Electrochemical behaviour of triclosan at a screen-printed carbon electrode and its voltammetric determination in toothpaste and mouthrinse products

Cyclic voltammetry was used to investigate the electrochemical behaviour of triclosan (2,2,4'-trichloro-2'-hydroxydiphenyl ether) at a screen-printed carbon electrode (SPCE). It was found that a single anodic peak occurred over the pH range 6.0-12.0; this peak was considered to result from an irreversible oxidation reaction at the phenolic moiety. A plot of E-p versus pH was constructed and from the break point a pK(a) value of 7.9 was obtained, thus agreeing with the literature value. Detailed voltammetric studies were performed at pH 10, where the analyte exists as an anion. It was demonstrated that, at an initial potential of 0 V, the anion underwent electrosorption prior to electrochemical oxidation. The oxidation reaction appeared to involve a one-electron transfer, as deduced from a calculated alpha n(a) value of 0.5; the same value was obtained at pH 7.0. In contrast to triclosan, triclosan monophosphate was found to be electrochemically inactive when subjected to voltammetry under the stated conditions. The electrochemical oxidation of triclosan at a SPCE was exploited for its determination (less than or equal to 0.3%) in commercial toothpaste and mouthrinse products using differential pulse voltammetry. The recovery and precision data indicated that this approach may have application in routine quality control analysis. (C) 1999 Elsevier Science B.V. All rights reserved.