Separation and determination of aristolochic acids in herbal medicines by microemulsion electrokinetic chromatography

A microemulsion electrokinetic chromatography (MEEKC) method has been firstly developed and validated for the separation of aristolochic acids A, B, C and D, 7-hydroxy-aristolochic acid A and aristolic acid in herbal medicines. With the optimized experimental conditions (octane 0.81% (w/w), SDS 3.31% (w/w), butan-1-ol 6.61% (w/w) and 10 mM sodium tetraborate buffer 89.27% (w/w), with 15 kV as applied voltage, pH 9.2, 25 °C as capillary temperature), all of the six analytes were baseline-separated (any resolution was over 2) in peaks of good shapes within 16 min. Aristolochic acids A, B, C and aristolic acid were quantitative determined and acceptable precision (intra-day repeatability (n = 6) and inter-day reproducibility (n = 3) of the method in terms of migration times were within 0.98 and 2.75% R.S.D. in terms of migration times and within 5.09 and 5.93% R.S.D. in terms of peak areas, respectively) and linearity (r > 0.995) and recovery (ranged between 97 and 104%) were obtained. Moreover, the method was successfully validated and applied to the determination of four analytes in herbal medicines.