Electrochemical investigations of reactive dyes; cathodic stripping voltammetric determination of anthraquinone-based chlorotriazine dyes at a hanging mercury drop electrode

Two anthraquinone-based chlorotriazine reactive dyes, Procion Blue MX-R and Cibacron Blue 3GA, have been determined at nanomolar levels using cathodic stripping voltammetry. When the differential pulse voltammetric stripping mode is used no peak is obtained for the reduction of the anthraquinone moiety in these dyes, although the signal is present when the linear sweep mode is used. The absence of this peak in the differential pulse mode is believed to occur because, when this group is reduced in the adsorbed state on application of the potential pulse, it is reduced so rapidly that reduction is complete before the current is monitored at the end of the pulse. The differential pulse signal is present for the reduction of the chlorotriazine active groups. The differential pulse peak for the anthraquinone reduction process does appear when boric acid is present in the supporting electrolyte, and it is also present when the chlorotriazine groups are hydrolysed or reacted with other hydroxy compounds. This means that hydrolysis or similar reactions of these dyes can be monitored by observing both the appearance of the anthraquinone peak and the disappearance of the chlorotriazine peak.