Determination of aspirin and salicylic acid in aspirin tablets by second derivative ultraviolet spectrometry.

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Abstract
The 2nd derivative UV spectra of aspirin and salicylic acid in a solution of powdered aspirin tablets were not interfered with by the intense and time-dependent signal background caused by excipients and antacids contained in the tablets. The promotion of aspirin hydrolysis to salicylic acid in the solution by antacids could be sufficiently suppressed by using ethanol containing 1% (w/v [wt/vol])of citric acid as a solvent. Three kinds of commercial aspirin tablets were assayed by 2nd derivative UV spectrometry without any procedure for separation of the pharmaceuticals from the tablet additives. The contents of aspirin and salicylic acid could be determined with relative SD of < 0.5% for aspirin and < 3.0% for salicylic acid.