Determination of ephedrine alkaloid stereoisomers in dietary supplements by capillary electrophoresis.

Three complementary capillary electrophoresis (CE) methods were developed for the separation and quantification of ephedrine and pseudoephedrine stereoisomers. Either single or dual cyclodextrin-based chiral selector systems provided enantioselective separation of the compounds of interest. The three methods were applied to the analysis of a suite of five standard reference materials (SRMs) containing ephedra. Use of a high-sensitivity UV detection cell enhanced quantification of the analytes of interest over the wide range of concentrations encountered in the SRMs. Results for (-)-ephedrine ranged from 0.31 to 76.43 mg/g, and for (+)-pseudoephedrine ranged from 0.049 to 9.23 mg/g in the materials studied. Results from the three methods agreed well with each other and with the results from other methods of analysis. The addition of known amounts of specific enantiomers was used to confirm the enantiomeric identity of the analytes. The results obtained by the three CE methods were utilized for value assignment of the ephedrine alkaloid content of these five SRMs.