Separation of benzodiazepines using capillary electrochromatography

Benzodiazepines are often used for the treatment of epilepsy, convulsions, and many psychiatric disorders. The widespread use of this class of drugs has occasionally raised concern about recreational benzodiazepine abuse and has led to the erroneous impression that benzodiazepines have a relatively high abuse liability among recreational drug users. Therefore, the separation and identification of these compounds is of great interest. In general, the separation of benzodiazepines is performed using high-performance liquid chromatography (HPLC). Recently, capillary electrochromatography, which combines the high efficiency of capillary zone electrophoresis and the high selectivity of HPLC, has gained much attention. The focus of the work reported here is the use of a 40-cm packed bed of Reliasil 3-μm C18 stationary phase to separate seven benzodiazepines. Optimal conditions are established by varying the mobile phase, amount of organic modifier, buffer concentration, applied voltage, and column temperature. A mobile phase composition of Tris-HCl (pH 8)-acetonitrile (60:40), an electrolyte concentration of 30mM, and a temperature of 15°C with an applied voltage of 20 kV proves to be optimum. In addition, the method developed here is applied to the characterization of oxazepam in a standard urine sample.