The electrochemical properties of an indium-tin oxide (ITO) electrode modified with 2,5-bis(phosphonomethyl)hydroquinone (BPH(2)Q) were studied by cyclic voltammetry. A novel derivative of hydroquinone, BPH(2)Q, has been synthesized and used for the chemical modification of a bare ITO and the zirconated ITO electrodes obtained from the pretreatment with Zr(IV) ion solutions. The BPH(2)Q molecule is spontaneously, irreversibly bound to ITO surface irrespective of presence of Zr(IV) pretreatment. Ionic binding of the BPH(2)Q molecule to the zirconium ion-treated ITO surface produces a layer with a coverage of 2.6 x 10(-10) mol cm(-2). The modified electrode exhibits interesting electrochemical molecular recognition for alkali metal cations and ammonium cations and shows unique redox peak potential shifts depending upon the molar concentration of each cation in the range of 0.01-1.0 M. This electrode presents a preferential selectivity of K+ in the presence of Nai. The surface formal potential of an ITO/Zr/BPH(2)Q electrode is pH dependent with a slope of 61.1 mV pH(-1) which is very close to Nernstian value due to a two-electron two-proton process of hydroquinone moiety,