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 carbohydrat es at a copper electrode using a continuous, large-amplitude sine wave as an excitation waveform. The background charging current response i s a phase-shifted sine wave with the major frequency component concent rated 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 an d sensitive detection of these sugars at a copper electrode. The selec tivity of this measurement relies on the inherent difference in the fr equency domain spectra (i.e., magnitude and phase of each harmonic) of sugars of different sizes. This frequency distribution is dramaticall y affected by temperature, indicating the effect of kinetics in the me chanism for the oxidation of sugars. The sensitivity of the measuremen t of glucose and maltose is demonstrated with now injection analysis a nd postprocessing the data with the digitial equivalent of a lock-in a mplifier. A limit of detection of 8 nM is obtained for glucose when th e isolated faradaic current is optimized for phase-and frequency.