Development of voltammetric sensors for the determination of sodium dithionite and indanthrene/indigo dyes in alkaline solutions Original Research Article

Linear sweep and cyclic voltammetric studies of indigo, indanthrene dyes and sodium dithionite in alkaline solutions are reported. The results were applied to develop amperometric determination methods for these vat dyes and reducing agent. On different electrode materials (Au, glassy carbon, Pd, Pt) the reduced dyes give an anodic voltammetric signal. This reaction referring to the oxidation of dyestuff is concentration, rotation and potential scan rate dependent. Adsorption of oxidized dyestuff on the electrode surface was found to impede the chronoamperometric determination. By introducing potential steps, in situ cleaning of the electrode surface leads to a repetitive renewal and activation of the electrode surface. The use of multi-pulse amperometry allowed to measure in a continuous way a voltammetric signal that is proportional to the dye concentration. The sodium dithionite concentration can also be monitored continuously using chronoamperometry but only in the absence of dyestuff due to the mentioned adsorption.