Flow injection–Fourier transform infrared spectrometric determination of paracetamol in pharmaceuticals

Abstract

A procedure for the direct FTIR spectrometric determination of paracetamol in pharmaceuticals is described. The method is based on the solubilization of paracetamol in a 10% v/v ethanol in CH₂Cl₂ solution and direct absorbance measurement at 1515 cm^–1, using the baseline established at 1900 cm^–1 for measurement correction. The procedure can be carried out in both the stopped-flow and flow injection (FI) modes. In both instances the sensitivity is approximately 0.09 A ml mg^–1, the limit of detection being 8 µg ml^–1 in the stopped-flow mode and 33 µg ml^–1 in the FI mode. Caffeine, acetylsalicylic acid, propyphenazone and ascorbic acid do not interfere with the FTIR determination of paracetamol, and the interference of citric acid can be eliminated by using measurements between 1518 and 1509 cm^–1 in the first-derivative mode. The FI-FTIR methodology provides a fast and appropriate technique for the routine analysis of pharmaceuticals with a throughput of 45 samples h^–1.