Effect of Surfactant Concentration on the Determination Oftrans,trans-Muconic Acid in Urine by Cationic Micellar Electrokinetic Chromatography With Thermo-Optical Absorbance Detection

A rapid method is described for the determination of trans,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 charged trans,trans-muconic acid ion migrates rapidly (< 3 min) toward the anode owing to its electrophoretic mobility supplemented by the surfactant–induced anodic EOF. A rigorous investigation into the effect of CTAB concentration on EOF showed that 0.05 to 5 mM surfactant permits trans,trans-muconic acid to elute before most endogenous urine components. For a urine sample doped with 0.8 mg/L trans,trans-muconic acid, the relative standard deviations of the analyte migration time and peak height were 1.5 % and 5.7 % respectively (n=6), for this home–built analysis system. The detection limit (3 SD) was 0.1 mg/L (7×10−7 M) trans,trans-muconic acid based on calibration standards and the linear dynamic range extended to 50 mg/L.