HPCE Determination of Ephedrine Hydrochloride and Pseudo-Ephedrine Hydrochloride in Drugs with Enrichment by Electro-stacking

HPCE with electro-stacking enrichment was applied to the determination of ephedrine hydrochloride and pseudo-ephedrine hydrochloride in 6 drugs. Analytical conditions were studied and following optimized parameters were given: ① wavelength for UV-detection: 205 nm; ② internal standard: resorcinol; ③ electrophoretic medium: 40 mmol·L-1 borax solution (pH 9.2); ④ separation voltage: 20 kV; ⑤ time of sample introduction: 10 s; ⑥ temperature of capillary: 25 ℃. Linear relationships between values of relative peak area (i.e., ratio of peak area of the analyte to peak area of internal standard) and concentration of ephedrine and pseudo-ephedrine were kept in the same range of 1 to 400 mg·L-1, with detection limits (3S/N) of 0.35 mg·L-1 and 0.29 mg·L-1 respectively. Recovery was tested by standard addition method using 2 drug samples as matrixes, giving values of average recovery of 101.1% (for ephedrine) and 103.6% (for pseudo-ephedrine).