Determination of related compounds in aspirin by liquid chromatography.

A rapid liquid chromatographic procedure has been validated for the determination of salicylic acid, salsalate, acetylsalicylsalicylic acid, and acetylsalicylic anhydride in aspirin. Samples are dissolved in methylene chloride and analyzed directly by adsorption chromatography in a 7-min separation using an isocratic mobile phase. Recoveries averaged 99% over a 200-10,000 ppm concentration range with standard deviations of less than 4% for the four compounds of interest. Detection limits ranged from 5 to 36 ppm. Compared to a recently published reversed-phase liquid chromatographic procedure for analyzing aspirin, this method is twice as fast, more sensitive, and avoids the use of hydroxylic solvents which lead to degradation of aspirin and acetylsalicylic anhydride.