The salicylate ion strongly fluoresces at about 400 nm after it has been excited at about 310 nm. A scries of standard solutions of salicylate ion are prepared; the fluorescence of the standards and the samples are measured; and the working curve method is used to determine the concentrations of salicylate ion in the sample solutions. The concentration is used to calculate the percentage of acetylsalicylic acid in the aspirin tablet.