PULSED AMPEROMETRIC DETECTION OF SULFUR-COMPOUNDS - THIOUREA AT GOLD ELECTRODES

Cyclic and pulsed voltammetry at a rotated disk electrode and pulsed amperometric detection (PAD) in a flow-injection cell are applied in studies of the anodic response of thiourea at gold electrodes in 0.1 M NaOH. The greatest voltammetric response corresponds to a peak-shaped anodic wave catalyzed by the oxide-formation process on the electrode surface. This anodic response is under mixed transport-surface control with sulfate concluded to be the predominate oxidation product. For high thiourea concentrations, electrode fouling can occur from accumulation of atomic sulfur formed by the incomplete oxidation of thiourea. Electrode fouling during PAD can be avoided using a pulsed waveform in which the cathodic reactivation process occurs at a potential < -1.0 V vs. SCE to achieve cathodic desorption of atomic sulfur. A change in the slope of calibration data for concentrations > 0.01 mM is interpreted to be a consequence of the decreased efficiency for oxidation of thiourea and a positive shift in the potential for the peak anodic response as concentration is increased.