STUDIES ON THE RETENTION MECHANISM OF SOME ACIDIC DRUGS ON A NORMAL SILICA COLUMN WITH REVERSED PHASE ELUENT

The retention mechanism of acidic drugs on a stationary phase of normal phase liquid chromatography (NPC) with a mobile phase of reversed phase liquid chromatography (RPLC) is presented using the stoichiometric displacement model for retention (SDM-R). The effects of pH value, ionic strength, solvent concentration of the mobile phase and column temperature on the retention of acidic drugs were investigated. It was found that the retention mechanism of the system studied should be a mixed one of RPLC and NPC. But the former mainly contributes to their retention. The system may be used to analyse and to isolate acidic drugs.