Sodium dodecylbenzenesulfonate (SDBS) was used as an additive in separating a broad range of polycyclic aromatic hydrocarbons (PAHs) by capillary electrophoresis. In the absence of micelles, using an acetonitrile-water (40:60) electrolyte, the separation mechanism was predicted as solvophobic association of the PAH molecules with hydrophobic chains of the SDBS surfactant and a possible pi-pi interaction between aromatic groups of PAHs and SDBS. The effects of voltage, acetonitrile and SDBS concentrations on separation were investigated. SDBS provides a good selectivity for PAHs not only between different ring numbers (1 to 5) but also between the pairs of structural isomers. Under optimum conditions, 11 aromatic compounds were separated with efficiencies between 130 000 and 230 000 theoretical plates. Reproducibilities of migration times range between 1.15 and 1.55% RSD and peak areas between 2 and 9% RSD. (C) 2002 Elsevier Science B.V. All rights reserved.