Electrochemical investigations of reactive dyes; polarographic determination of anthraquinone-based chlorotriazine dyes

Direct current and differential pulse polarographic and cyclic voltammetric studies of Procion blue MX-R (PB) and Cibacron blue 3GA (CB) and methods for the determination of PB and CB are reported. For both dyes reduction peaks are observed for the two-electron reversible reduction of the anthraquinone moiety, followed by one (CB) and two (PB) reduction processes associated with the reduction of the mono- and dichlorotriazine groups, respectively. These latter processes appear to involve the reductive elimination of the chlorine atoms: only the anthraquinone reduction process is observed when the dyes are hydrolysed. In alkaline solution the reduction processes are complicated by adsorption and kinetic effects. For this reason determination of the dyes is best carried out in acidic solution, but determination is also possible in alkaline solution, which would be more convenient for monitoring the dyes during dyeing and other nucleophilic reactions.