Determination of 4-aminophenol impurities in multicomponent analgesic preparations by HPLC with amperometric detection.

A method for the determination of 4-aminophenol, the main impurity of paracetamol, by high-performance liquid chromatographic (HPLC) method with amperometric detection has been developed. The analysis was performed in an isocratic mode on a reversed phase Luna column 5 microm C-18 (100 x 4.6 mm). A mobile phase (0.05 mol l(-1) LiCl solution containing 18% methanol adjusted to pH 4.0 with orthophosphoric acid) was suitable for the separation and determination of 4-APh. Chromatograms were recorded for 250 s by means of an amperometric detector at a potential of +325 mV of the glassy carbon electrode versus the reference electrode Ag/AgCl. The proposed liquid chromatographic method was successfully applied to the analysis of commercially available multicomponent dosage forms. The sensitivity of the detection for 4-aminophenol was 1 ng ml(-1) for substance and 4 ng ml(-1) for tablets or capsules. The method developed in this study is sensitive and selective and can be applied for routine studies of pharmaceuticals in the form of tablets or capsules.