A new cloud-point preconcentration approach for the spectrophotometric determination of p-aminophenol in the presence of paracetamol with 2-(2-hydroxyphenyl)-1H-benzimidazole as a coupling reagent

A preconcentration and determination method for trace p-aminophenol (PAP) in paracetamol was developed. Cloud-point extraction (CPE) was employed for the preconcentration of p-aminophenol prior to spectrophotometric determination using Triton X-100 (TX-100) as an extractant. The determination is based on the reaction of p-aminophenol with 2-(2-hydroxyphenyl)-1H-benzimidazole (HPBI) at room temperature in the presence of an oxidant to produce indophenol blue dye. The dye formed is subsequently entrapped in micelles of the surfactant TX-100. The surfactant-rich phase shows maximum absorbance at 650 nm and the proposed method is linear in the 0.1 to 5.0 mg mL(-1) concentration range. By preconcentrating 10 mL of the sample solution, a detection limit as low as 55 ng/mL was obtained after a single-step extraction and the experimental concentration factor achieved for this method was found to be 10. The stoichiometric composition of the dye is 1: 1 (PAP: HPBI). Some parameters such as HPBI, KIO4, Na2CO3, and TX-100 concentration, extraction temperature, incubation, and centrifugation time, and the sample volume were investigated in detail. The established procedure was successfully adopted for the determination of p-aminophenol in the presence of paracetamol in various pharmaceutical preparations.