Simultaneous determination of salicylic acid and acetylsalicylic acid in aspirin delayed-release tablet formulations by second-derivative UV spectrophotometry.

A rapid, simple assay procedure was developed for simultaneous analysis of aspirin (ASA) and salicylic acid (SA) in aspirin delayed-release tablet formulation by 'zero crossing' second-derivative UV spectrophotometry. The zero-order absorption spectra and second derivative spectra of ASA and SA were recorded in diluting solution acetonitrile-formic acid (99:1). The accuracy of the method was demonstrated by the determination of ASA and SA in five tablets formulations (each 20 tablets of the same batch) by the described method and by high performance liquid chromatographic method, and the results were in good agreement.