Microemulsion electrokinetic chromatography with laser‐induced fluorescence detection for sensitive determination of ephedrine and pseudoephedrine

A selective and sensitive microemulsion electrokinetic chromatography with laser‐induced fluorescence detection method was developed for the quantification of ephedrine (E) and pseudoephedrine (PE) derivatized with 4‐chloro‐7‐nitrobenzo‐2‐oxa‐1, 3‐diazol. By a series of optimization, a running buffer composed of 20 m M borate + microemulsion (23.3 m M Sodium dodecyl sulfate/180.85 m M 1‐butanol/16.4 m M n ‐heptane) +8% acetonitrile was applied for the separation of the derivatives. A linear relationship for E and PE was obtained in the range of 0.058–11.58 μg·mL −1 (correlation coefficient: 0.9993 for E, 0.9995 for PE), and the detection limits for E and PE were 5.3 and 3.9 ng·mL −1 . The method was applied to the analysis of the two alkaloids in Chinese traditional herbal preparations with recoveries in the range of 96.9–105.4%.