Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This work describes the in situ immobilization of Mn(II) phthalocyanine (MnPc) in a porous SiO2/SnO2 mixed oxide matrix obtained by the sol gel processing method. The chemically modified matrix SiO2/SnO2/MnPc, possessing an estimated amount of 8 x 10(-10) mol cm(-2) of MnPc on the surface, was used to prepare an electrode to analyze dissolved oxygen in water by an electrochemical technique. The electrode was prepared by mixing the material with ultrapure graphite and evaluated using differential pulse voltammetry. Dissolved O-2 was reduced at -0.31 V with a limit of detection (LOD) equal to 7.0 x 10(-4) mmol L-1. A mechanism involving four electrons in O-2 reduction was determined by the rotating disk electrode technique. (C) 2011 Published by Elsevier B.V.85212131216Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)