The simultaneous voltammetric determination of catechol (CC) and hydroquinone (HQ) has been achieved at a mesoporous carbon CMK-3 modified electrode in phosphate buffer solution (pH 7.0). At the electrode both CC and HQ can cause a pair of quasi-reversible and well-defined redox peaks and their peak potential difference increases. In comparison with multi-walled carbon nanotubes (MWCNTs) and Vulcan XC-72 carbon modified electrodes the CMK-3 modified electrode shows larger peak currents and higher adsorbed amounts for the two dihydroxybenzene isomers. This is related to the higher specific surface area of CMK-3. Under the optimized conditions, the linear concentration ranges for CC and HQ are 5 x 10(-7) to 3.5 x 10(-1) M and 1 x 10(-6) to 3 x 10(-5) M, respectively. In the presence of 5 mu M isomer, the linear concentration range of CC (or HQ) is 5 x 10(-7) to 2.5 x 10(-5) M (or 5 x 10(-7) to 2.0 x 10(-5) M). The sensitivity for CC or HQ is 41 A M-1 cm(-2) or 52 A M-1 cm(-2), which is close to that without isomer. The detection limits (S/N = 3) for CC and HQ are I X 10-7 M after preconcentration on open circuit for 240s. (c) 2008 Elsevier Ltd. All rights reserved.