Determination of acetaminophen by flow injection with on-line chemical derivatization: Investigations using visible and FTIR spectrophotometry

A new FI/FTIR method for the determination of acetaminophen (paracetamol, N-acetyl-p-aminophenol) involving on-line reaction is described. The proposed method is based on the alkaline hydrolysis of the analyte to produce p-aminophenol and its oxidation reaction with potassium ferricyanide to produce p-benzoquinone-monoimine which eventually oxidizes to form p-benzoquinone. The chemistry of the reaction was studied both, in the visible and IR regions of the spectrum and the method has been developed by the application of flow-injection methodology. The reaction was carried out in aqueous media and at room temperature. The micro-flow version of the CIRCLE® IR accessory, which is compatible with aqueous solutions, was used. Measurements were carried out at the OH-phenolic deformation (1274.1 cm−1) and the aromatic ring mode (1498.2 cm−1) infrared vibrations for the hydrolysis product, p-aminophenol. The method was applied to the determination of acetaminophen in commercial tablets, and mean detection values of 512 and 491 mg were found at 1274.1 and 1498.2 cm−1, respectively.