High-performance liquid chromatography (HPLC) using a column-switching technique has been applied to the on-line determination and resolution of the enantiomers of ketoprofen (KPF) as an acidic model compound. The system incorporates a mobile phase conversion stage (LC-2), which has a dilution tube and a trapping column, between the achiral chromatography stage (LC-1) and the chiral chromatography stage (LC-3). KPF in plasma was separated from plasma components and was determined with the aid of an internal standard in LC-1. The eluate containing KPF was selectively transferred to LC-2, where the eluate was adequately diluted with a new mobile phase by using the dilution tube to reduce the influence of the mobile phase from LC-1, and KPF was reconcentrated on the trapping column. Then the KPF enantiomers were resolved in LC-3 after column-switching. This system is accurate and rapid compared with conventional HPLC. Very high sensitivity could be achieved with our system when a microbore ovomucoid column was employed in LC-3. Incorporation of LC-2 allows the most favourable mobile phases for LC-1 and LC-3 to be used independently. This method is greatly superior to usual column-switching HPLC.
