Determination of ephedrine alkaloids in Ephedra natural products using HPLC on a pentafluorophenylpropyl stationary phase

Abstract

In this study a pentafluorophenylpropyl (PFPP) stationary phase was applied to the fast and reliable qualitative and quantitative analysis of ephedrine alkaloids in Ephedra plant material and derivatives. A Discovery HS F5 column (150 mm × 4.6 mm i.d., 5 μm) was used, with an isocratic mobile phase composed of ammonium acetate (7 mM) in acetonitrile–water (90:10, v/v), at a flow rate of 1.0 ml/min. The column temperature was set at 45 °C. UV detection was set at 215 and 225 nm. The total analysis time was 16 min. The validation parameters, such as linearity, sensitivity, accuracy, precision and specificity, were found to be highly satisfactory. Sonication and microwave extractions were compared in order to optimize the yield of the target analytes. Under the optimized extraction conditions (based on two cycles of sonication with methanol at 40 °C for 15 min), different matrices containing Ephedra were successfully analyzed for their alkaloid content. The method was applied to the analysis of standard reference materials (SRMs) containing Ephedra. Furthermore, the developed technique allowed the simultaneous determination of ephedrine alkaloids and synephrine, the main phenethylamine alkaloid of Citrus aurantium, that has replaced Ephedra in dietary supplements used in the treatment of obesity. The results indicated that this procedure is suitable for the phytochemical analysis of Ephedra plant material and extracts, and can be applied to demonstrate the label claims for product content, including the absence of ephedrine alkaloids in Ephedra-free products.