Determination of benzoic acid and salicylic acid in commercial benzoic and salicylic acids ointments by spectrophotometric method.

Commercial benzoic acid and salicylic acid ointments have been analyzed for benzoic acid and salicylic acid content by using a spectrophotometric method. Since benzoic acid and salicylic acid exhibit overlapping spectra, absorbance measurements are made at two wavelengths, i.e. 271 nm and 303 nm in ethanol (96%v/v) for simultaneous determination of the two compounds. The method is direct and involves only one step of absorbance measurement in the assay. The precision of the method, based on the analysis of synthetic mixtures of the two compounds, is within 2%. The recoveries of benzoic acid and salicylic acid in the ointments range from 99.9 to 100.6% and 99.5 to 101.3%, respectively and are comparable with those of the USP method (99.8 to 100.5% and 100.2 to 101.7%, respectively). The proposed method is simple, rapid, precise and convenient for the assay of benzoic acid and salicylic acid in commercial preparations.