This work presents the simultaneous determination of catechol (CC) and hydroquinone (HQ), employing a modified glassy carbon electrode with tetraruthenated oxovanadium (IV) porphyrin. The GCE was modified by electropolymerization of {VOTPyP[RuCl3(dppb)](4)} porphyrin, onto the GCE surface, by cyclic voltammetry. The modified electrode, labeled as VOTPRu-GCE, showed two pairs of well-defined redox peaks for the electrochemical processes of catechol and hydroquinone. In bare GCE, the potential difference (DEp) of CC and HQ were 469 mV and 457 mV, respectively, while with VOTPRu-GCE the potential difference decreased to 29 mV and 30 mV, indicating that the redox processes were reversible onto the VOTPRu-GCE surface. With differential pulse voltammetry, it was possible to simultaneously determine the CC and HQ, with peak-to-peak potential separation of 129 mV, in 0.1 mol L-1 acetate buffer (pH 4.75). Under the optimized conditions, the calibration curves were obtained in the linear concentration ranges of 2-38 mmol L-1 for both isomers using the VOTPRu-GCE, which showed high sensitivity in the determination of CC and HQ, 12.73 and 15.91 mA mmol L(-1)cm(-2), respectively. The detection limits were 0.41 and 0.55 mu mol L-1 for CC and HQ, respectively. (C) 2015 Elsevier Ltd. All rights reserved.