sinusoidal voltammetry for the analysis of carbohydrates at copper electrodes

A digital approach for the collection and analysis of electrochemical frequency domain spectra is presented for the oxidation of carbohydrates at a copper electrode using a continuous, large-amplitude sine wave as an excitation waveform. The background charging current response is a phase-shifted sine wave with the major frequency component concentrated at the fundamental frequency. A nonlinear faradaic response due to the oxidation of sugars produces significant signal intensities at the higher harmonics as well as the fundamental frequency. Examination of the frequency spectra of glucose and maltose leads to selective and sensitive detection of these sugars at a copper electrode. The selectivity of this measurement relies on the inherent difference in the frequency domain spectra (i.e., magnitude and phase of each harmonic) of sugars of different sizes. This frequency distribution is dramatically affected by temperature, indicating the effect of kinetics in the mechanism for the oxidation of sugars. The sensitivity of the measurement of glucose and maltose is demonstrated with now injection analysis and postprocessing the data with the digitial equivalent of a lock-in amplifier. A limit of detection of 8 nM is obtained for glucose when the isolated faradaic current is optimized for phase-and frequency.