Determination of anthraquinone in alkaline sodium dithionite solution by electrochemical analysis

Abstract

Anthraquinone dissolved in water containing an excess of sodium dithionite has been subjected to a voltammetric study. On different electrode materials (Pt, glassy carbon, Au, Pd) the sodium salt of anthrahydroquinone shows an oxidative voltammetric wave. This reaction involves the oxidation of anthrahydroquinone to the insoluble anthraquinone which strongly adsorbs on the electrode surface. The resulting blocking of the electrode surface can prevent the amperometric determination of anthraquinone. This interference can be minimized in two ways. The first involves the presence of a sufficiently large excess of sodium dithionite in solution, which chemically reduces the adsorbed anthraquinone to soluble anthrahydroquinone. This situation can only be obtained when the anthraquinone concentration is sufficiently low and then the diffusion limiting current of the reaction at a rotating disc electrode is proportional to the concentration of anthrahydroquinone. The adsorbed anthraquinone can also be removed by polarising the electrode at sufficiently negative potentials. This allows the determination of higher anthraquinone concentrations by linear sweep voltammetry but no longer by a continuous amperometric method.