High-performance liquid chromatographic method for the simultaneous determination of R-(−)- and S-(+)-hexobarbital in rat plasma

The enantiospecific determination of R- and S-hexobarbital in rat plasma is described. The method involves liquid-liquid extraction of racemic hexobarbital from plasma, separation of the underivatized enantiomers by high-performance liquid chromatography on an alpha-1-acid glycoprotein column and ultraviolet detection. The mobile phase consists of a phosphate buffer (pH 5.4) containing 0.4% 2-propanol as organic modifier. An alpha-1-acid glycoprotein guard column is used to increase the lifetime of the analytical column. Heptabarbital is the achiral internal standard. With detection limits of ca. 0.05-mu-g/ml for both R- and S-hexobarbital, the assay is suitable for pharmacokinetic studies of the enantiomers in rats