摘要：A method for the simultaneous determination of dl-methylephedrine hydrochloride (ME-H) and dihydrocodeine phosphate (DC-P) in antitussive syrups by using high performance liquid chromatograph (HPLC) was described. A sample solution for HPLC was prepared as follows. A sample syrup was poured into cation exchange resin column (Amberlite CG 50 NH4 type, 1 cm i.d.×8 cm). After washing the column with water, ME-H and DC-P were eluted with 0.1 N HCl. The eluate was alkalized and extracted with chloroform. The chloroform solution was evaporated to dryness and the residue was dissolved in methanol containing acetaminophen as an internal standard. An aliquot of the sample solution was injected into HPLC equipped with UV-254 nm detector. dl-Methylephedrine and dihydrocodeine were separated on a styrene-divinyl benzene copolymer column (4 mm i.d.×15 cm) by using ammonia-methanol (1 : 99, v/v) as a mobile phase. By washing the cation exchange resin column sufficiently, influence of caffeine on the recovery of DC-P was removed. This procedure was found to be applicable to almost all commercial syrups and to give satisfactory accuracy.
