Square-wave voltammetry of an aqueous solution of indigo

Indigo is dissolved in water in the concentration of 5×10−5 M and measured by highly sensitive adsorptive stripping square-wave voltammetry in order to determine the parameters of its electrochemical reduction. The formal potential of the indigo/leucoindigo redox couple dissolved in the aqueous 0.7 M KNO3, pH 12 (NaOH) is −0.566±0.003 V versus Ag ∣ AgCl ∣ 3 M KCl. Both indigo and leucoindigo are adsorbed on the surface of the mercury electrode, and the standard rate constant of this redox reaction is 920±130 s−1. The ratio of adsorption constants of indigo and leucoindigo is 0.75.