In this work, SiO2/Sb2O3 prepared by the sol-gel processing method, having a specific surface area, SBET, of 790 m2g-1, an average pore diameter of 1.9 nm and 4.7 wt. % of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μmolg-1. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid-solution interface, occurred at -0.25 V versus SCE in 1.0 moll-1 KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation-reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O2 concentrations, between 1.0 and 12.8 mgl-1, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples. © 2003 Elsevier Ltd. All rights reserved.495829834Hench, L.L., West, J.K., (1990) Chem. Rev., 90, p. 33Zaitseva, G., Gushikem, Y., (2002) J. Braz. Chem. Soc., 13, p. 611Zaitseva, G., Gushikem, Y., Ribeiro, E.S., Rosatto, S.S., (2002) Electrochim. Acta, 47, p. 1469Francisco, M.S.P., Gushikem, Y., (2002) J. Mater. Chem., 12, p. 2552Ribeiro, E.S., Rosatto, S.S., Gushikem, Y., Kubota, L.T., (2003) J. Solid State Electrochem., 7, p. 665Castellani, A.M., Gonçalves, J.E., Gushikem, Y., (2002) J. New Mater. Electrochem. Syst., 5, p. 169Alfaya, A.A.S., Kubota, L.T., (2002) Quim. Nova, 25, p. 835Castellani, A.M., Gonçalves, J.E., Gushikem, Y., (2001) Electroanalysis, 13, p. 1165Castellani, A.M., Gushikem, Y., (2000) J. Colloid Interface Sci., 230, p. 195Ferreira, C.U., Gushikem, Y., Kubota, L.T., (2000) J. Solid State Electrochem., 4, p. 298Walcarius, A., (2001) Chem. Mater., 13, p. 3351Walcarius, A., (2001) Electroanalysis, 13, p. 701Dias, S.L.P., Gushikem, Y., Ribeiro, E.S., Benvenutti, E.V., (2002) J. Electroanal. Chem., 523, p. 64Pessoa, C.A., Gushikem, Y., (2001) J. Porphyrins Phthalocyanines, 5, p. 537Ribeiro, E.S., Gushikem, Y., Biazzotto, J.C., Serra, O.A., (2002) J. Porphyrins Phthalocyanines, 6, p. 527Chung, T.D., Anson, F.C., (2001) J. Electroanal. Chem., 508, p. 115Yuasa, M., Nishihara, R., Shi, C., Anson, F.C., (2001) Polym. Adv. Technol., 12, p. 266Chang, C.J., Deng, Y.Q., Shi, C.N., Chang, C.K., Anson, F.C., Nocera, D.G., (2000) Chem. Commun., p. 1355Yamamoto, K., Taneichi, D., (2000) Chem. Lett., p. 4Ribeiro, E.S., Gushikem, Y., (1999) Electrochim. Acta, 44, p. 3589Yamamoto, K., Taneichi, D., (1999) J. Inorg. Organomet. Polym., 9, p. 231Song, E.H., Shi, C.N., Anson, F.C., (1998) Langmuir, 14, p. 4315D'souza, F., Hsieh, Y.Y., Wickman, H., Kutner, W., (1997) Electroanalysis, 9, p. 1093D'Souza, F., Hsieh, Y.Y., Wickman, H., Kutner, W., (1997) Chem. Commun., p. 1191Corwin, A.H., Chivvis, A.B., Poor, R.W., Whitten, D.G., Baker, E.W., (1968) J. Am. Chem. Soc., 90, p. 6577Pottier, R.H., Kennedy, J.C., Chow, Y.F.A., Cheung, F., (1988) Can. J. Spectrosc., 33, p. 57Ni, C.L., Abdalmuhdi, I., Chang, C.K., Anson, F.C., (1987) J. Phys. Chem., 91, p. 1158Durand, R.R., Bencosme, C.S., Collman, J.P., Anson, F.C., (1983) J. Am. Chem. Soc., 105, p. 2710Iler, R., (1979) The Chemistry of Silica, p. 185. , Wiley, New YorkBard, A.J., Faulkner, L.R., (1980) Electrochemical Methods, p. 221. , John Wiley & Sons, New YorkKarlin, K.D., Gultneh, Y., (1987) Progress in Inorganic Chemistry, 35, p. 219. , S.J. Lippard (Ed.), John, New YorkDurand, R.R., Anson, F.C., (1982) J. Electroanal. Chem., 134, p. 273Fair, G.M., Geyer, J.C., Okun, D.A., (1971) Elements of Water Supply and Wastewater Disposal, Second Ed., p. 449. , Wiley, New York