RETENTION CHARACTERISTICS OF CN, NH2 AND DIOL PRECOATED HIGH-PERFORMANCE THIN-LAYER CHROMATOGRAPHIC PLATES IN THE ADSORPTION AND REVERSED-PHASE SEPARATION OF SOME BENZODIAZEPINE DERIVATIVES

The retentions of eighteen benzodiazepine (BZD) derivatives on CN, diol and NH2 high-performance thin-layer chromatographic layers was determined using eight adsorption (carbon tetrachloride-ethyl acetate) and five reversed-phase (water-methanol) eluent systems. In most instances a linear correlation was found between the RM value of BZD and the ethyl acetate or methanol concentration in the eluent, which allows the calculation of the optimum eluent composition. In aqueous eluents the lipophilicity of BZD determines the retention, that is, the plates behave as real reversed-phase stationary phases. The differences in the reversed-phase retentions of BZD were lower than in adsorption chromatography, advocating the application of adsorption chromatography for their separation. The low retention capacity and elongated spot shape make the NH2 plate unsuitable for the reversed-phase separation of BZD without further modification of the composition of the mobile phase. As chlordiazepoxide and medazepam form distorted spots on CN and diol plates, for the best separation of these BZD, NH2 plates in the adsorption separation mode are recommended. © 1990.