Evaluation of high-performance liquid chromatography and gas chromatography for quantitation of dextromethorphan hydrobromide in cough-cold syrup preparations.

A rapid and sensitive high-performance liquid chromatographic (HPLC) procedure is described for the analysis of the antitussive dextromethorphan hydrobromide in several cough-cold syrup preparations and compared with a gas chromatographic (GC) procedure. In the HPLC procedure, the active ingredient is analyzed as the hydrobromide salt by dilution in the mobile phase and separation on a reverse-phase cyano column. In the GC method, the active ingredient is analyzed as the free base, in which an aqueous solution of the antitussive is made alkaline and extracted with dichloromethane before injection onto the GC column. Excellent resolution of the antitussive agent was obtained by both systems; however, the HPLC assay is preferred for routine analysis (RSD 1%), as compared with the GC assay (RSD 4%).