Meldola blue (MLB) was strongly retained inside the cavity of host layered barium and calcium phosphates, without leaching, and the intercalated compounds were characterized through elemental analysis, X-ray power diffraction (XRD), infrared spectroscopy, scanning electron microscopy, phosphorus nuclear magnetic resonance and electrochemical measurements. The intercalated dye compound was incorporated into a carbon paste electrode and, by means of cyclic voltammetry, its electrochemical properties were investigated. Upon changing the pH of the solution between 2.5 and 7.0, the midpoint potential remained practically constant, giving near -0.020 and -0.019 V versus SCE for barium and calcium phosphates intercalated with MLB. This is not the usual behavior of MLB since its midpoint potential changes considerably in solution phase as the pH is changed. The modified electrodes have proven to be stable and electrocatalytically active for hydrazine oxidation at pH 6.0. (c) 2004 Elsevier B.V. All rights reserved.1071446453