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

A selective and sensitive micellar electrokinetic chromatography method with laser‐induced fluorescence detection was developed for the quantification of ephedrine (E) and pseudoephedrine (PE) derivatized with 4‐chloro‐7‐nitrobenzo‐2‐oxa‐1,3‐diazole. After conducting a series of optimizations, a running buffer of 10 mM sodium borate + 16 mM SDS was used for separation of the derivatives. A linear relationship for E and PE was obtained in the range of 0.044–6.6 μg mL –1 (correlation coefficient: 0.9943 for E, 0.9946 for PE), and the detection limits for E and PE were 0.70 and 0.30 ng mL –1 , respectively. The sensitivity of E and PE was improved by several multiples of ten over those of CZE‐LIF method. The method was applied to the analysis of the two alkaloids in ephedra herbal medicine and preparations with recoveries in the range of 98.3–107.1%.