Enantiomeric separation and discrimination of 2-hydroxy acids as O-trifluoroacetylated (S)-(+)-3-methyl-2-butyl esters by achiral dual-capillary column gas chromatography

An efficient method is described for the simultaneous enantiomeric separati on of 18 different racemic 2-hydroxy acids for the determination of their a bsolute configurations. It involves the conversion of each enantiomer into a diastereomeric O-trifluoroacetylated (S)-(+)-3-methyl-2-butyl ester for t he direct separation by achiral dual-capillary column gas chromatography wi th subsequent identification and determination of its chirality by retentio n index (I) library matching. The enantiomers of each acid were well separa ted with high resolution values (R greater than or equal to 1.4) on DB-5 an d DB-17 columns of different polarity. When temperature-programmed I values of 2-hydroxy acid enantiomers as their diastereomeric derivatives were mea sured on both columns, the I values were characteristic of each enantiomer. Simple I matching with the reference values was thus useful in cross-check ing each acid enantiomer for the identification and chiral discrimination. When applied to urine samples, the present method allowed positive identifi cation of most of the spiked 2-hydroxy acids from normal urine and for endo genous (S)-lactic acid and (S)-2-hydroxybutyric acid from a clinical urine specimen. (C) 2000 Elsevier Science B.V. All rights reserved.