The discovery of sulphite in basic chromium sulphate, typically used as the source of Cr(III) ions in trivalent chromium electrolytes, sparked an investigation into the effects of this species on the reactions at a platinum electrode in a Cr(III)-formate electrolyte. The specific adsorption and oxidation-reduction reactions of sulphite were mapped using cyclic voltammetry and linked to competitive adsorption between sulphite, formic acid and the Cr(III)-formate complex. It was found that sulphite adsorption and reduction/oxidation dominates the cyclic voltammogrammetric response. Formic acid oxidation is completely inhibited as long as sulphite is present at the surface. A feasible way of removing any sulphite from a contaminated electrolyte is by applying a prolonged reductive current. (c) 2018 Elsevier Ltd. All rights reserved.