Separation and determination of ephedrine enantiomers and synephrine by high performance capillary electrophoresis in dietary supplements

The chiral separation of ephedrine alkaloids by high performance capillary electrophoresis is of great interest since the enantiomers exhibit quantitative and qualitative differences in pharmacological activity. The isomers of (-)-ephedrine, (+)-pseudoephedrine, (-)-N-methylephedrine, (+)-N-methylpseudoephedrine, (+)-norpseudoephedrine and (-)-norephedrine are the major bioactive components of E. sinica (Ma-Huang) which is a Chinese herb used for weight loss and as an energy booster in the US. However, the compounds stereoisomers are not present in the plant material. The electrophoretic separation was performed using a 110 cm x 50 mum I.D. (101.5 cm effective length) fused silica capillary. The samples were injected by pressure for 5 s at 50 mbar and the running voltage was 30 kV at the injector end of the capillary. Within 23 min, nine ephedrine compounds and synephrine were separated at 210 nm. The method was successively applied to the determination of the ephedrine compounds in dietary supplement products. Parameters affecting the resolution between (+) and (-)-enantiomers, such as pH, cyclodextrin concentration, temperature, organic modifier, buffer concentration and capillary dimensions were reported.