A High Performance Liquid Chromatographic Method for the Simultaneous Assay of aspirin, Caffeine, Dihydrocodeine Bitartrate and Promethazine Hydrochloride in a Capsule Formulation

A method for the simultaneous quantitation of aspirin, caffeine, dihydrocodeine bitartrate and promethazine HCl was developed using reversed-phase, solvent-programming high-performance liquid chromatography. Linear gradient elution with acetonitrile in phosphate buffer (from 15:85 to 56:44) allowed all compounds to elute from a C-18 column within 7 min with adequate resolution. This method also allowed the resolution and quantitation of salicylic acid, the principle decomposition product of aspirin. CV% of eight determinations each of aspirin, caffeine, dihydrocodeine bitartrate and promethazine HCl are 0.64, 1.25, 3.37 and 1.72, respectively, and percent recoveries from spiked preparations were 100.25, 100.03, 100.45 and 98.00, respectively. This assay method was shown also to be suitable for dissolution studies with water or acetate buffer as the dissolution medium.