PULSED VOLTAMMETRIC DETECTION OF ARSENIC(III) AT PLATINUM-ELECTRODES IN ACIDIC MEDIA

The oxidation of As(OH)3 at Pt is believed to occur by an anodic oxygen-transfer mechanism that involves anodic discharge of H2O to form adsorbed hydroxyl radicals (PtOH); however, anodic conversion of PtOH to the inert oxide (PtO) results in severe passivation of the electrode surface. Hence, a transport-limited response is not obtained at a Pt rotated-disk electrode by conventional linear scan or staircase voltammetry. The As(OH)3 response is compared for several pulsed voltammetric waveforms. The preferred waveform consists of four potential steps with an activation step to produce a small quantity of PtOH prior to the detection step which is followed by positive and negative potential stops to achieve reproducible cleaning of the Pt surface. This waveform produces a transport-limited signal with minimal background current.