A simple and reliable CE method with direct UV detection has been developed to separate eight isomeric benzoic acids in atmospheric aerosols and vehicular emission without complex sample pretreatment. Optimal electrophoretic conditions, with migration times under 5 min, were obtained by using a 50 mM acetate buffer (pH 4.7) containing a dynamic surface coating EOTrol (TM) LN (0.005% w/v). The separations were carried out in a cathode to anode direction (- 30 W) allowing the low cathodal EOF (similar to 1 x 10(-9) m(2)V(-1)s(-1)) to extend the effective separation by slowing the movement of the studied aromatic acids. Moreover, the sensitivity of the method at 200 nm was enhanced by using a field-amplified sample injection (FASI) with electrokinetic (EK) sample injection (-2 W 60 s). Prior to sample injection, a short water plug (3 s at 0.5 psi) was introduced. Under these conditions, the method was capable of detecting the analytes in deionized water with LODs (S/N = 3) as low as 0.1 pg/L for most of the studied acids. In the presence of 10 mg/L of sulphate (added to simulate a sample matrix), LODs ranged from 0.26 to 0.62 mu g/L. The validation of the method has proven an excellent separation performance and accuracy for the determination of isomeric benzoic acids in the studied matrices.