High performance liquid chromatographic method for the separation and quantification of some psychotherapeutic benzodiazepines optimized by the modified simplex procedure

An accurate high performance liquid chromatography method for the separation and quantification of a solution mixture of nitrazepam, diazepam and medazepam and medazepam was developed. The modified simplex program has been utilized for the optimization of the chemical and chromatographic parameters using the chromatographic response function as the quality criterion and a photodiode array as a detector. The separation was achieved in 2 min using a 20 cm long, 4.6 mm diameter Lichrosorb C18 reverse phase column. A 5 μl solution mixture containing 10 ppm of each drug was injected into a mobile phase containing 89:11 v/v acetonitrile: acetate buffer and a flow rate of 3.44 ml min^-1 was found to be optimal. The method was found to be suitable for the determination of these compounds in proprietary drugs without suffering interferences.