Square wave voltammetric measurements allows for determining the composition of system containing a reversibly reducible/oxidable electroactive species in two oxidation states. The method is based on recording the ratio of reverse to forward peak currents. That ratio can be correlated with the molar fraction of the oxidized (or reduced) form of the depolarizer. The method was compared with cyclic voltammetric methods suggested in literature and it was tested using Fe(CN)(6)(3-)/Fe(CN)(6)(4-) in solution phase. Application to solid state systems is illustrated by the dehydroindigo/indigo couple in synthetic Maya Blue-type specimens prepared from indigo plus different clays where account for oxidation state composition of the host dye species and its space distribution in the inorganic guest can be obtained. (C) 2012 Elsevier B.V. All rights reserved.