Separation and determination of ephedra alkaloids in traditional Chinese medicine and human urines by capillary electrophoresis coupled with electrochemiluminescence detection

A new approach for the simultaneous determination of ephedrine, methylephedrine, and pseudoephedrine is developed, using capillary electrophoresis coupled with electrochemiluminescence detection with internal standard method. Separation efficiency and sensitivity were improved by use of an ionic liquid. Parameters affecting separation and detection were investigated in detail. Under optimum conditions, the three ephedra alkaloids were well separated and detected. The limits of detection (S/N = 3) of ephedrine, methylephedrine and pseudoephedrine are 4.0 × 10−8, 6.5 × 10−8, and 4.6 × 10−8 mol/L, respectively. The limits of quantitation (S/N = 10) in human urine are 5.3 × 10−7 mol/L for ephedrine, 9.1 × 10−7 mol/L for methylephedrine, and 6.9 × 10−7 mol/L for pseudoephedrine, respectively. The precision (RSD%) of the peak area and the migration time were from 2.2% to 2.5% and from 0.1% to 0.2% within a day and from 2.7% to 3.9% and from 0.4% to 0.8% in three days. The proposed method was successfully applied to the determination of three analytes in traditional Chinese medicine and human urine, and the monitoring of pharmacokinetics of pseudoephedrine in human body.