Simultaneous spectrophotometric determination of paracetamol and p-aminophenol in pharmaceutical products with Tiron using dissolved oxygen as oxidant

A simple, rapid, and specific method was developed for the determination of paracetamol and p-aminophenol. The method is based on the hydrolysis of paracetamol to p-aminophenol, which, using dissolved oxygen as an oxidant in the alkaline region, was further transformed into benzoquinoneimine, capable of reacting with tiron to produce a green indophenol dye. The stabilization of indophenol dye was achieved by the addition of copper(II) solution. The absorbance was measured at 601 nm in alkaline medium, and the molar absorptivity was found to be 1.1 x 10(4) L/(mol cm). Paracetamol (PCT) and p-aminophenol (PAP) were determined in pharmaceutical products in the 1.5-15 mg/L PAP concentration range with a detection limit of 1.2 x 10(-6) M or 0.13 mu g/mL PAP. The developed method can be applied to the determination of p-aminophenol in the presence of paracetamol without prior separation. The proposed method is successfully employed for determination of paracetamol and p-aminophenol in various synthetic mixtures and pharmaceutical preparations. The obtained results were statistically compared with those given by the official method and the procedures evaluated as regards to both figures of merit and ease of applicability.