Spectrophotometric determination of phenothiazines, tetracyclines and chloramphenicol with sodium cobaltinitrite.

A spectrophotometric method for determining some phenothiazines, some tetracyclines and chloramphenicol is described. Chlorpromazine hydrochloride, promazine hydrochloride, promethazine hydrochloride, perphenazine and fluphenazine hydrochloride are reacted with sodium cobaltinitrite in phosphoric acid. The red colour developed is measured at 530, 513, 515, 530 and 500 nm, respectively. Tetracycline hydrochloride, oxytetracycline hydrochloride, chlortetracycline hydrochloride, doxycycline hyclate and demeclocycline hydrochloride are reacted with the reagent in aqueous acetic acid. The yellow colour produced is measured at 256, 294, 262, 243 and 246 nm, respectively. Chloramphenicol is determined similarly to the tetracyclines after hydrolysis with 40% sodium hydroxide solution and the colour is measured at 240 nm. The proposed method has been successfully applied to the determination of these drugs in various pharmaceutical preparations.