Simultaneous Determination of Dextromethorphan Hydrobromide, Pyrilamine Maleate and Sodium Benzoate in a Cough Cold Syrup by LC

A liquid chromatographic method for the simultaneous determination of dextromethorphan hydrobromide, pyrilamine maleate and sodium benzoate in cough cold syrup has been developed. The method was based on replacing heptane sulfonate by sodium chloride as ion pairing agent. The addition of sodium chloride to the mobile phase has changed the retention behaviour of the basic drugs. The separation of these compounds was achieved in less than 8 min with an isocratic mobile phase consisting of acetonitrile/0.1 M dihydrogenphosphate buffer containing 0.1 M sodium chloride (29:71 v/v) at pH 2.5 and using a Kromasil C18 column. The analysis was performed at a flow rate of 1 mL min−1 and at a detection wavelength of 220 nm. The selectivity, linearity of calibration, accuracy, within and between days precision, limit of detection and quantification, recovery were examined as parts of the method validation. Calibration curves were linear in the range 1–140 μg mL−1 with a regression coefficient (R2) better than 0.999. The results of the method repeatability (intra-day) and reproducibility (inter-day) were all less than 2% (n = 6). The lowest detectable concentration of dextromethorphan hydrobromide and pyrilamine maleate varied between 0.10 and 0.12 μg mL−1. The proposed liquid chromatographic method was satisfactorily applied for the routine quality control of dextromethorphan hydrobromide, pyrilamine maleate and sodium benzoate in cough cold syrup formulations.