Anodic Response of Cystine at Preanodized Au and Au-Ag Electrodes in Perchloric Acid Media

Autor: Matthew E. Johll, Dennis C. Johnson
Rok vydání: 1999
Předmět:
Zdroj: Electroanalysis. 11:534-540
ISSN: 1521-4109
1040-0397
Popis: This study involves a comparison of the anodic response of the disulfide moiety of cystine at preanodized Au and Au-Ag rotated disk electrodes (RDEs). The goal of the study was the determination of beneficial effects that might result from the introduction of Ag-sites into Au surfaces. An anodic wave is observed for cystine at oxide covered Au and Au-Ag electrodes appearing as a shoulder to the wave for anodic discharge of H2O with evolution of O2. Both the half-wave potential for the cystine wave (E12,RSSR) and the overpotential for anodic evolution of O2 (ηO2 ) are shifted by –3.6 mV per atomic percent Ag. These negative shifts are attributed to the higher rate of the anodic discharge of H2O at Ag sites in comparison to Au sites. Values for the apparent number of electrons (napp) transferred during oxidation of 1.0 mM cystine at 1.50 and 1.55 V (vs. SCE) are approximately 5 eq mol–1 for Au and 6eq mol–1 for Au80-Ag20, as calculated from the slopes of Koutecky-Levich plots. The larger value of napp at the Au-Ag electrode is attributed to the higher rate for H2O discharge at the Ag sites. Cysteine sulfonic acid is identified as the product of extensive electrolysis (n=10eq mol–1) at a Au electrode. A preanodized Auelectrode in a flow-through cell is demonstrated for cystine detection using a flow-injection system. A 6% loss in peak response observed over a 30-min period is attributed to the slow conversion of an active surface oxide, perhaps corresponding to the equivalent of a monolayer,to an inert oxide, probably corresponding to oxide coverage exceeding a monolayer.
Databáze: OpenAIRE
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