Flow injection analysis of doxycycline or chlortetracycline in pharmaceutical formulations with pulsed amperometric detection.

A flow injection with pulsed amperometric detection for determination of doxycycline or chlortetracycline in pharmaceutical formulations is described. Doxycycline or chlortetracycline were studied at a gold rotating disk electrode with cyclic voltammetry as a function of pH of supporting electrolyte solution. The optimized PAD waveform parameters were obtained with a flow injection system. The optimized pulsed conditions of doxycycline were 1150mV (versus Ag/AgCl reference electrode) detection potential (E(det)) for 220ms (150ms delay time and 70ms integration time), 1500mV (versus Ag/AgCl reference electrode) oxidation potential (E(oxd)) for 70ms oxidation time (t(oxd)) and 250mV (versus Ag/AgCl reference electrode) reduction potentail (E(red)) for 400ms reactivation time (t(red)). The optimized pulsed conditions of chlortetracycline were 1050mV (versus Ag/AgCl reference electrode) detection potential (E(det)) for 300ms (200ms delay time and 100ms integration time), 1300mV (versus Ag/AgCl reference electrode) oxidation potential (E(oxd)) for 70ms oxidation time (t(oxd)) and 250mV (versus Ag/AgCl reference electrode) reduction potentail (E(red)) for 400ms reactivation time (t(red)). The optimized PAD waveform was applied to the determination of doxycycline hydrochloride and chlortetracycline hydrochloride standard solution and in pharmaceutical formulations. The linear dynamic ranges of doxycycline hydrochloride and chlortetracycline hydrochloride were 1muM-0.1mM. The sensitivity of this method was found to be 23muA/mM for doxycycline hydrochloride and 33.76muA/mM for chlortetracycline hydrochloride. The detection limit for both compounds is 1muM. The doxycycline hydrochloride and chlortetracycline hydrochloride content in commercially available tablet dosage forms by the proposed method was comparable to those specified by the manufacturer.