Rapid and ultrasensitive determination of ephedrine and pseudoephedrine derivatizated with 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein by micellar electrokinetic chromatography with laser-induced fluorescence detection

This paper presents a micellar electrokinetic chromatography method with laser-induced fluorescence detection to analyze ephedrine (E) and pseudoephedrine (PE) after derivatizated with 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein. The optimum derivatization conditions were: 0.05 M Na2CO3/NaHCO3 (pH 9.5), reaction time 30 min at 45 °C, molar ratio of DTAF to E and PE mixture 20:1. The baseline separation was achieved within 8 min with running buffer composed of 20 mM borate + 20 mM SDS + 15% acetonitrile (v/v) (adjusted pH 9.8), and applied voltage of 20 kV. Good linearity relationships (correlation coefficients: 0.9906 for E and 0.9941 for PE) between the peak heights and concentration of the analytes were obtained (2.5–50 ng mL−1). The detection limits for E and PE were 3.85 × 10−4 and 1.41 × 10−4 ng mL−1, respectively, which indicated that the proposed method surpassed other chromatographic alternatives in terms of limit of detection by at least 103 folds. The method was applied to the analysis of the two alkaloids in ephedra herb plants and its preparations with recoveries in the range of 89.6–107.0%.