A novel sensitive colorimetric determination of catecholamine drug in dosage form via oxidative coupling reaction with MBTH and potassium ferricyanide

A new and direct colorimetric method has been established for the determination of catecholamine (methyldopa, MD) in both pure form pharmaceutical formulations. The is based on oxidative coupling reaction MD with 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH) potassium ferricyanide at pH 10.4 aqueous medium to an orange product that a maximum absorption 460 nm. Beer's law plot showed good correlation concentration range 1.0−56.0 µg mL-1, detection limit 0.31 mL-1. Molar absorptivity above was found be 6.56×103 L mol-1 cm-1. All measurements were carried out 25 ± 1.0 °C, formation constant (logKf) value colored species 9.48 standard free energy (DG‡) − 54.09 KJ mol-1. This applied successfully tablets results compared USP method. Common excipients used as additives do not interfere proposed accurate, precise highly reproducible, while being simple, cheap less time consuming hence can suitably routine analysis bulk dosage forms.