FAST-SCAN VOLTAMMETRY IN AQUEOUS-SOLUTIONS AT CARBON-FIBER ULTRAMICROELECTRODES WITH ONLINE IR COMPENSATION

Carbon fiber ultramicroelectrodes at scan rates up to 11000 V/s were used in the investigation of fast redox reactions of Ru(NH3)6(3+/2+) and Fe(CN)6(3-/4-) in aqueous solutions. An on-line iR compensation circuit and background subtraction were used to eliminate the iR drop and the interference of the background current. The standard reaction rate constants of Ru(NH3)6(3+/2+) and Fe(CN)6(3-/4-) at the carbon fiber in aqueous solutions are 1.22 +/- 0.07 (N = 15) and 0.13 +/- 0.02 cm/s (N= 12), respectively. The activity of a freshly cut carbon fiber electrode is much higher than that of untreated glassy carbon for both outer-sphere redox reactions. Uric acid, a 2e- and 2H+ system with a fast followup reaction, has also been investigated. The adsorption current of uric acid dominates the responses at high scan rates. Therefore, the standard reaction rate constant of adsorbed uric acid can be estimated under the assumption that only pure adsorption current contributes to the voltammograms.