Selective spectrophotometric determination of p-aminophenol and acetaminophen

A specific spectrophotometric method was developed for the determination of p-aminophenol and acetaminophen. The method is based on the reaction of p-aminophenol at ambient temperature with sodium sulphide in presence of an oxidant to produce a methylene blue-like dye. Different oxidizing agents were tried, e.g. Ce(IV) and Fe(III). The colour developed within 10 min and remained stable for at least 3 h. The method was applied successfully to the determination of p-aminophenol in the presence of acetaminophen without prior separation. The method was also applied to the analysis of various commercially available acetaminophen dosage forms and excellent recoveries were obtained comparable to those obtained by official procedures. The reaction product was isolated and a possible reaction mechanism was suggested.