Ion-pair reversed-phase high-pressure liquid chromatography of cough-cold syrups I: pseudoephedrine hydrochloride, brompheniramine maleate, and dextromethorphan hydrobromide.

Pseudoephedrine hydrochloride (I), brompheniramine maleate (II), and dextromethorphan hydrobromide (III) in a cough-cold sytup were separated and determined by ion-pair reversed-phase high-pressure liquid chromatography. The separation was carried out using a muBondapak C18 column (30 cm x 3.9 mm i.d.) and a mobile phase of acetonitrile-water-acetic acid (40:60:1) with 0.01 N 1-octanesulfonic acid sodium salt and 0.05 N potassium nitrate. Detection was accomplished using a UV detector at 265 nm for I and II; III was monitored at 280 nm. Concentration versus peak height plots in the ranges of 0.37-1.9 mg/ml for I, 0.025-0.126 mg/ml for II, and 0.125-0.625 mg/ml for III were linear. Ten consecutive injections of a mixture gave a percent relative standard deviation of less than 1% for all three components. Average recoveries from laboratory-prepared samples were 100.5% for I, 100.9% for II, and 100.1% for III. No precolumn cleanup was necessary, and the chromatogram was complete in 16 min.