A study of ethylamine at a gold rotating ring-disk electrode using pulsed electrochemical detection at the ring

Linear scan (cyclic) voltammetry at the disk with simultaneous pulsed electrochemical detection (PED) at the ring of a related ring-disk electrode (RRDE) is demonstrated to be applicable far studies of the complex anodic behavior of ethylamine at gold electrodes in 0.10 M NaOH. The oxidation of ethylamine at the disk occurs during positive scans concomitantly with formation of surface oxide (Au --> AuOH --> AuO). However, the final oxide-covered surface (AuO) is inert for further ethylamine oxidation. Data obtained at the RRDE demonstrate that the total ethylamine signal at the disk is composed of simultaneous contributions from: oxidative desorption of ethylamine preadsorbed at the oxide-free Au surface and oxidation of ethylamine transported to the disk simultaneously with oxide formation. Based on ring-disk data, preadsorbed ethylamine is estimated to correspond to a fractional surface coverage of 0.7 +/- 0.1 monolayer for 10 to 60 mu M ethylamine. Of this coverage, ca. 75% corresponds to ethylamine coadsorbed reversibly with OH- and 25% to ethylamine adsorbed irreversibly by a mechanism concluded to be chemisorption.