Colorimetric Determination of Seven Nonsteroidal Antiinflammatory Drugs Using 2-Nitrophenylhydrazine Hydrochloride

A simple, sensitive and convenient colorimetric method for the determination of seven nonsteroidal anti-inflammatory drugs, namely, flufenamic acid, mefenamic acid, niflumic acid, ketoprofen, ibuprofen, diclofenac sodium and indomethacin, was developed. The method is based on reaction of the abovementioned compounds - being carboxilic compounds, reacting with 2-nitrophenylhydrazine in presence of diclohexylcarbodiimide in ethanolic medium to give acid hydrazine, which showed intense violet colour with a maximum absorption at around 550 nm. The effect of reagent concentration (2-nitrophenylhydrazine hydrochloride, pyridine and dicyclohexylcarbodiimide), heating temperature and heating time were studied to optimize reaction conditions. The method was successfully applied to the determination of those drugs in pure and dosage forms, with a relative standard deviation less than 2%.