Determination of dextromethorphan hydrobromide by high-performance liquid chromatography using ion-pair formation

The chromatographic retention behavior of dextromethorphan hydrobromide on an octadecylsilane column was investigated as a function of the pairing ion and the mobile phase composition. Dramatic increases in the capacity factor were observed with pairing ions containing more than eight carbons and with decreasing organic modifier (acetonitrile) concentration. Several pharmaceutically important amines exhibited similar behavior with respect to acetonitrile concentration. An analytical method was developed for dextromethorphan hydrobromide bulk drug and syrups and was applied to commercial preparations.