Determination of the enantiomers of zopiclone and its two chiral metabolites in urine using an automated coupled achiral-chiral chromatographic system.

The enantiomers of zopiclone and its two chiral N-desmethyl and N-oxide metabolites were determined in urine using a coupled achiral-chiral liquid chromatographic method. After liquid-liquid extraction, zopiclone and its two metabolites were quantified on a cyanopropyl column. After fluorimetric detection on the achiral system, the eluent was switched through a silica precolumn in order to trap and concentrate the analytes. Each fraction was then backflushed separately onto a carbamate cellulose chiral stationary phase in order to determine the enantiomeric ratios. The coupled system was automated with an autosampler and a switching valve programmed by an integrator. The method was validated, and a first trial was performed on urine samples of a volunteer treated with 15 mg of racemic zopiclone.