A rapid method is described for the determination oftrans,trans-muconic acid (2,4–hexadienedioic acid), a biomarker of benzene exposure in urine, by micellar electrokinetic chromatography (MEKC) with thermo-optical absorbance (TOA) detection. Addition of the cationic surfactant cetyltri–methylammonium bromide (CTAB) to a pH 7.0 background electrolyte induces a reversal in the direction of electroosmotic flow (EOF), from cathode to anode. The negatively chargedtrans,trans-muconic acid ion migrates rapidly (< 3 min) toward the anode owing to its electrophoretic mobility supplemented by the surfactant–induced anodic EOF.