Indirect determination of dopamine and paracetamol by electrochemical impedance spectroscopy using azo coupling reaction with oxidized 2,4-dinitrophenylhydrazine (DNPH): Application in commercial tablets

Abstract A new method for the determination of dopamine (DA) and paracetamol (PCT), based on the azo “coupling reaction with oxidized 2,4-dinitrophenylhydrazine (DNPH), has been established. This method was based on the fact that in the HCl buffer solution, potassium ioadate oxidized 2,4-dinitrophenylhydrazine to form the diazonium chloride at 0–5 °C and then the diazonium ion reacted with the phenolic compounds to form azo-compounds. The products of the azo coupling reaction were characterized by UV/Vis spectrophotometry, infrared spectroscopy and square wave voltammetry. Using a MeOH/Water buffer solution (pH 9.0) and electrochemical impedance spectroscopy, DA and PCT were determined in the concentration range of 0.1–1000 μmol L−1, with limits of detection of 0.47 and 0.25 μmol L−1, respectively. The proposed method was successfully applied to the individual determination of DA and PCT in various pharmaceutical formulas, showing the practical feasibility of the proposed method as a novel platform for the sensitive determination of these phenolic compounds.