Abstract: The separation between ephedrine and pseudoephedrine with capillary electrophoresis and determination by the conductivity detector is reported. The separation mechanism is studied and the determination method is found. The effects of complex reagent concentration, concentration and pHof the running buffer, separation voltage and the organic solvent concentration are investigated and discussed. At 13.5 kVhigh voltage the ephedrine and pseudoephedrine are separated successfully in a citric acid sodium citrate buffer(pH=4.5) with the copper salt as the complex reagent. Ethanol is used to improve the peak shapes and separation effects. There are an excellent linearity between peak area and concentration of analytes in the concentration range of 1.4-165 mg/Lfor ephedrine and 0.825-165 mg/Lfor pseudophedrine with the detection limits(S/N =3) of 0825 and 0198 for ephedrine and pseudophedrine respectively. Relative standard deviations(RSD) of the ephedrine and psudoephedrine are 32%(ephedrine) and 28%(psudoephedrine) based on the determination of seven times. The ephedrine and pseudoephedrine in collunarium are detected and the satisfaction results are obtained.

Key words: Capillary electrophoresis, Conductivity detector, Ephedrine, Pseudoephedrine