ACTIVATED PULSED AMPEROMETRIC DETECTION OF CYSTEINE AT PLATINUM-ELECTRODES IN ACIDIC MEDIA

Anodic voltammetric detection of sulfhydryl compounds, represented her e by cysteine, at Pt electrodes in acidic media occurs concomitantly w ith anodic generation of surface oxide. It is speculated that the adso rbed hydroxyl species (PtOH), proposed to be the intermediate product in formation of the inert oxide (PtO), is the source of O-atoms transf erred to the sulfonic acid produced by oxidation of the sulfhydryl moi ety. However, as a consequence of this electrocatalytic response mecha nism, application of the traditional three-step waveform for pulsed am perometric detection (PAD) of sulfhydryl compounds is accompanied by a large background signal resulting from PtO formation. To diminish the background signal, the traditional three-step PAD waveform has been m odified by insertion of a brief (100 ms) anodization step prior to the detection step to activate the Pt surface by the generation of PtOH w ith minimal conversion to PtO. The subsequent negative step from the a ctivation potential (E-act) to the detection potential (E-det<E-act pe rmits the PtOH to be harvested within the detection mechanism without significant background signal.