Application of Mixed Micelle-Mediated Extraction for Selective Separation and Spectrophotometric Determination of P-Aminophenol Impurity in Pharmaceutical Formulations

A procedure for separation/preconcentration of para-aminophenol (PAP) in pharmaceutical formulation, based on cloud point extraction (CPE) as a prior step to determination by UV-Vis spectrophotometry has been developed. The analyte reacted with 4-dimethylamino benzaldehyde (DAB) in acidic media to form a shift base, which were separated and preconcentrated in a mixed micelle of the anionic surfactant sodium dodecylsulfate (SDS) and the nonionic surfactant Triton X-114. The parameters affecting the extraction efficiency of the proposed method, such acid concentration, reagent concentration, amount of surfactants, and incubation time were optimized. Under the optimum conditions, the linear range was 50-1000 ng ml-1 of PAP with a correlation coefficient (r) of 0.998. The limit of detection was 30 ng ml-1. Relative standard deviation (RSD) for five replicate determinations of 200 ng ml-1 PAP was 1.4 %. In this work, the concentration factor of 10 was reached. Also the improvement factor of the proposed method was 3.3. The proposed method was successfully applied for determination of p-aminophenol in pharmaceutical formulations. The advantages of this method are simplicity of operation, rapidity and low cost.