Simultaneous spectrophotometric determination in solid phase of aspirin and its impurity salicylic acid in pharmaceutical formulations.

We report the simultaneous determination of aspirin and its hydrolysis product, salicylic acid, in solid phase by fluorescence spectrophotometry. Aspirin is often the most labile component in a combination-type analgesic compound. Therefore, its stability is often the initial concern in any formulation-screening program. Preliminary screening of a large number of potential formulations can be arduous, because most current methods of analysis generally consist of several steps: extractions or column separations followed by UV, colorimetric, or gas-liquid chromatographic assays. The method proposed here is quite suited to large numbers of assays because it is not time consuming, it is straightforward, and it is not subject to interference from the substances present in the pharmaceutical formulations. In addition, the method is nondestructive, not dependent on the sampling procedure, and, above all, quite sensitive.