Simultaneous determination of aspirin and salicylic acid in bulk aspirin and in plain, buffered, and enteric-coated tablets by high-pressure liquid chromatography with UV and fluorescence detectors.

A quantitative high-pressure liquid chromatographic method that uses a reversed-phase column coupled to UV and fluorescence detectors was developed to determine aspirin and salicylic acid in bulk aspirin and in plain, buffered, and enteric-coated tablets. The aspirin was dissolved, filtered, and injected into the chromatograph. The UV absorbance of aspirin was determined at 254 nm, and the fluorescence of salicylic acid was measured at 425 nm. Excipients and impurities did not interfere. Recoveries of 100% were obtained for aspirin and salicylic acid from simulated tablet formulations. Results obtained by the USP XIX procedure and the proposed method were compared. The coefficient of variation for the aspirin analysis was 0.59%; for salicylic acid, it was 1.69%. The rate of hydrolysis of aspirin to salicylic acid in the solvents used was < 0.05%/hr.