Overpressured layer chromatographic study of retention behaviour of various benzodiazepine derivatives on layers impregnated with tricaprylmethylammonium chloride.

The retention behaviour of various benzodiazepine derivatives was investigated on silica gel layers impregnated with tricaprylmethylammonium chloride (TCMA). The chromatograms were developed by means of overpressured layer chromatography (OPLC). As for the case of amino- and nitrosalicylic acids, pyrimidine derivatives, barbiturates, penicillins, cephalosporins and tetracyclines, the retention of benzodiazepine derivatives increased with increasing layer TCMA concentration with eluents containing methanol and water, but not TCMA. On increase of the methanol content of the eluent, a retention-decreasing effect was observed. On layers impregnated with TCMA, a linear relationship existed between the RM values of the benzodiazepines and the methanol content of the eluent. A similar relationship held for silica gel layers impregnated with paraffin oil (traditional reversed-phase). There was no correlation between the results obtained on layers treated with TCMA or with paraffin oil. On TCMA-impregnated layers, the retention of compounds having different chemical structures showed no dependence on the pH of the eluent. There were two reasons for this. Firstly, as it was established, above a certain RF value, the pH of the layer in the presence of TCMA was almost identical irrespective of the original pH of the buffer. Secondly, below this RF value, the actual pH of the layer did not have a strong enough effect to cause appreciable differences between the retentions of the dissociated and undissociated species of the analytes. The conditions for optimum separation are given.